Losing weight is hard, which is why weight loss experts have long searched for different approaches to make it easier for people. One strategy gaining steam is intermittent fasting, where people fast or lower their calories substantially for a short period of time. (This diet plan also has potential lifespan-extending benefits.)
But new research published in JAMA Internal Medicine suggests that the fasting diet may not be the weight loss key it's been hyped up to be.
In the new trial, researchers wanted to know whether people who tried a fasting diet would be more successful than those on a standard diet. They told 100 people with obesity to follow one of three diets for a year. Some were told to cut their calorie consumption by 25% per day—a typical calorie restriction diet—while others did an alternate-day fasting diet, where they ate about 500 calories on “fast” days and whatever they wanted on “feast" days. The last group, which served as the control group, ate what they normally would.
The researchers expected that the people in the fasting group would lose more weight and have an easier time sticking to the diet than regular dieters, but the results didn't reflect that. At the end of the year, people who did the fasting diet and those who just cut calories both lost an average of 13 pounds. However, people in the fasting group actually had a harder time sticking to the diet, and more people in that group dropped out of the study.
“I really thought people would have an easier time and lose more weight on the [fasting diet] and I was shocked they lost the same amount,” says study author Krista Varady, an associate professor of nutrition the University of Illinois at Chicago and author of the book The Every-Other-Day Diet. “ The take-home message for me is that this diet isn’t for everyone.”
The researchers also did not find significant differences in other health measures between the dieting groups, like blood pressure, heart rate or insulin resistance. Varady says that while half of the people in the fasting group "could barely do the diet," there were several people who were very successful, losing between 20 to 50 pounds. Those findings suggest that some people do respond well to the diet.
Still, what works for one person clearly doesn’t work for everyone. “If people have failed other diets, maybe this will work,” Varady says. “People will pick what diet works best for them."