In the news: Flavonoid-Rich Foods and Walnuts For Intestinal Health

The Microbiota of the Intestinal Tract

We each have a collection of microbes or micro-organisms that call our bodies home. Our microbiome is made up of unique communities of these microbes called microbiota that inhabit the skin, mouth, eyes, genitals, and of course, the intestines. The intestinal microbiota is composed of a multitude of bacterial species (along with some fungi and viruses), and is referred to as “gut flora”.

Research has already revealed that gut microbes can affect the health of the gut locally, and that they can influence our immune response. Potentially, they also influence the brain and behavior. While scientists continue to unravel what constitutes a healthy balance of these inhabitants, there is evidence that our diet can make a difference in promoting a broad range of healthful bacteria in the gut.

A plant-based diet focused on fruits, vegetables, nuts, beans and whole grains seems to be key. Not only is the undigestible fiber they contain a “food” for beneficial bacteria, but other components in plant-based foods may also play a role in supporting healthful bacteria as new research suggests.

Polyphenols in Tart Cherries, Blueberries

The polyphenols (flavonoids) seem to mutually benefit bacteria and ultimately us, their hosts. Gut bacteria metabolize polyphenols into forms that we better absorb, and polyphenols may influence the make-up of gut flora by inhibiting bad bacteria and stimulating beneficial types.

University of Arkansas researchers, for example, have recently provided evidence that tart cherries and the flavonoids they contain such as anthocyanins, may positively influence the gut microbiota (1).

In lab studies that imitate the condition of human digestion along the GI tract, the researchers found that gut microbes were able to break down anthocyanins and other flavonoids, and increase a gut-friendly type of bacteria. When healthy adults drank 8 oz. of tart cherry juice daily in the second part of the study, they
found that the microbiota was favorably altered.

Interestingly, the type of friendly bacteria that was altered in participants who typically ate a more plant-based diet (Bacteroides and Bifidobacterium) was different than in those consuming a more Western diet (Collinsella).

In another, longer study (2), US and Italian researchers teamed up to test the effects of drinking a powdered blueberry drink on gut flora. Healthy men were randomly assigned to the blueberry beverage or placebo for 6 weeks, and then switched over to receive the other beverage for an additional 6 weeks.

While participants varied in their response, stool sample analysis showed that the blueberry drink increased a Bifidobacterial strain (B. longum subsp infantis) that has been reported to favorably influence the immune system and to have “demonstrated health-promoting activity” according to the authors.

Walnuts Beneficially Change Gut Flora

A study from the University of Illinois suggests that eating walnuts may be another way to produce beneficial changes in the gut microbiota (3). Walnuts contain fiber, “good” fats, and other plant compounds.

In the study, healthy participants consumed 48g of walnuts (about ½ cup) each day for 3 weeks, and then no walnuts for another 3 weeks.

Eating the nuts increased certain bacteria that produce a short chain fat (butyrate) that is anti-inflammatory and helps protect the walls of the intestine. The walnuts also reduced pro-inflammatory bacterial metabolites and, as a bonus, lowered LDL cholesterol.

References

1. Mayta-Apaza A, et al. Impact of tart cherries polyphenols on the human gut microbiota and phenolic metabolites in vitro and in vivo. J Nutr Biochem 59:160-72, 2018.
2. Guglielmetti S, et al. Differential modulation of human intestinal Bifidobacterium populations after consumption of a wild blueberry (Vaccinium angustifolium) drink. J Agric Food Chem. 34:8134-40, 2012.
3. Holscher HD, et al. Walnut consumption alters the gastrointestinal microbiota, microbially derived secondary bile acids, and health markers in healthy adults: a randomized controlled trial. J Nutr. Epub May, 2018.