Intermittent fasting reduces muscle mass, does not promote healthy weight loss, finds new study

Over the last decade, intermittent fasting (IF) has emerged as one of the biggest diet trends globally. Experts have promoted its benefits and celebrities from Hugh Jackman to Malaika Arora have endorsed it.

Myupchar September 29, 2020 16:34:22 IST
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Intermittent fasting reduces muscle mass, does not promote healthy weight loss, finds new study

Repersentational image. I Yunmai/Unsplash

Over the last decade, intermittent fasting (IF) has emerged as one of the biggest diet trends globally. Studies have been conducted on its benefits, like metabolic switching for weight loss, and combining it with the Mediterranean diet is considered to improve heart health.

Experts have promoted these benefits of IF and celebrities from Hugh Jackman to Malaika Arora have tried and endorsed it.

Given the growing popularity of IF, a new study that says this diet does not work comes as a shock.

This study was conducted by researchers at the University of California, San Francisco headed by Dr Ethan Weiss, a cardiologist who has reportedly tried IF himself, and recently published in JAMA Internal Medicine.

Here’s everything you need to know about the claims made by this study.

A brief note on previous indications that IF has side effects

There have, of course, been many studies on IF and specifically its subtype of time-restricted eating (TRE) which says restrict your eating to 8-12 hours a day and fast for the remaining 12-16 hours. Many of these studies have analysed both the benefits and the side-effects of IF.

A study in Behavioral Sciences in 2017 indicated that although IF aided weight loss, depleted adipose tissue and visceral fat stores and improved insulin sensitivity, amazing benefits for those grappling with obesity and being overweight,  it also promoted erratic eating patterns, bingeing and low mood.

A 2019 study in Current Obesity Reports similarly reports that IF may delay ageing and improve cardiovascular as well as cognitive health but at the same time, it may also lead to hyperphagia or binge-eating behaviour, low energy and mood and a lack of long-term adherence.

Despite such suggestions about the unhealthy practices that may emerge from following IF and the persistent notion that this diet cannot be sustained for longer durations, none of these studies claimed that IF doesn’t work or that it doesn’t aid weight loss.

That IF aids weight loss is, in fact, the one area where all previous studies agreed. That’s the biggest point of departure for this new study in JAMA.

Spoke in the IF and TRE wheels

The first point the researchers behind this new study make is that human clinical trials that analyse the benefits and side-effects of IF are either non-existent or use a very small pool of subjects. Most IF studies are animal, specifically mice-based.

Even the two other studies mentioned above were meta-analyses of already published animal studies on IF. This drives home the point that actual, large scale data on human subjects has been lacking where IF is concerned, until this new study came along.

This study included 116 participants recruited between 2018 and 2019 through the Eureka Research Platform and divided them into two randomized groups. Data was collected from them via a study app until October 2019. One group (called the consistent-meal timing or CMT group) was asked to eat three meals a day, with snacking allowed between meals.

The other group (called the time-restricted eating or TRE group) was instructed to eat whenever and however much they wanted between 12 pm and 8 pm, and then to completely abstain from calorie intake between 8 pm to 12 pm. Only non-alcoholic beverages were allowed to be consumed outside of the eating window.

After a 12-week intervention period, it was found that while those in the TRE group lost more weight, the difference between the two groups wasn’t considered significant enough by the researchers. The TRE group also had a decrease in the appendicular lean mass index, meaning that they lost skeletal muscle mass, and thereby skeletal strength, in the lower limbs. There were no differences in other factors like estimated energy, sleep or cardiovascular health between both groups.

Much harm instead of health benefits

The findings of this study indicate that there was no greater weight loss when a TRE diet is compared with a CMT diet, as a large part of the weight lost by the TRE group was muscle mass and not fat.

What’s more, when it comes to differences in fat mass, insulin sensitivity, glucose levels or lipid profiles, there wasn’t a significant difference between both groups either, indicating that there’s not much of an added health benefit attached to TRE or IF.

In fact, as the study pointed out, the decrease in lean muscle levels in those who followed the TRE protocol would likely lead to weakness, disability, impaired quality of life and even sarcopenia or exacerbated muscle loss.

The clincher, the researchers say, was that the extent of lean muscle mass loss during the TRE protocol was positively correlated with weight regain.

Restricted eating during this diet also suggests there may be a lower intake of proteins, which in turn can be harmful in the long run.

This means that even the participants who lost weight via IF, and particularly TRE, may not only end up gaining weight when they stop following the diet but also harm their overall health, specifically their musculoskeletal health in the long run.

For more information, read our article on How to lose weight fast and safely.

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