Study suggests eating walnuts may reduce risk of bowel cancer

By Stephen Beech

Eating walnuts reduces the risk of bowel cancer, according to new research.

The edible seeds of walnut trees also curb inflammation, say American scientists.

The findings come from a University of Connecticut School of Medicine clinical trial, published in the journal Cancer Prevention Research.

Study leader Dr. Daniel Rosenberg says eating "a handful" of walnuts every day provides "long-term" health benefits.

He explained that ellagitannins, plant-derived polyphenol compounds found in walnuts, are shown to be metabolized exclusively by the gut microbiome into a range of anti-inflammatory molecules called urolithins.

Dr. Rosenberg says those urolithins are associated with "very potent" anti-inflammatory properties and may even inhibit cancer.

He said: “Ellagitannins in the walnut are importantly providing the anti-inflammatory and anti-cancer 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."

Dr. Rosenberg has studied walnut properties for more than a decade and has researched the connection between walnut consumption and its anti-inflammatory properties.

The findings of the clinical trial show that high levels of urolithin A formation by the gut microbiome from walnut consumption has a "positive" impact on reducing inflammatory markers across blood, urine, and fecal samples, and may even positively affect the immune cells within colon polyps.

The clinical trial involved patients between the ages of 40 and 65 and at an elevated risk of bowel cancer, also known as colon cancer, referred for the study.

Each of the 39 participants were asked to avoid all ellagitannin-containing foods and drinks for a week to set their urolithin levels at or close to zero before they began consuming ellagitannin-rich walnuts as part of their closely monitored diet.

At the end of the three-week study, all participants underwent a high-definition colonoscopy .

The research team found that elevated urolithin A levels in the urine of patients correlated with the serum levels of peptide YY, an interesting protein that has been associated with inhibition of bowel cancer.

Reduced levels of several inflammation markers present in the blood were also found, especially in obese patients that had the greatest capacity to form urolithins by their gut microbiome.

Dr. Rosenberg also used high-dimensional spatial imaging technology that allowed the research team to develop a detailed view of the direct cellular interactions present inside colon polyps that were removed during colonoscopy at the end of the walnut study.

The cutting-edge advanced imaging technology revealed that patients with high levels of urolithin A formation following walnut consumption was "directly associated" with reduced levels of several important proteins that are often present in polyps, showing for the first time how eating walnuts may directly enhance bowel health.

The research team also discovered that the protein vimentin - often associated with more advanced forms of colon cancer - was greatly reduced inside polyp tissues obtained from patients who had also formed the highest levels of urolithin A by their gut microbiome.

The findings build on earlier work by Dr. Masako Nakanishi, an Assistant Professor in Dr. Rosenberg's lab, who showed in several earlier publications that walnuts had beneficial and anti-cancer effects in the colons of cancer-prone mice.

Dr. Rosenberg said: “Urolithin A has a very positive influence on inflammation and maybe even cancer prevention.

“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.”

He added: “Our study provides strong rationale for dietary inclusion of walnut ellagitannins for cancer prevention.

"Nutrients from walnuts can contribute to reduced cancer risk.

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