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The question

Fasting has gained some popularity as a weight-loss tactic, generally practiced intermittently or on alternate days. But is it a viable alternative to the standard method of restricting calories consumed daily?

This study

The study included 100 adults, more women than men, who averaged 44 years old, were obese and relatively sedentary. They were randomly assigned to one of three groups: For six months, one group restricted daily calorie consumption to 75 percent of their normal amount. A second group fasted on alternate days by consuming only 25 percent of their normal amount of calories on those days and consumed extra calories (125 percent of normal) on the other days (which were called “feast days”). The third group made no changes to their normal eating pattern. For the next six months, the goal for all participants was to maintain their weight where it was at the end of the first six months. Throughout the study, participants were asked to not change their daily physical activity habits. After a year, weight loss was essentially the same — 5 to 6 percent, on average — for the group that restricted calories daily and the group that fasted on alternate days. Those who did not change their eating habits recorded, on average, a slight gain. More people dropped out of the study from the fasting group than from the daily-calorie-restriction group (38 percent vs. 29 percent), primarily citing trouble adhering to the fasting regimen.

Who may be affected?

People trying to lose weight. More than 70 percent of adults in the United States are overweight or obese, which can contribute to a number of health problems. Excess weight has been shown to play a role in such diseases as diabetes, heart disease, arthritis and some types of cancer. Although a plethora of weight-loss programs and methods exist, plans with long-term success rates tend to be those in which participants take in fewer calories and burn more through physical activity.


All participants were obese; whether the weight-loss methods would have the same effect on other people was not tested. Some of the eating data came from records kept by the participants. The weight-maintenance period was relatively short. Participants were provided with food for all their meals for the first six months and then met weekly with a dietitian or nutritionist to learn how to continue the eating plan on their own.

Find this study

Online in JAMA Internal Medicine (jamainternalmedicine.­com; click “New Online”).

Learn more

Information on choosing a weight-loss program can be found at niddk.nih.gov (search for “choosing weight loss”). Learn more about the effects of weight on health at cdc.gov (search for “healthy weight”).

The research described in Quick Study comes from credible, peer-reviewed journals.