Consumption of walnuts may improve the growth of beneficial gut bacteria, and are associated with improvements in some risk factors for heart disease, according to a new study which may lead to new dietary recommendations for better cardiac health.
The study, published in the Journal of Nutrition, said walnuts may be a heart- and gut-healthy snack.
“Substantial evidence shows that small improvements in diet greatly benefit health. Eating two to three ounces of walnuts a day as part of a healthy diet could be a good way to improve gut health and reduce the risk of heart disease,” said Kristina Petersen, study co-author from the Pennsylvania State University in the US.
Earlier studies had revealed that when combined with a diet low in saturated fats, walnuts may have heart-healthy benefits.
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“Replacing your usual snack — especially if it’s an unhealthy snack — with walnuts is a small change you can make to improve your diet,” Petersen explained.
According to Petersen and her team, changes to the bacteria in the gastrointestinal tract — also known as the gut microbiome — may explain the cardiovascular benefits of walnuts.
For the current study, the scientists recruited 42 participants between the ages of 30 and 65, who were either overweight or obese. The participants were placed on an average American diet for two weeks before the study began.
They were then randomly assigned to one of three study diets — all of which included less saturated fat than the pre-study diet.
One of the three diets incorporated whole walnuts, and another included natural chemicals present in walnuts — alpha-linolenic acid (ALA) and polyunsaturated fatty acids.
The third diet had partially substituted oleic acid (another fatty acid) for the same amount of ALA found in walnuts.
In all the diets, walnuts or vegetable oils replaced saturated fat, the scientists said.
The participants followed each diet for six weeks with a break between diet periods, the study noted.
To assess the gut bacterial changes, the researchers collected fecal samples 72 hours before the participants finished the run-in diet, and each of the three study diet periods.
“The walnut diet enriched a number of gut bacteria that have been associated with health benefits in the past. One of those is Roseburia, which has been associated with protection of the gut lining. We also saw enrichment in Eubacteria eligens and Butyricicoccus,” Petersen said.
Based on their study, the researchers said there were significant links between changes in gut bacteria, and risk factors for heart disease.
Eubacterium eligens, they said, was inversely associated with changes in several measures of blood pressure, suggesting that more of the bacterium was associated with greater reductions in heart illness related risk factors.
“Foods like whole walnuts provide a diverse array of substrates — like fatty acids, fiber and bioactive compounds — for our gut microbiomes to feed on,” Lamendella said. “In turn, this can help generate beneficial metabolites and other products for our bodies,” said study co-author Regina Lamendella from Juniata College in the US.
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