Walnuts Impact Gut Microbiome and Improve Health

Diets rich in nuts, such as walnuts, have been shown to play a role in heart health and in reducing colorectal cancer. According to a new study from the University of Illinois, the way walnuts impact the gut microbiome—the collection of trillions of microbes or bacteria in the gastrointestinal tract—may be behind some of those health benefits.

Walnuts are just one in a line foods that contain dietary fiber and have interested scientists for their impact on the microbiome and health. Dietary fiber acts as a food source for gut microbiota, helping the bacteria to do their jobs—breaking down complex foods, providing us nutrients, or helping us feel full, for example.

Fruits, vegetables, whole grains, nuts, 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 to support health.

Findings from the study, published in The Journal of Nutrition, show that consuming walnuts not only impacted the gut microbiota and microbial derived secondary bile acids, but also reduced LDL-cholesterol levels in the adults participating in the study; good news for cardio, metabolic, and gastrointestinal 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,” says Hannah Holscher, assistant professor of food science and human nutrition at U of I, and lead author of the study. “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 adds.

For the controlled-feeding study, 18 healthy male and female adults consumed diets that either included 0 grams of walnuts or 42 grams—about a third cup or a palm-full of walnuts—for two, three-week periods. Fecal and blood samples were collected at the beginning and end of each period to assess secondary outcomes of the study, including effects of walnut consumption on fecal microbiota and bile acids and metabolic markers of health.

Walnut consumption resulted in higher relative abundance of three bacteria of interest: Faecalibacterium, Roseburia, and Clostridium.

“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 says. “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.”

The findings also show, with walnut consumption, a reduction in secondary bile acids compared to the control. “Secondary bile acids have been shown to be higher in individuals with higher rates of colorectal cancer,” Holscher explains. “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.”

Previous research that prompted this microbial research showed that the amount of energy (calories) derived from walnuts after we eat them is less than 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 says. “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.

“We need more research to look at additional microbial metabolites and how those are influencing health outcomes, instead of just characterizing the changes in the microbiome,” Holscher says.

Source: University of Illinois College of Agricultural, Consumer and Environmental Sciences


Today’s Comic

Study Reveals Mechanism of Walnuts’ Ability to Decrease Hunger

Packed with nutrients linked to better health, walnuts are also thought to discourage overeating by promoting feelings of fullness. Now, in a new brain imaging study, researchers at Beth Israel Deaconess Medical Center (BIDMC) have demonstrated that consuming walnuts activates an area in the brain associated with regulating hunger and cravings. The findings, published online in the journal Diabetes, Obesity and Metabolism, reveal for the first time the neurocognitive impact these nuts have on the brain.

“We don’t often think about how what we eat impacts the activity in our brain,” said the study’s first author Olivia M Farr, PhD, an instructor in medicine in the Division of Endocrinology, Diabetes and Metabolism at BIDMC. “We know people report feeling fuller after eating walnuts, but it was pretty surprising to see evidence of activity changing in the brain related to food cues, and by extension what people were eating and how hungry they feel.”

To determine exactly how walnuts quell cravings, Farr and colleagues, in a study led by Christos Mantzoros, MD, DSc, PhD hc mult, director of the Human Nutrition Unit at Beth Israel Deaconess Medical Center and professor of medicine at Harvard Medical School, used functional magnetic resonance imaging (fMRI) to observe how consuming walnuts changes activity in the brain.

The scientists recruited 10 volunteers with obesity to live in BIDMC’s Clinical Research Center (CRC) for two five-day sessions. The controlled environment of the CRC allowed the researchers to keep tabs on the volunteers’ exact nutritional intake, rather than depend on volunteers’ often unreliable food records – a drawback to many observational nutrition studies.

During one five-day session, volunteers consumed daily smoothies containing 48 grams of walnuts – the serving recommended by the American Diabetes Association (ADA) dietary guidelines. During their other stay in the CRC, they received a walnut-free but nutritionally comparable placebo smoothie, flavored to taste exactly the same as the walnut-containing smoothie. The order of the two sessions was random, meaning some participants would consume the walnuts first and others would consume the placebo first. Neither the volunteers nor the researchers knew during which session they consumed the nutty smoothie.

As in previous observational studies, participants reported feeling less hungry during the week they consumed walnut-containing smoothies than during the week they were given the placebo smoothies. fMRI tests administered on the fifth day of the experiment gave Farr, Mantzoros and the team a clear picture as to why.

While in the machine, study participants were shown images of desirable foods like hamburgers and desserts, neutral objects like flowers and rocks, and less desirable foods like vegetables.

When participants were shown pictures of highly desirable foods, fMRI imaging revealed increased activity in a part of the brain called the right insula after participants had consumed the five-day walnut-rich diet compared to when they had not.

“This is a powerful measure,” said Mantzoros. “We know there’s no ambiguity in terms of study results. When participants eat walnuts, this part of their brain lights up, and we know that’s connected with what they are telling us about feeling less hungry or more full.”

This area of the insula is likely involved in cognitive control and salience, meaning that participants were paying more attention to food choices and selecting the less desirable or healthier options over the highly desirable or less healthy options. Farr and Mantzoros next plan to test different amounts, or dosages, of walnuts to see whether more nuts will lead to more brain activation or if the effect plateaus after a certain amount. This experiment will also allow researchers to test other compounds for their effect on this system.

Similar studies could reveal how other foods and compounds, such as naturally-occurring hormones, impact the appetite-control centers in the brain. Future research could eventually lead to new treatments for obesity.

“From a strategic point of view, we now have a good tool to look into people’s brains – and we have a biological read out.” said Mantzoros. “We plan to use it to understand why people respond differently to food in the environment and, ultimately, to develop new medications to make it easier for people to keep their weight down.”

Source: Beth Israel Deaconess Medical Center

The Key to A Better Mood for Young Men is A Nut

College can be a stressful time for young adults as they figure out how to manage intense daily routines that include work, study and play. Eat well, exercise and get plenty of sleep is a familiar mantra to alleviate this stress, but now with the results of his latest study, UNM Nutrition Professor Peter Pribis is able to tell college students that walnuts could be a key to a happier state-of-mind.

In this first intervention study in humans, Pribis measured the effect of walnut consumption on mood.

“In the past, studies on walnuts have shown beneficial effects on many health outcomes like heart disease, diabetes and obesity,” said Pribis. “Our study was different because we focused on cognition, and in this controlled randomized trial (CRT) we measured mood outcomes in males and females.”

The participants of the study were 64 students between the ages of 18-25. They represented most ethnic groups: Caucasian, African American, Hispanic and Asian.

The participants were asked to eat three slices of banana bread every day for sixteen weeks–eight weeks of banana bread with walnuts and eight weeks of banana bread without walnuts. The nuts were finely ground into the dough so the two banana breads were similar in taste and appearance. While eating banana bread with walnuts the participants consumed half a cup of walnuts daily.

The mood of the students was measured at the end of each eight-week period.

“We used a validated questionnaire called Profiles of Mood States (POMS),” says Pribis. “It is one of the most widely used and accepted mood scales in studies on cognition. The test has six mood domains: tension, depression, anger, fatigue, vigor, confusion and also provides a Total Mood Disturbance score (TMD). The lower the TMD score the better the mood.”

In this double-blind, randomized, placebo controlled, cross-over feeding trial with walnuts for eight weeks, Pribis observed a significant improvement in mood in young, healthy males.

“There was a meaningful, 28 percent improvement of mood in young men,” said Pribis. “However we did not observe any improvement of mood in females. Why this is we do not know.”

There are several nutrients in walnuts that could be responsible for the improved mood like alpha-Linolenic acid, vitamin E, folate, polyphenols or melatonin. However, this was a whole food study, so in the end it was the synergy and interaction of all the nutrients in the walnuts combined.

For Pribis, the lesson learned from this food study is clear, “Eat more walnuts. This is an easy intervention. They’re not only good for your mood, but overall health as well. The recommended amount is one handful per day.”

With this knowledge in hand–and hopefully walnuts in the other–young men can happily tackle life’s daily stress.

Source: EurekAlert!