Eat-Stop-Eat

What it is

Eat-Stop-Eat means one or two full 24-hour fasts a week with usual eating on the other days. The name comes from a commercial book, and no trial has tested that branded programme. The closest trial, WONDERFUL, used water-only 24-hour fasts twice weekly for 4 weeks, then once weekly for 22 weeks.

What the research says

Evidence for weekly 24-hour fasting is limited to one small RCT. That trial found reduced insulin resistance and metabolic syndrome scores compared with usual eating, but no effect on its primary outcome (LDL cholesterol), on cognition, or on weight. Adverse events were mild but mostly in the fasting group. No trial has compared this schedule with daily calorie restriction. A Cochrane review covering periodic fasting among other types found little to no difference in weight loss compared with regular dietary advice.

Evidence grade: Limited evidence.

The schedule

• Pattern: weekly
• Fasting hours: 24
• Fast days per week: 1
• Calorie limit on fast days: zero calories (water only in the WONDERFUL trial), once or twice a week

Why people choose it

People may choose a weekly 24-hour fast because it asks for only one or two fast days and no calorie counting on the rest. The one RCT of this schedule found better insulin resistance and metabolic syndrome scores than a control group. It did not lower LDL cholesterol or improve cognition, and weight loss was not significant (P = 0.06). It has not been compared directly with daily calorie restriction, and nearly a quarter of the fasting group dropped out.

Cautions

• People with type 2 diabetes taking glucose-lowering medicines: The WONDERFUL trial excluded people taking anti-diabetic medicines, so it gives no safety data for them. In a 5:2 trial, 35% of people on sulfonylureas and/or insulin had glucose events even after their medicines were reduced. (Source 1)
• People taking insulin: A Johns Hopkins fasting researcher warns of unsafe hypoglycaemia during fasting periods for people with type 1 diabetes on insulin. (Source 2)
• People with diabetes, pregnant or breastfeeding women, and people with a history of eating disorders or disordered eating: The Academy of Nutrition and Dietetics does not recommend intermittent fasting for these groups. (Source 3)
• Older adults and anyone at risk of muscle loss: Meta-analyses of intermittent fasting trials found an association with reduced fat-free mass. The WONDERFUL trial enrolled adults up to age 70 but did not report body composition in the text reached. (Source 4)
• Anyone taking medicines: The Academy of Nutrition and Dietetics advises discussing fasting with a doctor first, especially when medicines may need adjusting. (Source 3)

What goes wrong

Adverse events were all mild, but most occurred in the fasting group, especially at the end of the twice-weekly phase. (Source 1)

• Randomized trial, Certainty not rated.
• Size: 103 randomised.
• Who: Adults with metabolic syndrome features or type 2 diabetes.
• How long: 26 weeks.
• Result: All adverse events mild, the majority in the fasting group, most at the end of the 4-week twice-weekly phase; details in supplementary Table S2, which could not be reached.
• Funding: not stated.

The adverse events reported at study visits were all mild (Supplementary material online, Table S2), with the majority occurring in the intermittent fasting group.

In a small study of repeated 36-hour zero-calorie fasts, hunger stayed elevated on fast days. (Source 5)

• Case series, Certainty not rated.
• Size: 16.
• Who: Non-obese healthy adults.
• How long: 22 days.
• Result: Hunger elevated throughout (P < 0.001)
• Funding: not stated.

Limit of this finding: Single-arm trial with no control group. This is indirect evidence: the fasts were every other day, not once or twice a week.

Hunger increased on the first day of fasting and remained elevated (P < 0.001).

What the evidence supports

The same trial found reduced insulin resistance (HOMA-IR) and metabolic syndrome score with fasting compared with control. (Source 1)

• Randomized trial, Certainty not rated.
• Size: 71 evaluable.
• Who: Adults with metabolic syndrome features or type 2 diabetes, not on diabetes medicines.
• How long: 26 weeks.
• Result: HOMA-IR -0.75 vs -0.10, P = 0.004; metabolic syndrome score -0.34 vs 0.31, P = 0.006.
• Funding: not stated.

Limit of this finding: These were secondary outcomes. The trial required P of 0.01 or less for them.

Intermittent fasting did not change LDL-C (0.2 ± 16.7 mg/dL) vs. control (2.5 ± 19.4 mg/dL; P = 0.59), but it improved HOMA-IR (−0.75 ± 0.79 vs. −0.10 ± 1.06; P = 0.004) and MSS (−0.34 ± 4.72 vs. 0.31 ± 1.98, P = 0.006).

An umbrella review filed fasts of 0 to 600 kcal on 1 to 2 days a week under the 5:2 category, which was associated with statistically significant weight loss compared with regular diet. (Source 4)

• Review of reviews, Certainty not rated.
• Size: 11 meta-analyses of 130 RCTs.
• Who: Adults with overweight or obesity.
• How long: median follow-up 3 months.
• Result: Not reported separately for zero-calorie 24-hour fasts.
• Funding: not stated.

Limit of this finding: This is indirect evidence. Most trials in this category used about 500 to 600 kcal on fast days, not a full 24-hour fast.

Types of IF included in this review were (1) zero-calorie alternate-day fasting (zero-calorie ADF), which involved alternating days of fasting with zero caloric intake and days of ad libitum eating; (2) modified alternate-day fasting (MADF), which alternated between days of ad libitum eating and days of fasting with total caloric intake ranging from 0% to 40% or 0 to 600 kcal per day for 3 to 5 days per week; (3) the 5:2 diet, in which participants fasted for 1 to 2 days per week (either consecutively and nonconsecutively) with total caloric intake ranging from 0% to 40% or 0 to 600 kcal per day and 5 days of ad libitum eating; and (4) time-restricted eating (TRE), which involved fasting for 12 to 24 hours per day.

What the evidence does not support

In adults with metabolic syndrome features or type 2 diabetes not on diabetes medicines, a weekly water-only 24-hour fast did not change LDL cholesterol (the primary outcome) or cognition over 26 weeks. (Source 1)

• Randomized trial, Certainty not rated.
• Size: 103 randomised (50 fasting, 53 control); 71 evaluable.
• Who: Adults aged 21 to 70 with modestly raised LDL-C and at least one metabolic syndrome feature or type 2 diabetes, not taking statins or anti-diabetic medicines; about two-thirds female.
• How long: 26 weeks.
• Result: LDL-C change 0.2 vs 2.5 mg/dL, P = 0.59; cognitive index P = 0.17.
• Funding: not stated.

Limit of this finding: Single-centre trial with high dropout in both arms.

A low-frequency intermittent fasting regimen did not reduce LDL-C or improve cognitive function but significantly reduced both HOMA-IR and MSS.

Weight loss with weekly 24-hour fasting was small and not statistically significant compared with control. (Source 1)

• Randomized trial, Certainty not rated.
• Size: 71 evaluable.
• Who: Adults with metabolic syndrome features or type 2 diabetes.
• How long: 26 weeks.
• Result: Weight -1.7 kg vs +0.2 kg, P = 0.06.
• Funding: not stated.

BDNF (P = 0.58), GCPi (P = 0.17), and weight (−1.7 ± 4.7 kg vs. 0.2 ± 3.5 kg, P = 0.06) were unchanged.

A Cochrane review covering periodic fasting and other types found little to no difference in weight loss compared with regular dietary advice. (Source 6)

• Systematic review, Low certainty.
• Size: 21 studies, 1,430 participants.
• Who: Adults with overweight or obesity.
• How long: 6 to 12 months.
• Result: MD -0.33 percentage points (95% CI -0.92 to 0.26)
• Funding: independent (no dedicated funding)

Limit of this finding: The review pools all intermittent fasting types, and its abstract gives no periodic-fasting subgroup result.

We included randomised controlled trials (RCTs) and cluster-RCTs that compared intermittent fasting (including time-restricted feeding, periodic fasting, alternate-day fasting, and modified alternate-day fasting) with regular dietary advice, no intervention or waiting list in men and women with overweight or obesity, with or without associated comorbid conditions.

Where the evidence is mixed

12 of 50 in the fasting arm dropped out, and 20 of 53 in the control arm. (Source 1)

• Randomized trial, Certainty not rated.
• Size: 103 randomised.
• Who: Adults with metabolic syndrome features or type 2 diabetes.
• How long: 26 weeks.
• Result: Dropouts 12 fasting (5 lost to follow-up, 7 withdrew), 20 control.
• Funding: not stated.

Limit of this finding: Dropout was higher in the control arm than the fasting arm. The investigators called the overall drop-out rate higher than anticipated.

Drop-outs (n = 12 fasting, n = 20 control) provided an evaluable sample of n = 71 (n = 38 fasting, n = 33 control).

The Cochrane authors note that the trials covered only up to 12 months, limiting what can be said about longer use. (Source 6)

• Systematic review, Certainty not rated.
• Size: 22 studies, 1,995 participants.
• Who: Adults with overweight or obesity.
• How long: up to 12 months.
• Result: not applicable.
• Funding: independent (no dedicated funding)

The included studies focused on short-term effects of the intervention (up to 12 months), limiting the applicability of the evidence in this review to inform decision-making for longer durations.

What official bodies say

The Academy of Nutrition and Dietetics reports strong hunger and reduced concentration on fasting days as side effects. (Source 3)

• Official position, Certainty not rated.
• Size: not applicable.
• Who: General public.
• How long: not applicable.
• Result: not applicable.
• Funding: not stated.

Side effects reported include strong feelings of hunger and decreased concentration on fasting days.

A common belief, and what the research shows

The belief: A weekly 24-hour fast is a proven way to lose weight and lower cholesterol.

What the research shows: In the one RCT of this schedule, 26 weeks of weekly water-only 24-hour fasts did not lower LDL cholesterol (the primary outcome), and weight loss was not significant (-1.7 kg vs +0.2 kg, P = 0.06). Insulin resistance did improve. No trial has compared it with ordinary daily calorie restriction.

References

1. European Heart Journal Open. Randomized controlled trial of once-per-week intermittent fasting for health improvement: the WONDERFUL trial. 2021. DOI 10.1093/ehjopen/oeab026. Read the source
2. Johns Hopkins Medicine. Intermittent Fasting: What Is It, And How Does It Work? (expert Q&A with Mark Mattson, PhD). Read the source
3. Academy of Nutrition and Dietetics (eatright.org). What is Intermittent Fasting? (Barbara Gordon, RDN, LD; reviewed by Academy staff RDNs, July 21, 2025). 2025. Read the source
4. JAMA Network Open. Intermittent Fasting and Obesity-Related Health Outcomes: An Umbrella Review of Meta-analyses of Randomized Clinical Trials. 2021. PMID 34919135, DOI 10.1001/jamanetworkopen.2021.39558. Read the source
5. American Journal of Clinical Nutrition. Alternate-day fasting in nonobese subjects: effects on body weight, body composition, and energy metabolism. 2005. PMID 15640462, DOI 10.1093/ajcn/81.1.69. Read the source
6. Cochrane Database of Systematic Reviews. Intermittent fasting for adults with overweight or obesity. 2026. PMID 41692034, DOI 10.1002/14651858.CD015610.pub2. Read the source