Going nuts for a healthy heart and gut Original paper

Cardiovascular disease (CVD) is the leading cause of death worldwide, and modifying diet is one of the main ways to reduce risk factors for CVD. Recent evidence suggests this effect may be related to changes in the gut microbiota. For example, eating walnuts, which are high in the omega 3 alpha-linolenic acid (ALA), improves gut microbiota and reduces CVD risk factors, but the active compound responsible for these benefits is unclear.

In this randomized crossover trial, 42 adults at risk for CVD, characterized by elevated BMI, blood pressure, and LDL-C, were provided a standard Western diet for three weeks followed by three six-week isocaloric study diets. The study diets were: a diet containing whole walnuts (57–99 grams per day; 2.7% ALA), a fatty acid matched diet without walnuts (2.6% ALA), and a diet with oleic acid instead of ALA (0.4% ALA). Fecal samples were collected and CVD risk markers (blood pressure and total cholesterol levels) were measured at the start of the study and after each of the three diets.

All three diets resulted in differentially enriched bacteria relative to the standard Western diet, suggesting replacing saturated fatty acids with unsaturated fatty acids in the presence or absence of walnuts affects the gut microbiome. The two ALA diets resulted in increased Roseburia population (a bacteria associated with reduced damage to the gut lining), and the walnut diet resulted in the largest increase in Gordonibacter population (a bacteria associated with reduced CVD risk). There was also a correlation between increased Lachnospiraceae population after the walnut diet and reduced blood pressure and cholesterol levels. Thus, it is possible that both the ALA and the bioactive compounds in walnuts modulate gut microbiome changes. Future studies on CVD outcomes, rather than risk factors alone, are needed to further this research.

Notes: While the analysis included all 42 participants, only 34 participants completed all diet periods, and two participants were on an antibiotic regimen during the course of the study, though removing these participants from the analysis did not affect the results. Furthermore, the conversion of ALA to EPA, which affects the gut microbiota, was not examined.