Walking, Junk Food, and Health

By Tom Farley

Our new and energetic Surgeon General just put out a “call to action” on walking and walkability for health. It’s something I couldn’t be more enthusiastic about. But it comes just a month after Coca-Cola got slammed on the front page of the New York Times for funding a handful of professors calling themselves the “Global Energy Balance Network” to push physical activity as a solution to obesity. I felt Coke deserved to be panned. Why is it wrong for Coca-Cola to praise exercise, you might ask, but right for the Surgeon General?

Because Coke was trying to divert attention from fattening sugary drinks. As I’ve written before, sugary drinks are a major cause of the obesity epidemic in the U.S. Coke should be ashamed of trying to get us to take our eyes off of that problem.

Still, Coke’s “network” does raise a fair question: just how important is physical activity in counteracting obesity, and for health more generally?

Earlier in the summer, Aaron Carroll wrote a nice review for the New York Times about the effectiveness of physical activity for weight loss. The summary is that physical activity does very little to help people lose weight. If you’re walking every day in the hopes of losing 10 pounds, prepare to be disappointed.

Now, over the longer term, higher levels of physical activity help prevent weight gain (which is very different from causing weight loss). And that means our society’s persistently low levels of physical activity may make us more vulnerable to obesity. But – this is a crucial point – during the rapid run-up of the U.S. obesity epidemic between about 1980 and 2000, there was no good evidence that our already-low physical activity levels in the nation were falling further. Over that same period, though, both dietary surveys and food production data (Figure 10 here) showed big increases in calories consumed. That says that our current obesity crisis is driven far more by increases in calories in than decreases in calories out.

If physical activity is a feeble way to lose weight and isn’t at the heart of the current obesity epidemic, then why is the Surgeon General harping on exercise?

Because there are health benefits – HUGE health benefits – to physical activity even if it doesn’t do a thing to your body weight. Just for starters, physical activity lowers blood pressure, lowers the risk of heart disease and stroke, strengthens bones, and increases the body’s sensitivity to insulin (lowering the risk of diabetes). It also reduces the risk of depression and dementia. If someone were to invent a drug with all of the health benefits of physical activity, she would get the Nobel Prize.

Junk food and exercise are not like matter and anti-matter. If your goal is weight loss, the best way to get there is to stick to a healthy diet – meaning avoiding sugary drinks, sweets, and calorie-dense processed foods and eating more fruits, vegetables and whole grains. If your goal is health, the best way to get there is more exercise.  Of course, we all should try to do both.