A reason to eat carbs

A ketogenic diet is a high-fat, low-carbohydrate eating plan that forces the body to burn fatty acids instead of carbohydrates for energy. Normally, the body uses carbohydrates (found in foods like bread, rice, and fruits) as its primary fuel source. When carbohydrates are scarce, the liver converts fats into molecules called ketone bodies, such as BHB (beta-hydroxybutyrate), which become the main energy source. This metabolic state is called ketosis. While this diet has been linked to weight loss and potential protection against colon cancer in some studies, new research suggests it may have different effects on other parts of the digestive system. The study was led by Omer Yilmaz, director of the MIT Stem Cell Initiative, along with postdocs Jessica Shay and Fangtao Chi, and was published in Technology Review on October 20, 2026.

In a study conducted by researchers at MIT, mice fed a ketogenic diet developed more tumors in the small intestine compared to mice on a regular diet. The small intestine is a long, coiled tube in the digestive system where most nutrients are absorbed. The tumors were linked to a metabolic process called fatty acid oxidation, where cells burn dietary fat for energy. This process activates proteins that signal stem cells—cells capable of developing into various cell types—to multiply more rapidly. While more stem cells can help the intestine repair itself after injury, they also increase the risk of tumor formation. The study found that BHB (the ketone body thought to protect against colon cancer) was not responsible for this effect, describing it as a metabolic bystander—a molecule present but not directly involved in the process.

The same ketogenic diet that may increase the risk of small intestine tumors appears to suppress the development of colon cancer, which is the final part of the digestive system. The colon, also called the large intestine, absorbs water and forms stool. Researchers confirmed that the diet had a protective effect against colon tumors in their experiments. This contrast—where the same diet has opposite effects in two adjacent parts of the gut—raises questions about how diet influences different regions of the digestive system. Fangtao Chi, one of the study’s authors, emphasized the need to understand why these opposing outcomes occur. The findings highlight the importance of not generalizing the effects of diets across different parts of the body.

The study suggests that commercial ketone supplements—products marketed to induce ketosis without dietary changes—are unlikely to significantly affect tumor development in the small intestine or colon. These supplements provide exogenous (external) ketone bodies, such as BHB, which the body can use for energy. However, the research indicates that BHB and other ketone bodies act more as bystanders in the metabolic processes linked to cancer risk rather than as active drivers. Therefore, taking ketone supplements probably does little to either help or harm people in terms of cancer risk in the gut. The deeper question remains why the same diet has such different consequences in nearby areas of the digestive system.