Walk into practically any neighborhood supermarket and think about how the store is laid out. Have you ever wondered why the easiest items to find are the sodas, cakes, chips and other snack foods? The reason is simple. Despite expanding shoppers’ waistlines, these unhealthy junk foods push supermarket revenues sky high.

A number of studies on food shopping habits have found that people grab what’s available—and the more of the product that there is, the more folks will reach for it. And this is even more the case when the product is at eye level. “So a store manager who wants to maximize profits knows instinctively to assign more shelf space to items for which he has a higher profit margin,” say doctors Tom Farley and Deborah A. Cohen in their book Prescription for a Healthy Nation: A New Approach to Improving Our Lives by Fixing Our Everyday World. Farley is currently the health commissioner of New York City, and Cohen is a natural scientist at the RAND Corporation where she studies how social and physical structures in the environment influence health.

When people buy food at a grocery store on impulse, they tend to eat it pretty quickly. This means if a store manager can increase snack food sales by “stacking a big end-aisle display, or moving it from the bottom shelf to eye level, as a group we consume much more of that product,” say Farley and Cohen. “If that product also happens to be bad for us—like Coke or potato chips—his reallocation of shelf space just made us unhealthier.”

But is the food industry really to blame for your bad eating habits? Industry trade groups as well as consumers argue that people are responsible for what they eat. In fact, one trade group, while countering a plan in New York City to reverse diabetes, said that it’s not fair to expect the food industry to deprive people of what they want—and that no food by itself causes obesity.

Farley and Cohen don’t buy that argument. They say that shelf space accessibility is a powerful influence. The two cite a marketing study that showed store managers could increase sales of lettuce and tomatoes, apples and oranges, as well as squash and eggplant just by doubling the amount of shelf space allotted to these fruits and veggies.

It’s not just the location of items on store shelves that matters. The location of the stores themselves—how convenient they are to get to—can influence people’s health. For example, the authors point out that neighborhoods with more bars, liquor shops and grocery stores selling alcohol tend to have more car crashes, violence and sexually transmitted infections.

The message, say Farley and Cohen, isn’t as simple as telling people what to eat or not to eat. Health behaviors are built upon people consuming or doing things that are either good for their health or not. Just minor changes “in the number of places that sell certain products, the way they are sold, the times they are sold, or the price at which they are sold,” say these authors, can make a major difference in how healthy we all are.