A new study suggests that walnut consumption may be beneficial for the health of digestive system by increasing the amount of good probiotic-type bacteria in the gut. Walnuts do this by acting as a prebiotic to help nourish and grow the bacteria that keeps the digestive system healthy. Researchers found that a diet with walnuts led to an overall significant increase in the diversity of probiotic bacteria in the gut.
A team of researchers found that mice that ate 7-10.5 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.
“Our results show for the first time that walnut consumption may reduce colon tumor development,” said Principal Investigator Dr. Daniel W. Rosenberg of UConn Health. “There is accumulating evidence that eating walnuts may offer a variety of benefits related to digestive system and other 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 and other digestive system problems.”
Walnuts are packed with compounds known to be important nutritionally. They have high content of polyunsaturated fatty acids of all the commonly eaten tree nuts, as well as the highest ratio of omega-3 to omega-6 fatty acids, and high levels of a form of Vitamin E with anti-cancer properties. But walnuts are not merely the sum of their chemical parts, and it may be as a whole food that they pack the most significant anti-cancer punch against colon cancer, the third most common cancer in the world. Other studies have shown walnuts have promise warding off diseases connected to diet and lifestyle, including heart disease, arthritis and dementia.
Walnut consumption tended to push the gut micro biome toward an ecology that was potentially protective against cancer. It’s not clear exactly how this works, but there are clues. For example, previous research has shown that some gut bacteria digest fiber into compounds with anti-inflammatory properties that may reduce tumor initiation. The micro biome analyses also reflected interesting differences between male and female. Males on walnut-free diets tended to have less-diverse gut flora than females. Adding walnuts to the diets of male mice brought their micro biomes closer to those of female mice on either of the diets. Whether this change contributes to the protection seen in male mice remains to be determined.
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.
This research was supported in part by the California Walnut Commission (CWC) and the American Institute for Cancer Research.