I spent last week canoeing. We puffed and sweated, paddling across lakes, then carrying our gear and canoes to other lakes, then paddling across those lakes.

“Days like this I feel like I can eat as much as I want,” said one of my friends.

That may be true – provided he doesn’t want to lose weight. Among the items we were hauling from one lake to another was a jumbo-sized bag of M&M’s.

I, for one, didn’t lose or gain a pound over the week. The experience touches on a controversy swirling through the fitness world right now: How effectively can a person achieve weight loss through exercise alone?

Mixed Data

Yesterday the New York Times reported that Coca Cola is spending hundreds of thousands of dollars to promote the idea that exercise is a better solution to obesity than dieting. In June the Times had published an analysis saying the opposite is true: that eating less is far more important than exercising if you want to lose weight. It reports that “most” experts (those not funded by food companies, at least) share this view.

In fact, the data we have is somewhat confusing and incomplete. For example it’s hard to tell whether people in the United States have become less active in recent decades.

Still a few facts are becoming well established by multiple studies:

• You can lose weight by exercising more, if you don’t eat more.
• You can lose weight by eating less, if you don’t exercise less.
• You will lose more weight faster if you exercise more and eat less at the same time.

The devil is in the details. As the Times points out, exercising more will make you hungrier. So if you are trying to lose weight that way, you will have to exercise a lot of will power to resist the temptation to eat more. You might need as much will power as you would if you were just trying to lose weight by eating less.

Factors like these could explain why the results of research have been so varied. In one study, researchers instructed people to exercise an hour a day, six days a week, without changing their diets. The participants lost about 1.5 kilograms (3.3 pounds) over the course of a year. The researchers suspected that participants cheated on their diets.

The Times cites that study as evidence that exercise is not very effective. And if you are very overweight, you might indeed feel frustrated with so little weight loss.

But researchers in another head-to-head trial took a different approach: they had one group diet and another group exercise. They brought the exercisers into their lab to actually measure how much energy they were expending. The dieters kept a food log.

The researchers were careful to match the two groups so that the exercisers burned the same amount of additional calories as the dieters cut from their diets: about 700 calories a day. Both groups lost 7.5 kilograms (16.5 pounds) in only three months.

What I take away from this research is that you can lose weight through either diet or exercise. You just have to be very, very disciplined and keep close track of both exercise and diet.

The Times writers also point out that losing weight through exercise is a lot more time consuming. Perhaps. But it does take time to prepare good-tasting, nutritious low-calorie meals, and also to count calories.

What’s Your Goal?

This brings up a more fundamental question you should consider if you’re trying to lose weight. What is your goal? Do you want to improve your health? Change the way you feel? Or just change the number on your bathroom scale?

The right sort of exercise can improve your health, trim fat and increase muscle mass. It can do all those things regardless of whether you lose weight.

If you start out overweight, dieting will also improve your health and trim fat, but it won’t do much to build muscle.

The bottom line? If I had to choose just one recommendation for overweight people, I’d say increase your exercise.

But there’s no reason to choose between the two. For best results, carry the bag of M&M’s from lake to lake… without ever opening it.

Photo by Robert Greenberg.

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