Walnuts may help prevent colon cancer: study

Eating a handful of walnuts every day may change your gut bacteria in a way that suppresses colon cancer, a new study has claimed.

Researchers from the University of Connecticut and The Jackson Laboratory for Genomic Medicine in the US found that mice that ate 7 per cent to 10.5 per cent of their total calories as walnuts developed fewer colon cancers.

The effect was most pronounced in male mice, which had 2.3 times fewer tumours when fed walnuts as part of a diet similar to the typical American's. That is equivalent to a human eating about an ounce of walnuts a day, researchers said.

"Our results show for the first time that walnut consumption may reduce colon tumour development," said Daniel W Rosenberg of the University of Connecticut.

"There is accumulating evidence that eating walnuts may offer a variety of benefits related to health issues like cancer," said Rosenberg.

"This study shows that walnuts may also act as a probiotic to make the colon healthy, which in turn offers protection against colon tumours," he said.

Walnuts are packed with compounds known to be important nutritionally. They have the most 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.

However, 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, diabetes and neurological disorders.

Researchers tested the cancer prevention qualities of walnuts on mice fed two different diets.

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

Male mice fed the Western diet fortified with 10.5 per cent walnuts showed the greatest decrease in colon tumours compared with mice fed no walnuts.

To figure out why walnuts were beneficial, researchers took fecal samples from the mice and analysed 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.

The microbiome analyses also reflected 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 microbiomes 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.

The study was published in the journal Cancer Prevention Research.