There’s a reason so many of us struggle with losing weight (and keeping it off). Cutting-edge research is pointing toward a surprising new explanation—one that has little to do with lack of willpower. (Thank goodness.) In fact, the problem is that you’ve been doing what you were told to do—slash calories, cut fat.

Conventional wisdom holds that weight loss is nothing more than simple math. Take in fewer calories than you expend, and the pounds will fall off as predictably as leaves from an autumn tree. But thousands of failed diets have shown that the low-calorie approach doesn’t work, says David Ludwig, MD, an endocrinologist at Boston Children’s Hospital and a professor at Harvard Medical School. “When you cut calories, the body fights back, making you hungrier, among other things,” he explains. “Weight is controlled by our biology more than our willpower.”

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What’s more, despite everything you’ve heard for…