The team identifies polyphenols’ role in altering the gut microbiome and encouraging the production of a metabolite with antioxidant, anti-inflammatory and neuroprotective properties.
The metabolite, indole 3-propionic acid (IPA), is derived from the degradation of tryptophan due to intestinal bacteria and is also linked to improving intestinal wall health.
“If we consider the beneficial effects of IPA on the gut microbiota and health in general, it is important to find reliable strategies to promote the production of this metabolite,” says Tomás Meroño, study team member and Lecturer/Professor in the Nutrition, Food Science and Gastronomy department at the University of Barcelona (UB).
Writing in the journal Molecular Nutrition & Food Research, the team devised a randomised, controlled, crossover trial involving 51 adults over 60 years during an 8-week polyphenol-rich (PR) diet versus control diet.
The diet consisted of foods rich in polyphenols (green tea, bitter chocolate, fruits including apples, pomegranate and blueberries).
Seven gut microbiota (GM)-tryptophan metabolites were measured in serum, and analysis of GM was performed on faecal samples.
The results revealed a diet rich in polyphenols generated a significant increase in the blood IPA levels, together with a decrease in inflammation levels and changes in the bacteria of the microbiota, from the order of Bacteroidales.
Unexpectedly, the researchers did not observe the same effects in the volunteers with kidney diseases, which could be explained due to the altered composition of their gut microbiota.
These people showed lower amounts of IPA at the beginning of the trial compared to the volunteers with normal kidney function.
“These results could be clinically relevant, since the low IPA levels have been associated with a rapid decline of kidney function and a chronic kidney disease”, points out Professor Cristina Andrés-Lacueva, study team leader, who is based at the Faculty of Pharmacy and Food Sciences at the UB.
Other findings pointed to a higher abundance of Clostridiales in participants with normal RF. During the trial, variations of IPA are associated with changes in C-reactive protein and GM, particularly with the Clostridiales and Enterobacteriales orders.
Beneficial effects on intestine
IPA is produced from the oxidative degradation of dietary tryptophan by intestinal microorganisms, among which the only strains recognised so far belong to the bacterial species Clostridium sporogenes, Peptostreptococcus anaerobius, and Clostridium cadaveris.
Circulating IPA levels have been positively correlated to microbiota α-diversity and to butyrate-producing gut bacteria such as Faecalibacterium prausnitzii, a species that is widely investigated for its beneficial effects on intestinal and systemic health.
Moreover, an inverse correlation between circulating levels of IPA and arterial stiffness and components of metabolic syndrome, i.e., increased fasting glucose, insulin resistance, and visceral fat, has been reported, although the mechanism(s) of action involved are still unclear.
The team suggests that a polyphenol-rich diet that increases levels of a postbiotic such as IPA in the elderly could be beneficial in delaying or preventing chronic diseases that harm quality of life.
“A PR diet caused an increase in the serum concentration of the GM-Trp metabolite IPA, and this effect was stronger in participants with preserved renal function and inversely correlated with serum CRP levels,” the team concludes.
“Changes in IPA levels were correlated with PR-diet-induced changes in the GM, positively with members of the Clostridiales order and negatively with Streptococcus spp. and members of the Entereobacteriaceae family.
“Further studies will be required to confirm the influence of polyphenols on GM composition and IPA levels in older adults affected by chronic conditions, such as chronic kidney disease (CKD).”
Source: Molecular Nutrition & Food Research
Published online: doi.org/10.1002/mnfr.202100349
“A polyphenol-rich diet increases the gut microbiota metabolite indole 3-propionic acid in older adults with preserved kidney function.”
Authors: Gregorio Peron et al.