What effect does exercise have on metabolism and weight loss?

MARYLAND (AP) — Many of us recall "The Biggest Loser," the somewhat infamous reality television program that aired for more than a decade beginning in 2004 and featured competitors competing fiercely to lose enormous amounts of weight in a short period.

One of the show's most important teachings seemed to be that severe exercise combined with stringent calorie restriction would result in massive weight reduction.

Years later, however, media coverage of the candidates seemed to convey a different tale, one of weight gain and slowing metabolisms, as well as the futility of pursuing long-term weight loss.

Many ideas about "The Biggest Loser" may be myths, according to a new scientific examination of the program and its aftermath published last month in the journal Obesity. The investigation aims to figure out what happened to the candidates' metabolisms and why some of them lost weight more quickly than others.

It also investigates the complicated function of exercise and whether or not keeping physically active helps the participants maintain their weight for years.

For those who may have forgotten, or attempted to forget, "The Biggest Loser" aired on NBC for more than a dozen seasons to typically good ratings. Extreme calorie restriction and hours of daily intense activity were used to see who could lose the greatest weight. In just a few months, "winners" can lose hundreds of pounds.

Dr. Kevin Hall, a senior scientist at the National Institute of Diabetes and Digestive and Kidney Diseases, which is part of the National Institutes of Health, was intrigued by the sudden and significant weight reduction.

Dr. Hall, a metabolism expert, understood that when patients lose a lot of weight in a short period, their resting metabolic rates — the calories we burn every day just by being alive — usually plummet. We may burn fewer calories overall if our resting metabolic rate is lower.

This impact was thought to be triggered in part by muscle loss during dieting. Muscle burns more calories than fat because it is a more active tissue, and having more muscle implies having a higher metabolic rate.

Dr. Hall questioned if the manic levels of exercise shown on "The Biggest Loser" would help dieters preserve muscle and maintain a high resting metabolism while cutting calories.

Dr. Hall and his colleagues launched the first in a series of trials to find out more than a decade ago. They contrasted 13 men and women who had dropped enormous amounts of weight by decreasing calories due to gastric bypass surgery with 13 participants from "The Biggest Loser," whose dramatic weight reduction included both exercise and dieting, in a 2014 research.

The bypass group lost both muscle and fat, as predicted, whereas "The Biggest Loser" competitors preserved most of their muscle while losing mostly fat. Regardless of whether they were well-muscled or not, everyone's resting metabolic rate decreased to the same level.

Dr. Hall and his colleagues were taken aback by the findings. They were even more perplexed when they rechecked 14 of the same candidates six years after their competition for a 2016 research, assuming their metabolisms to have recovered by then.

After dieters cease aggressively losing weight, and especially if they regain pounds, their resting metabolisms increase somewhat. Heavier people burn more calories at rest than those who are lighter. The majority of the participants had recovered their weight at this point. Their resting metabolisms, on the other hand, remained persistently sluggish, burning roughly 500 fewer calories per day than before they joined the show.

Follow-up research the following year found that physical exercise had helped some participants avoid weight gain. They gained fewer pounds if they walked around or exercised for roughly 80 minutes most days than if they rarely worked out.

Their resting metabolisms, however, were not boosted by their workout. The exercisers had the biggest relative decreases in resting metabolic rates.

Dr. Hall, perplexed, recently decided to rethink the "Biggest Loser" experiments in light of a new understanding of how human metabolism works fundamentally. This concept arose from a well-received 2012 study that found that extremely active Tanzanian hunter-gatherers burn roughly the same number of calories per day as the rest of us while moving around significantly more.

The researchers hypothesized that the tribespeople's bodies were compensating for some of the calories they burnt while foraging for food by slowing down other physiological functions like development. (Most of the tribespeople were short.)

The hunters' bodies would be able to keep the overall quantity of calories they burnt each day in balance, the researchers reasoned, regardless of how many miles they ran in search of tubers and animals. The restricted total energy expenditure hypothesis was coined by the scientists.

Dr. Hall became aware of this study and began to recognize connections in the outcomes of "The Biggest Loser." So, for the current study, he looked back at his group's data to see if the competitors' metabolisms had performed similarly to the hunter-gatherers' metabolisms. He discovered signs in their resting metabolic rates as well. He added that when they cut back on how much they ate early in their "Biggest Loser" shooting, their bodies, appropriately, lowered the calories they burnt to prevent starvation.

However, when participants returned to eating normally in subsequent years, their metabolisms remained sluggish because, he reasoned — and this was crucial — most of them continued to exercise.

He stated in the current study that, counterintuitively, regular physical activity appears to have caused their bodies to keep resting metabolic rates low, limiting total daily energy expenditure.

"It's still just a theory," Dr. Hall said, "but what we're seeing" in the "Biggest Loser" data "looks to be an illustration of the restricted energy model."

So, what does this reworking of "The Biggest Loser" tale mean for the rest of us who want to maintain a healthy weight? First and foremost, research shows that drastic and massive weight reduction is likely to backfire, as this method appears to send resting metabolic rates plummeting faster than would be predicted given people's lower body proportions.

He pointed out that when patients lose weight gradually in weight-loss studies, their metabolic alterations are less pronounced.

Second, and perhaps more perplexingly, if you've dropped a significant amount of weight in the "Biggest Loser" method, exercise will likely be both an ally and an adversary in your efforts to keep the pounds off. According to Dr. Hall's novel interpretation of participants' long-term weight management, regular exercise not only maintained contestants' resting metabolic rates low but also helped them avoid fat return.

In other words, even though they had the slowest relative resting metabolisms, the candidates who worked out the most lost the least weight.

It's still unclear how exercising helped them maintain their weight, according to Dr. Hall. He believes that exercise influenced people's appetites in ways that made them less likely to overeat while simultaneously burning calories. He plans to do further research in the future to better understand how exercise affects metabolisms, both positively and negatively, he added.

For the time being, though, the greatest enduring lesson of "The Biggest Loser" maybe that long-term weight loss, while difficult, is not impossible. Yes, most "Biggest Loser" competitors gained the weight back, but not all of it, according to Dr. Hall.

After six years, most former participants weighed roughly 12% less than they did before entering the program, a significant change, and those who continued to exercise were the most successful.

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