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What studies show about intermittent fasting

Intermittent fasting alternates eating and fasting periods. In the studies so far, its effect on weight differs little from cutting calories every day.

Last updated: November 2026

The forms

  • Eating in a time window: for example 16:8, meaning 8 hours of eating and 16 hours without.[1]
  • 5:2: eating normally on five days, and about a quarter of the usual energy on two days.[2]
  • Alternate-day fasting: fasting days with about 25% of the usual energy, alternating with days without limits.[2]

What studies found

A 2025 review analysed 99 randomised trials with 6,582 adults. Intermittent fasting and daily calorie restriction reduced weight more than eating without limits. They differed little from each other. Trials of 24 weeks or longer only showed the difference from eating without limits. The authors call for longer trials.[3]

A 12-month trial with 139 people with obesity compared calorie restriction with and without an eating window from 8 a.m. to 4 p.m. The difference in weight was not statistically significant.[4]

In a 12-week trial with 116 participants, 16:8 without other instructions was not more effective than eating throughout the day.[1]

What remains open

DGE rates intermittent fasting as equal to daily energy restriction, not better. Long-term data are missing. According to DGE, effects on mood, physical capacity and the risk of eating disorders cannot be assessed. Its page relies on literature up to 2017.[2]

Who it is not meant for

We found no official list for intermittent fasting alone. For the related fasting-mimicking diet, the German Federal Centre for Nutrition says children, teenagers, pregnant and breastfeeding women and people with eating disorders should not take part.[5] According to the German consumer advice centre, people with diabetes and other chronic illnesses should ask their doctor before starting the 5:2 diet.[6]

The app only offers eating windows, no full fasting days. Its limits are our own choice, not a study result. See also When to get medical advice.

The app does not replace medical advice.

Sources

  1. Lowe DA et al.: Effects of Time-Restricted Eating on Weight Loss and Other Metabolic Parameters. JAMA Intern Med, 2020
  2. DGE: Intermittent fasting (German)
  3. Semnani-Azad Z et al.: Intermittent fasting strategies and their effects on body weight and other cardiometabolic risk factors. BMJ, 2025
  4. Liu D et al.: Calorie Restriction with or without Time-Restricted Eating in Weight Loss. N Engl J Med, 2022
  5. Bundeszentrum für Ernährung: fasting-mimicking diet (German)
  6. Verbraucherzentrale: diets overview, as of 10 February 2022 (German)