Fasting glucose
Fasting glucose is the sugar in blood after at least 8 hours without food. US bodies place prediabetes at 100 to 125 mg/dL and diabetes at 126 mg/dL or above, while WHO starts its intermediate band at 110 mg/dL. Levels above 100 mg/dL go with more diabetes, heart disease and deaths. One reading varies about 6% between tests.
- Status
- A blood test ordered by a clinician, alone or within a metabolic panel, and also sold direct to consumers by some US laboratories. FDA classifies glucose test systems as class II devices, and its product classification also lists over-the-counter blood glucose test systems [1]. A joint laboratory guideline states that portable glucose meters are not to be used to diagnose diabetes [2].
- Measures
- The concentration of glucose in blood plasma after fasting, which the American Diabetes Association defines as at least 8 hours with nothing to eat or drink except water [3].
- Also called
- fasting plasma glucose, FPG, fasting blood glucose, FBG, fasting blood sugar, FBS, glucose fasting, fasting glucose, plasma glucose, serum glucose, blood glucose, blood sugar, GLU
- Tested for
- diabetes diagnosis, prediabetes screening, blood sugar check, metabolic health, insulin resistance, heart disease risk, low blood sugar
Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on
Linked in research4
- StrongLinked to more coronary heart disease above 100 mg/dL in 102 pooled cohorts, 11% to 17% more below the diabetes range, with no link between 70 and 100 mg/dL.
- StrongLinked to more deaths above 100 mg/dL and not between 70 and 100 mg/dL, in 97 pooled cohorts of 820,900 people.
- ModerateLinked to later type 2 diabetes: fasting glucose of 100 to 125 mg/dL went with about 4 times the risk in a Cochrane review of cohort studies.
- ModerateLinked to diabetic eye disease from about 6.4 to 6.8 mmol/L (about 115 to 123 mg/dL) upward, in pooled data on 41,411 people.
Reported risks0
No risks sourced yet.
Reference ranges
Each range is the one its source published, in mg/dL. Also reported in mmol/L. Where sources differ, each is shown.
American Diabetes Association
People being tested for diabetes or prediabetes · [3]
| Range | What the source calls it |
|---|---|
| below 100 mg/dL | "normal" |
| 100 to 125 mg/dL | "prediabetes" |
| 126 or above mg/dL | "diabetes" One to see a doctor about |
Taken from the association's public page on diagnosis, which states that a test usually needs to be repeated on a second day to diagnose diabetes. A laboratory guideline published jointly with the association reports that it lowered the threshold for a normal fasting result from below 110 to below 100 mg/dL in 2003, and that the change remains contentious and has not been accepted by all organizations. The same guideline gives the factor used on this page: mg/dL multiplied by 0.0555 gives mmol/L [2].
National Institute of Diabetes and Digestive and Kidney Diseases, US National Institutes of Health
People being tested for diabetes or prediabetes · [4]
| Range | What the source calls it |
|---|---|
| 99 or below mg/dL | "normal" |
| 100 to 125 mg/dL | "prediabetes" |
| 126 or above mg/dL | "diabetes" One to see a doctor about |
The same cut points as the American Diabetes Association. The institute defines fasting as having nothing to eat or drink except sips of water, and notes that some tests use different cutoffs in pregnancy. Page last reviewed July 2022 [4].
World Health Organization and International Diabetes Federation consultation, 2006
People being tested for diabetes or intermediate hyperglycemia · [5]
| Range | What the source calls it |
|---|---|
| below 110 mg/dL | No name given |
| 110 to 125 mg/dL | "impaired fasting glucose" |
| 126 or above mg/dL | "diabetes" One to see a doctor about |
The consultation kept the lower cut point for impaired fasting glucose at 6.1 mmol/L (110 mg/dL) and declined to lower it to 5.6 mmol/L (100 mg/dL). It cited the large rise in prevalence that would follow, a lack of evidence of benefit, and data that people identified at the lower cut point had about half the risk of developing diabetes. It reserves the word "normoglycaemia" for levels below those that define intermediate hyperglycemia, which also depends on the 2-hour value of a glucose tolerance test, so no name is given here to a fasting result below 110 mg/dL. It prints the bands as 6.1 to 6.9 mmol/L and 7.0 mmol/L or above [5].
Laboratory reference interval, adults, as described in the 2023 laboratory guideline of the American Association for Clinical Chemistry and American Diabetes Association
Adults, as the reference interval for fasting plasma glucose · [2]
| Range | What the source calls it |
|---|---|
| below 74 mg/dL | No name given |
| 74 to 99 mg/dL | "reference interval" |
| above 99 mg/dL | No name given |
The guideline gives the adult range as 4.1 to 5.5 mmol/L (74 to 99 mg/dL) and states that the diagnostic criteria of the American Diabetes Association and WHO, not reference values, are used to diagnose diabetes. A reference interval describes the spread of results in people tested, which is a different thing from the diagnostic cut points above [2].
Laboratory reference interval, children, as described in the 2023 laboratory guideline of the American Association for Clinical Chemistry and American Diabetes Association
Children, as the reference interval for fasting plasma glucose · [2]
| Range | What the source calls it |
|---|---|
| below 60 mg/dL | No name given |
| 60 to 100 mg/dL | "reference interval" |
| above 100 mg/dL | No name given |
The guideline states that glucose concentrations in healthy people vary with age and gives the interval in children as 3.3 to 5.6 mmol/L (60 to 100 mg/dL), without naming age bands. Diagnostic criteria, not reference values, are used to diagnose diabetes [2].
What has been shown to move it
Shown to lower it31
Blood sugar
Shown to lower fasting blood sugar and HbA1c in adults with type 2 diabetes. In apparently healthy participants, fasting glucose rose instead.
The numbers and sources
- Effect
- In 7 controlled trials in type 2 diabetes, ACV lowered fasting blood sugar by 21.9 mg/dL (95% CI -29.19 to -14.67) and HbA1c by 1.53 (95% CI -2.65 to -0.41), with no change in HOMA-IR [1]. Across 9 studies in adults, ACV lowered fasting glucose by 7.97 mg/dL (95% CI -13.74 to -2.21) and HbA1c by 0.50 (95% CI -0.90 to -0.09), with no change in fasting insulin or HOMA-IR [2]. A review of 6 studies in 317 people with type 2 diabetes found lower fasting glucose and HbA1c with vinegar [3].
- Population
- Adults with type 2 diabetes [1][3]. Adults with and without diabetes [2].
- Sources
- [1], [2], [3]
- Caveats
- Heterogeneity for HbA1c was high (I² 91%) [2]. Vinegar content varied across studies and samples were small [3]. In apparently healthy participants, fasting glucose rose [2].
Blood sugar in type 2 diabetes
Shown to lower fasting glucose and HbA1c in adults with type 2 diabetes, with HbA1c about 0.6 points lower. Many trials were small and low quality.
The numbers and sources
- Effect
- Across 37 trials (3,048 patients), berberine lowered fasting glucose by 0.82 mmol/L (95% CI -0.95 to -0.70), HbA1c by 0.63% (95% CI -0.72 to -0.53) and 2-hour glucose by 1.16 mmol/L, with larger effects at higher baseline glucose [1]. Against placebo in 20 trials (1,761 participants), it lowered fasting glucose by 0.52 mmol/L (95% CI -0.72 to -0.33) and HOMA-IR by 0.85 [2].
- Population
- Adults with type 2 diabetes [1]. Adults with and without diabetes [2].
- Sources
- [1], [2]
- Caveats
- Effects on fasting glucose were larger in people with diabetes and in Asian participants [2]. Many trials were small and of low methodological quality [3].
Blood sugar
Shown to lower fasting glucose by about 10 mg/dL and HbA1c by about 0.6 points in adults.
Oil lowered fasting glucose more than powder.
The numbers and sources
- Effect
- In 17 RCTs, fasting glucose fell 9.93 mg/dL (95% CI -13.44 to -6.41), post-meal glucose 14.79 mg/dL and HbA1c 0.57 percentage points (95% CI -0.77 to -0.37). Oil lowered fasting glucose more than powder [3]. The 2025 review also reported improved fasting glucose, HbA1c and post-meal glucose [2].
- Population
- Adults in clinical trials [2][3].
- Sources
- [3], [2]
- Caveats
- The authors call for longer, stronger trials [3].
Blood sugar in type 2 diabetes
Shown to lower HbA1c by about 0.6 points and lower fasting glucose in people with type 2 diabetes, with larger effects in poorer-quality trials.
The numbers and sources
- Effect
- HbA1c fell 0.6 points (95% CI -0.9 to -0.2) and fasting glucose 1.0 mmol/L (95% CI -1.4 to -0.5) on chromium [1]. A 2014 analysis found HbA1c -0.55 points (95% CI -0.88 to -0.22) and fasting glucose -1.15 mmol/L [2]. A 2020 analysis found HbA1c -0.71 points (95% CI -1.19 to -0.23) and fasting glucose -19.0 mg/dL (95% CI -36.2 to -1.9) [3].
- Population
- 41 trials, almost half poor quality [1]; 25 trials in diabetes [2]; 28 trials in type 2 diabetes [3].
- Sources
- [1], [2], [3], [4]
- Caveats
- Sources disagree on what this means. Larger effects came more often from poor-quality trials [1]. Heterogeneity for fasting glucose was 99.8% [3]. A 2016 review found few of 20 trials reached clinical treatment goals, with HbA1c falling 0.5 points or more in 5 of 14 [4]. FDA ranked the evidence for preventing insulin resistance or diabetes at its lowest level for a qualified claim [5].
Blood sugar in diabetes
Shown to lower fasting glucose by about 1 mmol/L and HbA1c by about 0.85% in people with diabetes, only at medium or high doses.
A 2023 meta-analysis of 10 RCTs (706 participants) with type 2 diabetes or prediabetes also reported lower fasting glucose, 2-hour glucose and HbA1c, and no change in HOMA-IR.
The numbers and sources
- Effect
- Across 10 trials, fenugreek seed changed fasting glucose by -0.96 mmol/L (95% CI -1.52 to -0.40, I² 80%), 2-hour glucose by -2.19 mmol/L and HbA1c by -0.85% (95% CI -1.49 to -0.22, 3 trials). Significant effects appeared only at medium or high doses in people with diabetes [1]. A 2023 meta-analysis of 10 RCTs (706 participants) with type 2 diabetes or prediabetes also reported lower fasting glucose, 2-hour glucose and HbA1c, and no change in HOMA-IR [2].
- Population
- People with and without diabetes [1]; type 2 diabetes and prediabetes [2].
- Sources
- [1], [2]
- Caveats
- Most trials in [1] were of low methodological quality. The 2023 abstract does not report effect sizes [2].
Weight and insulin resistance in PCOS
Shown in pooled studies to lower weight and insulin resistance in women with PCOS. Against other diets, the reviews disagreed on weight.
Compared with other diets [21]; low-calorie diets [22]; before the diet, in the same women [21][22][23]
In 2 RCTs against low-calorie diets, body weight did not differ significantly, while BMI, fat mass, glucose and HOMA-IR fell more on the ketogenic diets.
The numbers and sources
- Effect
- Against other diets, ketogenic diets lowered weight 4.98 kg more (95% CI 0.91 to 9.05), BMI 1.65 kg/m2 more and insulin resistance more (MD -1.71, 95% CI -2.98 to -0.43, I² 90%). From before to after the diet, weight fell 10.77 kg and BMI 3.38 kg/m2 [21]. In 2 RCTs against low-calorie diets, body weight did not differ significantly, while BMI, fat mass, glucose and HOMA-IR fell more on the ketogenic diets [22]. A third review of 7 studies found weight, BMI, glucose, insulin, HOMA-IR, LDL cholesterol and triglycerides fell from before to after the diet [23].
- Population
- Women with PCOS, most with BMI above 25, in 15 studies, 10 pooled [21]; 10 studies including 3 RCTs, 4 cohorts and 2 case series [22]; 7 studies [23].
- Sources
- [21], [22], [23]
- Caveats
- Heterogeneity was high for most outcomes [21]. Before-and-after results cannot separate the diet from weight loss or time. A published letter disputed whether the definition of real-world exposure in [21] matched its inclusion criteria [24].
Liver enzymes in fatty liver disease
Shown to lower liver enzymes in fatty liver disease, ALT by about 9 U/L. Liver fat and scarring were not measured.
LDL cholesterol fell 5.61 mg/dL, fasting glucose 4.05 mg/dL, HOMA-IR 0.70 and BMI 0.99 kg/m².
The numbers and sources
- Effect
- In people with metabolic dysfunction-associated steatotic liver disease, orlistat lowered AST by 4.01 U/L (95% CI 1.97 to 6.05), ALT by 8.70 U/L (95% CI 0.90 to 16.51) and GGT by 7.74 U/L (95% CI 0.59 to 14.88) against control. LDL cholesterol fell 5.61 mg/dL, fasting glucose 4.05 mg/dL, HOMA-IR 0.70 and BMI 0.99 kg/m². Blood pressure did not change [6]. A second meta-analysis also found lower ALT, AST, HOMA-IR, BMI, cholesterol, insulin and waist circumference [7].
- Population
- 6 RCTs [6]; 11 studies with 582 participants [7].
- Sources
- [6], [7]
- Caveats
- Both reviews measured blood markers, not liver fat on imaging or scarring on biopsy. The trials were small and likely overlap between the reviews. The abstract of [7] does not say whether all 11 studies were randomized.
Blood sugar in type 2 diabetes
Shown to lower HbA1c by about 0.66 points more than placebo in adults with type 2 diabetes, and about as much as other diabetes drugs.
Against other diabetes drugs in 13 studies HbA1c was 0.06 points lower (95% CI 0.18 lower to 0.05 higher), and the risk of low blood sugar was similar.
The numbers and sources
- Effect
- Against placebo in 45 studies, SGLT2 inhibitors lowered HbA1c by 0.66 percentage points (95% CI 0.58 to 0.73). Against other diabetes drugs in 13 studies HbA1c was 0.06 points lower (95% CI 0.18 lower to 0.05 higher), and the risk of low blood sugar was similar [14]. In a network meta-analysis of trials of at least 24 weeks, canagliflozin, dapagliflozin and empagliflozin each lowered HbA1c and fasting glucose against placebo. Canagliflozin 300 mg lowered HbA1c by 0.2 points (95% CI 0.1 to 0.3) more than dapagliflozin 10 mg or empagliflozin 25 mg [15].
- Population
- 11,232 participants in placebo-controlled studies and 5,175 in active-comparator studies [14]; 23,997 participants in 38 trials [15].
- Sources
- [14], [15]
- Caveats
- Most trials in the first review were rated at high risk of bias for missing data [14]. The glucose-lowering effect depends on kidney filtration and shrinks as kidney function falls.
Blood pressure and cardiometabolic markers
Not shown to change blood pressure, cholesterol or body fat in adults. Fasting glucose and CRP fell very slightly.
Fasting glucose fell by 0.51 mg/dL.
The numbers and sources
- Effect
- Across 10 RCTs, tart cherry juice did not change blood pressure, cholesterol, triglycerides or body fat. Fasting glucose fell by 0.51 mg/dL [4]. Across 21 trials, blood pressure, heart rate, hs-CRP and IL-6 did not change, while CRP fell by 0.39 mg/L (95% CI -0.74 to -0.05, moderate certainty) [5]. A 3-month trial in 50 middle-aged adults found no change in vascular or metabolic measures [6].
- Population
- Adults across 10 to 21 RCTs [4][5]; middle-aged adults, 30 mL concentrate twice a day [6].
- Sources
- [4], [5], [6]
- Caveats
- A 0.51 mg/dL glucose change is very small. The 3-month trial was funded by the Cherry Research Committee [6].
Blood sugar and blood lipids
Shown to lower fasting glucose about 6 mg/dL and triglycerides about 14 to 18 mg/dL, mostly in people with obesity, diabetes or metabolic syndrome. HDL did not change.
The numbers and sources
- Effect
- Fasting glucose fell by 5.9 mg/dL (95% CI -10.7 to -1.0) and triglycerides by 18.3 mg/dL (95% CI -25.6 to -11.0). HDL cholesterol did not change [4]. A second meta-analysis found fasting glucose 5.9 mg/dL lower, HbA1c 0.21% lower, triglycerides 14.4 mg/dL lower and LDL cholesterol 5.1 mg/dL lower [5].
- Population
- 25 RCTs, 1,024 participants [4]; 34 RCTs [5].
- Sources
- [4], [5]
- Caveats
- Most trials were short and enrolled people with obesity, diabetes or metabolic syndrome. Neither review measured hard outcomes such as heart attacks or diabetes onset.
Blood sugar
Shown to lower fasting glucose about 6 to 10 mg/dL and HbA1c about 0.3 points in adults with prediabetes or type 2 diabetes.
The numbers and sources
- Effect
- Across 34 RCTs in adults with prediabetes or type 2 diabetes, curcumin or turmeric lowered fasting glucose by 10.15 mg/dL (95% CI -12.59 to -7.72), HbA1c by 0.32% (95% CI -0.43 to -0.21) and HOMA-IR by 0.46 against control [6]. A meta-analysis of 63 trials drawn from 13 earlier reviews (3,706 participants) found fasting glucose 6.30 mg/dL lower (95% CI -9.33 to -3.27) and HbA1c 0.31% lower (95% CI -0.57 to -0.05) [7]. With piperine added, 15 RCTs (1,020 participants) showed fasting glucose 5.89 mg/dL lower, while HbA1c, fasting insulin and HOMA-IR did not differ significantly [8].
- Population
- Adults with prediabetes or type 2 diabetes [6][7]; adults, many overweight with metabolic disorders [8].
- Sources
- [6], [7], [8], [9]
- Caveats
- Heterogeneity was significant [6] and high [7]. GRADE certainty was low for fasting glucose and HbA1c in the piperine review [8]. In a network meta-analysis of 24 RCTs in prediabetes, turmeric extract was linked to fewer new cases of type 2 diabetes (RR 0.05, 95% CI 0.00 to 0.78), with low certainty and short trials [9].
Blood sugar in type 2 diabetes
Shown to lower HbA1c about 0.3 to 0.4 points against comparison diets in adults with type 2 diabetes.
Compared with comparator diets the source does not describe [1]; control diets the source does not describe [2]
The numbers and sources
- Effect
- In 6 controlled trials (255 participants), vegetarian diets lowered HbA1c by 0.39 points (95% CI -0.62 to -0.15), and fasting glucose did not change significantly [1]. In 9 RCTs (664 participants), HbA1c fell 0.29 points (95% CI -0.45 to -0.12) and fasting glucose 0.56 mmol/L, at moderate certainty, with no change in fasting insulin [2].
- Population
- Adults with type 2 diabetes, mean age 42.5 in [1]; adults with diabetes in trials of 3 weeks or more [2].
- Sources
- [1], [2]
- Caveats
- Both reviews pooled lacto-ovo and vegan diets. Trials were small and short.
Blood sugar
Mixed results: one large review found lower fasting glucose and HbA1c, while a review of overweight adults and neuropathy trials found no change.
The numbers and sources
- Effect
- Across 63 trials, fasting glucose fell 5.28 mg/dL (95% CI -7.21 to -3.35), HbA1c 0.40% (95% CI -0.66 to -0.14), fasting insulin 1.70 mU/mL and HOMA-IR 0.74 against control [8]. In 11 trials of 704 overweight or obese adults, fasting glucose (SMD 0.13, 95% CI -0.16 to 0.41) and HOMA-IR (SMD -0.23, 95% CI -0.60 to 0.15) did not differ from control [9]. In diabetic neuropathy trials, HbA1c did not change [5].
- Population
- 63 randomized trials [8]; adults with a BMI of 25 or more [9]; people with diabetic neuropathy [5].
- Sources
- [8], [9], [5]
- Caveats
- The reviews disagree. The overweight review rated 8 of its 11 trials at low risk of bias [9].
Blood sugar and blood lipids
Shown to lower fasting glucose by about 16 mg/dL and triglycerides in people with prediabetes or type 2 diabetes. Reviews disagree on LDL and total cholesterol.
The numbers and sources
- Effect
- In prediabetes and type 2 diabetes, astaxanthin lowered fasting glucose by 16.1 mg/dL (95% CI -29.0 to -3.3), HbA1c by 0.34 points, triglycerides by 20.9 mg/dL, total cholesterol by 12.2 mg/dL and LDL by 9.4 mg/dL, and raised HDL by 3.0 mg/dL. HOMA-IR, weight and BMI did not change [4]. At 6 to 20 mg a day, a second meta-analysis found higher HDL and lower triglycerides, with no change in LDL or total cholesterol [5]. In adults at risk of metabolic syndrome, effects on total cholesterol and systolic pressure were marginal, and LDL fell [6].
- Population
- 403 patients in 9 RCTs [4]; 8 studies with 11 results [5]; 321 adults in 7 RCTs [6].
- Sources
- [4], [5], [6]
- Caveats
- The reviews disagree on LDL and total cholesterol. All pooled small trials.
Blood sugar control in type 2 diabetes
Shown to lower HbA1c by about 1.0 to 1.2 points against almost no change on placebo in adults with type 2 diabetes, with 62% reaching under 7% against 22%.
Compared with placebo [1]; sitagliptin, metformin, exenatide and insulin glargine [1]; other diabetes drugs in a network meta-analysis [2]
HbA1c under 7% was reached by 56%, 62%, 39% and 22%, and fasting glucose fell 35, 41, 18 and 9 mg/dL.
The numbers and sources
- How common
- Very common: more than 1 in 10 people.
- Effect
- Added to metformin, HbA1c changed by -1.0 points on 0.75 mg, -1.2 on 1.5 mg, -0.6 on sitagliptin and +0.1 on placebo at 26 weeks. HbA1c under 7% was reached by 56%, 62%, 39% and 22%, and fasting glucose fell 35, 41, 18 and 9 mg/dL. In other placebo-controlled trials, dulaglutide lowered HbA1c more than placebo when added to glimepiride, to metformin with pioglitazone, and to SGLT2 inhibitors [1]. A network meta-analysis of 453 trials found that specific GLP-1 receptor agonists added to metformin, with insulin regimens, produced the largest HbA1c reductions [2].
- Population
- 972 adults on metformin in one trial and other placebo-controlled trials described in the label [1]; 453 trials of 21 glucose-lowering treatments [2].
- Sources
- [1], [2]
- Caveats
- The trials were funded by the manufacturer. The network meta-analysis abstract does not give a dulaglutide estimate [2].
Blood sugar
Shown to lower fasting glucose slightly with kimchi and kefir, in two meta-analyses. Probiotic yogurt did not differ from ordinary yogurt.
Compared with control groups the abstract does not describe [7][9]; conventional yogurt [10]
The numbers and sources
- Effect
- Kefir lowered fasting glucose (MD -8.46 mg/dL) and HOMA-IR (MD -1.71) [7]. Fermented kimchi lowered fasting glucose (WMD -1.93 mg/dL, 95% CI -3.82 to -0.03) [9]. Probiotic yogurt did not change HbA1c, fasting glucose, fasting insulin or HOMA-IR against mostly conventional yogurt in people with type 2 diabetes or obesity [10].
- Population
- 24 studies of kefir [7]. 205 participants in 5 kimchi trials [9]. 472 people with type 2 diabetes or obesity in 9 trials [10].
- Sources
- [7], [9], [10]
- Caveats
- Small trials of single foods. The yogurt review compared two fermented foods with each other, not fermented food with none [10].
Blood sugar
Shown to lower fasting glucose, and HbA1c by about 0.5 points, more in people with type 2 diabetes. Insulin did not change.
The numbers and sources
- Effect
- In 9 RCTs (768 patients with type 2 diabetes), fasting glucose was lower with garlic at 1 to 2, 3 to 4, 12 and 24 weeks. Fructosamine and HbA1c were lower at 12 and 24 weeks. Complications did not differ [5]. A 2026 GRADE-assessed meta-analysis of 27 RCTs (1,619 adults) found fasting glucose fell 2.76 mg/dL (95% CI -5.11 to -0.41) and HbA1c 0.53 percentage points (95% CI -0.86 to -0.20). Insulin and HOMA-IR did not change significantly [6]. In 8 trials in type 2 diabetes, fasting glucose fell 12.41 mg/dL and HbA1c 0.5 points [7]. The 108-trial review found fasting glucose 2.77 mg/dL lower [4].
- Population
- Adults with type 2 diabetes [5][7]. Adults in 27 RCTs [6] and 108 trials [4].
- Sources
- [4], [5], [6], [7]
- Caveats
- The reviews pooled different populations, and the fasting glucose drop in the type 2 diabetes review [7] is more than four times that in the all-adult reviews. The pooled standardized differences in [5] are very large (SMD -21.02 at 24 weeks), which points to small, varied trials. Heterogeneity in [7] was very high (I² 99.2% for fasting glucose), and its authors rate the included trials as low quality.
Fasting blood sugar
Shown to lower fasting glucose about 7 mg/dL in adults. In insulin resistance, the result lost significance under another analysis.
The numbers and sources
- Effect
- Fasting blood glucose was 7.44 mg/dL lower with glucomannan (95% CI -14.16 to -0.72). People with impaired glucose metabolism did not benefit to the same degree [1]. In 11 trials in adults with insulin resistance-related conditions, fasting glucose was 7.02 mg/dL lower (95% CI -13.56 to -0.49) [3].
- Population
- 14 studies with 531 participants [1]. Adults with insulin resistance-related conditions in 11 trials [3].
- Sources
- [1], [3]
- Caveats
- The two reviews studied different populations. The result in [3] lost statistical significance under an alternative correlation assumption, and its authors call for more high-quality trials.
Blood sugar
Shown to lower fasting glucose slightly in adults across 50 trials, with no change in HbA1c.
Blood sugar
Shown to lower fasting glucose slightly in adults with prediabetes or type 2 diabetes, while HbA1c did not change overall in pooled trials.
Compared with a control diet with no time restriction [10]; unrestricted eating [11]; daily calorie restriction or a control group [12]; standard-of-care nutritional counseling alone [13]
Fasting glucose fell 0.30 mmol/L (95% CI -0.53 to -0.07, moderate certainty).
The numbers and sources
- Effect
- In 10 trials with 599 participants, HbA1c changed by -0.30 percentage points (95% CI -0.63 to 0.02, p 0.06, moderate certainty), by -0.09 points in prediabetes and by -0.43 points in type 2 diabetes (95% CI -0.92 to 0.07). Fasting glucose fell 0.30 mmol/L (95% CI -0.53 to -0.07, moderate certainty) [10]. In adults without diabetes, time-restricted eating without calorie restriction lowered fasting glucose by 2.65 mg/dL (95% CI -3.92 to -1.39) and HOMA-IR by 0.58 [11]. In type 2 diabetes, HbA1c fell 0.91% on an 8-hour window and 0.94% on calorie restriction against control, with no difference between the two [12]. In metabolic syndrome, an 8 to 10 hour window lowered HbA1c by 0.10% (95% CI -0.19% to -0.003%) against standard care [13].
- Population
- Adults with prediabetes or type 2 diabetes, trials averaging 4 months with 4 to 10 hour windows [10]; 11 trials with 653 adults without diabetes [11]; 75 adults with obesity and type 2 diabetes over 6 months [12]; 108 adults with metabolic syndrome over 3 months [13].
- Sources
- [10], [11], [12], [13]
- Caveats
- Wide confidence intervals and small trials limited the pooled evidence, and effects on insulin sensitivity and continuous glucose monitoring were inconclusive [10]. Three authors of [10] work at a hospital partly funded by the Novo Nordisk Foundation.
Blood sugar and insulin resistance
Mixed results: most reviews found lower insulin resistance but disagreed on fasting glucose, and one review in people with diabetes found no significant change.
A 2021 meta-analysis of double-blind trials reported lower fasting glucose in people with diabetes and improved glucose and insulin-sensitivity markers in people at high risk.
The numbers and sources
- Effect
- One meta-analysis found magnesium lowered HOMA-IR (WMD -0.67, 95% CI -1.20 to -0.14) but not fasting glucose (WMD -0.20 mmol/L, 95% CI -0.45 to 0.05) or HbA1c overall. Trials of 4 months or longer showed lower fasting glucose and HOMA-IR [3]. A 2021 meta-analysis of double-blind trials reported lower fasting glucose in people with diabetes and improved glucose and insulin-sensitivity markers in people at high risk [4]. A 2026 meta-analysis of 78 RCTs found lower HOMA-IR (WMD -0.48, 95% CI -0.79 to -0.18), fasting glucose (WMD -3.60 mg/dL) and HbA1c (WMD -0.15%) [5]. A 2026 meta-analysis of 15 RCTs (1,085 people with diabetes or prediabetes) found no significant change in insulin (MD -1.73) or HOMA-IR (MD -0.74, 95% CI -1.58 to 0.09). Baseline insulin and HOMA-IR modified the effect [6].
- Population
- People with and without diabetes [3][5]; people with or at high risk of diabetes [4][6].
- Sources
- [3], [4], [5], [6]
- Caveats
- The sources disagree on fasting glucose and on HOMA-IR in people with diabetes. The 2021 abstract does not report effect sizes [4]. The authors of [5] rated certainty as variable across outcomes.
Blood sugar in type 2 diabetes
Shown to lower fasting glucose about 27 mg/dL and HbA1c about 1 point in adults with type 2 diabetes, in low quality trials.
The numbers and sources
- Effect
- In 5 trials (270 patients), silymarin lowered fasting blood glucose by 26.86 mg/dL (95% CI -35.42 to -18.30) and HbA1c by 1.07 points (95% CI -1.73 to -0.40). Lipids did not change [9]. A 2025 network meta-analysis of 17 studies (1,337 people with type 2 diabetes) found silymarin lowered fasting glucose, HOMA-IR and HbA1c against placebo (P < 0.05) [10]. Across 6 RCTs (673 participants), HOMA-IR fell by 2.29 (95% CI -4.55 to -0.03) with no change in fasting insulin. The fall was seen in type 2 diabetes but not in fatty liver disease [11].
- Population
- Adults with type 2 diabetes [9][10]; adults with type 2 diabetes, alcoholic cirrhosis or fatty liver disease in Iran, Egypt and Italy [11].
- Sources
- [9], [10], [11]
- Caveats
- The authors of [9] rated the evidence as low quality, with high heterogeneity. The network meta-analysis abstract reports p-values for silymarin against placebo without effect sizes [10]. The authors of [11] called the evidence limited.
Blood sugar in type 2 diabetes
Shown to lower HbA1c by 0.07 percentage points and fasting glucose slightly in people with type 2 diabetes, in one meta-analysis of short trials.
Compared with diets with the same calories without tree nuts [12]
The numbers and sources
- Effect
- A median 56 g a day of tree nuts lowered HbA1c (MD -0.07%, 95% CI -0.10 to -0.03) and fasting glucose (MD -0.15 mmol/L, 95% CI -0.27 to -0.02). Fasting insulin and HOMA-IR did not change significantly [12].
- Population
- 450 people with diabetes in 12 randomized trials of 3 weeks or more [12].
- Sources
- [12]
- Caveats
- The reviewers describe most trials as short and of poor quality [12].
Blood sugar in people with type 2 diabetes
Shown to lower HbA1c by 0.27 points and fasting glucose by 0.44 mmol/L in people with type 2 diabetes, in pooled trials against control groups.
Compared with control groups in the trials pooled [8]
The numbers and sources
- Effect
- In people with type 2 diabetes, olive oil lowered HbA1c (mean difference -0.27%, 95% CI -0.37 to -0.17) and fasting plasma glucose (-0.44 mmol/L, 95% CI -0.66 to -0.22) more than in control groups [8].
- Population
- People with type 2 diabetes in trials among the 29 pooled [8].
- Sources
- [8]
- Caveats
- The abstract does not describe the control groups. The authors note the finding applies to olive oil as a food, not its single components [8].
Stress hormones, heart rate and blood fats, against active controls
Shown in one meta-analysis to lower cortisol, ambulatory systolic pressure, resting heart rate, fasting glucose and LDL cholesterol more than active control activities.
Compared with active control interventions [11]
The numbers and sources
- Effect
- Across 42 trials, practices including yoga postures were associated with lower evening and waking cortisol, ambulatory systolic blood pressure, resting heart rate, fasting blood glucose, cholesterol and LDL cholesterol, and higher high-frequency heart rate variability, compared with active controls [11].
- Population
- Participants in 42 randomized trials in various populations [11].
- Sources
- [11]
- Caveats
- The abstract gives no effect sizes and describes the interventions as heterogeneous. Some included mindfulness-based stress reduction alongside postures [11].
Blood sugar and blood fats in type 2 diabetes
Shown in one meta-analysis to lower HbA1c by 0.47 points and fasting glucose by 24 mg/dL in adults with type 2 diabetes, with high heterogeneity.
Compared with control groups including usual care or standard treatment [12]
The numbers and sources
- Effect
- Pooled differences were -23.72 mg/dL for fasting blood glucose (95% CI -37.78 to -9.65, I² 82%), -0.47% for HbA1c (95% CI -0.87 to -0.07, I² 82%), -17.38 mg/dL for glucose after meals, -18.50 mg/dL for total cholesterol, +4.30 mg/dL for HDL cholesterol and -12.95 mg/dL for LDL cholesterol. Triglycerides did not differ (-12.57 mg/dL, 95% CI -29.91 to 4.76) [12].
- Population
- 864 adults with type 2 diabetes in 12 trials [12].
- Sources
- [12]
- Caveats
- The authors note limited methods and heterogeneity, and long-term effects were not studied [12].
Cycles, androgens and blood sugar in PCOS
Shown in one small meta-analysis to lower menstrual irregularity, signs of excess androgens, fasting glucose and insulin resistance in women with PCOS, at low strength of evidence.
Compared with controls the source abstract does not describe [21]; conventional physical activity, routine care or no intervention [22]
The numbers and sources
- Effect
- Pooling 2 RCTs, yoga lowered menstrual irregularity (MD -0.41, 95% CI -0.74 to -0.08), clinical hyperandrogenism (MD -0.70, 95% CI -1.15 to -0.26), fasting glucose (MD -0.22 mmol/L, 95% CI -0.44 to -0.01), fasting insulin (MD -28.21 pmol/L, 95% CI -43.79 to -12.63) and HOMA-IR (MD -0.86, 95% CI -1.29 to -0.43) [21]. A 2026 review of trials with 258 participants found fasting glucose fell 4.50 mg/dL more than in controls in one trial (95% CI 2.39 to 6.61) and did not differ significantly in another. In one trial, testosterone did not change significantly and LH fell [22].
- Population
- 515 women with PCOS in 11 studies, 2 RCTs pooled [21]; 258 women with PCOS in RCTs [22].
- Sources
- [21], [22]
- Caveats
- The authors of [21] rated the strength of evidence low. [22] could not pool its trials, and three of its five reports came from one trial.
Blood sugar
Shown to lower fasting glucose about 14 mg/dL and HbA1c about 0.55% in people with and without diabetes.
The numbers and sources
- Effect
- Across 32 placebo-controlled interventions (1,700 participants, 14 countries), zinc lowered fasting glucose by 14.15 mg/dL (95% CI -17.36 to -10.93), 2-hour glucose by 36.85 mg/dL, HbA1c by 0.55% (95% CI -0.84 to -0.27) and hs-CRP by 1.31 mg/L [3]. Across 18 RCTs (1,023 participants) with diabetes, gestational diabetes or prediabetes, zinc lowered serum insulin (MD -2.50, 95% CI -4.69 to -0.31) and HOMA-IR (MD -1.10, 95% CI -2.05 to -0.15), and LDL cholesterol rose slightly (MD 3.46, 95% CI 1.48 to 5.43) [4].
- Population
- People with and without diabetes [3]; people with diabetes or prediabetes [4].
- Sources
- [3], [4]
- Caveats
- The fasting glucose effect depended on diabetes status and on the zinc formulation [3].
Inflammation markers
One small trial found 1,000 mg a day lowered IL-6 in 60 women with PCOS. Trials of other inflammation markers conflicted.
The numbers and sources
- Effect
- In 60 women with polycystic ovary syndrome, 1,000 mg a day of oil for 12 weeks lowered serum IL-6 against placebo (adjusted mean difference -4.21, 95% CI -6.34 to -2.08) and fasting glucose by 8.16 mg/dL. Fasting insulin and HOMA-IR did not differ [9]. A review of 4 human trials found conflicting results for the adhesion molecules VCAM-1 and ICAM-1 [10].
- Population
- 60 women with PCOS [9]. Patients with coronary artery disease, type 2 diabetes, Hashimoto's thyroiditis or cardiovascular risk factors [10].
- Sources
- [9], [10]
- Caveats
- One small trial for IL-6 [9]. The adhesion molecule review also included 15 animal and in vitro studies, which are not counted here [10].
Blood sugar in children and teenagers with type 2 diabetes
One trial in youths with type 2 diabetes found dulaglutide lowered HbA1c by 0.9 points while it rose 0.6 on placebo, with no difference in BMI.
Compared with placebo [5]
Fasting glucose rose 17.1 mg/dL on placebo and fell 18.9 mg/dL on dulaglutide.
The numbers and sources
- Effect
- At 26 weeks, HbA1c rose 0.6 points on placebo and fell 0.6 on 0.75 mg and 0.9 on 1.5 mg. HbA1c under 7% was reached by 51% on dulaglutide against 14% on placebo. Fasting glucose rose 17.1 mg/dL on placebo and fell 18.9 mg/dL on dulaglutide. BMI change did not differ [5].
- Population
- 154 youths aged 10 to under 18 with type 2 diabetes, on lifestyle changes alone or with metformin, with or without basal insulin [5].
- Sources
- [5]
- Caveats
- One small trial, funded by the manufacturer. Gastrointestinal adverse events were more frequent than on placebo [5].
Blood sugar
Limited evidence: psyllium lowered fasting glucose and HbA1c in type 2 diabetes but not in normal blood sugar. Other fiber results were small or inconsistent.
The numbers and sources
- Effect
- In people treated for type 2 diabetes, psyllium taken before meals lowered fasting glucose by 37.0 mg/dL and HbA1c by 0.97%. There was no glucose lowering in people with normal blood sugar and a modest effect in prediabetes [5]. Across 12 RCTs in overweight and obese adults, isolated soluble fiber lowered fasting glucose by 0.17 mmol/L (95% CI -0.28 to -0.06) and fasting insulin by 15.88 pmol/L [6]. A 2026 meta-analysis of 11 glucomannan trials in adults with insulin resistance-related conditions found fasting glucose 7.02 mg/dL lower (95% CI -13.56 to -0.49), an effect that lost significance under an alternative correlation assumption [7]. In a 4-week trial of 131 adults, inulin lowered 1-hour and 2-hour glucose on a glucose tolerance test in overweight or obese participants but not in healthy-weight ones, and fructooligosaccharides did not change glucose in either group [8].
- Population
- 35 psyllium RCTs across three groups [5]; 609 overweight and obese adults [6]; 11 glucomannan trials [7]; 131 adults in China [8].
- Sources
- [5], [6], [7], [8]
- Caveats
- Reference [5] searched clinical records held by Procter & Gamble, a psyllium supplement maker, as well as published studies, and its abstract does not report confidence intervals. The glucomannan result was not robust to the analysis method [7]. In the inulin trial, fasting insulin rose [8].
Shown to raise it3
Blood sugar and cholesterol
Shown to raise fasting blood sugar to diabetic levels in 2.4% on quetiapine against 1.4% on placebo in trials of up to 12 weeks.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- In short-term trials, fasting glucose shifted from normal to 126 mg/dL or above in 2.4% of 2,907 people on quetiapine and 1.4% of 1,346 on placebo. The label states that hyperglycemia, in some cases with ketoacidosis, coma or death, has been reported with atypical antipsychotics [3]. Across 18 antipsychotics, changes against placebo ranged from -0.29 to 1.05 mmol/L for glucose, -0.09 to 0.56 mmol/L for total cholesterol and -0.01 to 0.98 mmol/L for triglycerides, with clozapine and olanzapine at the high end [16]. At low doses, new type 2 diabetes was not more frequent on quetiapine than on SSRIs in a matched cohort (incidence rate ratio 0.99, 95% CI 0.87 to 1.13) [17].
- Population
- 4,253 adults in quetiapine trials of up to 12 weeks [3]; 25,952 patients in 100 trials [16]; 54,616 matched pairs starting low-dose quetiapine or an SSRI in Denmark [17].
- Sources
- [3], [16], [17]
- Caveats
- The glucose figure is for quetiapine. The low-dose cohort is observational and compared quetiapine with another drug class.
Diabetes and raised blood sugar
Shown to raise fasting glucose and diabetes risk in older adults and adults with obesity. The label warns of glucose intolerance and diabetes.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Healthy older adults on growth hormone were somewhat more likely to develop diabetes and impaired fasting glucose [1]. In adults with obesity, low-dose growth hormone raised fasting glucose by 4.18 mg/dL against placebo (95% CI 0.68 to 7.67) [4]. The somatropin label lists glucose intolerance and diabetes among its warnings [7].
- Population
- 220 treated older adults [1]; 420 adults with obesity in 10 RCTs [4]; label [7].
- Sources
- [1], [4], [7]
- Caveats
- Few events in small trials. The obesity meta-analysis reported no serious adverse events [4].
High blood sugar and new diabetes
Shown to raise blood sugar, with fasting glucose rising within 2 weeks in healthy men and new diabetes in 14.7% of patients on long courses.
The numbers and sources
- How common
- Very common: more than 1 in 10 people.
- Effect
- In healthy men, prednisolone 7.5 mg and 30 mg a day for 2 weeks raised fasting plasma glucose against placebo in a dose-dependent way, and lowered the ability of insulin to suppress glucose production by 17% and 46% [18]. In COPD flare-ups, high blood sugar was more frequent on systemic corticosteroids (OR 2.79, 95% CI 1.86 to 4.19) [3]. Among patients without diabetes given more than 20 mg a day of prednisolone equivalent for at least 4 weeks, 34 of 231 (14.7%) developed steroid-induced diabetes [21]. The prednisone label states that corticosteroids may raise blood glucose and that doses of diabetes medicines may need adjusting [20].
- Population
- 32 healthy men aged about 22 [18]; 1,787 people in 16 COPD studies [3]; 231 patients with respiratory disease, median treatment 193 days [21].
- Sources
- [18], [3], [21], [20]
- Caveats
- The healthy-volunteer abstract reports the direction of the glucose change and not its size [18]. The diabetes figure comes from one retrospective hospital series with no comparison group [21].
Studies disagree6
Insulin resistance and blood sugar in PCOS
Shown to lower insulin resistance and fasting glucose slightly against placebo in women with PCOS. Added to lifestyle change, one review found no extra effect.
Compared with placebo [34][31]; lifestyle change with or without placebo [33]; combined oral contraceptive pills [35]
The numbers and sources
- Effect
- Against placebo, metformin lowered HOMA-IR by 0.50 (95% CI 0.09 to 0.91) and fasting glucose by 0.13 mmol/L (95% CI 0.07 to 0.19), both moderate certainty [34]. A second review also found lower fasting glucose than placebo (SMD -0.23, 95% CI -0.40 to -0.06) [31]. Lifestyle change plus metformin did not differ from lifestyle change with or without placebo on surrogate markers of insulin resistance or fasting glucose after 6 months [33]. Against combined oral contraceptive pills, metformin lowered insulin by 27.12 pmol/L (95% CI 13.59 to 40.65) [35].
- Population
- RCTs in women with PCOS published through July 2022 [34]; 24 RCTs with 564 women given metformin [31]; 12 RCTs with 608 women [33]; 36 RCTs in women with PCOS [35].
- Sources
- [34], [31], [33], [35]
- Caveats
- The changes are small. The add-on comparison rests on small, short trials [33].
Blood sugar
Mixed results: one review found fasting glucose about 0.3 mmol/L lower, and a larger review found no significant effect on blood sugar.
The numbers and sources
- Effect
- Across 16 trials of 30 days or longer, ginseng lowered fasting blood glucose by 0.31 mmol/L (95% CI -0.59 to -0.03). Fasting insulin, HbA1c and HOMA-IR did not change overall [5]. A 2025 meta-analysis of 70 studies (4,506 participants) on cardiovascular risk factors found no significant effect on the glycemic profile, with a dose-response association for fasting glucose and fasting insulin [6].
- Population
- 770 people with and without diabetes [5]. 4,506 participants in 70 studies [6].
- Sources
- [5], [6]
- Caveats
- The two reviews disagree on fasting glucose. Two thirds of trials in [5] ran under 12 weeks, and most participants already had well-controlled glucose [5].
Blood sugar in trials
Mixed results: pooled trials of green tea and extracts found small falls in fasting glucose and HbA1c, while a trial of a catechin-rich drink found no difference.
Compared with control groups in randomized trials [7]; a green tea drink with 96.3 mg of catechins a day [8]
The numbers and sources
- Effect
- Across 17 trials, green tea lowered fasting glucose by 0.09 mmol/L (95% CI 0.03 to 0.15) and HbA1c by 0.30% (95% CI 0.22 to 0.37), and fasting insulin in higher-quality trials [7]. In people with type 2 diabetes, a drink with 582.8 mg of catechins a day for 12 weeks showed no apparent difference in glucose or HbA1c from a low-catechin drink, except in people on insulin-releasing drugs [8].
- Population
- 1,133 participants in 17 randomized trials of green tea or green tea extract [7]. 43 adults with type 2 diabetes not on insulin [8].
- Sources
- [7], [8]
- Caveats
- The pooled trials included extracts, and the abstract gives no separate result for the drink [7].
Raised blood sugar and lower insulin sensitivity
Shown to raise fasting blood sugar about 5 mg/dL and lower insulin sensitivity in older adults, with poorer glucose handling in obese men.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Fasting blood glucose rose an average of 0.3 mmol/L (5 mg/dL) on MK-677, and insulin sensitivity fell [1]. In obese men, fasting glucose and insulin did not change, but an oral glucose tolerance test showed impaired glucose handling at 2 and 8 weeks [2].
- Population
- 65 older adults [1]; 24 obese men [2].
- Sources
- [1], [2]
- Caveats
- Two small trials.
Raised blood sugar and diabetes
Shown to raise HbA1c into the diabetes range in 5% against 1% on placebo by 26 weeks in adults with HIV. Later glucose measures did not differ.
Fasting glucose rose 7 mg/dL more than placebo at 2 weeks, with no difference at 6 months.
The numbers and sources
- How common
- Common: between 1 in 100 and 1 in 10 people.
- Effect
- In the phase 3 trials, HbA1c reached 6.5% or more by week 26 in 5% on tesamorelin and 1% on placebo, a hazard ratio of 3.3 (CI 1.4 to 9.6) [6]. Fasting glucose rose 7 mg/dL more than placebo at 2 weeks, with no difference at 6 months [7]. Fasting glucose and HbA1c did not differ from placebo at 12 months in the liver trial [8].
- Population
- 806 adults with HIV in the phase 3 program [3][6]; 50 adults [7]; 61 adults [8].
- Sources
- [6], [7], [8]
- Caveats
- Mean baseline HbA1c was 5.3% in the phase 3 trials [6]. The pooled trial report found no clinically meaningful glucose differences [3], and a 2026 meta-analysis of 5 RCTs reported no change in glucose [5].
Blood sugar and insulin in PCOS
Shown in one review to lower fasting glucose and insulin slightly against placebo in women with PCOS. An earlier review found changes mainly with other nutrients.
Compared with placebo [71][72]
The numbers and sources
- Effect
- Across 13 RCTs (691 women), vitamin D lowered fasting glucose by 2.91 mg/dL (95% CI 1.04 to 4.78) and insulin by 1.98 µIU/mL (95% CI 0.64 to 3.32) more than placebo, with lower triglycerides, total cholesterol and LDL cholesterol [71]. An earlier review of 11 RCTs (601 women) found lower fasting glucose and HOMA-IR when vitamin D was given with other micronutrients, and lower HOMA-IR at doses under 4,000 IU a day [72].
- Population
- Women aged 18 and older with PCOS in 13 RCTs [71]; 601 women with PCOS in 11 RCTs [72].
- Sources
- [71], [72]
- Caveats
- The changes are small. The earlier review's abstract gives no effect size and does not report a significant effect for vitamin D alone at all doses [72].
Tested, and not shown to change it22
HbA1c and fasting glucose in type 2 diabetes
Shown to lower HbA1c by about 0.4% to 0.6% with resistance training in type 2 diabetes in pooled trials, more at high intensity, without a clear fasting glucose change.
Compared with control groups in randomized trials [6][7][8]; aerobic training [6]
Fasting blood glucose fell only as a nonsignificant trend across 15 trials.
The numbers and sources
- Effect
- Resistance training lowered HbA1c by 0.39% against controls (95% CI -0.60 to -0.18), more when strength rose more, and did not differ from aerobic training [6]. High-intensity training lowered HbA1c by 0.61% and low to moderate intensity by 0.23%. Fasting blood glucose fell only as a nonsignificant trend across 15 trials [7]. A third review found a 0.57% fall (95% CI -1.14% to -0.01%) [8].
- Population
- 1,172 adults with type 2 diabetes in 20 trials [6]. 962 patients in 24 trials, 443 in the fasting glucose analysis [7]. Patients with type 2 diabetes in trials of at least 12 weeks [8].
- Sources
- [6], [7], [8]
- Caveats
- Heterogeneity was high (I² 69.2% [6], 92.5% [8]).
Weight loss compared with no diet or brief advice
Shown to lower body weight against control diets in adults with overweight or obesity. As one-off self-help instructions, it matched standard brief advice at one year.
Compared with a daily energy-restricted diet or a routine diet [7]; standard brief weight-management advice [8]
Visceral fat, total cholesterol, triglycerides, HDL, diastolic pressure, fasting glucose and HbA1c did not differ.
The numbers and sources
- Effect
- In 20 articles with 1,393 participants, 5:2 lowered body weight, BMI, waist circumference, body fat percentage, fat mass, fat-free mass, LDL cholesterol, systolic blood pressure and HOMA-IR against control groups. Visceral fat, total cholesterol, triglycerides, HDL, diastolic pressure, fasting glucose and HbA1c did not differ [7]. One-off 5:2 self-help instructions lost 1.9 kg at one year against 1.8 kg with standard brief advice (p 0.79), and 18% against 15% lost at least 5% of body weight [8].
- Population
- Adults with overweight or obesity in 20 trials [7]; 300 UK adults with obesity followed for one year [8].
- Sources
- [7], [8]
- Caveats
- The meta-analysis abstract reports significance without effect sizes [7]. Adherence to self-help 5:2 fell over the year [8].
Blood sugar in type 2 diabetes
Mixed results: HbA1c fell about as much as on daily calorie restriction, rose back above baseline by 24 months, and fell more than on metformin with meal replacement fasting days.
Compared with continuous energy restriction [1], [3], [9]; a daily energy-restricted diet or a routine diet [7]; metformin or empagliflozin [10]
In adults with overweight or obesity, fasting glucose and HbA1c did not differ from control.
The numbers and sources
- Effect
- At 12 months, HbA1c fell 0.3% on 5:2 and 0.5% on daily restriction (P .65), meeting the equivalence margin [3]. At 24 months, HbA1c was 0.1% and 0.4% above baseline in the two groups [9]. A 5:2 plan using meal replacements on fasting days lowered HbA1c by 1.9% over 16 weeks, 0.3% more than metformin and 0.4% more than empagliflozin, with weight loss of 9.7 kg against 5.5 and 5.8 kg [10]. In adults with overweight or obesity, fasting glucose and HbA1c did not differ from control [7]. In premenopausal women, fasting insulin and insulin resistance fell slightly more on 5:2 than on daily restriction (both P 0.04) [1].
- Population
- 137 adults with type 2 diabetes, mean HbA1c 7.3% [3][9]; 405 Chinese adults with overweight or obesity and early type 2 diabetes [10]; adults with overweight or obesity [7]; 107 women [1].
- Sources
- [1], [3], [7], [9], [10]
- Caveats
- The meal replacement trial was open-label and lasted 16 weeks with 8 weeks of follow-up [10]. Weight loss was kept at 24 months, yet HbA1c rose in both groups [9].
Blood sugar in people without diabetes
Not shown to change fasting glucose or insulin resistance against control or daily calorie restriction in adults without diabetes.
Compared with eating every day, with no fasting days or daily fasting window
The numbers and sources
- Effect
- Fasting glucose (p 0.09) and HOMA-IR (p 0.55) did not differ from control [2]. Fasting glucose, fasting insulin and insulin resistance did not differ from daily calorie restriction at 6 or 12 months [3]. HbA1c did not differ between intermittent fasting, continuous restriction and unrestricted diets [6].
- Population
- 269 adults [2]; 100 adults with obesity [3]; 99 trials [6].
- Sources
- [2], [3], [6]
- Caveats
- Few participants had diabetes in these trials.
Blood pressure and other heart risk markers
Shown to lower systolic blood pressure by about 1.6 mmHg for plant sterols and stanols as a class. HDL, blood sugar and weight did not change.
HDL cholesterol, fasting glucose, HbA1c, body weight, waist and fat mass did not change.
The numbers and sources
- Effect
- Plant sterols and stanols lowered systolic blood pressure by 1.55 mmHg (95% CI 0.42 to 2.67), diastolic by 0.84 mmHg, apoB by 0.06 g/L and hs-CRP by 0.25 mg/L. HDL cholesterol, fasting glucose, HbA1c, body weight, waist and fat mass did not change [5].
- Population
- Adults of mixed health status in trials pooled across 14 meta-analyses. Blood pressure came from one of them [5].
- Sources
- [5]
- Caveats
- Class-level evidence, not beta-sitosterol alone. These are risk markers, not heart attacks or strokes. Certainty was moderate to high for most outcomes, downgraded for inconsistency, imprecision or publication bias [5].
Insulin resistance
Shown to lower HOMA-IR and fasting insulin slightly in overweight adults and women with PCOS. Fasting glucose and HbA1c did not change significantly.
Fasting glucose (-1.60 mg/dL, 95% CI -3.28 to 0.07) and HbA1c (-0.05 points, 95% CI -0.19 to 0.07) did not change significantly.
The numbers and sources
- Effect
- In 20 trials in overweight and obese adults, HOMA-IR fell 0.26 (95% CI -0.48 to -0.03) and fasting insulin 12.55 pmol/L (95% CI -23.62 to -1.47). Fasting glucose (-1.60 mg/dL, 95% CI -3.28 to 0.07) and HbA1c (-0.05 points, 95% CI -0.19 to 0.07) did not change significantly [6]. In 10 RCTs in 683 women with polycystic ovary syndrome, chromium lowered fasting insulin (p 0.01) and raised the insulin sensitivity index QUICKI (p 0.02) against placebo. Against metformin, HOMA-IR fell more on chromium (p < 0.00001) [7].
- Population
- Overweight and obese adults, with trial sizes of 1 to 137 [6]; women with polycystic ovary syndrome [7].
- Sources
- [6], [7]
- Caveats
- The two reviews studied different populations. The PCOS abstract gives p-values without effect sizes [7]. The overweight analysis abstract calls the fasting glucose fall significant though its interval crosses zero [6]. In 2005 FDA ranked the evidence for chromium picolinate and insulin resistance at its lowest level for a qualified claim [5].
Blood sugar and insulin
Not shown to change fasting blood sugar or insulin in adults. Subgroup results pointed in different directions.
In subgroups, insulin rose in women, insulin and fasting blood sugar rose in those with BMI of 30 or more, and insulin fell in trials longer than 8 weeks.
The numbers and sources
- Effect
- Across 9 publications with 444 participants, garcinia did not change fasting blood sugar (1.02 mg/dL, 95% CI -1.29 to 3.33) or insulin (-0.12 mU/L, 95% CI -1.50 to 1.25) compared with control. In subgroups, insulin rose in women, insulin and fasting blood sugar rose in those with BMI of 30 or more, and insulin fell in trials longer than 8 weeks [6].
- Population
- Adults in RCTs [6].
- Sources
- [6]
- Caveats
- Subgroup results point in different directions and come from few trials.
HbA1c in type 2 diabetes
Shown to lower HbA1c about 0.5% more than standard-protein diets within 6 months in type 2 diabetes, in one meta-analysis of nine small trials.
Compared with diets with less protein
Fasting glucose and blood lipids did not differ.
The numbers and sources
- Effect
- Against diets with 15% to 20% of energy from protein, diets with 25% to 32% lowered weight 2.08 kg more (95% CI 0.90 to 3.25) and HbA1c 0.52% more (95% CI 0.14 to 0.90). Fasting glucose and blood lipids did not differ [8].
- Population
- 418 adults with type 2 diabetes in 9 trials lasting 4 to 24 weeks [8].
- Sources
- [8]
- Caveats
- Two studies had a large influence on the weight and HbA1c results [8]. The indexed abstract prints minus signs as the digit 2. The figures here follow its text, which reports reductions.
Blood pressure, cholesterol and blood sugar markers
Shown to lower blood pressure about 3/2 mmHg and LDL cholesterol and HbA1c slightly in adults, at low to moderate certainty.
Compared with no or minimal intervention, and another dietary intervention the abstract does not name [2]; a low-fat diet, a low-carbohydrate diet and the American Diabetes Association diet [7]; control diets the source does not describe [10]
Fasting glucose, insulin, insulin resistance and HDL did not change.
The numbers and sources
- Effect
- Against no or minimal intervention, systolic blood pressure fell 2.99 mmHg (95% CI -3.45 to -2.53) and diastolic 2.0 mmHg (95% CI -2.29 to -1.71) at moderate quality, with little or no effect on LDL or HDL. Against other diets, LDL fell 0.15 mmol/L (95% CI -0.27 to -0.02) and triglycerides 0.09 mmol/L, with little or no effect on blood pressure [2]. In 9 RCTs (1,337 people at raised risk of diabetes or heart disease), HbA1c fell 0.18 points (95% CI -0.35 to -0.01), LDL 0.10 mmol/L and triglycerides 0.20 mmol/L. Fasting glucose, insulin, insulin resistance and HDL did not change [10]. Over 12 months or more, blood pressure and lipids changed about as much as on comparator diets [7].
- Population
- Healthy adults and adults at high cardiovascular risk [2]; adults at increased risk of type 2 diabetes and heart disease [10]; adults with overweight or obesity [7].
- Sources
- [2], [7], [10]
- Caveats
- The Cochrane review rated the lipid evidence low or very low quality for most comparisons [2]. The changes are small next to drug effects.
Insulin sensitivity and metabolic markers
Not shown to change weight, glucose, HbA1c or lipids across trials. One small trial found better insulin sensitivity in women with prediabetes.
The numbers and sources
- Effect
- In women with prediabetes and overweight or obesity, insulin-stimulated glucose disposal measured by clamp rose after 10 weeks of NMN and did not change on placebo [7]. Across 15 trials, NMN did not change body weight, BMI, fasting glucose, HbA1c or lipids. HOMA-IR showed a downward trend that was not significant [8]. In the 60-day dose trial, HOMA-IR did not differ from placebo [1].
- Population
- Postmenopausal women with prediabetes [7]; 15 RCTs at 250 to 2,000 mg a day for 14 days to 24 weeks [8]; 80 middle-aged adults [1].
- Sources
- [7], [8], [1]
- Caveats
- The clamp result comes from a single small trial in one population [7]. The pooled trials were short [8].
Blood sugar and insulin
Mixed results: fasting glucose did not change in adults, while fasting insulin and insulin resistance fell slightly.
Compared with an average Nordic diet with the same calories [4]; control diets the source does not describe [7]
The numbers and sources
- Effect
- In 6 RCTs (618 participants, 6 to 26 weeks), fasting glucose did not change (-0.05 mmol/L, 95% CI -0.13 to 0.01), while fasting insulin fell 1.12 mU/L and HOMA-IR 0.34 against control diets. The insulin result depended on one study [7]. Insulin sensitivity did not change in SYSDIET [4].
- Population
- Adults in Nordic countries with cardiometabolic risk factors [4][7].
- Sources
- [4], [7]
- Caveats
- Two-hour glucose and the Matsuda index did not change [7].
Blood sugar and insulin
Mixed results: two reviews found lower fasting insulin, while a review against Mediterranean, diabetes and guideline diets found no difference in glucose, insulin or HbA1c.
Compared with control diets the source does not describe [3]; a control group the source does not describe [5]; the Mediterranean diet, a diabetes diet and a diet following Dutch Health Council advice [6]
The numbers and sources
- Effect
- Against Mediterranean, diabetes and Dutch guideline diets, fasting glucose (SMD -0.34, 95% CI -0.87 to 0.18), fasting insulin, HOMA-IR and HbA1c (SMD -0.38, 95% CI -0.87 to 0.11) did not differ [6]. In people with metabolic disorders, HOMA-IR fell 0.39 (95% CI 0.08 to 0.70) and fasting insulin 12.17 μU/mL (95% CI 0.08 to 24.26) [5]. In 19 RCTs, fasting insulin fell 1.01 (95% CI 0.57 to 1.45) [3].
- Population
- 98 people with altered glucose metabolism in 4 studies [6]; adults with metabolic disorders [5]; adults in 19 RCTs [3].
- Sources
- [3], [5], [6]
- Caveats
- The null review was small [6]. The reviews used different comparison diets.
Insulin resistance and weight in PCOS, in trials
Shown in trials to lower fasting insulin and insulin resistance slightly in women with PCOS. Fasting glucose did not change, at very low to low quality.
Compared with usual care or control groups [27]; before exercise, including trials with no control group [28]
Fasting glucose and blood pressure did not change.
The numbers and sources
- Effect
- Against control, exercise lowered fasting insulin (MD -2.44 µIU/mL, 95% CI -4.24 to -0.64) and HOMA-IR (MD -0.57, 95% CI -0.99 to -0.14), both very low quality, and LDL cholesterol and triglycerides. Waist fell 2.62 cm and BMI 1.02 kg/m2 after the programs. Fasting glucose and blood pressure did not change. Exercise added to diet did not differ from diet alone [27]. Vigorous exercise was linked to a 36.2% fall in HOMA-IR, a 4.2% fall in waist circumference and a 24.2% rise in VO2peak [28].
- Population
- 18 trials in women with PCOS [27]; 777 women in 19 studies, including uncontrolled trials, of 6 to 26 weeks [28].
- Sources
- [27], [28]
- Caveats
- Many effects were modest with wide intervals and shifted when single trials were added or removed [27]. [28] pooled controlled and uncontrolled studies.
Insulin resistance markers in older adults
Shown to raise fasting insulin and insulin resistance markers in older adults on whey, with no change in fasting glucose or lipids.
Fasting glucose and lipids did not change.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- In a meta-analysis of 25 trials in older adults, whey supplementation raised fasting insulin and HOMA insulin resistance compared with control. Fasting glucose and lipids did not change [4].
- Population
- 1,454 adults aged 64 to 84 [4].
- Sources
- [4]
- Caveats
- One review. The abstract does not give the size of the change [4].
Blood sugar, cholesterol and blood pressure
Not shown to change HbA1c, fasting glucose, cholesterol or blood pressure against placebo, with one spore oil trial finding lower lipids.
Fasting glucose, blood pressure and triglycerides did not differ.
The numbers and sources
- Effect
- In a Cochrane review of 5 trials (398 participants), 1.4 to 3 g a day for 12 to 16 weeks did not change HbA1c (WMD -0.10%, 95% CI -1.05 to 0.85), total cholesterol, LDL or BMI against placebo. Fasting glucose, blood pressure and triglycerides did not differ. Post-meal glucose results were inconsistent [2]. A 2025 meta-analysis of 17 RCTs (971 participants) at 200 to 11,200 mg a day for 1 to 24 weeks found no effect on blood pressure, fasting glucose or the lipid profile. BMI fell by 0.43 (95% CI 0.10 to 0.77) and heart rate by 3.92 beats a minute (95% CI 0.40 to 7.45) [3]. In 110 adults with dyslipidemia, a spore oil extract for 12 weeks lowered total cholesterol, triglycerides and LDL and raised HDL compared with placebo. The abstract gives no effect sizes [4].
- Population
- Adults with type 2 diabetes in the analyzed trials [2]. Healthy, at-risk and chronically ill adults [3]. Adults with dyslipidemia [4].
- Sources
- [2], [3], [4]
- Caveats
- Data in [2] came from 3 small trials, and risk of bias was unclear in 4 of 5 [2]. The 2025 review rated the certainty of evidence very low for every outcome [3]. The spore oil trial tested a different product and disagrees with both reviews on lipids [4].
Blood sugar and insulin sensitivity
Mixed results: one review found lower glucose and insulin resistance in people with diabetes, while a later review found no effect. No effect without diabetes.
The numbers and sources
- Effect
- Across 11 RCTs, resveratrol reduced fasting glucose, insulin, HbA1c and HOMA insulin resistance in participants with diabetes. No significant effect on any glycemic measure was found in participants without diabetes [1]. A 2026 umbrella review pooling 10 meta-analyses in type 2 diabetes found no significant effect on fasting glucose, HbA1c, insulin or HOMA insulin resistance [2].
- Population
- 388 participants in 11 RCTs [1]. Meta-analyses of trials in type 2 diabetes [2].
- Sources
- [1], [2]
- Caveats
- The two sources disagree on people with diabetes [1][2]. The pooled effects in people without diabetes did not vary by BMI, dose, duration or trial quality [1]. Heterogeneity was significant in [2].
Sleep extension and blood pressure, glucose and insulin
Mixed results: pooled sleep extension trials found no overall change in blood pressure, fasting glucose or insulin resistance. Blood pressure fell in people with raised pressure.
Compared with control or baseline conditions the source does not describe [14]; control or baseline conditions the source does not describe [15]
Pooled effects on fasting glucose and insulin resistance were not significant.
The numbers and sources
- Effect
- Sleep extension lengthened total sleep by 51 minutes (95% CI 39 to 63) and did not change blood pressure overall. In people with pre-hypertension or stage 1 hypertension, 24-hour systolic pressure fell 7.8 mmHg (95% CI -10.6 to -4.9) and diastolic pressure 4.2 mmHg. Pooled effects on fasting glucose and insulin resistance were not significant [14]. A systematic review of 7 extension studies reported better direct and indirect measures of insulin sensitivity, less appetite and less desire for sweet and salty foods [15].
- Population
- 13 studies from 11 trials, 3 days to 6 weeks, adults without a sleep disorder [14]. 138 participants in 7 studies, mostly short sleepers [15].
- Sources
- [14], [15]
- Caveats
- Small and short trials. The blood pressure fall is a subgroup result. The review of 7 studies gave no pooled estimates [15].
Blood sugar in trials
Shown to lower the rise in blood sugar after a meal against refined foods. Longer trials found no change in fasting glucose, and one review found HbA1c fell.
Compared with similar refined foods [12]; refined grains or placebo [9]
The numbers and sources
- Effect
- In 14 single-meal trials, whole grain foods reduced the 2-hour glucose response by 29.71 mmol·min/L (95% CI -43.57 to -15.85) and the insulin response. In 16 trials lasting weeks to months, fasting glucose, fasting insulin and HOMA-IR did not change significantly [12]. Another review found whole grains lowered HbA1c (SMD -0.33, 95% CI -0.61 to -0.04) [9].
- Population
- Healthy adults in 30 trials [12]. 25 trials of adults with or without cardiovascular risk factors [9].
- Sources
- [12], [9]
- Caveats
- Most longer trials enrolled healthy people with normal blood sugar [12].
Preventing type 2 diabetes
One trial found ramipril did not lower new diabetes or death over 3 years in adults with raised blood sugar, 18.1% against 19.5% on placebo.
More people on ramipril returned to normal blood sugar (HR 1.16, 95% CI 1.07 to 1.27).
The numbers and sources
- Effect
- Diabetes or death occurred in 18.1% on ramipril and 19.5% on placebo (HR 0.91, 95% CI 0.81 to 1.03). More people on ramipril returned to normal blood sugar (HR 1.16, 95% CI 1.07 to 1.27). Glucose 2 hours after a glucose load was lower on ramipril (135.1 against 140.5 mg/dL), and fasting glucose did not differ significantly [16].
- Population
- 5,269 adults without cardiovascular disease with impaired fasting glucose or impaired glucose tolerance, median 3 years [16].
- Sources
- [16]
- Caveats
- One trial, of ramipril up to 15 mg a day.
- Why limited
- This rests on one trial, of 5,269 people. Strength counts independent studies that agree, so one trial is limited at any size.
Long-term blood sugar (HbA1c)
One trial found 6 g a day of oat beta-glucan in bread did not change HbA1c over 16 weeks in adults at risk of type 2 diabetes.
Fasting glucose, insulin and LDL cholesterol (-0.11 mmol/L, 95% CI -0.27 to 0.05) did not differ either.
The numbers and sources
- Effect
- In 194 adults at risk of type 2 diabetes, bread enriched to 6 g of oat beta-glucan a day for 16 weeks did not change HbA1c compared with whole-grain wheat bread (difference -0.01%, 95% CI -0.03 to 0.06). Fasting glucose, insulin and LDL cholesterol (-0.11 mmol/L, 95% CI -0.27 to 0.05) did not differ either [6].
- Population
- Adults aged about 58 with a mean BMI of 32 in Germany, Norway and Sweden [6].
- Sources
- [6]
- Caveats
- One trial, run as an effectiveness trial in real-life conditions, against whole-grain wheat bread, not a fiber-free control [6].
Blood sugar
Small trials found HbA1c fell about 0.5 points. Pooled trials found no change in fasting glucose.
Compared with usual diets, and for fasting glucose also low-antioxidant and weight-loss diets, behavioral programs alone and usual gestational diabetes care [7]
Fasting insulin fell slightly, and fasting glucose and insulin resistance did not change.
The numbers and sources
- Effect
- A meta-analysis of 2 controlled trials (65 participants) found HbA1c fell 0.53 points (95% CI -0.62 to -0.43). Fasting insulin fell slightly, and fasting glucose and insulin resistance did not change [7].
- Population
- Adults with and without diabetes [7].
- Sources
- [7]
- Caveats
- Two small trials. Certainty ranged from very low to moderate across secondary outcomes [7].
Blood sugar and laboratory changes
Small studies found no change in fasting glucose, insulin or lipids in children over 1 year and in older men over 6 weeks.
The numbers and sources
- How common
- How often is not known: the sources give no rate.
- Effect
- Over 1 year in children, no adverse changes in general biochemical or hormonal tests were reported, with no change in fasting glucose and no excessive rise in IGF-1 [1]. In older men over 6 weeks, glucose, insulin and the glucose tolerance test did not change, lipids did not change, and no significant adverse effects were reported [4].
- Population
- 110 children [1]; 11 older men [4].
- Sources
- [1], [4]
- Caveats
- Small studies without placebo groups.
How it compares with the reference method
Mixed results2
Variation from one test to the next
Mixed results: fasting glucose varied 5.7% within a person over about 2 weeks, and 70% of people at 126 mg/dL or above were there again on a second test.
The numbers and sources
- Compared with
- A repeat fasting test in the same person about 2 weeks later
- Effect
- In repeat examinations about 2 weeks apart, the within-person coefficient of variation was 5.7% (95% CI 5.3 to 6.1) for fasting glucose, against 16.7% for 2-hour glucose and 3.6% for HbA1c. Of people with fasting glucose of 126 mg/dL or higher on the first test, 70.4% (95% CI 49.8 to 86.2) were at that level on the second. Requiring a second result lowered the prevalence of undiagnosed diabetes from 3.7% to 2.8% [16]. A laboratory guideline cites within-person variation of 4.8% to 6.1% and sets analytical goals of imprecision at or below 2.4% and total error at or below 6.1% [2].
- Population
- 685 fasting adults without diagnosed diabetes in a US national survey [16].
- Sources
- [16], [2]
- Caveats
- The study states no threshold for agreement, so the result is given as numbers only. The laboratory guideline notes that variation within a person is substantially greater than analytical variation [2].
Home glucose meters against a laboratory measurement
Mixed results: 6 of 18 cleared home glucose meters stayed within 15% of a laboratory value often enough to meet an accuracy standard in all three test rounds.
The numbers and sources
- Compared with
- Plasma glucose measured by a reference laboratory
- Effect
- In three blinded studies of 18 marketed meters bought from consumer outlets, a reading counted as compliant if it was within 15% of the reference plasma value at 100 mg/dL or above, or within 15 mg/dL below that. Six of the 18 systems met the predetermined accuracy standard in all three studies, five in two, three in one and four in none [17]. A laboratory guideline reports that FDA and ISO standards allow an error of about 15% for home meters, and that in a 2017 study only 2 of 17 commercial meters met the ISO standard. The same guideline puts the mean difference between capillary and venous glucose at 0.1 mmol/L (2 mg/dL) in fasting samples and 1.7 mmol/L (30 mg/dL) after a glucose load [2].
- Population
- 18 meters, each tested on an average of 115 people in each of three studies at three clinical sites [17].
- Sources
- [17], [2]
- Caveats
- The accuracy standard used was similar to but more lenient than regulatory standards. An error of 15% at 100 mg/dL spans 85 to 115 mg/dL, wider than the gap between some of the bands above. The laboratory guideline states that portable meters are not to be used to diagnose diabetes [2].
Did not match the reference method1
Sample handling before the laboratory measures it
Limited evidence: a laboratory guideline reports that glucose in a blood tube falls about 5 to 7% an hour, about 10 mg/dL, until the cells are removed.
The numbers and sources
- Compared with
- A sample whose cells are removed promptly
- Effect
- The guideline reports that the rate of glycolysis in a collected sample averages 5% to 7% an hour, about 0.6 mmol/L (10 mg/dL). It states that tubes containing only sodium fluoride are not to be relied on, because glycolysis continues for up to 4 hours in them. It advises a tube with a rapidly acting inhibitor such as citrate buffer, or placing the tube in an ice-water slurry and removing the cells within 15 to 30 minutes [2].
- Population
- Figures quoted by a guideline document from earlier studies, whose sizes it does not give in the passage read [2].
- Sources
- [2]
- Caveats
- Secondhand figures from guideline text, not a primary study. A delay lowers the result, so it can move a reading from one band to the one below.
What studies tie it to
Linked in research4
Developing type 2 diabetes
Linked to later type 2 diabetes: fasting glucose of 100 to 125 mg/dL went with about 4 times the risk in a Cochrane review of cohort studies.
The numbers and sources
- Effect
- Against normal glucose levels, the pooled hazard ratio for developing type 2 diabetes was 4.32 (95% CI 2.61 to 7.12) for fasting glucose of 100 to 125 mg/dL and 5.47 (3.50 to 8.54) for 110 to 125 mg/dL. In the 47 studies that reported it, 33% to 59% of people with intermediate hyperglycemia returned to normal levels within 1 to 5 years [6]. In a Dutch cohort, the odds ratio for diabetes in the highest against the lowest fifth of fasting glucose was 9.0 (95% CI 4.4 to 18.5), and the association rose more steeply at higher values [7].
- Population
- 103 prospective cohort studies, with 8 studies and 9,017 participants behind the first hazard ratio and 9 studies and 2,818 participants behind the second [6]. 1,349 people aged 50 to 75 without diabetes, followed a mean 6.4 years [7].
- Sources
- [6], [7]
- Caveats
- Observational. The review rated this evidence as low certainty because many studies did not adjust adequately for confounders and the intervals were wide [6]. Fasting glucose is itself one of the tests that diagnose diabetes, which strengthens the link [7].
Heart disease and stroke
Linked to more coronary heart disease above 100 mg/dL in 102 pooled cohorts, 11% to 17% more below the diabetes range, with no link between 70 and 100 mg/dL.
The numbers and sources
- Effect
- In 102 prospective studies, fasting glucose was non-linearly related to vascular risk, with no significant association between 3.90 and 5.59 mmol/L (70 to 100 mg/dL). Against that range, hazard ratios for coronary heart disease were 1.07 (95% CI 0.97 to 1.18) below 3.90 mmol/L, 1.11 (1.04 to 1.18) at 5.60 to 6.09 mmol/L and 1.17 (1.08 to 1.26) at 6.10 to 6.99 mmol/L. Diabetes went with a hazard ratio of 2.00 (1.83 to 2.19). In people without known diabetes, adding fasting glucose to conventional risk factors did not significantly improve prediction of vascular disease [8]. In a meta-analysis of 53 cohorts, impaired fasting glucose went with a relative risk of cardiovascular disease of 1.13 by the American definition and 1.26 by the WHO definition, and of stroke of 1.06 and 1.17 [9].
- Population
- 698,782 people without vascular disease in 102 prospective studies, with 52,765 vascular outcomes [8]. 1,611,339 people in 53 prospective cohort studies, median follow-up 9.5 years [9].
- Sources
- [8], [9]
- Caveats
- Observational. In the pooled cohorts, hazard ratios for diabetes did not change appreciably after further adjustment for lipid, inflammatory or kidney markers [8].
Death from any cause
Linked to more deaths above 100 mg/dL and not between 70 and 100 mg/dL, in 97 pooled cohorts of 820,900 people.
The numbers and sources
- Effect
- In 97 prospective studies, fasting glucose above 100 mg/dL was associated with death and levels of 70 to 100 mg/dL were not. Diabetes went with a hazard ratio for death from any cause of 1.80 (95% CI 1.71 to 1.90) [10]. In an updated meta-analysis, prediabetes by any definition went with a relative risk of death from any cause of 1.13 (95% CI 1.10 to 1.17) in the general population [11]. An earlier meta-analysis put the relative risk at 1.13 for impaired fasting glucose by both the American and WHO definitions [9].
- Population
- 820,900 people in 97 prospective studies, with 123,205 deaths [10]. 10,069,955 people in 129 studies, median follow-up 9.8 years [11].
- Sources
- [10], [11], [9]
- Caveats
- Observational. The updated meta-analysis pooled several definitions of prediabetes, and found impaired glucose tolerance carried a higher risk than impaired fasting glucose [11].
Diabetic eye disease
Linked to diabetic eye disease from about 6.4 to 6.8 mmol/L (about 115 to 123 mg/dL) upward, in pooled data on 41,411 people.
The numbers and sources
- Effect
- In pooled data from nine studies, the prevalence of diabetes-specific retinopathy was low at fasting glucose below 6.0 mmol/L and rose above that level. The threshold fell at 6.4 to 6.8 mmol/L by one method and 6.6 mmol/L by another. The authors suggested the diagnostic level for fasting glucose could be lowered from 7.0 to 6.5 mmol/L [15].
- Population
- 44,623 people aged 20 to 79 with gradable retinal photographs in nine studies from five countries, 41,411 of them with fasting glucose [15].
- Sources
- [15]
- Caveats
- Cross-sectional. WHO states that its diabetes criteria mark a group with more premature death and more microvascular and cardiovascular complications, while noting the limits of the data behind them [5].
Mixed results1
Diabetes and heart disease in trials that treated raised glucose before diabetes
Mixed results: in trials of people with raised glucose, lifestyle change cut new diabetes 58%, while neither it nor insulin aimed at normal fasting glucose cut cardiovascular events.
The numbers and sources
- Effect
- In people with elevated fasting and post-load glucose, a lifestyle program reduced the incidence of diabetes by 58% (95% CI 48 to 66) and metformin by 31% (95% CI 17 to 43) against placebo over 2.8 years [12]. Over a median 21 years of follow-up of the same participants, neither metformin (HR 1.03, 95% CI 0.78 to 1.37) nor the lifestyle program (HR 1.14, 95% CI 0.87 to 1.50) reduced major cardiovascular events [13]. In a trial that gave insulin glargine to reach a fasting glucose of 95 mg/dL or below, cardiovascular outcomes did not differ from standard care over 6.2 years (HR 1.02, 95% CI 0.94 to 1.11). New diabetes was less frequent (30% against 35%), severe hypoglycemia was more frequent (1.00 against 0.31 per 100 person-years) and weight rose [14].
- Population
- 3,234 people without diabetes, mean age 51, mean body mass index 34.0 [12][13]. 12,537 people, mean age 63.5, with cardiovascular risk factors plus impaired fasting glucose, impaired glucose tolerance or type 2 diabetes [14].
- Sources
- [12], [13], [14]
- Caveats
- A marker that tracks risk is not always one whose lowering changes it. In the long follow-up, all groups were offered a lifestyle program and many used statins and blood pressure drugs, which the authors say may have diluted any effect [13]. The insulin trial included people who already had type 2 diabetes [14].
Sources
- US Food and Drug Administration. 21 CFR 862.1345, Glucose test system. Electronic Code of Federal Regulations, with the FDA product classification entry for over-the-counter blood glucose test systems (product code NBW). https://www.ecfr.gov/current/title-21/section-862.1345
- Sacks DB, Arnold M, Bakris GL, et al. Guidelines and Recommendations for Laboratory Analysis in the Diagnosis and Management of Diabetes Mellitus. Clinical Chemistry. 2023. https://doi.org/10.1093/clinchem/hvad080
- American Diabetes Association. Diabetes Diagnosis. Accessed November 2026. https://diabetes.org/about-diabetes/diagnosis
- National Institute of Diabetes and Digestive and Kidney Diseases. Diabetes Tests and Diagnosis. US National Institutes of Health. Last reviewed July 2022. https://www.niddk.nih.gov/health-information/diabetes/overview/tests-diagnosis
- World Health Organization and International Diabetes Federation. Definition and Diagnosis of Diabetes Mellitus and Intermediate Hyperglycaemia: Report of a WHO/IDF Consultation. Geneva: World Health Organization, 2006. https://www.who.int/publications/i/item/definition-and-diagnosis-of-diabetes-mellitus-and-intermediate-hyperglycaemia
- Richter B, Hemmingsen B, Metzendorf MI, Takwoingi Y. Development of type 2 diabetes mellitus in people with intermediate hyperglycaemia. Cochrane Database of Systematic Reviews. 2018. https://doi.org/10.1002/14651858.CD012661.pub2
- Ruijgrok C, Dekker JM, Beulens JW, et al. Size and shape of the associations of glucose, HbA1c, insulin and HOMA-IR with incident type 2 diabetes: the Hoorn Study. Diabetologia. 2018. https://doi.org/10.1007/s00125-017-4452-7
- Emerging Risk Factors Collaboration. Diabetes mellitus, fasting blood glucose concentration, and risk of vascular disease: a collaborative meta-analysis of 102 prospective studies. The Lancet. 2010. https://doi.org/10.1016/S0140-6736(10)60484-9
- Huang Y, Cai X, Mai W, Li M, Hu Y. Association between prediabetes and risk of cardiovascular disease and all cause mortality: systematic review and meta-analysis. BMJ. 2016. https://doi.org/10.1136/bmj.i5953
- Emerging Risk Factors Collaboration. Diabetes Mellitus, Fasting Glucose, and Risk of Cause-Specific Death. New England Journal of Medicine. 2011. https://doi.org/10.1056/NEJMoa1008862
- Cai X, Zhang Y, Li M, et al. Association between prediabetes and risk of all cause mortality and cardiovascular disease: updated meta-analysis. BMJ. 2020. https://doi.org/10.1136/bmj.m2297
- Diabetes Prevention Program Research Group. Reduction in the Incidence of Type 2 Diabetes with Lifestyle Intervention or Metformin. New England Journal of Medicine. 2002. https://doi.org/10.1056/NEJMoa012512
- Goldberg RB, Orchard TJ, Crandall JP, et al. Effects of Long-term Metformin and Lifestyle Interventions on Cardiovascular Events in the Diabetes Prevention Program and Its Outcome Study. Circulation. 2022. https://doi.org/10.1161/CIRCULATIONAHA.121.056756
- ORIGIN Trial Investigators. Basal Insulin and Cardiovascular and Other Outcomes in Dysglycemia. New England Journal of Medicine. 2012. https://doi.org/10.1056/NEJMoa1203858
- Colagiuri S, Lee CM, Wong TY, et al. Glycemic Thresholds for Diabetes-Specific Retinopathy: Implications for diagnostic criteria for diabetes. Diabetes Care. 2011. https://doi.org/10.2337/dc10-1206
- Selvin E, Crainiceanu CM, Brancati FL, Coresh J. Short-term Variability in Measures of Glycemia and Implications for the Classification of Diabetes. Archives of Internal Medicine. 2007. https://doi.org/10.1001/archinte.167.14.1545
- Klonoff DC, Parkes JL, Kovatchev BP, et al. Investigation of the Accuracy of 18 Marketed Blood Glucose Monitors. Diabetes Care. 2018. https://doi.org/10.2337/dc17-1960