The global fitness industry will generate over US$80 billion in revenue in 2023, estimates suggest. And why not, given the many excellent reasons to exercise? Better cardiovascular health, lower risk of Type 2 diabetes, stronger immune system – the list goes on.
One of the biggest reasons many people choose to exercise is to lose weight. As a biobehavioral scientist, I study links between behavior and health, and I heed the time-honored advice that eating less and exercising more are necessary to lose weight. But a recent debate in the scientific community highlights the growing suspicion that the “exercising more” part of this advice may be erroneous.
At the center of the debate is the constrained total energy expenditure hypothesis, which asserts that exercise won’t help you burn more calories overall because your body will compensate by burning fewer calories after your workout. Thus, exercise won’t help you lose weight even if it will benefit your health in countless other ways.
Obesity researchers take issue with this hypothesis, because it’s based on observational research rather than randomized controlled trials, or RCTs, the gold standard of scientific evidence. In RCTs, participants are randomly assigned to either a treatment or a control group, which allows researchers to determine whether the treatment causes an effect. Randomized controlled trials have shown that exercise causes weight loss.
The verdict is actually more mixed when considering all the gold-standard evidence available.
Exercise provides many health benefits.
What the evidence says
Spectators of this hypothesis have emphasized the importance of systematically reviewing the evidence from all gold-standard trials. They pointed to a 2021 review of more than 100 exercise studies that examined the effect on weight loss in adults of aerobic, resistance or high-intensity interval training in combination or alone. The review concluded that supervised exercise regimens do cause weight loss, even if only a modest amount.
So that settles the debate, yes? If you eat too much dessert, then you can just go on an extra run to burn off those extra calories, right?
Well, not exactly.
If extra physical exertion burns extra calories overall, then exercise should also keep the weight from coming back after low-calorie dieting. But keeping those lost pounds off after dieting is a common challenge. The same 2021 review includes the few randomized controlled trials that address the question of whether exercise facilitates weight maintenance. However, the results weren’t as good as they were for weight loss. The researchers found that six to 12 months of aerobic exercise, resistance training or both after dieting did not prevent weight regain in adults.
Exercise adherence
But what about compliance? Did all the people in those studies actually exercise regularly?
The 2021 review found only…
