"Our results suggest that the unique polyphenol mixture in tart cherries may help positively shape the gut microbiome, which could potentially have far-reaching health implications," said principal investigator Franck Carbonero, PhD, assistant professor in the Department of Food Science at the University of Arkansas.
These results, available online, are due for publication in the September issue of The Journal of Nutritional Biochemistry.
The study was conducted by a group of researchers from the University of Arkansas, Ghent University in Belgium, and Szent István University in Hungary. The Cherry Marketing Institute, a trade group funded by US tart cherry growers, provided funding to the researchers as well as tart cherries used in the study.
Previous studies have posited that polyphenols have a prebiotic effect—which means they ‘feed’ gut microbiota selectively and help the beneficial gut microbes thrive to give health benefits to the host. But, both in the industry and in academia, thoughts are still mixed about whether polyphenols are prebiotics.
Nevertheless, “Montmorency tart cherries were a logical food to study due to their unique composition of polyphenols, including chlorogenic acids," Dr. Carbonero added.
Promising results… on a petri dish
There were two components in the study, an in vitro one (in a petri dish) and in vivo (a human clinical trial).
For the in vitro, researchers used concentrate juices of Montmorency tart cherries grown in Michigan. They also used commercially available concentrates—a Balaton and Montmorency tart cherry blend concentrate and sweet (Black Cherries) concentrate, as well as apricot cultivars from Hungary as a control. Researchers ensure that all concentrates were free of dietary fibers.
They then applied incubations to mimic gastric, intestine, and colon conditions, inoculated with enrichment cultures from a human stool sample.
All sixty-eight in vitro samples went through DNA extraction and sequencing to see how the fruits impacted the gut microbiota.
“As expected, fermentation with polyphenols and to a greater extent with fruit matrices significantly shifted the microbiota,” the authors reported.
“All tart and sweet cherries products led to similar gut microbiota modulation driven by very significant increase of Bacteroides relative abundance at all-time points, probably reflecting fermentation of sugars and carbohydrates which are the main energy sources for Bacteroides.”
Human trial results show how dietary pattern matters
For the human dietary intervention, nine healthy participants completed the study. To participate, participants must not have consumed any type of antibiotics for 12 weeks prior and during the intervention.
They completed a Food Frequency Questionnaire at intake to give the researchers a glimpse of their dietary habits. For five days, participants drank 8 oz. of Montmorency tart cherry juice per day.
They also received a stool collection kit to provide a stool sample before and after the dietary intervention.
Authors reported “strikingly different responses” due to the participants’ initial microbiome compositions.
“Individuals consuming a more Western diet [low in fruits, vegetables, and fiber] may have lower ability to metabolize polyphenols, thereby reducing bioavailability and any potential health benefits,” they reported.
But in sum, the researchers noted that the microbiome was positively altered after the intervention period, measured by the increase of Bacteroides and Bifidobacterium.
“While these findings are intriguing, the dietary intervention was based on a limited number of human volunteers, and therefore, studies with more subjects and longer dietary intervention will be needed to validate our conclusions,” they added.
Source: The Journal of Nutritional Biochemistry
Published online ahead of print, https://doi.org/10.1016/j.jnutbio.2018.04.001
“Impact of tart cherries polyphenols on the human gut microbiota and phenolic metabolites in vitro and in vivo”
Authors: Alba C. Mayta-Apaza, et al.