The Exercise Myth

The way people talk about going—or not going—to the gym to lose weight, the $4.7 billion fitness industry could rebrand itself the “guilt industry,” because that’s what many of us seem to get most from it. The drumbeat of get moving to lose weight has gotten so loud that almost everyone blames his or her weight problem on not spending enough time at the gym. The result is enough shame to wallow in for a lifetime.

It’s easy to see how we’ve arrived at this spot. Not only do gyms promote themselves as a great way to lose weight, reality shows like The Biggest Loser and Celebrity Fit Club add to the drumbeat by using exercise as entertainment. And we’re so eager to get help, we listen: The notion of going to the gym—burning, say, 500 calories a session, six days a week, and thereby eliminating 3,000 calories (or about a pound of body fat) in a single week—is very appealing. Just think: Lose 50 pounds plus get great abs over the course of a single year, all without dieting!

Even if your day is spent shoveling gravel, you’re still going to find yourself with a pot belly if you’re lunching each day on pizza and soda.

But a hard look at the evidence just doesn’t support the hype. The inconvenient truth is that we now eat about 500 more calories per day than we did 30 years ago. That's enough to explain our growing waistline without any need to factor in exercise.

Combine this fact with national surveys showing that people who do manual occupations—jobs like construction, farming, and domestic work—are heavier than people who sit in front of a computer screen all day. Indeed, these physically strenuous jobs carry a 30% increased risk of obesity when compared to office jobs. Of course, comparisons like this don’t factor in social class, or whether you eat brownies, or take a run after work, but that’s the whole point—compared to factors like what we eat and what our education level is, hard manual labor just doesn’t make as much of a difference. Even if your day is spent shoveling gravel, you’re still going to find yourself with a pot belly if you’re always lunching on pizza and soda.

The evidence isn’t just anecdotal. My lab at Tufts University summarized 36 years of published studies on exercise and weight, conducted between 1969 and 2005. What we found would frustrate anyone spending upward of $800 a year on a gym membership to lose weight. The averaged results of the studies showed that an hour of exercise per day results in an average fat loss of just six pounds over the course of several months—hardly the benefit one would expect from all that work. Perhaps more importantly, most of the studies only managed to get people to exercise 30 minutes a day, which is the maximum most people have the time and inclination for, at which point the average weight loss goes down to a meager three pounds. It is true that some of the studies showed greater fat losses than the average, but just as many showed less.

One research study in the Netherlands highlighted the problem that simply starting and sticking with a serious program of exercise is much easier after you’ve lost some weight. Men and women ranging from thin to very slightly overweight (whose maximum body mass index was 26.7) volunteered to train for a half marathon in a study lasting 40 weeks. The heavier subjects within this group were only slightly overweight, but even so, they were the ones who dropped out before the training was halfway through. It’s not that the overweight people were lazy, just that exercise is much harder if you are carrying around even 20 excess pounds—the equivalent of a large backpack full of textbooks—while you do it.

Research doesn’t have good answers to the question of why exercise doesn’t work for the average person as well as it seems it should, but I suspect the reasons are increased hunger (you eat almost as many extra calories as you burn) and reduced energy expenditure at other times (exercise may make you more relaxed and less fidgety). So, you end up fit, healthy, and less stressed out, but wondering why you still have pounds to lose.

On the other hand, 85 percent of people entering a no-exercise weight-loss program at my lab lost 10 to 50 pounds, giving us the clear message that exercise isn’t the key to getting slim. Which doesn’t mean you should tear up your gym membership—being fit remains good for your general health. It is also clear from research studies that one hour of exercise a day is helpful in keeping weight off after you have lost it with a diet program. Followers of my Instinct Diet tell me that the extra energy they have after losing some pounds makes exercise so much easier that they end up doing more just for the pleasure of it.

The important thing to know is that you have a choice. Exercise is great medicine for general health and a great add-on to dieting, so feel free to kill yourself in the gym if it makes you feel good. But it isn't essential, and by itself doesn't do much. All the evidence suggests that exercise is less important than what goes in your mouth, and when.

Dr. Susan Roberts is a professor of Nutrition and Psychiatry at Tufts University, and the author of a new approach to weight loss called The Instinct Diet, which was recently featured in The Daily Beast.