Dietary fibers boost beneficial bacteria levels, but what about diversity?
Pooling data from a total of 2,099 study participants also showed that fiber was associated with increases in levels of the short chain fatty acid (SCFA) butyrate, compared with placebo/low-fiber, according to findings published in The American Journal of Clinical Nutrition.
“Accepted prebiotic fibers had an effect on the abundances of both Bifidobacterium and Lactobacillus spp. whereas candidate prebiotic fibers had an effect on Bifidobacterium spp. abundance but not Lactobacillus spp,” wrote scientists from Bond University (Australia), King’s College, London (UK), The University of Queensland, and Princess Alexandra Hospital (both Australia).
“General fibers appear to have a limited effect on gut microbiota composition,” they added. “Although the diversity of the gut microbiota, abundances of other commonly measured bacterial groups, and concentrations of other fecal SCFAs were not significantly different compared with controls after dietary fiber intervention, it is worth noting that a short-term increase in fiber intake does not appear to be rate-limiting to these outcomes.
“These results further support the favorable effects of dietary fiber and contribute to our understanding of its effect on the gut microbiota.”
“An important paper”
The paper, which is said to be the first systematic review and meta-analysis to assess the effect of dietary fiber intervention on gut microbiota composition, was welcomed by Glenn Gibson, Professor of Food Microbiology and head of Food Microbial Sciences at the University of Reading in the UK, and a pioneer and world-renowned expert in prebiotics. Commenting independently, Prof Gibson told NutraIngredients-USA: “While there are not many surprises in that saccharolytic* genera mainly respond, it is good to see this consistency coming through in various studies.
“This will be a very useful article that pulls lots of human data together. It is also well written and conducted. I think this is an important paper.”
(*Saccharolytic refers to bacterial strains that break down carbohydrates for energy)
Highlights
The Australia and UK-based scientists pooled data from randomized clinical trials of fiber on the gut microbiota in healthy adults. To be included, the studies had to use culture and/or molecular microbiological techniques.
Data from 64 studies involving over 2,000 participants revealed that consumption of “accepted prebiotics” fructans and galacto-oligosaccharides were associated with increases in Bifidobacterium spp. and Lactobacillus spp., compared with controls.
On the other hand, “candidate prebiotic” fibers such as polydextrose and resistant starch were only associated with increases in Bifidobacterium spp., said the researchers.
No difference were observed between “general fiber” and control interventions.
In addition, total dietary fiber was not associated with changes in other potentially beneficial species such as Faecalibacterium prausnitzii, Akkermansia muciniphila, Eubacterium hallii, Eubacterium rectale, and Ruminococcus bromii.
The finding that dietary fiber was not associated with changes in diversity of the microbiota is at odds with previous observational studies, which found a correlation between fiber intakes and diversity. This may be linked to the relatively short duration of the RCTs included in this meta-analysis, said the researchers.
“Interestingly, a positive correlation has also been reported between dietary diversity and microbiota diversity. Taken together, long-term dietary diversity as opposed to changes in isolated nutrients or foods over a short period of time may be a stronger driver of microbial diversity.”
Research gaps
Future randomized clinical trials should measure the composition of the microbiota of the participants at the start of the study, said the authors.
“Scope may also need to be broadened to evaluate more taxa than those considered here, including the eukaryote (e.g., fungi) members of the gut microbiota. In addition, longer-duration studies are needed to better assess the chronic effect of fiber on microbiota diversity,” they concluded.
Source: The American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.1093/ajcn/nqy041
“Dietary fiber intervention on gut microbiota composition in healthy adults: a systematic review and meta-analysis”
Authors: D. So et al.
