Intermittent fasting: does it really work?

This is general information, not medical advice. Always discuss your blood values with your doctor.

1. 1

   What is it?

   Intermittent fasting is an umbrella term: time-restricted eating (for example only eating within an 8-hour window), alternate-day fasting or periodic fasting, such as the 5:2 schedule. In research these variants are often looked at together.

2. 2

   Weight: no clear advantage over simply eating less

   A Cochrane review from February 2026 (Garegnani et al.) pooled 22 randomised trials with 1,995 adults with overweight or obesity, mostly followed for up to 12 months. Intermittent fasting made little to no difference to weight loss and quality of life compared with standard dietary advice, and the difference compared with doing nothing was also small. The certainty of the evidence is limited: many studies are small and short, and long-term data are missing.

3. 3

   When you eat matters little at equal calories

   In a 12-month RCT in 139 people with obesity (Liu et al., NEJM 2022), both groups followed the same calorie-restricted diet, but one group only ate between 8:00 and 16:00. After a year, mean weight loss was 8.0 kg versus 6.3 kg, a difference that was not statistically significant (P = 0.11). Time-restricted eating was therefore not more effective than simply restricting calories.

4. 4

   And your muscles?

   A meta-analysis of 15 trials with 338 participants (2025) found that time-restricted eating combined with exercise can reduce fat mass, with no significant effect on fat-free mass (p = 0.07, borderline). An 8-week RCT in people with overweight (Kotarsky et al., 2021) showed more fat loss in the fasting group (9.0% versus 3.3%), while fat-free mass rose in both groups. The studies are small and short, so this is a cautious conclusion.

5. 5

   Not for everyone

   This is general medical caution, not a study result. Talk to your doctor first, or skip fasting, if you are pregnant or breastfeeding, have a history of eating disorders, have diabetes treated with insulin or medication that can cause low blood sugar, or are under 18.

Updated in October 2026