Exercise and Weight Loss: Debunking the Myth
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 Constrained Energy Expenditure Hypothesis
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.
Exercise and Energy Expenditure
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.
Modest Increase
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.
A More-Modest-Than-Expected Increase
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.
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.
Conclusion
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.
Frequently Asked Questions
Q: Does exercise really increase energy expenditure?
A: Yes, exercise does increase energy expenditure, though perhaps not as much as we might expect.
Q: How much does exercise increase energy expenditure?
A: The exact number is difficult to estimate, as it varies a lot between people.
Q: Why doesn’t exercise increase energy expenditure by as much as expected?
A: There are many possible reasons, including physical activity substitution and behavioural compensation.