Fasting vs. calorie restriction for weight loss: Which one wins?
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- Reviewed by Anthony L. Komaroff, MD, Editor in Chief, Harvard Health Letter; Editorial Advisory Board Member, Harvard Health Publishing
If you’re tired of counting calories to lose weight, you might consider a style of intermittent fasting called 4:3. It allows you to eat normally on four days of the week, and eat very little (fast) on the other three days, which can be spread throughout the week. This approach might even help you lose more weight than counting calories, notes a small randomized controlled trial published in the May 20, 2025, issue of Annals of Internal Medicine. The study involved 165 people (average age 42) who were divided into two groups. One group followed a 4:3 intermittent fasting plan, eating only 20% of their usual calories on fasting days. The other group reduced their daily calorie intake by 34%. After one year, people in the 4:3 group had lost more weight — an average of about 6 more pounds — than people in the calorie restriction group. Study authors say the 4:3 approach might be simpler to follow than calorie counting, making it easier to stick to the plan.
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About the Author
Heidi Godman, Executive Editor, Harvard Health Letter
About the Reviewer
Anthony L. Komaroff, MD, Editor in Chief, Harvard Health Letter; Editorial Advisory Board Member, Harvard Health Publishing
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