The study, published in the Journal of Nutrition, suggests walnuts as a part of healthy diet may be a heart- and gut-healthy nut.
Additionally, those changes in gut bacteria were associated with improvements in some risk factors for heart disease.
"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 study researcher Kristina Petersen from Penn State University in the US.
According to the researchers, another research has found that changes to the bacteria in the gastrointestinal tract also known as the gut microbiome may help explain the cardiovascular benefits of walnuts.
For the study, the researchers recruited 42 participants with overweight or obesity who were between the ages of 30 and 65.
Before the study began, participants were placed on an average American diet for two weeks.
After this "run-in" diet, the participants were randomly assigned to one of three study diets, all of which included less saturated fat than the run-in diet.
The diets included one that incorporated whole walnuts, one that included the same amount of alpha-linolenic acid (ALA) and polyunsaturated fatty acids without walnuts, and one that partially substituted oleic acid (another fatty acid) for the same amount of ALA found in walnuts, without any walnuts.
In all three diets, walnuts or vegetable oils replaced saturated fat, and all participants followed each diet for six weeks with a break between diet periods.
To analyse the bacteria in the gastrointestinal tract, 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," Petersen said.
"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 added.
The researchers also found that after the walnut diet, there were significant associations between changes in gut bacteria and risk factors for heart disease.
According to the study, Eubacterium eligens was inversely associated with changes in several different measures of blood pressure, suggesting that greater numbers of Eubacterium eligens was associated with greater reductions in those risk factors.
( With inputs from IANS )