Exercise, metabolism, and weight: New research from The Biggest Loser

The Biggest Loser was a popular reality television show that ran on NBC for over a decade starting in 2004. In it, participants with obesity competed with each other through intense physical challenges and ate a reduced-calorie diet to see who could lose the highest percentage of body weight.

Prior findings from studies of The Biggest Loser contestants showed not only that metabolism slows drastically following significant weight loss, but also that regaining the lost weight does not restore metabolism back to its pre-weight loss levels. This means people who have lost large amounts of weight must adhere to an extremely low-calorie intake in order to maintain that weight loss. One show contestant lost 239 pounds and achieved a weight of 191 pounds, yet six years later, after regaining 100 pounds of that lost weight, had to consume an 800-calorie-per-day diet to maintain his weight.

New research about physical activity and metabolic rate

A more recent study by the same researcher aims to explain and interpret the findings from The Biggest Loser in light of an energy conservation model. In what he calls the "constrained model of human energy expenditure," Dr. Kevin Hall theorizes that because the contestants engaged in large, sustained periods of intense physical activity, their metabolisms slowed substantially in order to reduce their metabolic rates and thereby minimize changes in total energy expenditure. In other words, their bodies made automatic compensatory changes to maintain energy balance.

Of particular interest is the fact that at the end of The Biggest Loser competition, the degree of metabolism reduction was not related to contestants' subsequent weight regain, and in fact, the contestants that maintained the greatest weight loss six years after the competition actually had the greatest amount of metabolism adaptation. This suggests that metabolic adaptation is a response to the change in lifestyle, namely the dramatic increase in physical activity observed in those who maintained the most weight loss. Fortunately for those trying to maintain significant weight loss, the compensatory mechanisms do not completely counteract lifestyle changes, so it is possible to keep off substantial amounts of weight.

What have we learned about weight loss from studying The Biggest Loser contestants?

Taken together, what we've learned from these studies on The Biggest Loser contestants is that while short-term reductions in resting metabolic rate are related to the extreme calorie restriction at the time of active weight loss, the larger, persistent metabolic adaptation that takes place later is related to substantial sustained increases in physical activity.

Results from the National Weight Control Registry (established in 1993 to determine characteristics of individuals successful at keeping weight off) have long demonstrated that physical activity is a key component of successful weight maintenance. What we don't yet know is how sustained increases in physical activity lead to improved maintenance of lost weight, despite the compensatory long-term reduction in resting metabolic rate. Dr. Hall theorizes this could potentially be because of the effect of physical activity on lowering appetite.

But as is always the case, additional studies are needed to fully clarify the relationship between body composition, physical activity, energy regulation, and weight maintenance. In the meantime, we should continue to follow the well-founded advice to eat healthy whole foods in moderation, avoid processed foods, and engage in regular physical activity to maintain a healthy body weight.