Ketogenic diet promotes intestinal tumour growth in mice, study finds

A ketogenic diet — high in fat and low in carbohydrate — increased the formation of tumours in the small intestine of mice that were already predisposed to such tumours, according to a study published in Nature (https://www.nature.com/articles/s41586-026-10779-y). The finding, reported in a Nature News & Views article by researchers at the Van Andel Institute (https://www.nature.com/articles/d41586-026-02039-w), complicates the popular idea that ketogenic eating may help fight cancer.

The research team, led by Shay et al., found that the tumour-promoting effect was driven not by ketone bodies — the fuel molecules the body produces in ketosis — but by the high amount of dietary fat, which cancer cells appear to exploit to grow (https://doi.org/10.1038/s41586-026-10779-y). Nature describes the result as a "cautionary finding," because ketogenic diets have been touted as a possible anti-cancer strategy on the theory that cancer cells consume sugar avidly and metabolise ketones poorly.

Writing in Nature, Souvik Patra and Evan C. Lien of the Van Andel Institute say the work suggests diet advice for cancer patients and those at risk may need to be tailored to individual circumstances rather than applied broadly (https://www.nature.com/articles/d41586-026-02039-w). They caution that the results were observed in mice with a predisposition to intestinal tumours and that implications for people remain to be established.

The ketogenic diet has gained widespread attention in popular culture and scientific research for potential health benefits, pushing the body into ketosis in which blood sugar and insulin fall and fat is converted into ketone bodies (https://www.nature.com/articles/d41586-026-02039-w). The new study adds nuance to a contested area, indicating that for some individuals the fat content of the diet — not ketosis itself — could be the relevant factor in tumour growth.