For many people looking to lose weight, the goal is to burn more calories than you eat by ramping up your total energy expenditure and forcing the body to draw on energy stores like fat. But a new study shows that exercise might not be burning all the calories we think it is.
Our bodies use up a basic level of energy for all sorts of things during the day, even if we’re not exercising — that’s what’s called our basal energy expenditure.
Everything from breathing to pumping blood to thinking requires at least some level of energy; you quite literally cannot think on an empty stomach.
But working out shifts our metabolic processes into overdrive, boosting what’s known as our activity energy expenditure. And we have a generally good idea of how many calories we burn during various exercises, reports The New York Times.
The idea is that by adding up those known quantities of calorie-burning activities and comparing it to the food we eat, we should be able to keep our calorie expenditure higher than our calorie intake, the Times notes.
But new research shows that reality may not be so straightforward. Exercise only boosts the average person’s total calorie use by about 72% of what you might predict, according to a study published last month in Current Biology.
If our bodies just added all the activity we used during exercise onto our basal level of energy use, our total energy expenditure would equal our basal plus activity energy levels. But in a review of over 1,700 people, researchers found that average total energy expenditure was less than expected activity plus basal levels, reports The Guardian.
The researchers haven’t pinpointed why or how, exactly, this happens. We might reduce some of the energy spent on background body processes, the Times reports, or even just laze around a bit more after exercising. Anyone who’s felt the urge to nap after a long run would probably second that latter hypothesis.
The magnitude of this effect isn’t universal, however, especially with regard to weight, the study says. The reduction from expected calorie use varies from about 28% for people with a very low BMI to around 50% for people with a very high BMI. The reasons for this aren’t immediately apparent either, The Guardian says.
The authors note that this adaptation may be evolutionary advantageous by reducing the total number of calories we need to stay nourished. But, they add, for those of us looking to lose weight, this trait isn’t exactly helpful.
This finding doesn’t mean that exercise is useless for weight loss — it just might be a little less helpful than promised. And there are plenty of benefits to exercise beyond losing weight, such as supporting brain health, heart health, and strength, or even just being able to keep up with your kids. Functional fitness is still super important, no matter what it means for how much you weigh.