Cutting the fat doesn't necessarily lead to weight loss. Cutting calories and increasing exercise counts more. While reducing the amount of fat you eat contributes to weight loss, some fatty foods that contain protein remain an important part of your diet. And as an added benefit, they may make you feel fuller longer. A recent study of mice and rats that ingested a fatty acid called oleic acid, found commonly in olive oil and other unsaturated fats, showed that once the fat reaches the intestine it can create a feeling of fullness and prolong the need to eat again. The study has not yet been done in humans, but findings may lead to better insight into how healthy fats help regulate body weight.

Indeed, most research suggests that people who eat moderate amounts of fat are at least as successful at losing weight as those who restrict fat intake sharply. For example, the National Weight Control Registry, which tracks 6,000 successful dieters nationwide, reports that members now consume more fat than previous members did—typically 30 percent of calories from fat compared with 24 percent about a decade ago. Yet registry members are still successfully keeping the weight off. So, provided you keep your total calorie count down and exercise regularly, eating a moderate amount of the right type of fat is recommended.