A perspective article challenges the ‘energy balance model,’ which says weight gain occurs because individuals consume more energy than they expend. According to the authors, ‘conceptualizing obesity as a disorder of energy balance restates a principle of physics without considering the biological mechanisms underlying weight gain.’ The authors argue for the ‘carbohydrate insulin model,’ which explains obesity as a metabolic disorder driven by what we eat, rather than how much. *Public health messaging exhorting people to eat less and exercise more has failed to stem rising rates of obesity and obesity-related diseases. *The energy balance model, which says weight gain is caused by consuming more energy than we expend, “restates a principle of physics without considering the biological mechanisms driving weight gain.” *The carbohydrate-insulin model makes a bold claim: overeating doesn’t cause obesity; the process of getting fat causes overeating. *The current obesity epidemic is due, in part, to hormonal responses to changes in food quality: in particular, high-glycemic load foods, which fundamentally change metabolism. *Focusing on what we eat rather than how much we eat is a better strategy for weight management.