The links between poverty and obesity in the United States are well known:  poorer people tend to be heavier.  In fact, the highest rates of obesity are found among groups with the highest rates of poverty and the least education.

This excellent article, by researchers from the University of Washington’s Center for Public Health Nutrition, helps explain why.  It’s not just that people with lower incomes have fewer opportunities to exercise, or that they’ve been targeted by fast food advertisers.  It may be simple economics:  the cheapest foods are also the most "energy dense."

Oil, shortening, margerine, and white flour are cheap. Fresh fruits, vegetables, and lean meats aren’t.  In fact, calorie for calorie, healthier foods are often 10 or 100 times as expensive as the cheaper alternatives. 

So families that can’t afford healthier foods may still be able to purchase plenty of junk; and families that try to hold down food costs tend to gravitate, almost of necessity, towards energy-dense foods.  Thus, one of the article’s more interesting points:  households that are "food insecure"–which means, in part, that householders don’t always get  enough of the kinds of foods they want to eat—tend to be heavier. 

The basic insight isn’t new.  Everyone knows that junk foods are cheap.  But it’s very helpful to see that intuition quantified.  And it’s also helpful to see that the way to cure obesity among the poor isn’t simply by educating them about the best way to eat; it’s also about helping them to lift themselves out of poverty.

(Tip of the hat to Ellen Chu for pointing out the study.)