The Unexpected Role of Walnuts in Promoting Heart Health via the Gut
[Mar. 28, 2023: JD Shavit, The Brighter Side of News]
The findings could help identify other foods or supplements with similar nutritional benefits. (CREDIT: Getty Images)
Walnuts have long been recognized as a healthy snack, packed with vitamins and nutrients. However, recent research suggests that the benefits of walnuts go beyond just their nutritional value.
A new study examining the gene expression of gut microbes suggests that the heart-healthy benefits of walnuts may be linked to beneficial changes in the mix of microbes found in our gut. The findings could help identify other foods or supplements with similar nutritional benefits.
The study, led by Kristina S. Petersen from Texas Tech University in Lubbock, found that introducing walnuts into a person’s diet may alter the gut’s mix of microbes — known as the microbiome — in a way that increases the body’s production of the amino acid L-homoarginine. Homoarginine deficiency has been linked to higher risk for cardiovascular disease.
“Research has shown that walnuts may have heart-healthy benefits like lowering cholesterol levels and blood pressure,” said Mansi Chandra, an undergraduate researcher at Juniata College in Huntingdon, Pennsylvania. “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.”
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Chandra presented the new findings at Discover BMB, the annual meeting of the American Society for Biochemistry and Molecular Biology in Seattle.
The researchers used an approach known as metatranscriptomics to study the gene expression of gut microbes. This recently developed technology can be used to quantify gene expression levels and monitor how these levels shift in response to various conditions such as dietary changes.
“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 said. “These exploratory analyses contribute to our understanding of walnut-related modulation of gut microbiome, which could be very impactful in learning how gut health impacts our heart health in general.”
The metatranscriptomics analysis used samples acquired from a previously performed controlled-feeding study in which 35 participants with high cardiovascular risk were put on a two-week standard Western diet and then randomly assigned to one of three study diets. The study participants followed each diet for six weeks with a break between each.
The diets included one that incorporated whole walnuts, one that included the same amount of omega-3 fatty acid alpha-linolenic acid, or ALA, and polyunsaturated fatty acids as the walnut diet but without walnuts, and one that partially substituted another fatty acid known as oleic acid for the same amount of ALA found in walnuts but without consumption of any walnuts. The diets were designed to provide 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 work, researchers used metatranscriptomics to analyze gene expression and the bacteria in the gastrointestinal tract from fecal samples collected shortly before the participants finished the run-in diet and each of the three study diets.
The analysis revealed higher levels of Gordonibacter bacteria in the gut of participants on the walnut diet. This bacterium converts the plant polyphenols ellagitannins and ellagic acid into metabolites that allow them to be absorbed by the body. Participants consuming the walnut diet also showed higher levels of expression for several genes that are involved in important metabolic and biosynthetic pathways, including ones that increase the body’s production of the amino acid L-homoarginine.
In addition to potential dietary interventions based on walnuts, the study's findings could also have broader implications for understanding the complex relationship between the gut microbiome and cardiovascular health.
Research has increasingly shown that the gut microbiome plays a critical role in a wide range of physiological processes, including immune function, digestion, and metabolism. In recent years, scientists have also discovered that the gut microbiome can affect cardiovascular health.
For example, previous studies have found that certain gut microbes produce compounds that contribute to the development of atherosclerosis, a condition in which fatty deposits build up in the arteries and can lead to heart disease. Other research has shown that certain microbes can affect blood pressure levels and inflammation, which are also key risk factors for cardiovascular disease.
The new study's focus on the potential impact of walnuts on the gut microbiome highlights the growing recognition of the importance of diet in shaping the microbial communities that live within us. By altering the mix of bacteria and other microorganisms in our gut, certain foods may be able to promote health and prevent disease.
However, as the researchers note, more work is needed to fully understand the mechanisms behind these effects and to identify other foods or supplements that may have similar benefits. The study's use of metatranscriptomics is an important step forward in this effort, as it allows scientists to study the complex interactions between diet, the gut microbiome, and gene expression in a more detailed and comprehensive way.
As research in this area continues to advance, it may eventually lead to new approaches for preventing and treating cardiovascular disease, as well as other conditions that are influenced by the gut microbiome. And for those looking to improve their heart health through diet, the humble walnut may prove to be a powerful ally in the fight against heart disease.
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