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This Popular Weight-Loss Diet May Cause Muscle Loss, Study Finds

The diet showed no special weight loss benefits, but yielded some fitness drawbacks.

Intermittent fasting is by definition one of the more challenging diets to follow. But whether you're doing it for the science-backed health benefits like reducing inflammation and reversing diabetes, or to shed some pounds and boost your fat loss, it is a lifestyle choice that seems to promise major gains in return for some major restriction. However, the latest study on this type of restrictive eating may put a damper on our enthusiasm for the diet.

Not only did a 116-participant study out of University of California, San Francisco find that intermittent fasting alone is in no way more beneficial than regular patterns of eating, it showed that this type of dieting may result in a significant amount of muscle loss. (Related: 21 Best Healthy Cooking Hacks of All Time.)

Researchers compared two groups of participants: ones that ate a regular diet of three meals a day plus snacks, and ones that limited their calorie intake to a strict daily period between noon and 8 pm. What they found was that at the end of the 12-week study, the groups didn't significantly differ in terms of weight loss, fat mass, cholesterol levels, or blood sugar control. In other words, the intermittent fasting lifestyle didn't actually improve the participants' metabolic health or weight loss.

However, participants in both groups showed a small amount of weight loss, and those in the intermittent fasting group lost a slightly greater amount of weight. And while this difference in weight loss wasn't big enough to say that fasting played a role in it, there was a slightly more troubling pattern that emerged. About 65% of the total weight loss among the participants in the intermittent fasting group was comprised of muscle mass. This is far more muscle mass being lost than you'd experience on a regular calorie-restricting diet, which would be around 20–30%.

An important thing to point out is that people in this study were not instructed to adhere to a specific calorie count, type of diet by macros, or exercise routine. They simply started fitting all their eating within an 8-hour window, which provided no benefits compared to the group that didn't follow such drastic measures.

While previous research has shown that intermittent fasting can aid weight loss, researchers at UCSF hypothesized that people's calorie intake would usually decrease on this type of diet, which would be the more significant factor causing them to shed the pounds. Another theory was that the 8-hour window was too long, as some previous studies showed metabolic benefits and weight loss tied to a 6-hour eating window.

So before you restrict yourself to a specific daily window of eating, keep in mind you may need to change what and how much you're eating in order to see the benefits of fasting and prevent muscle mass loss. Check out these 17 Protein-Packed Dinners for Muscle Building and Weight Loss to achieve healthy weight loss goals.

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Mura Dominko
Mura is ETNT's Executive Editor, leading the coverage of America's favorite restaurant chains, grocery stores, and viral food moments. Read more about Mura