MIT scientists find a hidden cancer risk of the keto diet

ScienceDaily reports on a new MIT study that found ketogenic diets increased small intestinal tumor risk in mice while reducing colon tumor risk. The research, published in Nature, adds nuance to the popular diet's health profile.

Researchers led by Omer Yilmaz, director of the MIT Stem Cell Initiative, studied mice genetically predisposed to intestinal cancer. The animals were fed a ketogenic diet, a control diet, or a high-fat, high-calorie diet. Mice on the keto diet developed small intestinal tumors more often than the control group, and at rates comparable to or higher than the high-fat group, even though they did not become obese.

The team expected ketone bodies, compounds like BHB that rise on keto, to be the cause. A 2022 Nature study had linked BHB to colon cancer protection. But in this study, ketones did not appear to drive the tumor growth. Instead, the effect traced to fatty acid oxidation. When intestinal cells burn fat, they activate PPAR proteins, which push stem cells to divide faster. More divisions mean more chances for cancer.

The colon showed the opposite pattern. Keto suppressed tumors there, matching the 2022 result. But again, ketones weren't the drivers. Yilmaz said the molecules were essentially metabolic bystanders; the real effect came from how stem cells processed the heavy influx of dietary fat.

The findings carry implications for commercial ketone supplements. Because both outcomes were tied to fat metabolism rather than ketones themselves, supplements would not be expected to reproduce either effect. That matters because small intestinal tumor incidence has risen in recent decades, and people with inherited conditions like familial adenomatous polyposis are especially vulnerable.

This is a mouse study, not a human one. Yilmaz emphasized that ketogenic diets have distinct effects on different tissues, and generalizations are dangerous. The team is working to understand why the same diet has opposite consequences in two adjacent parts of the gut.

• cancer risk
• keto diet
• mice
• MIT
• nature
• small intestine