Consumption of walnuts reduced the growth of colon cancer, a result of the affect of walnuts on the gut microbiome. Researchers saw a reduction in tumor growth in mice that received 7% to 10.5% of their daily calories from walnuts, particularly male mice, which exhibited 2.3 times fewer tumors when fed walnuts.1

“Our results show for the first time that walnut consumption may reduce colon tumor development,” said Daniel W. Rosenberg, PhD, professor of medicine and investigator, Center for Molecular Medicine, UConn Health, Farmington, Connecticut, and senior author of this study.

“There is accumulating evidence that eating walnuts may offer a variety of benefits related to health issues like cancer. This study shows that walnuts may also act as a probiotic to make the colon healthy, which in turn offers protection against colon tumors.”

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The volume of walnuts consumed by the mice was equivalent to a human eating approximately 1 ounce of walnuts per day. Other research suggests a role for walnuts in preventing heart disease, diabetes, and neurologic disorders.

The researchers divided the mice into 2 groups and fed each group a different diet. One group was fed standard laboratory mouse chow, and the other group was fed a mouse chow that more closely resembled the usual American diet. Each group was then divided into subgroups; one subgroup’s diet was supplemented with walnuts and the other subgroup’s diet was not supplemented.

The greatest reductions in colon tumors occurred in male mice eating the Western diet supplemented with walnuts.

To determine the potential mechanism by which walnut consumption was beneficial, researchers collected fecal samples from the mice to examine the bacteria living in the digestive tracts of the animals. The gut microbiomes of mice that consumed walnuts were similar to each other, favoring bacterial communities that might protect against colon cancer.

The analyses of gut bacteria also revealed differences between male and female mice. Males on diets without walnuts tended to have less diverse bacteria than females without walnuts. When males ate walnuts, the diversity of the gut bacteria more closely resembled that of females on any diet. Whether bacterial diversity affects the risk of colon cancer is not known.

Additional research in humans could reveal the effects of regular walnut consumption on colon cancer and whether any of these effects are gender-specific.


1. Nakanishi M, Chen Y, Qendro V, et al. Effects of walnut consumption on colon carcinogenesis and microbial community structure [published online May 23, 2016]. Cancer Prev Res (Phila). doi:10.1158/1940-6207.CAPR-16-0026