Rozin has been looking at the differences between Americans and Europeans, specifically the French, to understand why we have so many troubling issues about food and body weight. His comparison of best-seller lists found no diet book in the top 15 in France, while in the United States the top book was The South Beach Diet. (The Atkins diet books were also frequently on our lists.) He is arranging a pedometer study to test his hypothesis that the French—notorious for their dislike of gyms—actually get more exercise than we do. "They walk, bicycle, and just move more," he says. A paper he published in 2003, "The Ecology of Eating," received a fair amount of press by proposing that at least part of the French paradox (the question of how they can eat a rich diet and yet be slimmer and have less heart disease than Americans) can be explained by the fact that French portion sizes are substantially smaller than ours. "Although the French eat less than Americans, they seem to eat for a longer period of time, and hence have more food experience," he wrote in his abstract of the study. "The French can have their cake and eat it as well."

Food experience—that talent for appreciation—is what it's all about, Rozin explains as we wander the market, admiring rows of bright vegetables and glass cases full of huge brown country hams. All around us is ample evidence of the astonishing variety and bounty that confronts Americans every day—a confrontation that Rozin wants to address in the book he's writing. "I want to do a primer on eating sensibly and try to put the risks of eating in context: Is there really a pleasure-health trade-off? Or can things like chocolate actually be good for you? Well, they can be—it is! The nutrition fads have gotten out of control. I think a varied diet is what everyone should eat."

Rozin stops short in front of a bookstall and picks up a children's book titled It's Disgusting and We Ate It! "I have to add this to my disgust collection," he says. How we decide what is disgusting is another area of interest for Rozin, but we decide to leave that discussion for another time; pleasure is the order of this day. And in Rozin's philosophy, if it were the order of more of our days—if we looked at eating as an activity to relish rather than as an invitation to gluttony—we'd all be not only healthier but happier.

Michelle Stacey's most recent book is The Fasting Girl: A True Victorian Medical Mystery (Tarcher/Putnam).