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One Surprising Side Effect of Intermittent Fasting, New Study Says

It's not just weight loss you may experience on your time-restricted eating plan... which isn't a good thing.

Intermittent fasting has recently become the talk of the weight loss world, gaining countless devotees and being heralded as a simple weight loss plan that can help even those who've struggled to shed weight in the past. However, a new study suggests that it may be more than just pounds you lose when you adopt an intermittent fasting plan.

According to a study published in the journal Science Translational Medicine on June 16, 2021, researchers who participated in intermittent fasting during a control trial actually lost fewer pounds than those who followed a diet that didn't incorporate time-restricted eating. Perhaps even more surprisingly, this was true even though adherents to both diets consumed the same number of total calories.

To reach their conclusion, researchers from the University of Bath's Centre for Nutrition, Exercise & Metabolism had study participants break into three groups: group one fasted on alternate days and ate 50% more than usual on the day after a fast, group two reduced the number of total calories they consumed by 25% across meals with no fasting, and group three fasted every other day, but ate 100% more than usual on the day following their fast day. All groups consumed between 2,000 and 2,500 calories at the beginning of the three-week study period, with groups one and two reducing their overall calorie intake to between 1,500 and 2,000 calories a day, and group three fasting but not reducing their total caloric intake.

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Researchers found that individuals in group two shed just over four pounds, on average, over a three-week period, virtually all of which was fat loss. Group one, which consumed the same number of calories as group two, but incorporated fasting, lost slightly less weight—3.5 pounds on average—but the pounds lost were approximately half fat, half muscle mass. Among the third group, the total weight loss was not significant.

weight loss measuring

"Intermittent fasting is no magic bullet and the findings of our experiment suggest that there is nothing special about fasting when compared with more traditional, standard diets people might follow," said James Betts, PhD, the study's lead author and director of the Centre for Nutrition, Exercise & Metabolism, said in a statement.

What's more, Betts explained that the loss of muscle mass might make it more difficult for individuals to stay physically active or maintain their muscle mass, which burns more calories at rest than fat mass. So, while sticking to an intermittent fasting plan may help you shed a few pounds, that weight loss may come at a cost to your other health and fitness goals.

For some simple ways to shed those extra pounds, check out how Making This One Change to Your Diet Could "Reprogram" Your Metabolism, New Study Says, and for more health and weight loss news delivered to your inbox, sign up for our newsletter!

Sarah Crow
Sarah Crow is a senior editor at Eat This, Not That!, where she focuses on celebrity news and health coverage. Read more about Sarah