Farm Progress

The California Walnut Board is touting numerous studies linking the nut to improved gut health, as efforts to improve domestic demand continue.

Tim Hearden, Western Farm Press

July 18, 2018

3 Min Read
Hemera Technologies/Thinkstock

As its push continues to boost domestic demand — and grower prices —  the California Walnut Board is touting numerous studies that link regular consumption of the nuts to improved gut health.

Board members note that while sources of probiotics, such as yogurt and other fermented foods, have taken center stage in conversations about the microbiome, whole foods that contain fiber or prebiotics are seen as equally important as the “building blocks” of a healthy gut.

Probiotics are good bacteria that provide health benefits, the board explains in a newly-published newsletter published. Prebiotics are found in certain whole plant-based foods or as added ingredients in food products, and help nourish and grow the beneficial bacteria in the gut.


Among the emerging research on how walnuts can positively impact gut health, according to the board:

  • A study from the USDA and the University of Illinois, published in the Journal of Nutrition, found that a sampling of 18 healthy adults ages 35-68, who ate about 1.5 ounces of walnuts each day for three weeks, experienced a change in gut bacteria, including a decrease in secondary bile acids that can play a role in colon cancer.

Another study, published in Nutrients, found that consuming a walnut-enriched diet positively impacted the gut microbiome by enhancing good probiotic and butyric acid-producing bacteria. The study included 194 healthy older German adults who were randomized with two 8-week diet phases — one a walnut-enriched diet and the other free of tree nuts.

The scientists acknowledged that more research is needed to understand how specific bacterial species may be associated with favorable effects on health, such as heart health. The board also cites two animal studies that suggest an association between walnut consumption and a healthier gut.

One, published in the Journal of Nutritional Biochemistry, found that eating walnuts may be beneficial for digestive health by increasing the amount of probiotic-type bacteria in the gut, and they may do so by acting as a prebiotic to help nourish and grow the good bacteria that keeps the digestive system healthy.

The other study, published in Cancer Prevention Research, found that eating walnuts may modify gut bacteria in mice to make the colon healthy, which is considered when looking at the ability to protect against colon tumors.

The board highlights the gut health studies after reporting earlier this month that a new epidemiological study, representing more than 34,000 American adults, suggests that those who consume walnuts may have about half the risk of developing Type 2 diabetes, compared to adults who don’t eat nuts.


The health research is a big part of the walnut industry’s mission to improve domestic demand, as acreage and production keep expanding, and as international trade gets murkier.

In recent years, international markets accounted for about 65 percent of the walnut industry’s business, but as competition overseas intensified and walnut prices dropped, the Walnut Board has invested more effort to boost U.S. sales.

In one program, the board marked this year’s Heart Month observance in February by teaming with retail chains in two targeted markets — Charlotte, N.C., and Minneapolis-St. Paul, Minn. In some cases, the promotions appeared to have succeeded in generating more sales.

California’s walnut acreage ballooned to 400,000 acres in 2017, a 10 percent increase from 2015, the National Agricultural Statistics Service estimates.

To sign up for the board's newsletters, visit its website at

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