Exercise Does Increase Calorie Burn But Probably Not As Much As You Might Hope

(MENAFN- The Conversation) 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”.

Building on this, Pontzer suggests that,“The bottom line is that your daily (physical) activity levels have almost no bearing on the number of calories that you burn each day.”

But before you pack away your running shoes, let's look at what the research shows us. The most rigorous and robust evidence available on the topic actually shows that exercise does increase energy expenditure – though perhaps not as much as we might expect.

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 .

Indeed, Pontzer's own observational data shows that daily energy expenditure can vary by more than 1,000 calories per day in a group of older people. This directly contradicts his suggestion that it's fixed at 3,000 calories a day for everyone.

When we look at data from randomised controlled trials, we can clearly see that exercise does have an effect on energy expenditure.

Randomised controlled trials allow researchers to establish cause and effect from a specific treatment or intervention. They allow groups of people to be fairly compared with just one variable manipulated at a time.

Trials show that a structured, supervised exercise programme done up to five times a week for six and ten months increases daily energy expenditure. These effects were shown in both young and middle-aged men and women.

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.

However, a more-modest-than-expected increase in energy expenditure is a far cry from bold statements that exercise does not increase daily energy expenditure at all. The exact number is difficult to estimate though, as it varies a lot between people.

As we discuss in our review, there are many possible reasons why exercise does not increase energy expenditure by as much as would be expected. Some factors might include physical activity substitution (when your new workout substitutes for physical activity you would normally have done at that time – so you might only end up burning a few calories more than you normally would have) and behavioural compensation (doing less activity later in the day after a morning workout).

This also highlights a common misunderstanding about the magnitude of exercise's effects. Exercise can feel hard – so people might reasonably expect a large return on their investment. But five hours of exercise a week is only about 4% of our typical waking time. So this will only go so far in shifting the dial upwards in terms of how many calories we burn through physical activity.

Part of the misunderstanding about changes in energy expenditure and potential weight loss through exercise is perhaps related to unrealistic expectations about how many calories we burn when working out.

So, despite what you might have heard or read, the strongest evidence from robust trials clearly demonstrates that exercise can increase daily energy expenditure. Though this might not be as much as you expect or hope.

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