Diets rich in walnuts have played a role in heart health and in reducing colorectal cancer as confirmed by several previous studies.
Epidemiological data suggest that diets rich in walnuts have beneficial health effects, including reduced mortality, particularly in the case of certain types of cancer and heart disease.
While there is accumulated pre-clinical evidences that walnuts have a beneficial effect on the gastrointestinal microbiota and intestinal and metabolic health, these relationships have not been studied in humans.
A study by the University of Illinois (United States) published on May 3, 2018 in The Journal of Nutrition, explains how walnuts impact the gut microbiota – which is made up of billions of microbes or bacteria in the digestive tract – which may be behind some of these health benefits.
Walnuts benefits have been confirmed by new results
Walnuts are foods of interest to scientists for their impact on the microbiota and health in general.
The dietary fiber they contain acts as a food source for the gut microbiota, helping bacteria do their job – by breaking down complex foods, providing us with nutrients, or helping us feel full.
Fruits, vegetables, whole grains, walnuts and legumes are important plant sources of dietary fiber. Eating a variety of these foods helps promote a diverse gut microbiota, which in turn helps support health.
The results of this latest study show that eating walnuts did not only affect the gut microbiota and microbial-derived secondary bile acids, but also reduced LDL cholesterol (“bad cholesterol”) levels in adults participating in the study. It also emphasizes the benefits of walnuts for cardiovascular, metabolic and gastrointestinal health.
The interaction of walnuts with the microbiota
Researchers have found that when you consume walnuts, it increases the microbes that produce butyrate, a metabolite that is good for colon health.
The interaction of walnuts with the microbiota helps to produce some of these health effects. The goal of the researchers is to get to the “black box”, which is all the microbes in our gastrointestinal tract, to see how they interact with the food we eat and the effects on downstream health. Some of these health effects are thought to be related to metabolites produced by bacteria.
For this controlled eating study, 18 healthy adult men and women consumed diets that included either 0 g of walnuts or 42 g for two periods of three weeks. Faecal and blood samples were collected at the start and end of each period to assess the study’s secondary outcomes, including the effects of eating nuts on fecal microbiota and bile acids and metabolic markers of health .
Faecalibacterium, Roseburia and Clostridium…
Consumption of walnuts has resulted in a higher relative abundance of three bacteria of interest: Faecalibacterium, Roseburia and Clostridium.
The microbes that have grown in relative abundance in this walnuts study come from one of the Clostridium microbe groups, and there is increased interest in them because they have the ability to make butyrate. Unfortunately, the researchers explain that in this study, they did not measure the level of butyrate, so they cannot say that it is only because these microbes have increased that the butyrate has increased.
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 sensitivity to insulin. There is also a growing interest in Faecalibacterium as potential probiotic bacteria.
Finally, the results also show, with the consumption of walnuts, a reduction in secondary bile acids compared to control. Secondary bile acids have been found to be higher in people with higher rates of colorectal cancer. Secondary bile acids can damage cells in the gastrointestinal tract, and microbes are secondary bile acids.
Previous researches that led to this microbial research has shown that the amount of energy (calories) derived from walnuts after we eat them is less than previously thought.
As a conclusion, the researchers point out that, “When you do the math to determine the amount of energy that we had planned by eating walnuts, it did not correspond to the energy absorbed. You only take in 80% of the energy from walnuts, which means microbes have access to those 20% extra calories, the fats and fiber they contain, and what happens then? Positive or negative health result? Our study provides initial results that suggest that microbe interactions with the undigested components of the walnut fruit produce positive results. “
Other research on the beneficial properties of walnuts is underway, with the goal of examining other microbial metabolites and how these influence health outcomes, rather than just characterizing changes in the microbiota.