Walnuts might support heart health by changing the gut microbiome

By Sarah MooreMar 24 2023

Previous studies have found that eating walnuts may help reduce the risk of cardiovascular disease (CVD). The exact underlying mechanisms of this relationship, however, have remained unclear.

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Now, scientists at Texas Tech University have revealed that the heart-healthy benefits of eating walnuts could be a result of the changes they induce in the gut microbiome. This research will help identify other foods with similar benefits, which could result in the development of novel nutritional strategies to disease prevention.

The gut microbiome and health

In recent years there has been an increased focus on the connection between the gut and health, both physical and mental. It is widely accepted that the gut microbiome is essential for health; deviations in gut microbiota have been linked to numerous diseases, including obesity, type 2 diabetes, hepatic steatosis, intestinal bowel diseases (IBDs), CVD, and several types of cancer. This is unsurprising given that an estimated 40 trillion bacterial cells are in the human body, surpassing the 30 trillion human cells that make up the body itself.

The link between imbalances in gut microbiota and heart health, in particular, has become increasingly studied. It is now recognized that host-microbial interaction can influence homeostatic mechanisms that govern numerous pathways implicated in CVD.

At the same time, there is an increasing scientific interest in nutrition's role in disease. In CVD, it has been suggested that consuming walnuts, in particular, might reduce a person's risk of the disease. The exact underlying mechanisms of this association, however, have been unclear. Now, a new study published in the journal American Society for Biochemistry and Molecular Biology has revealed that the benefits of eating walnuts can be found in the gut.

Gordonibacter bacteria found elevated in the guts of those who eat walnuts

A team of researchers, led by Kristina S Peterson, used the analytical tool of metatranscriptomics to investigate the gene expression of gut microbiomes to understand the impact of walnuts on the gut microbiome. The approach is a relatively new technology that quantifies gene expression levels and reports how these levels fluctuate in response to factors such as dietary changes.

The study was the first of its kind, as previously, no other study has used metatranscriptomics to study the impact of walnut consumption on gene expression of the gut microbiota. The analysis investigated samples collected from a controlled-feeding study where participants at a high risk of CVD were put on different diets for six weeks, including one diet that included whole walnuts. Other diets were designed to match the walnut diet in omega-3 alpha-linolenic acid (ALA) levels or in polyunsaturated fatty acids, but without the walnuts.

The analysis showed that participants who ate the walnut diet had higher levels of Gordonibacter bacteria in their guts. These bacteria produce urolithins with anti-inflammatory, anti-cancer, and lipid-lowering properties. In addition, participants consuming the walnut diet also had higher levels of expression of genes involved in metabolomic and biosynthetic pathways, such as those that increase amino acid L-homoarginine production, a deficiency of which has been identified as a risk factor for CVD.

Future directions

The findings show that consuming walnuts might alter the gut microbiome so that the production of acid L-homoarginine is increased, which may explain why previously links have been made between diets where walnuts are consumed and a reduced risk of CVD.

"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."

Mansi Chandra, Juniata College Huntingdon

In the future, these results could help to develop dietary interventions based on walnuts and other supplements that boost the production of homoarginine, which will be important for those with nut allergies.

Next, the researchers will look to identify the final products of the genes that were shown to have higher levels of expression in this study to gain a deeper understanding of the underlying biological mechanisms at work.