The Yilmaz lab found that ketogenic diets can promote tumor formation in the small intestine — an effect driven by how intestinal stem cells burn dietary fat, not by the ketone bodies these diets produce. The study, published in Nature, also showed that the diet's protective effect against colon tumors is independent of ketone bodies, challenging the prevailing view. Together, the findings reveal that the same diet can have opposite effects in different tissues, underscoring the need for caution in generalizing the effect of any diet on cancer.This work was supported by the Bridge Project, the MIT Stem Cell Initiative and the Koch Institute Frontier Research Program through the Kathy and Curt Marble Cancer Research Fund.