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Walnuts Improve Gut Microbiome and Overall Health


Diets plentiful in nuts, such as walnuts, have been shown to enhance heart health and cut colon cancer recurrence in half. A new study found the factor that underlies these benefits might involve the way nuts affect the microbiome, which is the community of trillions of bacteria in the gut.

Walnuts are rich in fiber. This dietary element nourishes gut microbes, thus boosting the performance of their functions, including breaking down food and promoting a feeling of satiety following a meal. Other sources of fiber are fruits, vegetables, nuts, whole grains and legumes. Eating a variety of these foods leads to a more diverse gut microbiome, an effect that improves general health.

Findings from the study showed eating walnuts resulted in an increase in beneficial gut bacteria and a decrease in microbial-derived secondary bile acids. The nuts also reduced LDL, or bad, cholesterol, a benefit that promotes better cardio, intestinal and metabolic health.

“We found that when you consume walnuts it increases microbes that produce butyrate, a beneficial metabolite for colonic health. So the interaction of walnuts with the microbiome is helping to produce some of those health effects,” said lead author Hannah Holscher, assistant professor of food science and human nutrition at the University of Illinois.

“It is about getting to the ‘black box’ that is all the microbes in our GI tract to see how they are interfacing with the food we eat and having downstream health effects. Some of those health effects are hypothesized to be related to the metabolites bacteria produce,” she added.

In the study published in the Journal of Nutrition, 18 adults followed diets that included either 42 grams or zero grams of walnuts for two three-week periods. Forty-two grams of walnuts is approximately one-third cup. Blood and fecal samples were taken at the beginning and end of each period to evaluate the effects of the food on fecal bacteria and bile salts, as well as on metabolic markers of health.

Walnut-Augmented Diet Increased Population of Beneficial Bacteria

Participants who consumed the walnut-augmented diet had greater numbers of the following bacteria: Clostridium, Faecalibacterium and Roseburia.

“The microbes that increased in relative abundance in this walnut study are from one of the Clostridium clusters of microbes, and there’s increased interest in those because they have the ability to make butyrate,” Holscher said. “Unfortunately in this study we didn’t measure butyrate, so we can’t say that just because these microbes increased that butyrate did increase. We still need to answer that question.

“There is a lot of interest in Faecalibacterium because it has also been shown in animals to reduce inflammation. Animals with higher amounts also have better insulin sensitivity. There is also growing interest in Faecalibacterium as a potential probiotic bacteria, and so we are trying to follow up on foods that help support Faecalibacterium.”

Walnut-Augmented Diet Reduced Secondary Bile Acids

Participants who ate the walnuts also experienced a reduction in secondary bile acids compared to the control group. “Secondary bile acids have been shown to be higher in individuals with higher rates of colorectal cancer,” Holscher explained. “Secondary bile acids can be damaging to cells within the GI tract, and microbes make those secondary bile acids. If we can reduce secondary bile acids in the gut, it may also help with human health.”

Undigested 20 Percent of Walnuts Feeds Microbiome

Earlier research on walnuts shows that the energy derived from them is only 80 percent of what was previously thought.

“When you do calculations to determine how much energy we predicted we would get from eating walnuts, it didn’t line up with the energy that was absorbed,” Holscher said. “You’re really only absorbing around 80 percent of the energy from walnuts that labels say. That means that the microbes get access to that extra 20 percent of calories and the fats and fiber left in them, and so what happens then? Does it produce a positive health outcome, or a negative health outcome? Our study provides initial findings that suggest that the interactions of microbes with the undigested walnut components are producing positive outcomes.”

The Connection Between Gut Bacteria, Diet and Health

A fascinating focus of research in recent years involves the gut microbiome, as it profoundly affects physiology far beyond the intestinal tract. Studies show the gut plays a primary role in the risk of an array of chronic illnesses, including cancer, cardiovascular disease, obesity, diabetes and inflammatory bowel disease. In addition to affecting physical health, the bacteria in the gut also affects mental health.

Along with discovering the importance of the microbiome on disease, researchers are finding that the health of the microbiome is largely impacted by diet. Consumption of the Western diet, which is high in animal fat and protein, reduces the total gut microbial population, as well as the numbers of beneficial strains like lactobacillus. Conversely, the Mediterranean diet, which is high in fiber and low in red meat, increases the total gut microbial population, along with the beneficial strains. It’s clear that one of the keys to wellness lies in following a fiber-rich diet, an eating plan plentiful in fruits, vegetables and whole grains.


Mary West is a natural health enthusiast, as she believes this area can profoundly enhance wellness. She is the creator of a natural healing website where she focuses on solutions to health problems that work without side effects. You can visit her site and learn more at Ms. West is also the author of Fight Cancer Through Powerful Natural Strategies.

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