In a rigorous clinical trial published in Microbiome, researchers looked at the gut microbes of participants who were fed three different types of prebiotic fiber supplements (inulin, dextrin, and galactooligosaccharides) across three, week-long periods, in different orders.
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 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 nutrient to begin with. Essentially, your gut will largely benefit from a fiber supplement if you're not getting enough to begin with, but how responsive you are can be predicted by your diet and the baseline concentrations of short-chain fatty acids 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 fiber, keep up the good work—although most people are not!