One of the basic principles that well-meaning health practitioners have promoted for years is that weight loss always comes down to calories in versus calories out—that whether you eat a balanced, health-promoting diet of vegetables, fruit, whole grains and lean protein or a bunch of processed junk, as long as the calories are right, you’ll lose weight. The truth I’ve discovered contradicts that long-held belief. Not only should you eat a healthy, whole-foods diet because it boosts your energy and reduces your risk of disease, you should also do so because a calorie is not, in fact, just a calorie.