The Biggest loser reality show has gotten a lot of attention lately off of a recent study that tracked 14 of the contestants who all lost massive amounts of weight in a short amount of time. Six years later most of them gained the weight back. Scientists concluded this wasn't just because of a breakdown in will power but a slowed down metabolism.

To find out if this means that those of us who want to lose weight are doomed to gain it back,  we checked in with Dr. David Ludwig.

According to Dr. David Ludwig, there’s a reason why a low-calorie diet is so hard to maintain—and it has a lot to do with America’s larger problem with diets in general—we’ve been stuck in a low-fat mode for too long, and it’s making us obese.

Dr. David Ludwig is a professor of pediatrics at Harvard Medical School and a professor of nutrition at the Harvard TH Chan school of public health. His new book on nutrition is: Always Hungry: Conquer Cravings, Retrain Your Fat Cells, and Lose Weight Permanently.