Heart Benefits Of Walnuts Are Linked With Microbes In The Gut, Study Says. Know The Science Behind It

The study examined the gene expression of gut microbes, and found that the heart-healthy benefits of walnuts may be linked to beneficial changes in the mix of microbes found in the gut. 

The study found that the consumption of walnuts may alter the gut microbiome in a way that increases the body's production of the amino acid L-homoarginine. The deficiency of homoarginine has been linked to a higher risk for cardiovascular disease.

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The heart-healthy benefits of walnuts may come from the gut, according to a new study. The study examined the gene expression of gut microbes, and found that the heart-healthy benefits of walnuts may be linked to beneficial changes in the mix of microbes found in the gut. 

The study, led by Kristina S Peterson from Texas Tech University in Lubbock, could help identify other foods or supplements with similar nutritional benefits. The findings were presented on March 25 at Discover BMB, the annual meeting of the American Society for Biochemistry and Molecular Biology, in Seattle. 

Walnut consumption increases production of an amino acid

The study found that the consumption of walnuts may alter the gut microbiome in a way that increases the body's production of the amino acid L-homoarginine. The deficiency of homoarginine has been linked to a higher risk for cardiovascular disease.

In a statement released by the American Society for Biochemistry and Molecular Biology, Mansi Chandra, one of the researchers involved in the study, said research has shown that walnuts may have heart-healthy benefits like lowering cholesterol levels and blood pressure, and this motivated the team to look at how walnuts benefitted the gut microbiome, and whether those effects led to the potential beneficial effects. The study findings represent a new mechanism through which walnuts may lower cardiovascular disease risk.

What is metatranscriptomics?

The researchers studied the gene expression of gut microbes using an approach called metatranscriptomics. The analysis of the collective transcriptomes, or the sum total of all the messenger RNA molecules, of a given habitat, is called metatranscriptomics. Using this recently developed technology, researchers can quantify gene expression levels and monitor how these levels shift in response to various conditions such as dietary changes. 

Chandra said that to the team's knowledge, this is the first study to use metatranscriptomics analysis for studying the impact of walnut consumption on the gene expression of the gut microbiota. Researchers can better understand walnut-related modulation of gut microbiome, which could be very impactful in learning how gut health impacts the heart health in general. 

How the study was conducted

As part of the metatranscriptomics analysis, the researchers used samples acquired from a previously performed controlled-feeding study which involved 35 participants with high cardiovascular risk. These participants were put on a two-week standard Western diet, and then randomly assigned to one of three study diets. The participants were asked to follow the three diets for six weeks each, with a break between each. 

What were the three test diets?

One of the diets incorporated whole walnuts, while another included the same amount of omega-3 fatty acid alpha-linoleic acid, or ALA, and polyunsaturated fatty acids (that are provided by walnuts) without walnuts. The third diet partially substituted another fatty acid known as oleic acid for the same amount of ALA found in walnuts, but without the consumption of any walnuts. 

The controlled-feeding study had designed the diets in this way to obtain information about how walnuts affected cardiovascular health due to their bioactive compounds and ALA content, and whether walnut ALA is the best substitute for dietary saturated fat compared to oleic acid. 

For the new study, the researchers analysed gene expression and the bacteria in the gastrointestinal tract from faecal samples using metatranscriptomics. The faecal samples were collected shortly before the participants finished the run-in diet and each of the three study diets. 

Participants on walnut diet had higher levels of a certain bacteria

The new study found that the gut of participants on the walnut diet had higher levels of Gordonibacter bacteria, which convert the plant polyphenols ellagitannins and ellagic acid into metabolites that know them to be absorbed by the body. Ellagitannins have anti-inflammatory, anticancer, antioxidant, cardioprotective and prebiotic properties. Ellagic acid has antioxidant and anti-inflammatory properties.

Participants on walnut diet had higher levels of gene expression for L-homoarginine

The participants who consumed the walnut diet showed higher levels of expression for several genes that are involved in important metabolic and biosynthetic pathways. These pathways include the ones that increase the body's production of the amino acid L-homoarginine.

The researchers calculated the Dysbiosis Index Value, of the ratio of bad bacteria to good bacteria, at baseline and following each test diet in the participants at elevated risk of cardiovascular disease. 

Significance of the study

The study found that the standard western diet had the highest Dysbiosis Index Value compared to other diet groups, indicating a greater number of bad bacteria as compared to good bacteria. 

The study is important because it could help inform dietary interventions based on walnuts, and find food supplements for people allergic to nuts, in order to boost the endogenous production of homoarginine.