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Research · Diets

Alternate-day fasting

Meta-analyses find alternate-day fasting lowers weight, fat mass and total cholesterol against usual eating, and loses about 1.3 kg more than daily calorie restriction in mostly short trials. A year-long trial found no weight difference from daily restriction, more dropouts and higher LDL cholesterol. Fasting glucose did not change in people without diabetes.

Add to Bio HackChecked 2026-11-13
Status
A dietary pattern, not a regulated product.
Also called
alternate-day fasting, alternate day fasting, ADF, modified alternate-day fasting, mADF, every-other-day fasting, Every Other Day Diet, 4:3 intermittent fasting, 4:3 diet
Followed for
weight loss, fat loss, cholesterol, blood sugar, blood pressure, heart health, longevity

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 help5

Reported risks5

What people follow it for, and what was found

Shown to help5

Strong

Weight loss compared with usual eating

Shown to lower weight, BMI and fat mass against control in adults with overweight, by about 1.3 kg of fat mass, mostly in trials under 6 months.

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

The numbers and sources
Effect
In 8 trials with 728 participants, BMI fell 0.73 kg/m² (95% CI -1.13 to -0.34) and fat mass 1.27 kg (95% CI -2.09 to -0.46) against control, with significant effects in participants with overweight and in trials under 6 months [1]. In 7 trials with 269 participants, weight, BMI and fat mass fell against control (weight p below 0.00001) [2]. In a year-long trial, weight fell 6.0% (95% CI -8.5% to -3.6%) against no intervention [3]. In healthy non-obese adults, 4 weeks of strict alternate-day fasting cut calorie intake 37% and lowered fat mass, mostly trunk fat [4]. In adults with BMI 23 to 30, total fat volume fell 1,059.8 cm³ more than in controls over 4 weeks (95% CI -1,380.0 to -739.6) [5].
Population
Adults aged 18 and over in 8 trials [1]; 269 adults in 7 trials [2]; 100 adults with obesity, 86 women [3]; healthy middle-aged adults without obesity [4]; 76 adults aged 18 to 40 [5].
Sources
[1], [2], [3], [4], [5]
Caveats
The pooled effects held for trials under 6 months [1]. The reviews are small, and [2] reports p values without effect sizes.
Moderate

Cholesterol

Shown to lower total cholesterol by about 8 mg/dL against control in adults with overweight, mostly in trials under 6 months.

Compared with control diets the source does not describe [1]; eating freely every day or keeping the present lifestyle [2]; no change in eating times [5]; time-restricted eating [6]

The numbers and sources
Effect
Total cholesterol fell 8.14 mg/dL (95% CI -14.59 to -1.69) against control [1]. Total cholesterol, LDL and triglycerides fell against control in a second review, which reported p values only [2]. Alternate-day fasting lowered total cholesterol, triglycerides and non-HDL cholesterol more than time-restricted eating [6]. Non-HDL cholesterol fell against control over 4 weeks [5].
Population
728 participants in 8 trials [1]; 269 in 7 trials [2]; 99 trials [6]; 76 adults [5].
Sources
[1], [2], [5], [6]
Caveats
In a year-long trial, LDL cholesterol ended higher on alternate-day fasting than on daily calorie restriction (see Risks) [3].
Moderate

Blood pressure

Shown to lower systolic and diastolic blood pressure against control in a pooled analysis of 7 trials, with no difference from daily calorie restriction in a year-long trial.

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

The numbers and sources
Effect
Systolic (p 0.003) and diastolic (p 0.007) blood pressure fell against control [2]. Blood pressure did not differ between alternate-day fasting and daily calorie restriction at 6 or 12 months [3].
Population
269 adults in 7 trials [2]; 100 adults with obesity [3].
Sources
[2], [3]
Caveats
The review reports p values without the size of the fall [2].
Limited

Blood sugar in insulin-treated type 2 diabetes

One trial found 3 fasting days a week lowered HbA1c by 7.3 mmol/mol against control over 12 weeks in insulin-treated type 2 diabetes.

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

The numbers and sources
Effect
HbA1c fell 7.3 mmol/mol (SD 12.0) on fasting against 0.1 mmol/mol in controls (P 0.012). Eight people on fasting and none in control reached the combined goal of 2% weight loss, 10% lower insulin dose and a 3 mmol/mol HbA1c drop [10].
Population
46 adults with insulin-treated type 2 diabetes, with dietary counseling and continuous glucose monitoring [10].
Sources
[10]
Caveats
One small 12-week trial, published as a brief report [10].
Limited

Markers of aging

One trial in healthy adults without obesity found 4 weeks of strict alternate-day fasting improved cardiovascular markers, with lower sICAM-1 and LDL after longer use.

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

The numbers and sources
Effect
Strict alternate-day fasting for 4 weeks improved cardiovascular markers and the fat-to-lean ratio and raised β-hydroxybutyrate. After long-term alternate-day fasting, sICAM-1, LDL and triiodothyronine were lower [4].
Population
Healthy middle-aged adults without obesity [4].
Sources
[4]
Caveats
The abstract gives no participant numbers or effect sizes. Lifespan was not measured [4].

Mixed results1

Moderate

Weight loss compared with daily calorie restriction

Mixed results: alternate-day fasting lost about 1.3 kg more than daily calorie restriction in pooled trials, mostly short ones, and longer trials found no difference or a small one.

Compared with daily calorie restriction or no intervention, in Chicago adults with obesity [3]; time-restricted eating or no change in eating times [5]; continuous energy restriction, unrestricted eating, time-restricted eating and whole-day fasting [6]; continuous calorie restriction, the 5:2 diet and time-restricted eating [7]; daily calorie restriction with the same weekly deficit, both within a behavioral weight-loss program [8]; a calorie-restricted Mediterranean diet [9]

The numbers and sources
Effect
Against continuous energy restriction, alternate-day fasting lowered weight by 1.29 kg (95% CI -1.99 to -0.59, moderate certainty). In trials of 24 weeks or longer, only comparisons against unrestricted eating showed a benefit [6]. A network analysis of 24 trials ranked alternate-day fasting first for weight loss, while intermittent fasting overall matched continuous restriction [7]. Over one year, weight fell 6.0% on alternate-day fasting and 5.3% on daily restriction against control, with no difference between them [3]. A 4:3 schedule lost 2.89 kg more than daily restriction at 12 months (95% CI 0.14 to 5.65) within a high-intensity behavioral program [8]. Over 3 months of calorie-restricted diets, modified alternate-day fasting lost 3.14 kg more than a Mediterranean diet (95% CI -4.98 to -1.30) [9]. Alternate-day fasting cut fat volume 695.7 cm³ more than time-restricted eating over 4 weeks [5].
Population
99 trials with 6,582 adults [6]; 24 trials with 1,768 people [7]; 100 adults with obesity [3]; 165 adults with BMI 27 to 46 [8]; 160 adults with obesity [9]; 76 adults without obesity [5].
Sources
[3], [5], [6], [7], [8], [9]
Caveats
The 4:3 schedule restricts 3 non-consecutive days a week, not every other day [8]. In the year-long trial, people on alternate-day fasting ate more than prescribed on fast days and less on feast days [3].

Not shown to help1

Moderate

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.

How trials defined it

In the year-long trial, fast days provided 25% of energy needs and alternating feast days 125%, against 75% every day on calorie restriction [3]. A 4-week trial used strict alternate-day fasting with ad libitum eating days, and calorie intake fell 37% [4]. Another alternated fasting and ad libitum days for 4 weeks [5]. The 4:3 schedule cut intake 80% on 3 non-consecutive days a week with unrestricted eating on the other 4, against a 34% daily cut matched for the weekly deficit [8]. A trial in insulin-treated diabetes used 3 non-consecutive fasting days a week for 12 weeks [10]. One trial compared calorie-restricted modified alternate-day fasting with calorie-restricted ketogenic, time-restricted and Mediterranean diets for 3 months [9].

Risks

Reported risks4

LimitedHow often is not known

Dropout

One year-long trial found more dropouts on alternate-day fasting, 38%, than on daily calorie restriction, 29%.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Dropout was 13 of 34 (38%) on alternate-day fasting, 10 of 35 (29%) on daily calorie restriction and 8 of 31 (26%) in controls [3].
Population
100 adults with obesity, 86 women [3].
Sources
[3]
Caveats
One trial, without a significance test for dropout in the abstract [3].
LimitedHow often is not known

Higher LDL cholesterol

One trial found LDL cholesterol 11.5 mg/dL higher on alternate-day fasting than on daily calorie restriction at 12 months.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
LDL cholesterol was 11.5 mg/dL higher (95% CI 1.9 to 21.1) on alternate-day fasting than on daily calorie restriction at month 12 [3].
Population
100 adults with obesity [3].
Sources
[3]
Caveats
One trial. Pooled trials found lower total cholesterol against control [1].
LimitedHow often is not known

Lower metabolic rate and thyroid hormone

Small trials found alternate-day fasting lowered resting metabolic rate and triiodothyronine against control.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Over 4 weeks, alternate-day fasting, but not time-restricted eating, lowered resting metabolic rate and triiodothyronine against control [5]. Triiodothyronine was also lower after long-term alternate-day fasting [4].
Population
76 adults aged 18 to 40 [5]; healthy middle-aged adults [4].
Sources
[4], [5]
Caveats
Short trials. The abstracts do not give the size of the changes [4][5].
LimitedHow often is not known

Low blood sugar with diabetes medication

One trial of 2 fasting days a week doubled low blood sugar episodes on glucose-lowering drugs. A trial of 3 fasting days a week on insulin had no severe episodes.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
In type 2 diabetes on glucose-lowering drugs, fasting raised the rate of hypoglycemia (RR 2.05, 95% CI 1.17 to 3.52) despite medication cuts [12]. With 3 non-consecutive fasting days a week, counseling and continuous glucose monitoring, no severe hypoglycemia occurred in insulin-treated type 2 diabetes [10].
Population
41 adults with type 2 diabetes [12]; 46 adults with insulin-treated type 2 diabetes [10].
Sources
[10], [12]
Caveats
The hypoglycemia rate trial used 2 fasting days a week, not alternate days [12]. Neither trial tested strict alternate-day fasting.

Mixed results1

ModerateHow often is not known

Lean mass

Mixed results: one pooled analysis found no lean mass difference from daily restriction or control, and another found a lean mass difference against control without giving its size.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Lean body mass did not differ between alternate-day fasting and continuous energy restriction, time-restricted feeding or control [1]. The ratio of fat-free mass to total mass rose equally on alternate-day fasting and daily restriction over 24 weeks [11]. A second review found lean mass differed from control (p 0.002) [2].
Population
728 participants [1]; 100 adults [11]; 269 adults [2].
Sources
[1], [2], [11]
Caveats
The second review does not report the direction or size of the lean mass change in its abstract [2].

Claims tested and not found

  1. That alternate-day fasting is easier to stick to than daily calorie restriction. Over one year it did not produce better adherence, and more people dropped out [3].

Sources

  1. Park J, Seo YG, Paek YJ, et al. Effect of alternate-day fasting on obesity and cardiometabolic risk: A systematic review and meta-analysis. Metabolism. 2020. https://doi.org/10.1016/j.metabol.2020.154336
  2. Cui Y, Cai T, Zhou Z, et al. Health Effects of Alternate-Day Fasting in Adults: A Systematic Review and Meta-Analysis. Frontiers in Nutrition. 2020. https://doi.org/10.3389/fnut.2020.586036
  3. Trepanowski JF, Kroeger CM, Barnosky A, et al. Effect of Alternate-Day Fasting on Weight Loss, Weight Maintenance, and Cardioprotection Among Metabolically Healthy Obese Adults: A Randomized Clinical Trial. JAMA Internal Medicine. 2017. https://doi.org/10.1001/jamainternmed.2017.0936
  4. Stekovic S, Hofer SJ, Tripolt N, et al. Alternate Day Fasting Improves Physiological and Molecular Markers of Aging in Healthy, Non-obese Humans. Cell Metabolism. 2019. https://doi.org/10.1016/j.cmet.2019.07.016
  5. Derron N, Güntner AT, Weber IC, et al. Alternate-day fasting elicits larger changes in fat mass than time-restricted eating in adults without obesity: A randomized clinical trial. Clinical Nutrition. 2025. https://doi.org/10.1016/j.clnu.2025.08.033
  6. 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
  7. 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
  8. Catenacci VA, Ostendorf DM, Pan Z, et al. The Effect of 4:3 Intermittent Fasting on Weight Loss at 12 Months: A Randomized Clinical Trial. Annals of Internal Medicine. 2025. https://doi.org/10.7326/annals-24-01631
  9. Martínez-Montoro JI, Bandera B, Gutiérrez-Bedmar M, et al. Effect of a ketogenic diet, time-restricted eating, or alternate-day fasting on weight loss in adults with obesity: a randomized clinical trial. BMC Medicine. 2025. https://doi.org/10.1186/s12916-025-04182-z
  10. Obermayer A, Tripolt NJ, Pferschy PN, et al. Efficacy and Safety of Intermittent Fasting in People With Insulin-Treated Type 2 Diabetes (INTERFAST-2): A Randomized Controlled Trial. Diabetes Care. 2023. https://doi.org/10.2337/dc22-1622
  11. Trepanowski JF, Kroeger CM, Barnosky A, et al. Effects of alternate-day fasting or daily calorie restriction on body composition, fat distribution, and circulating adipokines: Secondary analysis of a randomized controlled trial. Clinical Nutrition. 2018. https://doi.org/10.1016/j.clnu.2017.11.018
  12. 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

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