Photo: Bettmann/Corbis

There are a lot of unhealthy people in the world’s richest countries. Many of them are unhealthy both because they eat too much of the wrong things and because they don’t exercise. So, given how hard it was to turn someone’s lifestyle upside-down overnight, it’s understandable that researchers (and journalists) often focus on which sorts of diet and exercise tweaks, rather than major changes, offer the most bang for the buck.

A big new study just published in the American Journal of Clinical Nutrition offers some important evidence that even just a little bit of physical exercise can play a big role. This isn’t necessarily obvious: Calorie-centric views of healthy living sometimes end up downplaying the importance of exercise, since there’s a pretty big mismatch, effort- and self-restraint-wise, between calories burned and calories eaten. That is, it takes about 20 minutes to walk a mile and burn 100 calories or so, which is equal to one or two bites of a buttered roll that can be scarfed down in 15 seconds.

But this study adds to mounting evidence that exercise matters, even when you’re pigging out. The researchers, led by Ulf Ekelund of the University of Cambridge, examined data from 334,161 Europeans whose health and exercise stats — height, weight, waist circumference, frequency of exercise, and drinking and smoking habits, among other stuff — were tracked for an average of 12.4 years.

This, naturally, provided the researchers with a lot of potential correlations to sift through. But the one that jumped out the most was that “across all strata for both general and abdominal adiposity [fatness], a markedly reduced hazard was observed between those categorized as inactive and those categorized as moderately inactive.” In the context of this study, that means going from no exercise to walking briskly for 20 minutes a day, and the researchers showed that, holding everything else equal, doing so brought with it a 20–30 percent reduction in overall mortality risk.

Going back to that bang-for-the-buck thing: This is pretty impressive. Sure, for someone who never gets any exercise, even walking 20 minutes a day might be a challenge at first, but it’s far from an insurmountable one. And the study suggests that even for those of us who just can’t lay off the doughnuts and pizza (or doner kebabs and baklava, for Europeans), walking a few extra blocks to a slightly further junk-food establishment might help mitigate the damage to your body.