Keto Diet Raised Small Intestine Tumors in Cancer-Prone Mice, MIT Finds

This is animal research. The authors used mouse models of spontaneous intestinal adenoma formation, meaning the animals were genetically prone to developing these growths. It also does not say how long the mice were fed the diets. No people were studied.

The question matters because ketogenic diets are popular for weight loss and are sometimes promoted for longevity. They are very high in fat and very low in carbohydrate. The researchers point out that obesogenic high-fat diets are already known to boost the activity of small-intestinal stem cells and tumor formation. Ketogenic diets contain even more fat, but they also lower circulating insulin and raise ketones. Their effect on intestinal cancer has been poorly understood.

According to the study, the ketogenic diet accelerated tumor burden and shortened survival, regardless of ketone metabolites. The team changed the ketone-making pathway in several ways. They blocked or boosted a key ketogenic enzyme, known as HMGCS2, and they disrupted the breakdown of ketones. None of these changes altered tumor development. That points away from ketones as the driver.

The evidence points instead to how intestinal cells handle dietary fat. When the researchers removed three related fat-sensing proteins (PPARα, PPARδ and PPARγ) from the intestine, the diet's effects on stem cells weakened. Stem cell expansion, proliferation and the ability to form colonies all dropped. Removing an enzyme called CPT1A, which is needed to burn fatty acids, limited adenoma formation specifically on the ketogenic diet. The authors conclude that tumor initiation is linked to burning dietary fat, not to fat simply building up.

According to ScienceDaily, which summarized an MIT release, the small intestine and the colon responded in opposite ways. The ketogenic diet suppressed colon tumors in the mice. The coverage also says the keto-fed mice did not become obese, yet had tumor rates similar to or higher than mice on a high-fat, high-calorie diet.

"Ketogenic diets have distinct effects on different tissues even within the gastrointestinal tract," senior author Omer Yilmaz of MIT told ScienceDaily. "What might be beneficial for one tissue may be detrimental for another tissue."

What does this mean for personal choices? The findings come from genetically engineered mice and may not carry over to people with ordinary cancer risk. The study does not show that keto causes cancer in humans. The authors single out people with familial adenomatous polyposis, an inherited condition with a high risk of small-intestinal tumors. They call for careful thought about diet and cancer prevention in genetically susceptible groups.

The study also bears on ketone supplements. According to ScienceDaily, because the effects tracked fat metabolism rather than ketones, ketone drinks would not be expected to reproduce either the harm in the small intestine or the benefit in the colon. That is the coverage's inference, not a test reported in the study.

The next step is to learn why the same diet pushes neighboring parts of the gut in opposite directions. Researcher Fangtao Chi told ScienceDaily that this is what the team is working on. Human data on ketogenic diets and intestinal tumors, especially in people with inherited risk, will be the key thing to watch.

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