Low carbohydrate, high protein diets slow/prevent cancer. Mice fed low carbohydrate (Carbs), high protein diets have lower insulin (Ins) and blood glucose levels than mice on Western-like diets. If these mice are injected with tumor cells or are genetically predisposed to mammary tumors, the growth rate or incidence, respectively, of their tumors is significantly reduced. Moreover, these low Carb, high protein diets reduce tumor growth in an additive fashion when combined with the mTOR inhibitor CCI-779 or the COX-2 inhibitor Celebrex. For details, see the article by Ho and colleagues on page 4484 of this issue.