If people lose a lot of weight, do their bodies fight to regain it?
Sixteen obese contestants on NBC’s “The Biggest Loser” lost an average of 128 pounds after an intensive seven months of dieting and exercise in 2009. That amounted to shedding an average of 39 percent of their body weight.
Could they keep that weight off? Researchers at the National Institutes of Health set out to find out from the 14 contestants who agreed to be studied.
Six years later
Unfortunately, after six years, most of the 14 had regained a significant amount of their lost weight, an average of 90 pounds per person. Only one hadn’t regained at least some of the lost weight. On average, the 14 weighed just 12 percent less than when they made their first appearance on the reality show.
Metabolism slows down
Researchers know that losing weight leads to a slower resting metabolism. That’s the number of calories your body needs to keep your heart beating, keep your kidneys filtering blood, and to do whatever else is necessary to keep you alive 24 hours a day
“Your metabolism slows down when you cut calories,” says Kevin Hall, senior investigator in the Laboratory of Biological Modeling at the National Institute of Diabetes and Digestive and Kidney Diseases. “It’s as though your body is hunkering down to face scarcity, so it burns fewer calories per minute.”
The metabolic rate of “The Biggest Loser” contestants had fallen by an average of about 660 calories per day by the end of the competition. “You could explain only about 350 of the 660 calories by their smaller size,” says Hall. The remaining 310 calories were due to slower metabolism.
Here’s what stunned the researchers
The big surprise was what happened over the long term. Hall found that six years later, after the “Biggest Losers” had regained much of their weight, their resting metabolic rates hadn’t climbed back up toward where they were before the competition began. In fact, their metabolisms were even slower than before, given the weight they had regained. That’s what stunned the researchers.
It was as if their bodies were still fighting to restore the lost weight, even though they had already regained much of it. On average, the contestants would have to eat 500 fewer calories a day than other people of the same weight just to avoid putting on even more pounds.
What about other people?
“Now, their case is an extreme,” Hall cautions. But even if you went from, say, 165 pounds to 145 pounds, to stay at 145 you would have to eat fewer calories than you ate when you used to weigh 145.
“Once you lose at least 10 percent of your weight and your weight is stable, you may need to eat about 10 percent fewer calories to keep the weight off,” says Hall. That’s because your now-lighter body burns fewer calories both at rest and when you move.
Another reason not to gain the extra weight in the first place.
Source: Obesity (Silver Spring). 2016 May 2. doi:10.1002/oby.21538.
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