Many diets lack the one special ingredient that could make them work: motivation. We count calories or fret over carbs, but few of us grapple with the real dynamics behind our dietary habits. Why can the sight of a particular label cause us to forfeit weeks of belt-tightening moderation? Food psychologist Dr. Brian Wansink has spent his adult life studying meal and snack patterns for principles that can help us to eat more sensibly. For example, the director of the Cornell University Food and Brand Lab notes that we should be especially alert when we are eating with friends: "The more people, the more you eat, up to 90% more than you eat when you're alone." A healthy curb to mindless eating.