Intermittent Fasting for Weight Loss: What the Trials Show

Last updated October 30, 2026

Short answer: In randomized trials, intermittent fasting worked about as well as ordinary calorie cutting, not better. In a 2022 NEJM trial of 139 adults, eating only between 8 a.m. and 4 p.m. plus calorie limits led to 8.0 kg lost over a year, versus 6.3 kg with calorie limits alone, a gap that was not statistically significant. A 2017 trial found alternate-day fasting and daily calorie cutting produced similar results, with more people dropping out of the fasting group.

What the two trials compared

Time-restricted eating: the 2022 trial

Both groups followed a calorie-controlled diet (1,500 to 1,800 calories a day for men and 1,200 to 1,500 for women). One group also ate only between 8 a.m. and 4 p.m. After 12 months the fasting-window group had lost an average of 8.0 kg (about 17.6 lbs) and the other 6.3 kg (about 13.9 lbs). The 1.8 kg difference could have been chance, and the authors concluded time-restricted eating was not more beneficial than daily calorie restriction for weight, body fat or metabolic risk factors. Adverse events did not differ substantially. Of the 139 people, 118 (84.9%) finished the year.

Alternate-day fasting: the 2017 trial

One hundred adults with obesity were randomly assigned to alternate-day fasting, daily calorie restriction, or no intervention for a year. Against the no-intervention group, alternate-day fasting lost 6.8% at 6 months and 6.0% at 12 months, and daily calorie restriction lost 6.8% and 5.3%. The authors found alternate-day fasting did not produce better adherence, weight loss, weight maintenance or heart-health markers. More people dropped out of the fasting group: 38%, compared with 29% on daily calorie restriction and 26% in the no-intervention group.

What this suggests

• Fasting windows are one way to eat less, not a way around eating less.
• The best plan in these trials was the one people could stick to. Alternate-day fasting had the highest dropout.
• If a fasting schedule makes it easier for you to control calories, it appears to be a reasonable choice. If it makes you feel worse or overeat later, daily calorie control works as well.

Limits of this evidence

• Two trials of 100 and 139 people, so neither is large.
• Both were in adults with obesity, and the second trial was mostly women. Results may differ for others.
• Both lasted a year. We do not know how people do over many years.
• The trials tested specific schedules. Other versions of fasting have not been tested here.
• If you take medicine for diabetes or another condition, check with your prescriber before changing when you eat.

Related: low-carb vs. low-fat diet, Mediterranean diet and lifestyle vs. GLP-1 weight loss.