Weight loss diets will always have a place in an affluent, overfed culture. The answer to the obesity epidemic is compliance to any diet rather than choosing a specific diet. Results of weight loss trials suggest it is not difficult to lose weight, but difficult to maintain the weight lost. Unfortunately, these trials provide little insight into long-term sustainability and compliance. This class will review the biochemistry of fat loss (lipolysis) and how various popular diets (low fat, low carbohydrate, intermittent fasting) work to increase lipolysis. The challenge of applying any of these diet approaches long-term after successful short-term weight loss will be discussed.