Metabolic

How exercise affects metabolism and weight loss

Dr. Hall recently reconsidered the Biggest Loser studies in the face of a new conception of the basic workings of human metabolism. This idea grew out of an influential 2012 study that showed that highly active hunters and gatherers in Tanzania burn roughly the same relative number of calories every day as the rest of us, despite being much more active.

The scientists involved in this research posited that tribal bodies must automatically compensate for some of the calories they burned while foraging by reducing other physiological activities such as growth. (The tribesmen were usually short.) This way, no matter how many miles they jogged in search of tubers and game, the hunters’ bodies were able to keep the total number of calories they burned in check. Scientists called this idea the Total Energy Consumption Theory.

With this research in mind, Dr. Hall saw potential parallels in the results of “The Biggest Loser”. For the new analysis, he looked at his group’s data to get clues as to whether the metabolism of the participants actually behaved like the metabolism of the hunter-gatherer. And he found clues in their resting metabolic rates. That number fell early on their Biggest Loser filming, he noted, as they cut down on the amount of food they eat and, understandably, their bodies cut the calories they burned to avoid starvation.

But in later years, when participants usually returned to eating, as they had before, their metabolism remained depressed because, he concluded – and this was key – most of them were still exercising. Contrary to intuition, he wrote in the new analysis, frequent physical activity appears to have caused your body to keep resting metabolic rate low, so that total daily energy expenditure could be curtailed.

“It’s still just a hypothesis,” said Dr. Hall, “but it appears that what we observe in the Biggest Loser data is” an example of the constrained energy model. “

What could this rethinking of The Biggest Loser story mean for the rest of us if we hope to keep our weight in check? First and foremost, it suggests that abrupt and colossal weight loss will generally backfire, as this strategy drops resting metabolic rate more than would be expected given people’s smaller heights. As he pointed out, when people gradually lose pounds in weight loss experiments, their metabolic changes tend to be less drastic.

Second, and even more confusing, if you’ve lost significant weight, the “Biggest Loser” style, exercise will likely be both an ally and an underminer in your efforts to keep those pounds in check. In Dr. Hall’s new interpretation of long-term weight control of participants, frequent exercise kept participants’ resting metabolic rate low, but also helped them prevent fat build-up. Essentially, the participants who exercised the most added the least weight, although they also had the slowest relative resting metabolism.

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