Losing weight is so easy, right? Just eat veggies for dessert, skip lunch hour, and poach a personal chef from the local health spa. Scrapping a lifetime of eating habits—especially ones that we all enjoy—is unrealistic. Our expert Dr. Brian Wansink asked 2,000 people to make one of 20 small, manageable changes and see whether they lost weight and felt better after one month. Here’s what worked—and what flopped.