How exercise affects metabolism and weight loss

A new analysis of data from “The Biggest Loser” highlights the complex ways the body compensates when we drop pounds.

Many of us remember “The Biggest Loser,” the somewhat notorious reality television show in which contestants competed feverishly to drop massive amounts of weight over a short period of time. One of the biggest lessons of the show appeared to be that extreme exercise, along with draconian calorie restriction, would lead to enormous weight loss.

Media coverage of the contestants years later, though, seemed to tell a different story, of weight regain and slowed metabolisms and the futility of attempting long-term weight loss.

Now a new scientific analysis of the show and its aftermath, published last month in the journal Obesity, suggests many beliefs about “The Biggest Loser” may be misconceptions. The analysis tries to untangle what really happened to the contestants’ metabolisms and why some of them kept off weight better than others. It also looks into the complex role of exercise and whether staying physically active helped the contestants keep their weight under control for years, or not.

Contestants competed to drop the most pounds using extreme calorie restriction and hours of daily strenuous exercise. “Winners” typically shed hundreds of pounds in a few months. Such rapid and extreme weight loss caught the attention of Kevin Hall, a senior investigator at the National Institute of Diabetes and Digestive and Kidney Diseases, which is part of the National Institutes of Health. An expert on metabolism, Dr Hall knew that when people drop lots of weight in a short period of time, they typically send their resting metabolic rates — the baseline calories we burn every day just by being alive — into free-fall. A lower resting metabolic rate can mean we burn fewer calories over all.

This effect was believed to be caused, in part, by the loss of muscle during dieting. A relatively active tissue, muscle burns more calories than fat, and more muscle typically means elevated metabolic rates. So, Dr Hall won

Frequent exercise kept contestants’ resting metabolic rates low

dered, would the maniacal levels of exercise during “The Biggest Loser” help dieters hold onto muscle and keep their resting metabolism high, even as they cut calories?

Dr Hall and his colleagues began a series of experiments to find out.

So, what could this rethinking of “The Biggest Loser” story mean for the rest of us, if we hope to keep our weight under control? First and most fundamentally, it suggests that abrupt and colossal weight loss generally will backfire, since that strategy seems to send resting metabolic rates plunging more than would be expected, given people’s smaller body sizes. When people drop pounds gradually in weight-loss experiments, he pointed out, their metabolic changes tend to be less drastic.

Second and more befuddling, if you have lost substantial weight, “Biggest Loser” style, exercise likely will be both ally and underminer in your efforts to keep those pounds at bay. In Dr Hall’s new interpretation of contestants’ long-term weight control, frequent exercise kept contestants’ resting metabolic rates low but also helped them stave off fat regain. In essence, the contestants who worked out the most wound up adding back the least weight, even though they also sported the slowest relative resting metabolisms.

For now, though, the most reverberant lesson of “The Biggest Loser” may be that longterm weight loss, although daunting, is not unfeasible.