How do you lose weight? Diet and exercise. That much has been ingrained in us since youth. So you take up a fad diet, get a gym membership, toil away for weeks and are left wondering why the formula for weight loss does not work for you. It turns out, you’re not so different from everybody else. Over the past several years, studies have shown us that half of what we learned about weight loss is wrong.
As it turns out, exercise is great for your overall health, immune system, and longevity, but it’s not so great at shedding those extra pounds. In the end, it really isn’t all that helpful for losing weight.
One of the biggest fallacies in the advice that we receive again and again is that you can have a cheat day, if you put in extra time at the gym. Marketing has convinced us that the sports drink we take on our morning jog, with all its calories, is of no concern, because you will just burn it off.
But the truth is that exercise only makes up a small portion of the calories you burn each day. And those few calories are only a small part of your daily energy expenditure.
There are three parts to energy expenditure:
We have little to no control over our basal metabolic rate, yet it makes up the vast majority of the calories we burn. Depending on the person, the basal metabolic rate makes up 60 to 80 percent of your daily energy expenditure, while digestion accounts for about 10 percent. Leaving 10 to 30 percent for physical activity. This may still seem like quite a bit, but exercise is only a portion of this. Physical activity includes all movement, sitting down, standing up, walking around, reaching, pushing, pulling, lifting your stapler, fidgeting, and so on.
So while the food you eat accounts for 100 percent of the energy that goes into your body, exercise burns off less than 10 to 30 percent of it. That’s a pretty big discrepancy, and definitely means that erasing all your dietary transgressions at the gym is a lot harder than the peddlers of gym memberships make it seem.
It's hard to create a significant calorie deficit through exercise
Using the National Institutes of Health's Body Weight Planner — which gives a more realistic estimation for weight loss than the old 3,500 calorie rule — mathematician and obesity researcher Kevin Hall created this model to show why adding a regular exercise program is unlikely to lead to significant weight loss.
If a hypothetical 200-pound man added 60 minutes of medium-intensity running four days per week while keeping his calorie intake the same, and he did this for 30 days, he'd lose five pounds. "If this person decided to increase food intake or relax more to recover from the added exercise, then even less weight would be lost," Hall added. (More on these "compensatory mechanisms" later.)
So if one is overweight or obese, and presumably trying to lose dozens of pounds, it would take an incredible amount of time, will, and effort to make a real impact through exercise alone.
Exercise can undermine weight loss in other, subtle ways
How much we eat is connected to how much we move. When we move more, we sometimes eat more too, or eat less when we’re not exercising.
One 2009 study shows that people seemed to increase their food intake after exercise — either because they thought they burned off a lot of calories or because they were hungrier. Another review of studies from 2012 found that people generally overestimated how much energy exercise burned and ate more when they worked out.
"You work hard on that machine for an hour, and that work can be erased with five minutes of eating afterward," Hall says. A single slice of pizza, for example, could undo the benefit of an hour's workout. So could a cafe mocha or an ice cream cone.
There's also evidence to suggest that some people simply slow down after a workout, using less energy on their non-gym activities. They might decide to lie down for a rest, fidget less because they're tired, or take the elevator instead of the stairs.
These changes are usually called "compensatory behaviors" — and they simply refer to adjustments we may unconsciously make after working out to offset the calories burned.
We need to re-frame how we think about exercise
Obesity doctor Yoni Freedhoff has called for a rebranding of how we think of exercise. Exercise has staggering benefits — it just may not help much in the quest for weight loss:
By preventing cancers, improving blood pressure, cholesterol and sugar, bolstering sleep, attention, energy and mood, and doing so much more, exercise has indisputably proven itself to be the world’s best drug – better than any pharmaceutical product any physician could ever prescribe. Sadly though, exercise is not a weight loss drug, and so long as we continue to push exercise primarily (and sadly sometimes exclusively) in the name of preventing or treating adult or childhood obesity, we’ll also continue to short-change the public about the genuinely incredible health benefits of exercise, and simultaneously misinform them about the realities of long term weight management.
The evidence is now clear: Exercise is excellent for health; it’s just not that important for weight loss. So don't expect to lose a lot of weight by ramping up physical activity alone.
As a society, we also need to stop treating a lack of exercise and diet as equally responsible for the obesity problem in this country. Public-health obesity policies should prioritize fighting the over-consumption of low-quality food and improving the food environment.