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How Diet and Exercise Affect Metabolism and Weight Loss

A recent study in the Journal of Obesity sheds additional light on the role metabolism plays in achieving and maintaining significant weight loss.

Metabolism is the process by which cells in our bodies turn food into energy. Resting metabolic rate is the baseline of calories our bodies burn every day to perform basic life-sustaining functions – in other words, just being alive.

Scientists have long known that sudden weight loss through calorie reduction alone often fails and individuals regain the pounds. During rapid weight reduction, people tend to lose both muscle and fat. Even during rest, muscle burns more calories than fat so the loss of muscle lowers metabolic rate.

Researchers at the National Institutes of Health wondered whether individuals who rapidly lost huge amounts of weight through diet and exercise would maintain more muscle mass and have more success keeping the weight off.

They studied large individuals who had gastric bypass surgery that helped them significantly cut calorie intake and contestants on the once popular television show, “The Biggest Loser.” The latter group shed enormous weight through a combination of extreme calorie reduction and intense exercise.

The results offered some surprises.

  • As expected, the bypass group lost both muscle and fat while “The Biggest Loser” contestants retained most of their muscle and primarily dropped fat. But the resting metabolic rate for both groups dropped about equally.

  • Years later, even when the contestants had stopped actively losing weight and even had regained some pounds, their metabolisms remained lower than when they had joined the show. Researchers hypothesized that their bodies compensated for the sharp diet restrictions by slowing the metabolism to conserve calories – like a reflexive response to perceived starvation.

  • A key takeaway is that abrupt and large weight loss generally will backfire due to plummeting metabolic rates. Gradual is better.

  • Exercise can reduce appetite and overeating while burning calories. Finding the right amount of activity is critical as too much or too little exercise can contribute to a slower metabolism.


Energy Compensation and Metabolic Adaptation: “The Biggest Loser” Study Reinterpreted. First published: 23 November 2021


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