How Much Exercise Is Enough?

A new study in the Journal of the American Medical Association is making people nuts.

If you don’t read the actual study and only listen to the sound bite headlines in the media, you’d walk away thinking that women need at least an hour a day of exercise to keep weight off. That’s understandably discouraging for a lot of people, especially those with busy lives. It also is about twice the current federal guidelines of 150 minutes a week (or 30 minutes five days a week).

And it’s partly true– but God is in the details.

Let’s start with the federal guidelines, (30 minutes of moderate-to-intense exercise, 5 days a week). Those were meant to prevent disease. And a ton of research has shown that walking at a moderate clip five days a week for a half hour at a time will do just that. That kind of exercise will indeed lower your risk for dying, improve your heart health and actually- according to research at the University of Michigan- even grow new brain cells!

But- as I’ve said many times- it won’t make your body bikini ready, and for many people it won’t result in weight loss at all.

To prevent weight gain, you need a lot more. A 2002 report by the Institute of Medicine suggested 60 minutes 7 days a week for that purpose, closer to what the present study found.

But- and this is a really big but- there’s one important detail that everyone reporting on this study seems to have forgotten: diet.

In the current study, diet wasn’t monitored at all. The researchers reported on the amount of exercise it took to keep weight off for women “eating a normal diet”.

A normal diet?

In America?

You’re kidding, right?


As trainers like to say, “you can’t outtrain a bad diet”. So if you don’t tackle the eating issue, it’s gonna be really hard to lose (or even maintain) weight with exercise alone. Unless, of course, you’re Michael Phelps.

In defense of the researchers, they didn’t just accidentally “forget” to control for diet. They wanted to see how much impact physical activity alone would have on weight assuming people didn’t change the way they eat.

And the answer was: not all that much.

Truth be told, exercising alone- without dietary changes- did help a bit, particularly for women who weren’t very overweight to begin with. For those not-too-overweight women, about 60 minutes a day kept weight gain to a minimum over the course of the fifteen-year study. But 60 minutes had less of an impact on people who were significantly overweight to begin with, which makes sense, since without dietary changes we can assume these women were eating an awful lot to begin with and were continuing to do so throughout the length of the study.

So the bottom line is not that exercise doesn’t matter- it most certainly does. It’s just not enough to get the job done if you don’t make some serious changes to the way you eat.

Unless of course, you are Michael Phelps. Then I guess you can eat whatever you want.

As long as you spend 8-10 hours a day training.