This 2021 rodent study investigated:

“We studied long-term dynamics of gut microbiome and short-chain fatty acids (SCFAs) in isogenic mice with distinct microbiota baselines fed with fermentable fiber inulin compared to non-fermentable fiber cellulose.

• We found that inulin produced generally rapid response followed by gradual stabilization to new equilibria, and those dynamics were baseline-dependent.
• Levels of SCFAs such as propionate were associated with abundance of inulin responders, yet inter-individual variation of gut microbiome impedes prediction of SCFAs by machine learning models.
• Our methods and major findings are generalizable to dietary resistant starch.

We divided the entire gut microbiota into three eco-groups: 5 primary degraders of inulin; 32 generic responders to inulin intervention; and non-responders. Primary degraders and their competitions are key drivers of baseline-dependent ecological dynamics of microbiota response to dietary fibers.

SCFA concentrations cannot be maintained at its peak, and drop by 35%-40% even under continuous inulin intake until four weeks. 90%-95% SCFAs produced in colonic lumen are absorbed by gut mucosa. The declining phase of SCFAs in our study may be explained by reduced production rate, increased absorption rate, or both.

Our study confirms findings in the literature and advances understanding of effects of dietary fibers on the gut microbiome at the system level:

1. The small number of fiber degraders (five for inulin and two for resistant starch) suggested that fiber-induced bacterial shifts are very selective and occur to a restricted number of taxa.
2. Absolute abundance of many fiber-degrading bacteria, such as taxa related to genus Bifidobacterium, failed to expand in both fibers. This indicates that fiber-induced bacterial enrichment cannot be simply predicted from in vitro growth, and suggests that dietary response of a gut bacterial taxa depends on the ecological context.
3. Personalized fiber-induced response of gut microbiota were largely determined by baseline abundance of fiber degraders and ecological interactions among these degraders.”

https://www.biorxiv.org/content/10.1101/2021.08.20.457175v1.full “Ecological dynamics of the gut microbiome in response to dietary fiber”