Dietary fiber digestion may depend on gut bacteria strains
Cornell researchers say resistant starch benefits may hinge on whether a person carries the right gut bacteria strains.
By Priya Raghavan · Science Reporter
3 min read
A Cornell University study suggests dietary fiber digestion may depend on more than eating the right foods: people may also need the right strains of gut bacteria to process some starches. The finding could help explain why earlier studies of resistant starch have produced uneven results, with some participants benefiting and others showing little change.
The study, published in Microbiology Spectrum, focused on how gut microbes respond to resistant starches, a type of dietary fiber. Cornell said dietary fiber is found in foods including legumes, nuts, seeds, vegetables, fruits and whole grains, and is linked to constipation prevention, support for beneficial gut microbes and slower digestion that helps regulate blood sugar.
Does dietary fiber help digestion?
According to Angela Poole, an assistant professor in Cornell’s Division of Nutritional Sciences and senior author of the paper, one reason fiber responses may differ is that people need the right gut bacteria to process resistant starch. The study found that even within one bacterial species, different strains responded differently when resistant starches were eaten.
Resistant starch is starch that the body’s own enzymes do not readily digest, so gut bacteria and their enzymes are needed to break it down. Cornell said the researchers examined resistant starch types 2 and 4, along with a control starch that could be digested without bacterial enzymes.
The team collected fecal bacteria from more than 50 people to study their gut bacterial communities. Participants ate three different crackers during separate periods: one containing resistant starch 2, one containing resistant starch 4 and one containing the control starch.
Poole and colleagues studied strains of Bifidobacterium adolescentis, a gut microbe species. Cornell said the researchers found that the right strain, not merely the right species, was needed to process the complex carbohydrates in resistant starch.
How did researchers find strain-level differences?
Cornell said many earlier studies used 16S sequencing, a method that can identify bacteria and show which bacterial groups are present. In this study, the team used shotgun metagenomics, which can identify bacteria at the strain level and detect genes that may point to what those bacteria do.
The researchers also used a sensitive bioinformatics tool called Cayman. Cornell said Cayman helped detect additional genes in bacteria involved in degrading resistant starch.
The analysis found previously uncharacterized bacteria whose genes increased in the presence of resistant starch, suggesting they may help process those carbohydrates. Cornell said the researchers plan to study those bacteria further.
What could this mean for precision nutrition?
Poole said the results point toward a need for higher-resolution tools in precision nutrition, especially tools that can show not only which bacteria are present but what genes and enzymes they carry. That could matter if clinicians try to match dietary advice to a patient’s microbiome.
Poole gave diabetes as an example, saying that seeing Bifidobacterium adolescentis in a patient may not be enough to predict whether a resistant-starch diet would help. According to Cornell, the strain a person carries could determine whether that microbe has the enzymes needed to break down a particular fiber.
This story draws on original reporting from Medical Xpress.