What does the research show about 5:2 diet?

5:2 diet

Trials find the 5:2 diet loses about as much weight as daily calorie restriction over 6 to 12 months, and more than no diet. In type 2 diabetes, HbA1c fell about as much as with daily restriction. Fasting days doubled low blood sugar episodes on diabetes drugs. Intakes of calcium, zinc, magnesium, potassium and fiber ran low in diet records.

Add to Bio HackChecked 2026-11-13

Status: A dietary pattern, not a regulated product.
Also called: 5:2, 5:2 diet, five two diet, Fast Diet, intermittent energy restriction, IER, two-day diet, twice-weekly fasting, 5:2 intermittent fasting
Followed for: weight loss, blood sugar, type 2 diabetes, insulin resistance, heart health, 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 help1

ModerateShown 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.

Reported risks10

ModerateMild physical and psychological side effects were reported on fasting days in pooled trials, with no serious adverse events.How often is not known
LimitedLimited evidence: one diet record study found calcium intake below guidelines during 5:2.How often is not known
LimitedLimited evidence: one diet record study found zinc intake below guidelines during 5:2.How often is not known
LimitedLimited evidence: magnesium intake ran below guidelines in one study and fell more than on daily calorie restriction in a trial.How often is not known
LimitedLimited evidence: potassium intake ran below guidelines in one study and fell more than on daily calorie restriction in a trial.How often is not known
LimitedOne trial found folate intake fell more on 5:2 style restriction than on daily calorie restriction over 3 months.How often is not known
LimitedLimited evidence: fiber intake fell during 5:2 in one study and rose less than on daily restriction in a trial, and a third trial found no difference from brief advice.How often is not known
LimitedOne trial found two fasting days a week doubled low blood sugar episodes in type 2 diabetes on glucose-lowering drugs, despite medication cuts.How often is not known
LimitedOne trial found higher hunger scores on 5:2 than on daily calorie restriction over a year.How often is not known
LimitedOne trial found adherence to self-help 5:2 fell from 74% at 6 weeks to 22% at one year.How often is not known

What people follow it for, and what was found

Shown to help1

Moderate

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]

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].

Mixed results1

Moderate

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]

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].

Not shown to help1

Moderate

Weight loss compared with daily calorie restriction

Not shown to cause more weight loss than daily calorie restriction in adults with overweight, obesity or type 2 diabetes over 6 to 12 months.

Compared with continuous energy restriction [1], [2], [3], [6]; continuous energy restriction and alternate-day fasting [4]; continuous calorie restriction [5]

The numbers and sources

Effect: In premenopausal women, weight changed by -6.4 kg (95% CI -7.9 to -4.8) on 5:2 and -5.6 kg (95% CI -6.9 to -4.4) on daily restriction over 6 months (P 0.4) [1]. In adults with abdominal obesity, weight loss at one year was 8.0 kg against 9.0 kg (p 0.6), and regain was 1.1 kg against 0.4 kg [2]. In type 2 diabetes, weight change at 12 months was -6.8 kg against -5.0 kg (P .25) [3]. A network meta-analysis found whole-day fasting did not lose more weight than continuous energy restriction, and alternate-day fasting lost 1.05 kg more than whole-day fasting [4]. Across 24 trials of intermittent fasting, weight loss matched continuous restriction (MD 0.26 kg, 95% CI -0.31 to 0.84) [5]. In adolescents with obesity, BMI z score fell 0.28 on both intermittent and continuous restriction at 52 weeks [6].
Population: 107 premenopausal women with overweight or obesity [1]; 112 adults aged 21 to 70 with BMI 30 to 45 [2]; 137 adults with type 2 diabetes [3]; 99 trials with 6,582 adults [4]; 24 trials with 1,768 people [5]; 141 adolescents aged 13 to 17 with obesity-related complications [6].
Sources: [1], [2], [3], [4], [5], [6]
Caveats: In the diabetes trial, the weight difference of -1.8 kg did not meet the prespecified equivalence margin (90% CI -3.7 to 0.07) [3]. The network meta-analysis abstract reports whole-day fasting as a group without separating 5:2 schedules [4], and [5] pooled 5:2 with alternate-day fasting and time-restricted eating.

How trials defined it

Trials restricted intake on 2 days a week and allowed usual eating on the other 5. Fasting days were about 2,710 kJ a day, part of a 25% weekly restriction, against 6,276 kJ every day on continuous restriction [1]. Other trials used 400 kcal for women and 600 kcal for men on 2 non-consecutive days [2], or 500 to 600 kcal on 2 non-consecutive days against 1,200 to 1,500 kcal daily [3]. A hypoglycemia trial used 2,092 to 2,510 kJ on 2 days a week, consecutive or not, for 12 weeks [11]. The EARLY trial used meal replacements on 2 non-consecutive fasting days [10]. One UK trial gave one-off written instructions with or without six weekly group sessions [8]. In diet records, 5:2 diets averaged 22% of energy from protein, 33% from fat and 39% from carbohydrate [12].

Risks

Reported risks9

LimitedHow often is not known

Calcium

Limited evidence: one diet record study found calcium intake below guidelines during 5:2.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Calcium intake was below guideline intakes during 5:2, weighted across fasting and non-fasting days [12].
Population: 38 adults with overweight or obesity, 27 men and 11 women, with and without type 2 diabetes, using 4-day food records at baseline and week 6 [12].
Sources: [12]
Caveats: Estimated intake, not blood levels. The abstract does not say how many fell short or whether intake was already low at baseline [12].

LimitedHow often is not known

Zinc

Limited evidence: one diet record study found zinc intake below guidelines during 5:2.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Zinc intake was below guideline intakes during 5:2 [12].
Population: 38 adults with overweight or obesity [12].
Sources: [12]
Caveats: Estimated intake, not blood levels. The abstract does not say how many fell short [12].

LimitedHow often is not known

Magnesium

Limited evidence: magnesium intake ran below guidelines in one study and fell more than on daily calorie restriction in a trial.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Magnesium intake was below guideline intakes during 5:2 [12]. In a randomized trial, magnesium intake fell more on intermittent than on continuous restriction at 3 months (p below 0.014) [13].
Population: 38 adults [12]; 98 adults with obesity completing weighed dietary records [13].
Sources: [12], [13]
Caveats: Estimated intake, not blood levels. The abstracts do not give the size of the shortfall [12][13].

LimitedHow often is not known

Potassium

Limited evidence: potassium intake ran below guidelines in one study and fell more than on daily calorie restriction in a trial.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Potassium intake was below guideline intakes during 5:2 [12], and fell more on intermittent than on continuous restriction at 3 months [13].
Population: 38 adults [12]; 98 adults with obesity [13].
Sources: [12], [13]
Caveats: Estimated intake, not blood levels [12][13].

LimitedHow often is not known

Folate

One trial found folate intake fell more on 5:2 style restriction than on daily calorie restriction over 3 months.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Folate intake decreased more on intermittent than on continuous energy restriction (p below 0.014) [13].
Population: 98 adults with obesity and at least one other metabolic syndrome component [13].
Sources: [13]
Caveats: A fall in estimated intake, not a measured deficiency. The abstract does not say whether intake fell below guidelines or give the fasting schedule, which in the same 112-person trial was two days of 400 or 600 kcal a week [2][13].

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 and no difference between consecutive and non-consecutive fasting days [11]. In a 12-month trial, low or high glucose events in the first 2 weeks were similar on 5:2 and continuous restriction (4.9 against 3.2) and affected 35% of participants using sulfonylureas or insulin [3].
Population: 41 adults with type 2 diabetes on metformin or other glucose-lowering drugs [11]; 137 adults with type 2 diabetes, 46 on sulfonylureas or insulin [3].
Sources: [3], [11]
Caveats: Both trials cut medication at the start by protocol, and fewer events occurred than the authors expected [11].

LimitedHow often is not known

Hunger

One trial found higher hunger scores on 5:2 than on daily calorie restriction over a year.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Hunger on a numeric rating scale was 4.7 on intermittent restriction against 3.6 on continuous restriction (p 0.002) [2].
Population: 112 adults with abdominal obesity [2].
Sources: [2]
Caveats: One trial, self-rated hunger [2].

LimitedHow often is not known

Falling adherence

One trial found adherence to self-help 5:2 fell from 74% at 6 weeks to 22% at one year.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Adherence was 74% at 6 weeks, 31% at 6 months and 22% at one year. Adding six weekly group sessions raised early weight loss, and the difference was no longer significant at one year [8].
Population: 300 UK adults with obesity [8].
Sources: [8]
Caveats: Participants received instructions once, without ongoing support [8].

ModerateHow often is not known

Side effects on fasting days

Mild physical and psychological side effects were reported on fasting days in pooled trials, with no serious adverse events.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: No serious adverse events occurred on 5:2. Participants had mild physical and psychological side effects during fasting periods that resolved on their own [7].
Population: 1,393 participants in 20 trials [7].
Sources: [7]
Caveats: The abstract does not list the side effects or their frequency [7].

Mixed results1

LimitedHow often is not known

Fiber

Limited evidence: fiber intake fell during 5:2 in one study and rose less than on daily restriction in a trial, and a third trial found no difference from brief advice.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Carbohydrate and fiber intake fell from baseline to week 6 and were lower on fasting days (p below 0.001), giving a low-fiber diet overall [12]. Fiber rose 1.0 g per MJ a day on continuous restriction against 0.2 g on intermittent restriction (p below 0.001) [13]. Self-help 5:2 had no negative effect on fat and fiber intake against brief advice [8].
Population: 38 adults [12]; 98 adults [13]; 300 adults [8].
Sources: [8], [12], [13]
Caveats: Estimated intake from food records.

Supplements to consider

The nutrients research linked to this diet running short, each with its own page.

Claims tested and not found

That 5:2 produces more weight loss than eating less every day. Weight loss did not differ from daily calorie restriction over 6 to 12 months [1][2][3].

Sources

Harvie MN, Pegington M, Mattson MP, et al. The effects of intermittent or continuous energy restriction on weight loss and metabolic disease risk markers: a randomized trial in young overweight women. International Journal of Obesity. 2011. https://doi.org/10.1038/ijo.2010.171
Sundfør TM, Svendsen M, Tonstad S. Effect of intermittent versus continuous energy restriction on weight loss, maintenance and cardiometabolic risk: A randomized 1-year trial. Nutrition, Metabolism and Cardiovascular Diseases. 2018. https://doi.org/10.1016/j.numecd.2018.03.009
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
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
Elortegui Pascual P, Rolands MR, Eldridge AL, et al. A meta-analysis comparing the effectiveness of alternate day fasting, the 5:2 diet, and time-restricted eating for weight loss. Obesity. 2023. https://doi.org/10.1002/oby.23568
Lister NB, Baur LA, House ET, et al. Intermittent Energy Restriction for Adolescents With Obesity: The Fast Track to Health Randomized Clinical Trial. JAMA Pediatrics. 2024. https://doi.org/10.1001/jamapediatrics.2024.2869
Wu C, Chen B, Yu J, et al. Effect of the 5:2 Diet on Weight Loss and Cardiovascular Disease Risk Factors in Overweight and/or Obesity: A Systematic Review and Meta-Analysis. International Journal of Endocrinology. 2025. https://doi.org/10.1155/ije/6658512
Hajek P, Przulj D, Pesola F, et al. A randomised controlled trial of the 5:2 diet. PLOS ONE. 2021. https://doi.org/10.1371/journal.pone.0258853
Carter S, Clifton PM, Keogh JB. The effect of intermittent compared with continuous energy restriction on glycaemic control in patients with type 2 diabetes: 24-month follow-up of a randomised noninferiority trial. Diabetes Research and Clinical Practice. 2019. https://doi.org/10.1016/j.diabres.2019.03.022
Guo L, Xi Y, Jin W, et al. A 5:2 Intermittent Fasting Meal Replacement Diet and Glycemic Control for Adults With Diabetes: The EARLY Randomized Clinical Trial. JAMA Network Open. 2024. https://doi.org/10.1001/jamanetworkopen.2024.16786
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
Scholtens EL, Krebs JD, Corley BT, et al. Intermittent fasting 5:2 diet: What is the macronutrient and micronutrient intake and composition? Clinical Nutrition. 2020. https://doi.org/10.1016/j.clnu.2020.02.022
Sundfør TM, Tonstad S, Svendsen M. Effects of intermittent versus continuous energy restriction for weight loss on diet quality and eating behavior. A randomized trial. European Journal of Clinical Nutrition. 2019. https://doi.org/10.1038/s41430-018-0370-0

Everything in the library

Shown to help1

Reported risks10

What people follow it for, and what was found

Shown to help1

Mixed results1

Not shown to help1

How trials defined it

Risks

Reported risks9

Mixed results1

Supplements to consider

Calcium

Zinc

Magnesium

Potassium

Folate

Fiber supplements

Claims tested and not found

Sources