Doctors and nutritionists think they know what makes people fat: "It's because they take in more calories than they expend." But if that theory is wrong, all of the analysis and advice that falls out of that paradigm is likely to be wrong, too. Which might explain why, in spite of kale, My Fitness Pal, and yoga pants, so many of us just can't keep our weight under control. 

So, what is really causing Americans' struggles with weight? Nutrition expert and contrarian Gary Taubes thinks hormones and metabolic defects should take center stage. And SUGAR is a key offender. Read on and also listen to Gary Taubes live on Bite's podcast, "You Don’t Get Fat For the Reasons You Think." (2nd of two guests.)

MOTHER JONES reports: The Most Popular Theory About What Causes Obesity May Be Very Wrong