This just in: those high-fat, low-carb diets really work! So do those low-fat, high-carb diets! You really can lose weight on the chocolate-eclair plan! The catch is, you have to eat less.

Thus concludes a new report from the U.S. Department of Agriculture. Faced with a growing obesity epidemic--and an onslaught of fad diets that restrict some type of food--the agency assembled an expert panel to review the evidence on diet and weight. Its findings, released in summary form last week, reaffirm what most obesity experts have maintained all along. As the report's authors put it, "Caloric balance (calories in vs. calories out), rather than macronutrient composition, is the major determinant of weight loss." If you're slimming down on a diet of bacon and butter, it's not because you've reset your metabolism, as some diet gurus would claim. The truth is, people on low-carb diets average only 1,414 calories a day, whereas the typical American downs 2,200.

The question is whether there are more healthful ways to shed pounds. Low-carb diets are often high in artery-clogging saturated fat and short on nutrient-rich fruits and vegetables. Do these diets really make weight loss easier? If so, do their benefits outweigh their risks? The USDA will soon launch clinical trials to find out. For now, the best remedy is to exercise--by pushing yourself away from the table.