Posted on Jan 17, 2020, 5 p.m.
A randomized, controlled study published in the Journal of Nutrition found that eating walnuts every day as part of a healthy well balanced diet was associated with increases in certain bacteria that helps to promote health; those changes in gut bacteria were also associated with improvements in some risk factors for heart disease.
"Replacing your usual snack -- especially if it's an unhealthy snack -- with walnuts is a small change you can make to improve your diet," said Kristina Petersen, assistant research professor at Penn State. "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."
Previously walnuts when consumed with a diet low in saturated fats have been suggested to have heart healthy benefits such as lowering cholesterol levels and blood pressure; research has also found that changes to gut microbiome may help to explain the cardiovascular benefits of consuming whole raw walnuts.
"There's a lot of work being done on gut health and how it affects overall health," said Penny Kris-Etherton, distinguished professor of nutrition at Penn State. "So, in addition to looking at factors like lipids and lipoproteins, we wanted to look at gut health. We also wanted to see if changes in gut health with walnut consumption were related to improvements in risk factors for heart disease."
42 participants between the ages of 30-65 who were overweight or obese were placed on an average American diet for two weeks before beginning the study, after which they were placed into one of three diets groups at random, all of which included less saturated fat than their previous diet. One of the diet incorporated whole walnuts, one included the same amount to ALA and polyunsaturated fatty acids without walnuts, and one that partially substituted oleic acid for the same amount of ALA found in walnuts without any walnuts. All 3 diets had walnuts or vegetable oils replacing saturated fats and all diets were followed for 6 weeks with a break between diet periods. Fecal samples were collected 72 hours before finishing the intro diet and in each of the three study diets to analyze bacteria in the GI tract.
"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."
After the walnut diet there were significant associations found between changes in gut bacteria and risk factors for heart disease; Eubacterium eligens was inversely associated with changes in several different measures of blood pressure suggesting that greater numbers of it was associated with greater decreases in those risk factors. Lachnospiraceae were associated with greater reductions in blood pressure, total cholesterol, and non-HDL cholesterol; there were no significant correlations between risk of heart disease and enriched bacteria in the other 2 diets.
"Foods like whole walnuts provide a diverse array of substrates -- like fatty acids, fiber and bioactive compounds -- for our gut microbiomes to feed on. In turn, this can help generate beneficial metabolites and other products for our bodies,” said Regina Lamendella, associate professor of biology at Juniata College.
"The findings add to what we know about the health benefits of walnuts, this time moving toward their effects on gut health," Kris-Etherton said. "The study gives us clues that nuts may change gut health, and now we're interested in expanding that and looking into how it may affect blood sugar levels.”
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