Exercise can reduce your metabolism after losing weight

Many are familiar with the American sitcom “The Biggest Loser”, a well-known reality show that aired on American television for more than a decade, in which competitors competed to lose a lot of weight in a short time.

One of the biggest lessons the program teaches seems to be that intense exercise can lead to drastic weight loss along with draconian calorie reduction.

But years later, the media coverage of the participants seems to reveal another reality, the need to regain weight, slow down metabolisms and try to lose weight in the long run.

A new scientific study of the show, published in Obesity magazine in May, and its implications suggests that many of the show’s common ideas may be wrong. The analysis seeks to shed light on what actually happened to participants ’metabolism and why some of them managed to maintain weight loss better than others.

The study examines the complex role that exercise plays and whether being physically active has helped participants control their weight.

For those unfamiliar, “The Biggest Loser” aired on NBC, with a large audience, for more than 12 seasons. Participants competed to lose the most pounds using extreme calorie reduction and hours of intensive exercise. “Winners” usually shed a lot of pounds in a few months.

This rapid and extreme weight loss attracted the attention of Kevin Hall, a senior researcher at the National Institutes of Diabetes and Digestive and Kidney Diseases (USA), part of the U.S. National Institutes of Health.

An expert in metabolism, Hall knew that when people lose a lot of weight in a very short amount of time, it usually causes a big drop in their basal metabolic rate – to keep the calories we burn every day alive. Lower basal metabolic rates generally burn fewer calories.

This effect was thought to have been caused in part by the loss of muscle mass created when people went on a diet. A relatively active tissue burns more calories than fat, and more muscle mass generally means higher metabolic rates.

So Hall asked: Would the extreme levels of exercise practiced in “The Biggest Loser” help participants maintain muscle mass and keep their basic metabolism high while reducing calories?

Beginning more than a decade ago, Hall and his colleagues began the first of a series of experiments to find the answer.

In a 2014 study, gastric bypass surgery compared 13 men and women who had lost a lot of weight as a result of calorie reduction to 13 participants in “The Biggest Loser,” whose extreme weight loss included exercise and diet.

As predicted, the bariatric surgery team lost muscle mass in addition to fat, while participants in “The Biggest Loser” maintained most of their muscle mass, mostly losing fat. But everyone’s basic metabolic rate dropped, and at roughly the same rate, whether people maintained muscle or not.

Hall said he and his colleagues were impressed with the results. And their confusion was exacerbated, according to a 2016 study, when they re-examined 14 of the same participants six years after the competition, believing that their metabolism would rise again.

In most cases, the basic metabolism of the diet increases considerably after people stop actively losing weight, and especially if they regain weight. Heavy people burn more basal calories than lighter ones.

By 2016, most of the reality show contestants had already regained their weight. But their basal metabolism remained very low, with an average of 500 fewer calories burned per day before participating in the program.

A study the following year found that physical activity helped some competitors gain weight.

On most days, those who moved or exercised formally for about 80 minutes gained less pounds than those who rarely exercised. But the exercise they were doing did not increase their basal metabolism. In fact, those who exercised experienced the largest relative decreases in their basal metabolic rate.

Surprised, Hall has recently begun re-evaluating his research on “The Biggest Loser,” looking at a concept that is really looking at how human metabolism actually works. This idea came from an effective 2012 study that showed that very active people in Tanzania who live by hunting and gathering burn the same amount of calories as the rest of us, even though we move a lot more.

The scientists involved in the study postulated that the bodies of Tanzanian hunters should automatically compensate for some of the calories burned during food hunting by reducing other physiological activities such as growth (hunters used to be low altitude).

In this way, researchers believe that the bodies of hunters could limit the number of calories they burned each day, regardless of the number of miles they spent searching for roots and animals for hunting. Scientists have called this idea the theory of limited total energy expenditure.

Aware of this research, Hall began to see potential parallels in the results of “The Biggest Loser.” Therefore, for the new analysis, he re-examined the data of his group for the metabolism of the participants, looking for signs that would be in practice similar to the metabolism of hunter-gatherers. And they found traces of their basal metabolic rate.

These rates dropped significantly at the beginning of “The Biggest Loser,” because the participants reduced their food intake and, of course, reduced the number of calories they burned in their bodies so as not to starve them to death.

But in recent years, when competitors returned to their first eating patterns, their metabolism slowed, Hall concluded, and that was a key factor, as most of them were exercising.

Intuitively, he wrote in the new analysis, it appears that frequent physical activity caused his body to have a low basal metabolic rate, so the total daily energy expenditure could be limited.

“This is still a hypothesis,” Hall said, “but what we are seeing seems to be an example of a limited energy model in the data on participants in The Biggest Loser.”

Translated by Clara Allain

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