The Latest Gut Health Research and Uncovering the Role of Walnuts
As gut health continues to be a topic of conversation surrounding health and wellness, consumers are looking for simple ways to support their gut and ultimately their overall health. While there is still so much we don’t know about the gut microbiome, one thing is relatively certain: the foods we eat have an impact on the health and diversity of the community of beneficial bacteria living in our gut otherwise known as the gut microbiome.
Fiber, probiotics, prebiotics, and a variety of other nutrients help promote overall gut health. Fiber stimulates beneficial fermentation and progression of diversity in the gut. Prebiotics are a subset of fibers that are non-digestible and ultimately “feed” the good bacteria found in the gut. Probiotics are the “good” bacteria found in the gut that can also be consumed through food or supplements. A newer concept in the gut health realm is postbiotics which are inactivated microbial cells or gut bacteria, or what is left behind after prebiotics and probiotics are digested.
When it comes to food, research has shown that consuming walnuts may help promote gut health. A study from the USDA and University of Illinois found that a small sample of 18 healthy adults (ages 35-68) who ate 42 grams (about 1.5 ounces) of walnuts each day for three weeks experienced a decrease in secondary bile acids, which may play a role in colon cancer, inflammation, and gastrointestinal diseases. The study also found that eating walnuts seemed to result in an increase in gut bacteria that is thought to be beneficial for health.1 While these results are promising, more research is needed to explore the relationship between cause and effect. Walnuts also provide a variety of other nutrients per one ounce serving. They are the only nut to provide an excellent source of the anti-inflammatory omega-3 alpha-linolenic acid, or ALA (2.5g/oz), plus 2 grams of fiber and a mix of tocopherols (5.91mg/oz) and antioxidant polyphenols (69.3 ± 16.5 µmol catechin equivalents/g).2,3,4,5,*
Now new evidence suggests that walnuts may have prebiotic potential.6 Prebiotics have been shown to promote the growth of beneficial gut bacteria.7 This evidence was reported in two recently published review papers in Nutrients and Antioxidants, which explored the relationship between walnuts and a compound called urolithin A (UA). UA is produced by gut bacteria and may play a role in the gut microbiome and personalized, precision health benefits. UA is a gut microbiome-derived natural compound produced by gut bacteria after they digest plant-based substances called ellagitannins (ETs) and ellagic acid (EA), which are complex polyphenols abundant in foods such as pomegranates, berries, and nuts, including walnuts.
In a 2023 review published in Nutrients, researchers summarized findings surrounding nut consumption and its impact on the gastrointestinal system. Specific to walnuts, the review showed a beneficial role this nut may play in supporting beneficial gut bacteria, related to composition and diversity. While the findings are promising, the review ultimately showed inconsistent results associated with improved health benefits related to critical gut bacteria such as microbial alpha- and beta-diversity.8
A second 2023 review, published in Antioxidants and comprised of 33 studies, investigated the evidence supporting the benefits of walnuts in relation to inflammation and overall disease risk. The findings suggest that walnuts, as part of a healthy diet, may help reduce inflammation and promote normal digestive function, due in part to their unique nutrient matrix and metabolites produced during digestion. This paper suggests much of the beneficial properties of walnuts associated with anti-inflammatory effects are linked to ellagitannins, or polyphenols found in walnuts which are ultimately metabolized by gut microbiota to bioactive, anti-inflammatory urolithins as discussed above.6
While additional research is needed to fully explore the relationship between UA and cellular function, researchers suggest UAs may enhance cellular health by increasing how our cells function and stay working their best, while also reducing inflammation within the intestinal mucosa. As it relates to gut health, it appears UA may alter the gut microbiota by improving its diversity.6,8 To more accurately assess the health benefits and functionality associated with consumption of foods, such as walnuts and UA, further studies are needed to better define the mechanisms responsible for their extraction during digestion, and how foods, like walnuts, may ultimately affect bioavailability.
When considered together, both reviews illuminate impactful findings from pre-clinical and human studies suggesting that when walnuts are digested there is a process that takes place converting walnut-derived ellagitannins into a complex family of anti-inflammatory urolithins that may influence the growth of “good” bacteria in the gut.6,8,~ However, they’re narrative reviews that involved animal studies, cellular studies, and some promising human trials. These narrative reviews do have systematic searching which could offer a comprehensive look at findings among patients of various backgrounds; however, it can be limited by the methods, reported outcomes and quality of the individual studies involved. Future clinical studies are needed in other research settings and populations to better understand how walnuts impact gut health and at what amounts.
Researcher and Professor of Medicine at the University of Connecticut School of Medicine, Dr. Daniel W. Rosenberg, Ph.D. shares, “Evidence that microbial metabolism of walnut-derived ellagitannins is highly patient-dependent has prompted our NIH-funded clinical trial to study ellagic acid metabolism in subjects at elevated risk of colorectal cancer. Our goal is to better understand how two ounces per day of walnuts added to the regular diet may affect an individual’s microbiome and to define the specific microbes responsible for these metabolic reactions required to form urolithins.”
To learn more about walnuts and the emerging gut health research watch the latest video from Dr. Daniel W. Rosenberg, Ph.D. entitled, “Science In Seconds: The Wonders of Walnuts,” published on the UConn Today website.
Walnuts offer a simple, cost-effective (and delicious!) strategy for providing a wide range of potential health benefits that may improve gut bacteria and overall gut health. As research continues to evolve in this space, it can’t hurt to give your gut some love with walnuts!
For simple ways to incorporate walnuts in your eating pattern try gut health-promoting recipes like this fiber-rich Toasted Walnut, Black Bean, Corn and Tomato Salad or this Steak Sandwich with Walnut Kimchi Slaw.
For more information on how walnuts can contribute to overall gut health check out this Gut Health Research Summary or this Digest the Latest on Gut Health and Walnuts blog post and be sure to read our Cancer Research Summary for information surrounding that topic.