Eating walnuts might help suppresses colon cancer by altering the gut microbiome so as to discourage development of cancerous tumors, said a new study by UConn Health and The Jackson Laboratory for Genomic Medicine. An ounce a day might be enough to do the trick

Researchers believe walnuts as a whole food pack the most significant anti-cancer punch against colon cancer, the third most common cancer in the world. In addition, other studies show walnuts are promising tools in warding-off heart disease, diabetes, neurological disorders and other diseases connected to diet and lifestyle.

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The results of the research to be published in the journal Cancer Prevention Research "show for the first time that walnut consumption may reduce colon tumor development," said principal investigator Dr. Daniel Rosenberg of UConn Health.

"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."

Researchers said walnuts are packed with nutritionally important compounds. Walnuts contain the most polyunsaturated fatty acids of all commonly eaten tree nuts. It also has the highest ratio of omega-3 to omega-6 fatty acids, and high levels of a form of Vitamin E with anti-cancer properties.

Dr.Rosenberg, a cancer researcher and professor of medicine at UConn Health and Dr. Masako Nakanishi, a research associate in the Center for Molecular Medicine at UConn Health tested the cancer prevention qualities of walnuts on mice fed two different diets.

One group of mice ate a standard lab mouse diet while the other group ate meals that captured the nutritional profile of the typical American diet. Subsets of both groups were supplemented with walnuts.

Interestingly, male mice fed the Western diet fortified with 10.5 percent walnuts showed the greatest decrease in colon tumors compared to mice fed no walnuts.

Researchers found mice that ate seven percent to 10.5 percent of their total calories as walnuts developed fewer colon cancers. The effect was most pronounced in male mice, which had 2.3 times fewer tumors when fed walnuts as part of a diet similar to the typical American's. That's equivalent to a human eating about an ounce of walnuts a day.

To understand why walnuts were beneficial, the UConn Health team collaborated with Dr. George Weinstock and colleagues at The Jackson Laboratory. Weinstock's lab took fecal samples from the mice and analyzed the communities of bacteria living in their digestive tracts.

They found that walnut consumption tended to push the gut microbiome toward an ecology that was potentially protective against cancer.

It's not exactly clear how this works, but there are clues. Previous research has shown that some gut bacteria digest fiber into compounds with anti-inflammatory properties that may reduce tumor initiation.

Because the studies were done only in mice, more testing needs to be done in humans before walnuts can be unequivocally recommended as a cancer-prevention agent. Rosenberg's group is working with a nutritionist and surveying human colonoscopy patients about their diets as part of a longer term study in humans.

"I try to eat walnuts every day," said Dr.Rosenberg.

"We're excited about future studies where we will be able to look at food consumption patterns to see how these results apply to humans."

This research was supported in part by the California Walnut Commission and the American Institute for Cancer Research.

Tagswalnuts, Colon cancer, UConn Health, The Jackson Laboratory for Genomic Medicine, Dr. Daniel Rosenberg