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Dieting quietly cuts fidgeting
Metabolic adaptation
Losing weight also lowers resting metabolic rate, partly because a smaller body needs less energy. On top of that comes metabolic adaptation, a further reduction beyond what the lost body mass explains, averaging around 15%.
When it happens
New evidence suggests metabolic adaptation happens mostly in the transition phases. Within the first few weeks of a diet, resting metabolic rate drops, and after that any further reduction mostly follows the loss of body mass. When calories return to maintenance, resting metabolic rate starts climbing back within a few weeks, with a small reduction remaining.
Why plateaus occur
Metabolic adaptation was once considered a big reason weight loss plateaus. NEAT now looks like the better candidate. Step counts can fall spontaneously on a fat loss diet without people noticing, which is one way NEAT shrinks.
When did researchers first see metabolic adaptation?
The Minnesota Starvation Experiment of 1944 and 1945, led by Ancel Keys, was an early demonstration. Over six months of semi-starvation, the men's resting metabolic rate dropped by roughly 40 percent. Part of that drop reflected weight lost, and part exceeded what body size predicted. The exceeding part is what researchers later called adaptive thermogenesis.
What happened to Biggest Loser contestants' metabolism?
In a 2016 study in Obesity, Erin Fothergill and colleagues at the National Institutes of Health followed 14 contestants from season eight of the show. Six years later, their resting metabolic rates were about 500 calories per day lower than expected for their body size. Most had regained a large share of the lost weight. The study was small.
How does leptin tie into metabolic rate?
Leptin is a hormone released by fat cells, and levels fall as fat is lost. Rudolph Leibel and Michael Rosenbaum showed that low leptin is linked to lower energy expenditure and increased hunger. In a 2005 study in the Journal of Clinical Investigation, giving leptin to people who had lost weight reversed much of the drop in energy expenditure.
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