Researchers studied 42 overweight or obese patients between the ages of 30 and 65. Before the study began, participants were placed on an average American diet for two weeks. They were then randomly assigned to one of three study diets, all of which included less saturated fat than the average American diet: one that incorporated whole walnuts, one that included the same amount of alpha-linolenic acid and polyunsaturated fatty acids without the walnuts, and one that partially substituted oleic acid for the same amount of ALA found in walnuts, All participants followed each diet for six weeks with a break between diet periods.
Researchers collected fecal samples 72 hours before the participants finished the average American diet and 72 hours before participants finished each of the three study diet periods.
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After the walnut diet, there were significant associations between changes in gut bacteria and risk factors for heart disease. Roseburia,Eubacteria eligens, Lachnospiraceae, and Butyricicoccus bacteria all increased; all four are associated with health benefits, including blood pressure, protection of the gut lining, and lower cholesterol, benefits which the walnut group received. The other two diets showed none of the same benefits.Penny Kris-Etherton, Professor of Nutrition at Penn State, said in a press release: “We wanted to see if changes in gut health with walnut consumption were related to improvements in risk factors for heart disease. The walnut diet enriched a number of gut bacteria that have been associated with health benefits in the past. The findings add to what we know about the health benefits of walnuts, this time moving toward their effects on gut health. 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.”
Kristina Petersen, Assistant Research Professor at Penn State, added: “Replacing your usual snack—especially if it’s an unhealthy snack—with walnuts is a small change you can make to improve your diet. 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.”
