Health Benefits of Walnuts Linked to Gut Microbiome Effects


Diets rich in nuts are known to play a role in heart health and in reducing colorectal cancer. According to a new study, the way walnuts impact the gut microbiome may be behind some of those health benefits.


Walnuts are a great natural source of dietary fiber and have many health-related benefits. Dietary fiber is an essential food source for good gut bacteria and helps them do their jobs.


Fruits, vegetables, nuts, whole grains, and legumes are important sources of dietary fiber. Eating a variety of these foods helps promote a diverse gut microbiota, which in turn helps support health.


In a new study published in The Journal of Nutrition, researchers set out to figure out how walnuts affect the gut microbiome and how any such effects might influence health.


The researchers fed eighteen healthy men and women balanced diets containing 0-42 g of walnuts per day for two three-week periods with a one-week break in between.


Microbiome and blood samples were collected before beginning the study and at the end of each three-week period. 


The researchers found that consuming walnuts increased the good gut bacteria that make butyrate (a beneficial short-chain fatty acid), which is most likely how walnuts are beneficial for inflammation and digestive health.


Specifically, walnut consumption resulted in higher relative abundance of three bacteria of interest: Faecalibacterium, Roseburia, and Clostridium. There’s growing interest in Clostridium clusters of bacteria because they have the ability to make butyrate. Unfortunately, the researchers didn’t measure butyrate levels in the study participants, so there’s more work to do.


Faecalibacterium is interesting because it has been shown to reduce inflammation and is being tested as a probiotic.


In addition, walnut consumption had positive effects on microbial-derived secondary bile acids and reduced LDL-cholesterol levels in the adults participating in the study.


Walnut consumption reduced secondary bile acids compared to the control. Secondary bile acids are made by some gut bacteria and have been shown to be elevated in people with higher rates of colorectal cancer and can be damaging to cells within the gastrointestinal tract.

Thus, reducing secondary bile acids with healthy gut bacteria could be beneficial to human health.


This initial study shows that the interactions of the gut microbiome with undigested walnut components are producing positive outcomes. However, further research is needed to determine precisely how these changes influence health outcomes.



Holscher, HD et al. (2018). Walnut Consumption Alters the Gastrointestinal Microbiota, Microbially Derived Secondary Bile Acids, and Health Markers in Healthy Adults: A Randomized Controlled Trial. The Journal of Nutrition. DOI: 10.1093/jn/nxy004