Is fasting an effective weight-loss method?

If you are obese or overweight, fasting is an effective weight-loss method, if you stick to it. But it is no more effective than a diet that restricts your daily calories. We know this because there were no additional weight-loss or cardiovascular benefits of fasting two days per week, over an ordinary calorie-restriction diet, in a study of 150 obese adults over the course of 50 weeks.

But you should also consider how difficult the diet will be to stick to. In a study of 100 randomized obese and overweight adults published in 2017, the dropout rate was higher with those who were fasting, 38 percent, compared with 29 percent for calorie restrictors and 26 percent for those who kept eating as they normally did.

“Some people really struggle with having to monitor their intake and constantly record food in an app every day. So the takeaway of the study was if daily calorie restriction doesn’t work for you, maybe alternate-day fasting would be a little easier,” said Krista Varady, Ph.D., professor of nutrition at the University of Illinois at Chicago and the senior author of the study. “There’s nothing magical here. We’re tricking people into eating less food, in different ways,” she said in 2017.

There is some new evidence that shows different forms of fasting are not equal — in part because some are easier than others, but also because some forms of fasting better match our body’s natural circadian rhythm, thus lowering insulin levels, increasing fat-burning hormones and decreasing appetite.

Basically, because our metabolism has evolved to digest food during the day and rest at night, changing the timing of meals to earlier in the day may be beneficial.

In a study done in Dr. Peterson’s lab, 11 adults did time-restricted feeding (eating from 8 a.m. to 2 p.m.) and a control 12-hour eating period, for four days each. On the last day of each session, researchers measured energy expenditure and hunger hormones and found that time-restricted feeding improves the appetite hormone ghrelin and increases fat burning. “It’s shown to reduce the amount of fat in the liver, which is a risk factor for diabetes and cardiovascular disease,” said Dr. Peterson.