Walnuts may be more than just a tasty snack. Researchers from the University of Pennsylvania have found that they may promote healthy gut bacteria, which may reduce the risk of heart disease.
For their study, the researchers recruited 42 people who were either overweight or obese aged between 30 and 65. Before the research, they were each placed on an average American diet for two weeks. They were then randomly assigned to one of three study diets. One included whole walnuts. Another involved the same amount of alpha-linolenic acid (ALA) and polyunsaturated fatty acids only without walnuts. The third diet partially replaced oleic acid for the same amount of ALA in walnuts, also without including the nut.
In each diet, saturated fat was replaced by either walnuts or vegetable oils. Each participant followed their meal plans for six weeks. To analyze differences in gut bacteria among the participants, the researchers examined their fecal samples 72 hours before they finished their preparatory diets and 72 hours before they finished their study diets.
In particular, they found that the walnut diet enriched gut bacteria previously linked to health benefits. For example, they found higher quantities of Roseburia, associated with the protection of the gut lining, in the feces of those on the walnut diet.
The researchers also found that those on the walnut diet had more gut bacteria linked to a reduced risk of heart disease compared to their counterparts. They noticed elevated levels of eubacterium eligens, bacteria negatively correlated with changes in several measures of blood pressure.
They also found that those eating walnuts had higher quantities of Lachnospiraceae in their microbiomes, something linked to reduced blood pressure, cholesterol, and non-high-density lipoprotein (HDL) cholesterol. Meanwhile, the researchers noted that the walnut-free diets did not correlate with enriched bacteria nor risk factors for heart disease.
According to Penny Kris-Etherton, a nutrition professor from the University of Pennsylvania, "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."