Exercise does increase calorie burn – but probably not as much as you might hope

It is widely accepted that exercise is a key element in losing weight. But this long-held view has been challenged in recent years – and there’s no shortage of articles and podcasts claiming it’s a myth that exercise boosts your metabolism and helps burn calories after exercise.

The central tenet of these reports is that the amount of calories we burn each day is somehow limited. This hypothesis was first proposed by evolutionary anthropologist Herman Pontzer in 2012. He hypothesized that if you increase your daily energy expenditure (calories burned) through physical activity, your body will find ways to reduce energy expenditure on other biological processes – such as your resting metabolism. This means your total daily energy consumption remains unchanged.

This theory has since been popularized in Pontzer’s 2021 book Burn, in which he theorizes that “we burn calories within a very narrow range: almost 3,000 calories per day, regardless of our activity level.”

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

But before you put away your running shoes, let’s look at what the research shows us. The most conclusive and robust evidence available on this topic actually shows that exercise increases energy expenditure – although perhaps not as much as we might expect.

Movement and energy consumption

The evidence Pontzer used to support his hypothesis came from observational studies comparing the energy consumption of different populations around the world. In an observational study, researchers only take measurements and compare between groups without actually making any changes.

The most striking 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 believed to be very active in order to survive. However, the study found that the Hadza did not use more energy than the average Westerner per day.

We tested the constrained energy consumption hypothesis in 2023. We concluded that Pontzer’s theory raises some interesting questions. However, due to the flaws in the nature of the evidence, it is generally not very convincing.

In fact, Pontzer’s own observational data shows that daily energy expenditure among a group of older people can vary by more than 1,000 calories per day. This is in direct contradiction to his proposal to set everyone’s daily calorie intake at 3,000 calories.

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

Randomized controlled trials allow researchers to determine the cause and effect of a particular treatment or intervention. They enable a fair comparison of groups of people, each with only one manipulated variable.

Studies show that a structured, supervised exercise program performed up to five times per week for six and 10 months increases daily energy expenditure. These effects were observed in both young and middle-aged men and women.

This research clearly shows that physical activity increases the number of calories burned per day.

Modest climb

It is important to note that while these studies report that the increase in daily energy expenditure was not always as large as expected. To put it simply, if you burn 600 calories in the gym, your daily energy expenditure won’t necessarily increase by the same amount.

However, a more modest than expected increase in energy expenditure is a far cry from the bold statement that exercise does not increase daily energy expenditure at all. However, the exact number is difficult to estimate because it varies greatly from person to person.

As we discuss in our report, there are many possible reasons why exercise does not increase energy expenditure as much as one would expect. Factors may include physical activity substitution (when your new workout replaces the physical activity you would have normally done at the time – so you may end up burning just a few more calories than you normally would) and behavioral compensation (less activity later perform) include the day after a morning workout).

This also highlights a common misunderstanding about the extent of the effects of physical activity. Exercising can feel strenuous – so people can expect a high return on their investment. But five hours of exercise per week only accounts for about 4% of our typical waking time. So this will just move part of the scale up the scale when it comes to how many calories we burn through physical activity.

Part of the misunderstanding about changes in energy expenditure and possible weight loss through exercise may be related to unrealistic expectations about how many calories we burn while exercising.

Despite what you may have heard or read, the strongest evidence from solid studies clearly shows that exercise can increase daily energy expenditure. Although this may not be as much as you expect or hope.