外刊阅读20250215｜健身教练集体破防！每天运动反而瘦不了？

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It's generally accepted that exercise is a key element of losing weight. But this long-held view has been called into question in recent years – with no shortage of articles and podcasts claiming it's a myth that exercise increases your metabolism and helps you burn calories after you work out.

The central tenet of these reports is that the amount of calories we burn each day is somehow constrained. This hypothesis was first proposed in 2012 by the evolutionary anthropologist Herman Pontzer. He posited that as you increase your daily energy expenditure (calories burned) through physical activity, your body will find ways to cut back on energy expended on other biological processes – such as your resting metabolism. This leaves your overall daily energy expenditure unchanged. This theory has since been popularised in Pontzer's 2021 book Burn, in which he theorises that "we burn calories within a very narrow range: nearly 3,000 calories per day, no matter our activity level".

The evidence Pontzer used to support his hypothesis came from observational studies that compared energy expenditure in different populations around the world. In an observational study, researchers only take measurements and make comparisons between groups without actually introducing any changes.

The most eye-catching of the studies Pontzer used to support his hypothesis was research on the Hadza tribe – one of the last remaining hunter-gatherer groups in Africa. Hunter-gatherers are assumed to be highly active in order to survive. But the study observed that the Hadza expended no more energy than the average Westerner did each day.  We reviewed the constrained energy expenditure hypothesis in 2023. We concluded that Pontzer's theory raises some interesting questions. However, it's generally not very convincing due to flaws in the nature of the evidence.

This research clearly shows that physical activity does increase how many calories you burn each day. It's important to note that these trials do report, however, that the increases in daily energy expenditure were not always as big as expected. Put simply, burning 600 calories in the gym will not necessarily increase your daily energy expenditure by the same amount.