According to a new study, the underlying mechanism may be explained by how nuts nourish and influence the microbiota.
The high fiber content of nuts
Nuts contain a significant portion of dietary fiber, like fruits, vegetables and legumes. Dietary fiber is a good food source for the gut microbiota. They help bacteria break down complex foods and supply them with nutrients. They therefore promote diversity in the microbiota, which has a positive effect on health.
42g of nuts per day
The University of Illinois demonstrated the impact of nut consumption on gut microbiota and secondary bile acids in adults. The researchers performed a randomized study on healthy men and women. Participants followed an isocaloric diet with 0 or 42 g of nuts per day. The researchers collected stool and blood samples before and after the isocaloric diet to analyze microbiota, bile acids and health markers like LDL cholesterol.
Walnuts help gut-protecting bacteria grow
Participants who ate nuts had higher levels of fecal bacteria, Roseburia and Clostridium. These three bacteria have the ability to produce butyrate, an essential element for the intestine. The study also found a reduction in secondary bile acids during the period when participants consumed nuts, compared to the control period. Previous studies had found that these acids were present in large amounts in people with colon cancer. Secondary bile acids can indeed damage cells in the gastrointestinal system. A reduction in secondary bile acids in the gut can therefore be beneficial to health. After nut consumption, the concentration of cholesterol and LDL cholesterol appeared to be lower than during the control.
However, the researchers found no significant association between cholesterol and gut microbiota. In short, nut consumption alters the composition of the microbiota in the gastrointestinal system, which may explain the positive effects of nuts on health.
Holscher HD: Walnut Consumption Alters the Gastrointestinal Microbiota, Microbially Derived Secondary Bile Acids, and Health Markers in Healthy Adults: A Randomized Controlled Trial. J Nutr. doi: 10.1093/jn/nxy004.