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Research · Diets

Intermittent fasting

Meta-analyses find intermittent fasting, mostly time-restricted eating, lowers weight against usual eating but no more than daily calorie restriction. Fasting glucose and blood pressure fell slightly. About 0.4 to 0.9 kg of lean mass was lost alongside fat. Two fasting days a week doubled low blood sugar episodes on diabetes drugs, and cohorts linked very short eating windows to cardiovascular deaths.

Add to Bio HackChecked 2026-11-13
Status
A dietary pattern, not a regulated product.
Also called
intermittent fasting, IF, time-restricted eating, TRE, time-restricted feeding, 16:8, 16/8, 14:10, 18:6, early time-restricted eating, eating window
Followed for
weight loss, fat loss, blood sugar, insulin resistance, blood pressure, heart health, longevity, appetite control

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

Shown to help3

Reported risks5

What people follow it for, and what was found

Shown to help3

Strong

Weight loss compared with usual eating

Shown to lower body weight against usual eating in adults, by about 1.6 kg in pooled trials, though one 12-week trial without other changes found no difference.

Compared with no intervention or a waiting list [1]; eating over 10 or more hours a day [4]; no restriction [7]; usual diets, and late time-restricted eating for the early-window result [8]; three structured meals a day [9]

The numbers and sources
Effect
Against no intervention or a waiting list, percentage weight loss differed by -3.42 points (95% CI -4.95 to -1.90, 6 studies, 427 participants, moderate certainty) [1]. Time-restricted eating alone lowered weight by 1.59 kg (95% CI -2.02 to -1.15) and fat mass by 0.93 kg (95% CI -1.22 to -0.63) against no restriction [7]. In 41 trials with 2,287 participants, time-restricted eating lowered body weight, BMI, fat mass and waist circumference against usual diets, and early windows lost 1.15 kg more than late windows (95% CI -1.86 to -0.45, high certainty) [8]. An 8-hour window lost 4.61 kg more than control at 12 months (95% CI -7.37 to -1.85) [4]. In the 12-week TREAT trial, a noon to 8 p.m. window and three structured meals a day differed by -0.26 kg (95% CI -1.30 to 0.78, P .63) [9].
Population
Adults with overweight or obesity [1]; 20 trials with 1,242 adults [7]; 41 trials with 2,287 participants [8]; 90 adults with obesity [4]; 116 adults aged 18 to 64 with BMI 27 to 43 [9].
Sources
[1], [4], [7], [8], [9]
Caveats
The Cochrane authors describe the -3.42 point difference as likely little to no difference [1]. In the 12-month trial, calorie intake fell 425 kcal a day on the 8-hour window, close to the 405 kcal fall on calorie restriction [4]. Early eating windows ended before 5 p.m. [8].
Moderate

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]

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.
Moderate

Blood pressure

Shown to lower blood pressure by about 2 mm Hg against unrestricted eating in adults without diabetes, more in those starting with high pressure.

Compared with eating every day, with no fasting days or daily fasting window

The numbers and sources
Effect
Time-restricted eating without calorie restriction lowered systolic pressure by 1.79 mm Hg (95% CI -3.30 to -0.27), diastolic by 1.75 mm Hg (95% CI -3.07 to -0.43) and heart rate by 2.19 beats a minute, with larger falls when baseline pressure was high [11]. An early 8-hour window plus calorie restriction lowered diastolic pressure 4 mm Hg (95% CI -8 to 0) more than calorie restriction with a 12-hour window [6]. Blood pressure did not differ between an 8-hour window, calorie restriction and control in type 2 diabetes [12], nor between time-restricted eating with calorie restriction and calorie restriction alone [3].
Population
11 trials with 653 adults without diabetes [11]; 90 adults with obesity over 14 weeks [6]; 75 adults with type 2 diabetes [12]; 139 adults with obesity [3].
Sources
[3], [6], [11], [12]
Caveats
The pooled falls are small. When calorie intake was matched, blood pressure did not differ [3].

Not shown to help2

Strong

Weight loss compared with daily calorie restriction

Not shown to cause more weight loss than daily calorie restriction or regular diet advice in adults with overweight or obesity, in trials of up to 12 months.

Compared with regular dietary advice [1]; continuous energy restriction, and time-restricted eating as another fasting form [2]; daily calorie restriction alone [3]; 25% daily calorie restriction [4]

The numbers and sources
Effect
Against regular dietary advice, intermittent fasting changed percentage weight loss by -0.33 points (95% CI -0.92 to 0.26, 21 studies, 1,430 participants, low certainty), and the chance of losing 5% of body weight did not differ (RR 0.98, 95% CI 0.82 to 1.18) [1]. In a network meta-analysis of 99 trials, alternate-day fasting was the only form to lose more weight than continuous energy restriction (-1.29 kg, 95% CI -1.99 to -0.59), and alternate-day fasting lost 1.69 kg more than time-restricted eating [2]. Eating only from 8 a.m. to 4 p.m. on a calorie-restricted diet lost 8.0 kg at 12 months against 6.3 kg on calorie restriction alone, a net difference of -1.8 kg (95% CI -4.0 to 0.4, P 0.11) [3]. An 8-hour window without calorie counting and 25% daily calorie restriction differed by 0.81 kg at 12 months (95% CI -3.07 to 4.69) [4].
Population
22 randomized trials with 1,995 adults with overweight or obesity, published 2016 to 2024 [1]; 99 trials with 6,582 adults, most with existing health conditions [2]; 139 adults with obesity in China, 118 completing 12 months [3]; 90 adults with obesity in Chicago, 33% Black and 46% Hispanic [4].
Sources
[1], [2], [3], [4]
Caveats
Follow-up in the Cochrane review was 12 months or less [1]. In the network meta-analysis, trials of 24 weeks or longer showed weight benefits only against unrestricted eating [2]. An earlier Cochrane review found -0.88 kg against continuous energy restriction in the short term (very low certainty) and -0.56 kg (95% CI -1.68 to 0.56) at 3 to 12 months [5]. One 14-week trial found an early 7 a.m. to 3 p.m. window plus calorie restriction lost 2.3 kg more (95% CI -3.7 to -0.9) than calorie restriction over 12 hours or more, equal to eating 214 kcal a day less, and body fat did not differ [6].
Limited

Longevity and heart disease

Limited evidence: no pooled trial measured deaths, heart attacks or strokes, and cohort studies linked eating windows of 8 hours or less to more cardiovascular deaths.

Compared with no trial reported these outcomes [5]; US adults whose eating window was 12 to 14 hours [14]; US adults with other eating windows [15]

The numbers and sources
Effect
A Cochrane review of 18 pooled trials with 1,125 participants found no data on all-cause death, cardiovascular death, stroke, heart attack or heart failure [5]. In US survey cohorts, eating windows under 8 hours were linked to higher cardiovascular death against 12 to 14 hours [14], and mortality was lowest at about 11 to 12 hours a day [15]. These cohort results appear under Risks.
Population
Trials of 4 weeks to 6 months [5]; observational cohorts of 19,831 and 33,052 US adults [14][15].
Sources
[5], [14], [15]
Caveats
The cohorts measured habitual eating duration from two 24-hour diet recalls, not a chosen fasting plan [14][15].

How trials defined it

Time-restricted eating trials limited eating to a daily window. Windows of 8 hours ran from noon to 8 p.m. without calorie counting [4][12], from 8 a.m. to 4 p.m. on 1,500 to 1,800 kcal a day for men and 1,200 to 1,500 kcal for women [3], or from 7 a.m. to 3 p.m. with calorie restriction [6]. One trial personalized an 8 to 10 hour window that cut at least 4 hours from the usual one [13]. TREAT allowed food from noon to 8 p.m. and nothing with calories from 8 p.m. to noon [9]. Pooled trials used windows of 4 to 10 hours [10] or 6 to 10 hours [11], and classed windows as early, mid or late by a last meal before 5 p.m., between 5 and 7 p.m., or after 7 p.m. [8]. The Cochrane review also counted periodic fasting and alternate-day fasting, with at least 4 weeks of intervention [1]. Two-day fasting schedules used 2,092 to 2,510 kJ (about 500 to 600 kcal) on 2 days a week [16].

Risks

Reported risks4

ModerateHow often is not known

Lean mass loss

Shown to lower fat-free mass by about 0.4 to 0.9 kg alongside fat loss in adults with overweight, with no loss found in resistance-trained adults.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In 30 studies with 1,341 participants, fat-free mass fell 0.86 kg (95% CI -1.23 to -0.49) against non-matched controls and 0.41 kg (95% CI -0.79 to -0.03) against calorie-matched controls [17]. In 20 trials, fat-free mass fell 0.58 kg on time-restricted eating against no restriction and 0.56 kg on time-restricted eating plus calorie restriction against calorie restriction alone [7]. In TREAT, appendicular lean mass index fell 0.16 kg/m² more than on three structured meals (95% CI -0.27 to -0.05) [9]. In 8 trials of resistance-trained adults, fat-free mass changed by 0.27 kg (95% CI -0.80 to 1.34) [18].
Population
Adults with overweight or obesity [17]; 1,242 adults [7]; 50 adults tested in person [9]; resistance-trained adults on 8 to 10 hour windows [18].
Sources
[7], [9], [17], [18]
Caveats
Fat-free mass falls with most weight loss, and the time-restricted groups often lost more weight than controls [17]. Lean mass did not differ between time-restricted eating with calorie restriction and calorie restriction alone over 12 months [3]. The resistance training trials were few, small and short [18].
LimitedHow often is not known

Low blood sugar with diabetes medication

One trial found two fasting days a week doubled low blood sugar episodes in type 2 diabetes on glucose-lowering drugs, despite medication cuts.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Fasting raised the rate of hypoglycemia (RR 2.05, 95% CI 1.17 to 3.52), with a mean of 1.4 events over 12 weeks, whether fasting days were consecutive or not [16]. In a 12-month trial, low or high glucose events in the first 2 weeks were similar on 2-day intermittent and continuous restriction (3.2 against 4.9 events) and affected 35% of participants using sulfonylureas or insulin [19]. An 8-hour window without calorie counting in type 2 diabetes reported no serious adverse events over 6 months [12].
Population
41 adults with type 2 diabetes on metformin or other glucose-lowering drugs [16]; 137 adults with type 2 diabetes, 46 on sulfonylureas or insulin [19]; 75 adults with type 2 diabetes [12].
Sources
[12], [16], [19]
Caveats
The two trials reporting low blood sugar used 2 fasting days a week, not a daily eating window. Both reduced medication at the start by protocol [16][19].
ModerateHow often is not known

Hunger

Shown to raise hunger ratings against calorie-matched diets in adults with overweight or obesity, in a pooled analysis of 4 trials.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Hunger rose against calorie-matched control diets (MD 2.05, 95% CI 1.46 to 2.64, I² 0%) [20]. A systematic review of 16 studies found higher appetite at bedtime and lower or unchanged appetite in the morning [21].
Population
323 adults with overweight or obesity in 4 trials [20]; adults on windows of 12 hours or less [21].
Sources
[20], [21]
Caveats
Only 4 trials were pooled, and the abstract does not name the hunger scale [20].
LimitedHow often is not known

Cardiovascular death in cohort studies

Linked to 2.35 times the cardiovascular death rate with eating windows under 8 hours, against 12 to 14 hours, in a US survey cohort.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Over a median 8.1 years, eating duration under 8 hours was associated with higher cardiovascular mortality (HR 2.35, 95% CI 1.39 to 3.98) and not with all-cause or cancer mortality [14]. A second analysis found a U-shaped pattern with the lowest mortality at about 11 to 12 hours. Windows of 8 hours or less were linked to at least 30% higher all-cause mortality, and windows of 15 hours or more to 25% higher [15].
Population
19,831 adults [14] and 33,052 adults [15] from the US National Health and Nutrition Examination Survey 2003 to 2018. Observational.
Sources
[14], [15]
Caveats
Observational. Eating duration came from two 24-hour diet recalls, not a fasting plan. The authors of [14] note the link may reflect residual confounding.

Mixed results1

LimitedHow often is not known

Disordered eating

Linked to higher eating disorder symptoms in two observational studies of young adults, while trials of time-restricted eating found no change on eating disorder questionnaires.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In a systematic review of 16 studies, disordered eating questionnaires did not change with time-restricted eating. Qualitative findings included fear of hunger and eating in the absence of hunger [21]. Among 2,762 Canadian adolescents and young adults, 47.7% of women and 38.4% of men reported intermittent fasting in the past year, and it was associated with eating disorder psychopathology in every gender group [22]. In 491 Chinese adults followed for 8 months, current or past intermittent fasting was associated with higher eating disorder psychopathology at follow-up [23].
Population
Trial and qualitative studies of adults [21]; observational surveys [22][23].
Sources
[21], [22], [23]
Caveats
The surveys are observational and cannot show whether fasting led to symptoms or the reverse [22][23].

Claims tested and not found

  1. That time-restricted eating causes more weight loss than counting calories. Over 12 months, weight loss did not differ from daily calorie restriction [3][4], and pooled trials found little to no difference from regular diet advice [1].
  2. That an eating window alone leads to weight loss. In a 12-week trial with no other changes, weight loss did not differ from three structured meals a day [9].

Sources

  1. Garegnani LI, Oltra G, Ivaldi D, et al. Intermittent fasting for adults with overweight or obesity. Cochrane Database of Systematic Reviews. 2026. https://doi.org/10.1002/14651858.cd015610.pub2
  2. Semnani-Azad Z, Khan TA, Chiavaroli L, et al. Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors: systematic review and network meta-analysis of randomised clinical trials. BMJ. 2025. https://doi.org/10.1136/bmj-2024-082007
  3. Liu D, Huang Y, Huang C, et al. Calorie Restriction with or without Time-Restricted Eating in Weight Loss. New England Journal of Medicine. 2022. https://doi.org/10.1056/nejmoa2114833
  4. Lin S, Cienfuegos S, Ezpeleta M, et al. Time-Restricted Eating Without Calorie Counting for Weight Loss in a Racially Diverse Population: A Randomized Controlled Trial. Annals of Internal Medicine. 2023. https://doi.org/10.7326/m23-0052
  5. Allaf M, Elghazaly H, Mohamed OG, et al. Intermittent fasting for the prevention of cardiovascular disease. Cochrane Database of Systematic Reviews. 2021. https://doi.org/10.1002/14651858.cd013496.pub2
  6. Jamshed H, Steger FL, Bryan DR, et al. Effectiveness of Early Time-Restricted Eating for Weight Loss, Fat Loss, and Cardiometabolic Health in Adults With Obesity: A Randomized Clinical Trial. JAMA Internal Medicine. 2022. https://doi.org/10.1001/jamainternmed.2022.3050
  7. Sun Y, Liu Y, Ye W, et al. Efficiency of time-restricted eating and energy restriction on anthropometrics and body composition in adults: a systematic review and meta-analysis of randomized controlled trials. International Journal of Behavioral Nutrition and Physical Activity. 2025. https://doi.org/10.1186/s12966-025-01812-w
  8. Chen YE, Tsai HL, Tu YK, et al. Effects of timing and eating duration of time restricted eating on metabolic outcomes: systematic review and network meta-analysis. BMJ Medicine. 2026. https://doi.org/10.1136/bmjmed-2024-001071
  9. Lowe DA, Wu N, Rohdin-Bibby L, et al. Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters in Women and Men With Overweight and Obesity: The TREAT Randomized Clinical Trial. JAMA Internal Medicine. 2020. https://doi.org/10.1001/jamainternmed.2020.4153
  10. Viple F, Pedersen SS, Andersen TH, et al. Effects of time-restricted eating on markers of glucose metabolism and regulation in individuals with prediabetes or type 2 diabetes: a systematic review and meta-analysis of randomised controlled trials. Diabetologia. 2026. https://doi.org/10.1007/s00125-026-06792-5
  11. Yi X, Yan J, Daut UN, et al. Effects of time-restricted eating without caloric restriction on blood pressure and cardiometabolic profile in non-diabetic adults: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Nutrition. 2025. https://doi.org/10.3389/fnut.2025.1631477
  12. Pavlou V, Cienfuegos S, Lin S, et al. Effect of Time-Restricted Eating on Weight Loss in Adults With Type 2 Diabetes: A Randomized Clinical Trial. JAMA Network Open. 2023. https://doi.org/10.1001/jamanetworkopen.2023.39337
  13. Manoogian ENC, Wilkinson MJ, O'Neal M, et al. Time-Restricted Eating in Adults With Metabolic Syndrome: A Randomized Controlled Trial. Annals of Internal Medicine. 2024. https://doi.org/10.7326/m24-0859
  14. Chen M, Xu L, Van Horn L, et al. Association of eating duration less than 8 h with all-cause, cardiovascular, and cancer mortality. Diabetes & Metabolic Syndrome: Clinical Research & Reviews. 2025. https://doi.org/10.1016/j.dsx.2025.103278
  15. Mao Z, Grant H, Kritchevsky SB, et al. Association of Eating Window With Mortality Among US Adults: Insights From a Nationally Representative Study. Aging Cell. 2025. https://doi.org/10.1111/acel.70230
  16. Corley BT, Carroll RW, Hall RM, et al. Intermittent fasting in Type 2 diabetes mellitus and the risk of hypoglycaemia: a randomized controlled trial. Diabetic Medicine. 2018. https://doi.org/10.1111/dme.13595
  17. Fernandes-Alves D, Teixeira GP, Guimarães KC, et al. Systematic Review and Meta-analysis of Randomized Clinical Trials Comparing Time-Restricted Eating With and Without Caloric Restriction for Weight Loss. Nutrition Reviews. 2026. https://doi.org/10.1093/nutrit/nuaf053
  18. Ali AM, Messenburger GP, Neves Collares LD, et al. Time-restricted eating shows a modest reduction in fat mass in resistance-trained individuals: A systematic review and meta-analysis. Nutrition Research. 2026. https://doi.org/10.1016/j.nutres.2026.01.001
  19. Carter S, Clifton PM, Keogh JB. Effect of Intermittent Compared With Continuous Energy Restricted Diet on Glycemic Control in Patients With Type 2 Diabetes: A Randomized Noninferiority Trial. JAMA Network Open. 2018. https://doi.org/10.1001/jamanetworkopen.2018.0756
  20. Silva AD, Guimarães KC, Oliveira RA, et al. Time-restricted eating increases hunger in adults with overweight and obesity: A systematic review and meta-analysis of randomized controlled studies. Nutrition Research. 2025. https://doi.org/10.1016/j.nutres.2025.04.003
  21. Vizthum D, Katz SE, Pacanowski CR. The impact of time restricted eating on appetite and disordered eating in adults: A mixed methods systematic review. Appetite. 2023. https://doi.org/10.1016/j.appet.2023.106452
  22. Ganson KT, Cuccolo K, Hallward L, et al. Intermittent fasting: Describing engagement and associations with eating disorder behaviors and psychopathology among Canadian adolescents and young adults. Eating Behaviors. 2022. https://doi.org/10.1016/j.eatbeh.2022.101681
  23. He J, Chen X, Cui T, et al. Engagement in Intermittent Fasting is Prospectively Associated With Higher Body Mass Index, Higher Eating Disorder Psychopathology, and Lower Intuitive Eating in Chinese Adults. International Journal of Eating Disorders. 2025. https://doi.org/10.1002/eat.24322

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