Walnuts and the gut-heart axis: Study suggests increased production of Homoarginine

27 Mar 2023 --- The benefits on heart health from consuming walnuts may be explained by the nut’s effects on the gut microbiome, as it increases the production of amino acid L-homoarginine naturally in the body, according to the researchers. Eating walnuts also showed a higher expression level for genes involved in biosynthetic and metabolic pathways. 

The researchers point out that having a deficiency of Homoarginine has been linked to an increased risk of cardiovascular disease.

“Research has shown that walnuts may have heart-healthy benefits like lowering cholesterol levels and blood pressure,” says Mansi Chandra, an undergraduate researcher at Juniata College in Huntingdon, Pennsylvania. 

All about the gut?
Adding walnuts to one’s diet may improve the mixture of gut microbes. The study used the recently developed technology known as metatranscriptomics to examine the gut microbe’s gene expression.

With this technology, researchers quantified the gene expression levels while monitoring how they responded and shifted to diet changes. 

“This motivated us to look at how walnuts benefited the gut microbiome and whether those effects led to the potential beneficial effects. Our findings represent a new mechanism through which walnuts may lower cardiovascular disease risk.”

“To our knowledge, this is the first study to use metatranscriptomics analysis for studying the impact of walnut consumption on the gut microbiota gene expression,” Chandra underscores.

The technology quantified the gene expression levels while monitoring how they responded and shifted to dietary changes.Study set-up 
The trial included data from 35 participants, all with a high risk of cardiovascular disease. They were put on a “standard Western diet” for two weeks and then assigned randomly to one of three diets.

One diet included whole walnuts, another contained equal omega 3 fatty acids alpha-linolenic acid (ALA) or polyunsaturated fatty acids but without walnuts. The third had partially substituted fatty acid with the same amount of oleic acid as walnuts, but without the nuts. 

The diets were chosen to see whether walnut ALA is the best substitute for dietary saturated fat compared to oleic acid.

“These exploratory analyses contribute to our understanding of walnut-related modulation of the gut microbiome, which could be very impactful in learning how gut health impacts our heart health in general,” Chandra details.

Going deeper
She further details that the findings also indicate the health benefits of supplements and foods that boost the body’s production of homoarginine as alternatives to nuts for those with allergies. 

The researchers found a higher level of Gordonibacter – a bacterium that converts the plant polyphenols ellagitannins and ellagic acid into metabolites that allow them to be absorbed by the body – in the gut microbiome among participants eating walnuts.

Previously, walnuts have demonstrated the ability to improve cognition and gut health and to reduce the risk of cancer, as it showed in a study that it reduces cell migration and invasion in several carcinomas. Harvard researchers earlier demonstrated that walnut consumption reduced the risk of Type 2 diabetes by 17% and cardiovascular disease by 29%.

This week, the study results will be presented at the American Society for Biochemistry and Molecular Biology in Seattle, US.

Edited by Beatrice Wihlander