No. In randomised trials of adults, mostly with overweight or obesity, intermittent fasting lowered body weight about as much as cutting calories every day, and the one pattern that edged ahead did so by a margin the researchers themselves called trivial4.
Fasting is one way of eating less. On current evidence it is not a better way, and not a worse one.
The terms, in plain words
A few terms carry this whole topic, so here they are once.
- Intermittent fasting: eating nothing or very little for set stretches, and eating freely in between.
- Cutting calories every day (continuous energy restriction): eating somewhat less than you use, every day.
- Alternate-day fasting: a fast, or a very low-calorie day, every other day.
- Whole-day fasting, such as the 5:2 diet: two very low-calorie days a week, five ordinary days.
- Time-restricted eating: eating only inside a daily window of some hours, such as 8 hours.
- Eating as usual (ad libitum): no diet, the comparison group in many trials.
A randomised trial assigns people to a diet by chance, so the groups differ only by the diet. A network meta-analysis pools many trials and compares every diet with every other one, including pairs that were never tested head to head, by linking them through shared comparison groups.
In plain terms: the question is whether *when* you eat adds anything beyond *how much* you eat.
What was studied
The largest analysis is a 2025 network meta-analysis in the BMJ4. It pooled 99 randomised trials with 6,582 adults. The median age was 45, the median BMI (body mass index, weight relative to height) was 31, and 66% were women. Most participants had a health condition, often overweight or obesity. The median trial lasted 12 weeks, with a range of 3 to 52 weeks.
| What | Number |
|---|---|
| Trials | 99 randomised trials |
| Adults | 6,582 (66% women) |
| Median BMI | 31 |
| Median trial length | 12 weeks (range 3–52) |
| Trials for the weight analysis | 93 (6,247 people) |
| Trials of 24 weeks or more | 17 |
An earlier network meta-analysis from 2024 pooled 16 trials and 1,228 adults with overweight or obesity, comparing alternate-day fasting, the 5:2 diet and time-restricted eating with daily calorie cutting3.
In plain terms: dozens of mostly short trials in adults carrying extra weight, not lifters in a cut.
What the studies found
Everything beat eating as usual. Compared with no diet, the average weight differences were4:
Weight difference vs eating as usual, by diet pattern · kg
Alternate-day fasting sat at about 3.4 kg below eating as usual, whole-day fasting at about 2.4 kg, daily calorie cutting at about 2.1 kg and time-restricted eating at about 1.7 kg4. These are pooled group averages over trials that mostly lasted about three months. They are not what one person should expect.
Against daily cutting, the gaps were small. Alternate-day fasting was the only fasting pattern that beat daily calorie cutting, by 1.29 kg on average (95% confidence interval 0.59 to 1.99 kg), with moderate certainty4. A confidence interval is the range the true value most likely sits in. The authors had set 2.0 kg as the smallest difference that matters, and they classed anything under it as trivial4.
Over longer trials, the edge disappeared. In the 17 trials that ran 24 weeks or more, alternate-day fasting, time-restricted eating and daily cutting still beat eating as usual, but there were no differences between the fasting patterns and daily cutting4.
The 2024 analysis leaned slightly toward fasting: alternate-day fasting beat daily cutting on waist size (and on body weight in a sensitivity analysis), and the 5:2 diet beat it on BMI. On fat mass and on how many people dropped out, all forms were comparable3. Its authors rated the quality of the trials low to moderate.
In plain terms: every approach that cut intake did something; the fasting schedule added little on top.
Two year-long trials, head to head
Pooled analyses lean on short trials. Two longer trials put fasting directly against daily cutting.
In a 2017 trial, 100 adults with obesity were randomised for a year to alternate-day fasting, daily calorie cutting of 25%, or no diet1. Relative to the no-diet group, both diet groups lost the same share of body weight at six months (6.8% on average in each). At twelve months the averages were 6.0% and 5.3%, not a significant difference. Dropout was highest in the fasting group: 38%, against 29% for daily cutting and 26% for no diet.
In a 2022 trial, 139 adults with obesity all followed the same calorie target for a year; half also ate only between 8 a.m. and 4 p.m.2. The eating-window group lost 1.8 kg more on average, but the confidence interval ran from 4.0 kg more to 0.4 kg less, so the difference was not significant. Body fat, lean mass, waist and blood markers followed the same pattern.
Fasting pattern minus daily calorie cutting, body weight · kg
In plain terms: when calories are matched or both groups cut, the clock adds little you can measure.
Why fasting feels easier to some people
A common view in comments under fasting videos is that fasting "reduces calories automatically". That is the mechanism the trials point to. Closing an eating window, or eating very little on set days, is a rule for eating less, and when intake falls, weight follows.
Adherence, meaning how well people keep to the plan, is where the patterns may differ. Most trials in the 2025 review reported high adherence, but most of the year-long ones reported poor adherence; in one, adherence to a 5:2-type diet fell from 74% at six weeks to 22% at a year4. In the 2017 trial, the fasting group ate more than planned on fast days and less than planned on the other days1.
The bold ideas about a fasting "metabolic switch" come mainly from animal studies, the BMJ authors note, and have not been shown in humans4.
In plain terms: pick the schedule on how it fits your life; the trials do not reward one over another.
What this means in practice
Any approach that lowers intake over weeks lowers weight in these trials. Whatever the schedule, the size of the deficit is the part a calculator can help with. Zyra Nutrition sizes a deficit from a weekly rate of body weight, caps it at 35% of TDEE (total daily energy expenditure) and does not go below floors of 1,500 kcal for a male profile or 1,200 kcal for a female profile (see how big a calorie deficit should be). The same daily target can be spread over three meals or one eating window; for weekly budgeting see daily vs weekly calorie deficits.
The studies at a glance
| Study | Who was studied | Key result | Year |
|---|---|---|---|
| Trepanowski et al., *JAMA Intern Med*1 | 100 adults with obesity, 1 year | Alternate-day fasting and daily cutting: same average weight loss at 6 and 12 months; more dropout with fasting | 2017 |
| Liu et al., *N Engl J Med*2 | 139 adults with obesity, 12 months | 8-hour eating window plus calorie cutting vs cutting alone: 1.8 kg difference, not significant | 2022 |
| Ma, Sun, Mu, *Int J Obes*3 | 16 trials, 1,228 adults with overweight or obesity | Alternate-day fasting beat daily cutting on waist size, 5:2 on BMI; fat mass and dropout comparable; quality low to moderate | 2024 |
| Semnani-Azad et al., *BMJ*4 | 99 trials, 6,582 adults | Only alternate-day fasting beat daily cutting, by 1.29 kg (trivial); no differences in trials of 24 weeks or more | 2025 |
Limits worth knowing
- Short trials dominate. The median trial ran 12 weeks; only 17 of 93 weight trials ran 24 weeks or more4.
- Few direct comparisons. Only three trials compared fasting patterns with each other directly; most such comparisons are indirect4.
- Many small trials. The median trial had 46 people, and certainty was low to moderate for most outcomes4.
- Population. Mostly adults with overweight, obesity or another condition. Lean people, athletes and people who lift were not the focus.
- Muscle not covered here. We did not extract lean-mass results from the pooled analyses; the 2022 trial reported lean mass moved in line with weight2.
- Abstract only. The 2024 analysis, the 2017 trial and the 2022 trial were read as abstracts; the BMJ paper in full text, without its online appendix.
- Funding. The BMJ review was commissioned by a diabetes nutrition study group; the authors state the funders had no role in the analysis4.
Latest research
The newest study we opened is the 2025 BMJ network meta-analysis, which searched trials up to November 20244. Its authors conclude that fasting patterns have similar benefits to daily calorie cutting for weight and blood markers, and that longer trials are needed. We found no newer trial that changes that picture.
The short version
- Fasting and daily calorie cutting lowered weight about equally in randomised trials.
- Only alternate-day fasting edged ahead, by about 1.3 kg on average, which the authors call trivial.
- In trials of six months or more, no fasting pattern beat daily cutting.
- The schedule is a matter of fit; the amount eaten drives the result.
Educational overview only — not medical advice.
