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Science, exercise, and weight loss: when our bodies scheme against us

I love it (okay, not really, need sarcasm font) when people suggest to me that to lose weight, I should get a bit of exercise, you know, walk more, or take the stairs instead of the elevator. When I tried Weight Watchers for the very last time they gave handy hints like getting off the bus one stop early and walking to your destination. (Um, I ride my bike to work most days. I ride hundreds of kilometers a week, in addition, for fun when the weather is good. How does that fit in?)

Of course, this advice is always from well-meaning people who don’t know me. Those who know me, know that I work out at a variety of sports and physical activities most days of the week, often twice a day. I run, ride my bike, play soccer, lift weights, practice Aikido, and most recently have taken up Crossfit. And yet, I’m very overweight. Fat, big, call it what you will.

How on earth can this be? Newcomers to cycling sometimes say “Oh keep riding the bike and you’ll lose weight,” thinking I’m new too. (I like passing those people, zoom!) Sometimes I’m aware I actually put other fat women off exercise because they are starting to exercise in order to lose weight and then they see me, and think it’s all pointless. But I don’t exercise to lose weight. My experience tells me that, on its own, it doesn’t do very much.

So why doesn’t exercise help with weight loss? (Or to put the question precisely, why doesn’t it help as much as it seems it ought to, when you consider the calories burned in our efforts at fitness?) Given my interests and personality type–geek, academic, fitness buff–I’ve read rather a  lot about this question.

There are a number of different answers.

The first answer is simple and it’s probably that first thing that came to your mind: when we exercise, we eat more. Indeed, if you care about performance and recovery, you need and ought to eat more. I was once told by a cycling coach that it’s foolish to try to lose weight during the racing season. Not eating enough–which is what you need to do to lose weight–cuts your speed and your recovery. Diet in the off season when you’re just riding for fun, he said. Don’t hurt your performance by dieting.

But there’s another answer that I find intriguing. Our bodies’ efforts at maintaining weight are ingenious. It turns out that when we exercise more, we also move less the rest of the day. This isn’t intentional. It isn’t anything we decide to do. The idea is that our bodies decide for us.

I’m interested, and fascinated by, the way our bodies undercut our best efforts. Heavy exercisers, it turns out, often move less the rest of the day and so burn not that many more calories than if they hadn’t exercised at all. When not exercising, they’re chronic sitters!

The study which sets out to prove this is cited in the Gretchen Reynolds’ book The First 20 Minutes  and she writes about it in her New York Times Phys Ed blog too. Following a group of young men assigned to a heavy exercise program, researchers were surprised at how little weight they lost. Yes, they ate more but more surprisingly, “They also were resolutely inactive in the hours outside of exercise, the motion sensors show. When they weren’t working out, they were, for the most part, sitting. “I think they were fatigued,” Mr. Rosenkilde says.”

Some people say we ought to “listen to our bodies.” But in my experience our bodies are sneaky experts at staying the same size. They need to be ready for feasts and famines and those women with extra body fat are more reproductively successful.

It’s another argument in favour of short, sharp, intense Crossfit style workouts since they don’t seem to have this effect. Once again, it’s High Intensity Interval Training (HIT) for the win. Thirty minutes, says Reynolds, is the sweet spot for exercise.

And it’s yet one more argument against sitting.

Some personal observations:

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