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A ketogenic diet—popularized for weight loss, blood sugar control and other potential health benefits—may increase the risk of certain intestinal cancers, according to new research.
The study, led by researchers at the Massachusetts Institute of Technology (MIT) and published in Nature, found that a high-fat, low-carbohydrate ketogenic diet promoted the growth of tumors in the small intestine of mice that were genetically predisposed to developing intestinal cancer.
The findings raise fresh questions about how the increasingly popular diet may affect cancer risk in different parts of the digestive system.
Ketogenic diets work by drastically reducing carbohydrate intake, forcing the body to burn fat for fuel instead of glucose.
This metabolic state, known as ketosis, leads to the production of molecules called ketone bodies.
The diet was originally developed to treat epilepsy but has since been widely adopted for weight loss and other health goals.
The ketogenic diet has become one of America’s most popular eating plans, with an International Food Information Council survey finding that 7 percent of U.S. adults were following the diet in 2022.
Researchers noted that previous studies had suggested ketogenic diets might help protect against colon cancer. However, the new investigation found a very different effect in the small intestine.
To investigate, the team fed cancer-prone mice a ketogenic diet, a standard control diet or a high-fat, high-calorie diet.
They discovered that animals on the ketogenic diet developed more small-intestinal tumors than those on the other diets.
Further experiments revealed that this effect was driven not by ketone bodies themselves, but by the large quantities of dietary fat consumed as part of the ketogenic regimen.
The researchers found that lipids from the diet activated a cellular signaling pathway known as PPAR-delta, which enhanced the activity of intestinal stem cells.
These cells are responsible for continuously renewing the gut lining, but when mutations occur they can also serve as the starting point for tumors.
According to the study authors, the results highlight how dietary interventions can affect different tissues in very different ways.
Importantly, the findings were observed in mice genetically susceptible to intestinal cancer, not in healthy humans. The researchers cautioned that more work is needed to determine whether the same mechanisms occur in people and whether particular groups may be more vulnerable than others.
Even so, the study adds to a growing body of research showing that the relationship between diet and cancer is complex.
While ketogenic diets have been investigated as potential treatments for certain diseases and may offer metabolic benefits for some individuals, the new findings suggest that their effects are unlikely to be universally beneficial.
The researchers say future studies will be needed to better understand how specific dietary fats influence cancer risk and whether modifying the composition of ketogenic diets could reduce potential harms while preserving any health benefits.
Reference
Shay, J.E.S., Chi, F., Constantine N, T., Han, S., Zhang, X., Ten Hoeve, J., Williams, K.J., Seda, N., Sever, T., Fuentes, I., Bhatia, S.N., Calibasi-Kocal, G., Vander Heiden, M.G., Shalek, A.K. and Yilmaz, Ö.H. (2026). Ketogenic diet mediates intestinal tumorigenesis through lipids not ketones. Nature, [online] pp.1–10. doi:10.1038/s41586-026-10779-y.
Contact Newsweek editors on this story: Kara Dolman and Emma Lee-Sang
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