There’s no debate that nuts can be a healthy snack. Packed with polyphenols and antioxidants, which can help reduce inflammation, and omega-3s to support brain health—in addition to healthy fats and protein—nuts are a frequently recommended snack by dietitians and nutrition experts.

But one type of nut stands out as a potential nutritional tool in the arsenal against the growing cases of colorectal cancer: walnuts.

A recent study published in Cancer Prevention Research from the UConn School of Medicine found that ellagitannins, polyphenol compounds found in walnuts, play a role in helping inhibit cancer.

“Ellagatannins in the walnut are importantly providing the anti-inflammatory and anticancer properties that we’re seeing in patients in our clinical trial research, particularly the gut’s conversion of ellagitannins to a potent anti-inflammatory agent, urolithin A,” said study author Daniel W. Rosenberg, who leads a team of researchers at the UConn School of Medicine.

How walnuts lower colorectal cancer risk

The study included 39 patients between ages 40 and 65 who were screened by the clinical research team at UConn John Dempsey Hospital and asked to complete an NIH food frequency questionnaire. They were asked to avoid all ellagitannin-containing foods and beverages for a week—to set their urolithin levels at or close to zero—and then start eating ellagitannin-rich walnuts as part of a closely monitored diet.

After three weeks of this diet, each participant underwent a colonoscopy. Researchers found that patients with high levels of urolithin A following walnut consumption had reduced levels of several crucial proteins often present in polyps—small growths that form on the lining of the colon and can lead to colorectal cancer. The study authors believe this may show how walnut consumption can directly improve colon health.

Additionally, the findings revealed that high levels of urolithin A—which is formed by the gut microbiome—from walnuts reduced inflammatory markers across blood, urine, and fecal samples, and could positively affect the immune cells within colon polyps.

The cancer-fighting properties researchers discovered didn’t stop there—patients with elevated urolithin A levels also had increased serum levels of peptide YY, a protein associated with inhibition of colorectal cancer. They also found that patients with obesity had the greatest capacity to form urolithins by their gut microbiome.

“Urolithin A has a very positive influence on inflammation and maybe even cancer prevention,” Rosenberg said. “Our study proves that dietary supplementation with walnuts can boost the general population’s urolithin levels in those people with the right microbiome, while significantly reducing several inflammatory markers, especially in obese patients.”

Researchers also discovered that the protein vimentin, which is often associated with more advanced forms of colon cancer, was significantly reduced inside the polyp tissues of patients who had the highest levels of urolithin A.

“There are many potential benefits one can get from eating walnuts, with so little downside risk,” Rosenberg added. “Just grabbing a handful every day is really something that you can easily do for your long-term health benefit.”

For more on nutrition and cancer risk:

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