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In a large meta-analysis of 116 randomized controlled trials including over 6,800 overweight and obese patients, exercise on its own was sufficient to drive clinically significant weight loss and body composition improvements, but only when performed at high enough doses and intensity.
Aerobic exercise of at least 150 minutes per week was associated with clinically important reductions in waist circumference and measures of body fat, while 300 minutes was observed to have a stronger effect. In both cases, vigorous-intensity exercise drove a more varied effect of not only weight loss but also body composition changes.
It’s often claimed that exercise on its own is not enough to drive meaningful weight loss—that it has to be coupled with changes in diet and, if possible, lifestyle choices as well.
This isn’t baseless; there are several factors driving this opinion, and anyone looking to lose weight who is willing to clean up their diet should almost certainly do so.
Aerobic exercise, the kind that was investigated in the study, involves non-explosive, typically repetitive movements, like that of a runner or swimmer, in which the body can use oxygen to drive energy production. It improves the strength of the heart, releases a soup of beneficial neurochemicals like BDNF into the brain, and drives mitochondrial biogenesis.
However, for the pure purpose of fat loss, something the American population desperately needs, aerobic exercise may not help as much as some may imagine. For example, it’s hard to burn 500 calories through aerobic exercise, but easy to eat 500 calories (or more) in a few minutes. 45 minutes of moderate-intensity exercise may genesis the feeling that one has earned a reward, but with just a few handfuls of nuts or potato chips, that person would be quickly erasing all their hard work.
The constrained energy expenditure hypothesis suggests that as habitual energy expenditure on exercise increases, the body naturally reduces the amount of energy expended on normal tasks like walking, standing, or movements during household chores. Lastly, it’s not uncommon for people to reduce the amount of non-exercise physical activity (i.e. walking) in their routines if they are making time for aerobic exercise, resulting in less total energy expenditure than they believe.
All this isn’t to say that exercise doesn’t work to drive weight loss; it can, but only in the right amounts.
The right amount
Most national governments recommend 150 minutes of moderate to intense physical activity per week, a standard that few, either in Europe or America meet. In the meta-analysis, examined doses (or time spent exercising) were 30 minutes, 150 minutes, and 300 minutes, and, as one might expect, 300 minutes of exercise drove the biggest weight loss at around 9 pounds or 4 kilograms.
Every 30 minutes was associated with better fat mass and body composition outcomes like waist circumference, but even at 100 minutes per week, these associated changes were not clinically significant. Sure enough, it was only at 150 minutes per week that clinically significant changes appeared, which is to say, changes that could not be supposed to have arisen for any other confounding factor.
The meta-analysis determined that the intensity of the exercise didn’t matter for pure weight loss, that is, making that number on the scale get smaller and smaller.
However, for improvements in total body composition, including waist circumference, total fat mass, and subcutaneous and visceral adipose tissue levels, it was clear that vigorous-intensity exercise led to greater improvements. These varied markers are all associated with various outcomes, positive or negative as the case may be, related to common chronic diseases and general morbidity.
“Claiming that exercise doesn’t promote weight loss isn’t accurate. At the right dose, exercise is effective for weight loss and improving body composition,” writes popular science communicator Dr. Rhonda Patrick. “At the same time, it elicits several other benefits on heart health, mitochondria, and the brain. That’s a ‘side effect’ that the other weight-loss drugs don’t have”.
While 300 minutes of moderate to intense physical exercise resulted in around 9 pounds of lost weight, 150 minutes of exercise per week also reduced body weight by nearly 3 kilograms or 6 pounds. WaL
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