Intermittent fasting — what the science says

In a nutshell

Intermittent fasting leads to similar weight loss as ordinary calorie restriction.^1,2
Only alternate-day fasting was slightly more effective in shorter trials — by about 1.3 kg.³
Eating within a time window without other changes did not help more than eating throughout the day.^4,5

1Types of fasting

The three most common: 16:8 — you eat only within eight hours a day; 5:2 — two days a week you eat at most about a quarter of your usual energy; alternate-day fasting — days of eating alternate with days of very low intake.^1,2

2Do you lose more weight?

Moderate evidence −0.6 kg A summary of 11 randomised trials (8–24 weeks): intermittent energy restriction led to similar weight loss as continuous restriction; the 0.6 kg difference was not significant.¹

Moderate evidence 24 studies A summary of 24 trials with 1,768 people: alternate-day fasting, 5:2 and time-restricted eating led to similar weight loss as ordinary calorie restriction. In trials shorter than 3 months, people mostly stuck to the fasting (over 80%).²

Moderate evidence — 99 studies −1.3 kg The largest comparison: 99 trials with 6,582 adults. All forms of fasting and ordinary calorie restriction reduced weight compared with unrestricted eating. Only alternate-day fasting was 1.3 kg more effective than ordinary restriction — in trials longer than six months, differences between the diets were no longer seen.³

No type of fasting had a different effect on long-term blood sugar (HbA1c) or “good” HDL cholesterol than an ordinary diet.³

3Time-restricted eating

Moderate evidence — a randomised trial −0.26 kg The TREAT trial: 116 overweight people ate either only between 12:00 and 20:00 or three meals a day without limits for 12 weeks. The weight difference between groups was 0.26 kg and not significant. In the subgroup measured with scanners, people eating in the window lost more muscle mass in their limbs.⁴

Moderate evidence — a one-year randomised trial −8.0 / −6.3 kg In a trial with 139 people with obesity, everyone ate the same restricted number of calories for a year, and half of them ate only between 8:00 and 16:00. They lost 8.0 and 6.3 kg — the difference was not significant.⁵

What to take from this

Do you like eating in a window or fasting? It is just as good a way to a deficit as ordinary restriction.^1,2,3
A window alone, regardless of how much you eat, works no miracles.^4,5
ForkRep adds up energy over the whole day — it does not matter what time you eat.

Sources

Written on 9 Oct 2026, based on studies available at that date. Newer research may change the conclusions.

Cioffi I. et al. (2018). Intermittent versus continuous energy restriction on weight loss and cardiometabolic outcomes: a systematic review and meta-analysis of randomized controlled trials. J Transl Med 16:371. doi.org/10.1186/s12967-018-1748-4
Elortegui Pascual P. et al. (2023). A meta-analysis comparing the effectiveness of alternate day fasting, the 5:2 diet, and time-restricted eating for weight loss. Obesity 31 Suppl 1:9–21. doi.org/10.1002/oby.23568
Semnani-Azad Z. et al. (2025). 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 389:e082007. doi.org/10.1136/bmj-2024-082007
Lowe D. A. et al. (2020). Effects of time-restricted eating on weight loss and other metabolic parameters in women and men with overweight and obesity: the TREAT randomized clinical trial. JAMA Intern Med 180:1491–1499. doi.org/10.1001/jamainternmed.2020.4153
Liu D. et al. (2022). Calorie restriction with or without time-restricted eating in weight loss. N Engl J Med 386:1495–1504. doi.org/10.1056/NEJMoa2114833

This is general information and does not replace a doctor or dietitian. If you have diabetes, are pregnant or breastfeeding, are a teenager or have an eating disorder, talk to a doctor before fasting.