Plate Nº 73 · recorded October 10, 2026
Health & Medicine ResearchReported finding
Keto Diet Raises Small-Intestine Tumor Risk in MIT Mouse Study
MIT researchers found a ketogenic diet increased small-intestinal tumors in cancer-prone mice while suppressing colon tumors — and the driver was fat metabolism, not ketones.
By Marcus Bennett4 min read760 words
In brief
- A ketogenic diet increased small-intestinal tumors in cancer-prone mice while suppressing colon tumors, MIT researchers reported in Nature on October 5, 2026.
- The tumor-driving mechanism was fatty acid oxidation in intestinal stem cells, not ketone bodies such as BHB.
- Keto-fed mice that stayed lean had tumor rates similar to or higher than mice on an obesogenic high fat/high calorie diet.
- Ketone supplements would not be expected to reproduce either the harmful or protective effects, since both traced to fat metabolism.
- The study involved mice, so the findings are preliminary and may not translate directly to humans.
A ketogenic diet increased small-intestinal tumors in cancer-prone mice while simultaneously reducing tumors in the colon, according to a new MIT study published in Nature on October 5, 2026. The finding reveals that the popular high-fat diet can produce strikingly opposite effects in two neighboring parts of the digestive tract.
The researchers traced the increased cancer risk not to ketones — the compounds the diet is famous for producing — but to how intestinal stem cells process the diet's heavy load of dietary fat.
What did the study find?
Omer Yilmaz, director of the MIT Stem Cell Initiative, senior author of the study, and a member of MIT's Koch Institute for Integrative Cancer Research, said the results argue for caution when generalizing about ketogenic diets.
"Ketogenic diets have distinct effects on different tissues even within the gastrointestinal tract," Yilmaz said. "I think the message here is that we need to be very careful in generalizing the effects that these diets can have, because what might be beneficial for one tissue may be detrimental to another tissue."
The study's lead authors are MIT postdoctoral researchers Jessica Shay and Fangtao Chi. Scientists from the labs of Alex K. Shalek, director of MIT's Institute for Medical Engineering and Science, and Matthew Vander Heiden, director of the Koch Institute, also contributed.
How did the mice respond?
The team studied mice genetically predisposed to developing intestinal cancer. The animals received one of three diets:
- A ketogenic diet (high fat, very low carbohydrate)
- A control diet
- A high fat/high calorie diet
Mice on the ketogenic diet developed small-intestinal tumors more often than animals on the control diet. Strikingly, although the keto-fed mice did not become obese, their tumor rates matched — and in some cases exceeded — those of mice eating the obesogenic high fat/high calorie diet.
In the colon, the picture reversed. The ketogenic diet suppressed tumor formation there, consistent with a 2022 Nature study that suggested keto might protect against colon cancer.
What drives the effect, if not ketones?
The researchers expected ketone bodies to be the culprits. They were wrong.
Ketogenic diets, first developed in the 1920s to treat epilepsy, force the body to burn fat instead of sugar. Breaking down that fat generates ketone bodies such as β-hydroxybutyrate (BHB) and acetoacetate — molecules that also appear during fasting.
But further experiments showed the ketone bodies themselves did not cause the increased tumor growth. Instead, the effect came from fatty acid oxidation, the process intestinal cells use to burn dietary fat for energy. Heightened activity in this pathway switches on a family of proteins called PPARs, which then push intestinal stem cells to divide more rapidly. Faster division creates more opportunities for some cells to turn cancerous.
Rapid stem cell activity is not inherently harmful — it helps the intestinal lining repair itself after injury. But it carries a cost.
"Having more stem cells means that when you injure the small intestine, it can repair itself better, but the downside is that having more active stem cells can lead to tumor formation," Yilmaz said.
Yilmaz noted that ketone bodies, despite the commercial attention they attract, turned out to be "essentially metabolic bystanders" in the experiments with genetically engineered mice. The tumor acceleration, he said, is driven entirely by how stem cells process and burn the dietary fat itself.
Why does the colon respond differently?
That remains an open question. "The deeper question is why the same diet has opposite consequences in two adjacent parts of the gut. That is what we are working to understand next," Chi said.
The findings also carry implications for the ketone supplement industry. Because both the increased tumor growth in the small intestine and the reduced tumor development in the colon stemmed from fat metabolism rather than ketones, ketone supplements or drinks would not be expected to reproduce either effect.
The distinction may matter for people with inherited disorders that raise susceptibility to intestinal cancer, such as familial adenomatous polyposis, and for the wider public as small-intestinal tumor incidence has risen in recent decades.
What are the limitations?
The study involved mice genetically predisposed to intestinal cancer, so the results do not directly translate to humans. The researchers say that with ketogenic diets growing in popularity, understanding these tissue-specific effects is essential before drawing broad conclusions about health consequences.
The research received funding from the National Institutes of Health, the Koch Institute, the American Federation for Aging Research, a Damon Runyon Postdoctoral Research Fellowship, and several other awards and grants.
via dx.doi.org (Original)
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