This 2021 paper covered a 2016 human clinical trial, and several in vitro and rodent follow-up studies:
“Oat has been widely accepted as a key food for human health. It is becoming increasingly evident that individual differences in metabolism determine how different individuals benefit from diet. Both host genetics and gut microbiota play important roles on metabolism and function of dietary compounds.
- Avenanthramides (AVAs), the signature bioactive polyphenols of whole-grain (WG) oat, were not metabolized into their dihydro forms, dihydro-AVAs (DH-AVAs), by both human and mouse S9 fractions.
- DH-AVAs were detected in colon and distal regions, but not in proximal and middle regions of the perfused mouse intestine, and were in specific pathogen–free (SPF) mice but not in germ-free (GF) mice.
- A kinetic study of humans fed oat bran showed that DH-AVAs reached their maximal concentrations at much later time points than their corresponding AVAs (10.0–15.0 hours vs. 4.0–4.5 hours, respectively).
- We observed interindividual variations in metabolism of AVAs to DH-AVAs in humans.
- Faecalibacterium prausnitzii was identified as the individual bacterium to metabolize AVAs to DH-AVAs by 16S rRNA sequencing analysis.
- Moreover, as opposed to GF mice, F. prausnitzii–monocolonized mice were able to metabolize AVAs to DH-AVAs.
These findings demonstrate that intestinal F. prausnitzii is indispensable for proper metabolism of AVAs in both humans and mice. We propose that abundance of F. prausnitzii can be used to subcategorize individuals into AVA metabolizers and nonmetabolizers after WG oat intake.
Our findings pave the way to use AVAs and DH-AVAs as exposure biomarkers to reflect WG oat intake, which could more accurately record WG oat intake. Whether production of DH-AVAs is part of the beneficial effect of oats on human health will require further investigation.”
https://academic.oup.com/jn/article/151/6/1426/6165027 “Avenanthramide Metabotype from Whole-Grain Oat Intake is Influenced by Faecalibacterium prausnitzii in Healthy Adults”
This study advanced an understanding of inter-individual variability, rather than usual practices that try to sweep individual differences under a statistical rug. Study designs such as four mentioned in Part 2 of Switch on your Nrf2 signaling pathway could have benefited from a similar approach to their research areas.
Not sure why it took over five years to get this paper published after its clinical trial’s January 21, 2016 completion. Meanwhile, science marched on to study effects of specific F. prausnitzii strains, providing results such as three human studies curated in Gut microbiota strains:
- The third 2018 study found:
“Only a small number of bacteria with genetic capacity for producing SCFAs were able to take advantage of this new resource and become dominant positive responders. The response, however, was strain specific: only one of the six strains of Faecalibacterium prausnitzii was promoted.”
- The second 2021 study investigated 135 known strains of F. prausnitzii; and
- The first 2021 study found beneficial F. prausnitzii strains not yet covered in genomic databases.
Resistant starch therapy recommended de-emphasizing relative gut microbiota abundance measurements, because:
“Relative abundances of smaller keystone communities (e.g. primary degraders) may increase, but appear to decrease simply because cross-feeders [like F. prausnitzii] increase in relative abundance to a greater extent. These limitations illustrate the necessity of sufficiently powering resistant starch interventions where microbiome composition is the primary endpoint, collecting critical baseline data and employing appropriate statistical techniques.”
Four humpback whales successively diving for lunch