In a rigorous clinical trial published in Microbiome, researchers from Duke University assessed the gut microbes and key postbiotic metabolites (especially the short-chain fatty acid butyrate) of healthy adults who consumed three different types of prebiotic fiber supplements (9 grams of inulin, 9 grams of dextrin, or 3.6 grams of galactooligosaccharides) across three, week-long periods.
In this rigorous study design (aka randomized, three-way, cross-over), each participant served as their own “control” group. They incorporated each fiber supplement into their diet, split across two daily doses, for five days. Then they “washed out” (i.e., no fiber supplement) for a week before switching to their next randomly assigned fiber intervention. In that way, every person in the study experienced all three fiber types for a true side-by-side comparison.
The results revealed that in people who entered into the study consuming the least amount of fiber, their gut health displayed the most noticeable benefit from supplementation of this complex carbohydrate. Conversely, those who already consumed ample fiber experienced less significant changes within the gut.
These findings were novel because in those who were initially consuming the least amount of fiber, it didn’t so much matter what kind of fiber was in their supplement—it more so mattered that they were getting more of this functional nutrient.
Essentially, your gut will largely benefit from a fiber supplement if you’re not getting enough to begin with, but how responsive you are is personalized and can be predicted by your diet and the baseline concentrations of short-chain fatty acids (SCFA) in your stool. These are produced by beneficial bacteria in the gut and have a supportive and protective role for gastrointestinal health and function.
Bottom line? How much fiber you’re currently consuming and the overall quality of your diet or baseline of your health is going to determine how effective taking a fiber supplement will be. That being said, if you’re already consuming a diet filled with recommended levels of fiber daily, keep up the good work (because you’re in the fiber minority!).