Starch-degrading gut microbes Ruminococcus bromii and Bifidobacterium adolescentis differ in their ability to degrade resistant starch type 3.
Level 5 - mechanism / opinion, no new human data
In vitro bench microbiological study (CEBM Level 5).
PubMed 40312028 · doi:10.1163/18762891-bja00077
What was done
Researchers evaluated the capacity of two known starch-degrading gut bacterial strains (Ruminococcus bromii ATCC27255 and Bifidobacterium adolescentis L2-32) to break down intrinsic resistant starch type 3 (RS-3) with distinct crystal types and chain lengths: A-type (degree of polymerisation 16 or 21) and B-type (degree of polymerisation 32 or 76). Degradation was compared against granular maize and potato starch. Outcomes included time-course quantification of remaining glucose, malto-oligosaccharides, and non-degraded insoluble RS-3, along with structural visualisation via scanning electron microscopy.
What was found
The abstract does not report exact numerical metrics. R. bromii degraded all tested RS-3 substrates irrespective of crystal type or chain length, primarily producing maltose and glucose (which it did not further metabolise). In contrast, B. adolescentis failed to degrade B-type RS-3 and only minimally fermented A-type RS-3 to acetate, despite readily fermenting granular maize and potato starch into acetate and lactate.
Why it matters
This study demonstrates that the breakdown of highly retrograded resistant starch (RS-3) in the colon relies on specialised enzymatic machinery, showing that key starch degraders like B. adolescentis cannot process B-type crystalline structures that R. bromii can readily hydrolyse.
Limits
This was an in vitro monoculture study using only two isolated bacterial strains, which does not capture cross-feeding dynamics, competitive interactions, or the broader community effects of a complete human gut microbiome. The abstract provides no quantitative yields, kinetics, or statistical variance data.
Cited by
- supports Cooking a starchy food like a potato or rice, letting it cool, and then eating it increases resistant starch, which benefits the gut microbiome and improves sleep.