Variable responses of human microbiomes to dietary supplementation with resistant starch
Design
Twenty healthy adults (10 female and 10 male; age 19–20 years) continued their habitual diets while completing a baseline period, a three-day dose ramp (12, 24, then 48 g/day), and seven additional days at 48 g/day unmodified potato-starch powder. The product was estimated by the authors to contain approximately 50% resistant starch, so the full powder dose supplied about 24 g/day resistant starch. Four fecal samples per participant were collected before supplementation and four during the maximum dose, then analyzed by V4 16S rRNA sequencing and high-performance liquid chromatography for organic acids. This was a small, uncontrolled dietary intervention rather than a randomized efficacy trial; gastrointestinal symptoms were not reported as outcomes.
Findings
Across all participants, median fecal butyrate rose from 8 to 12 mmol/kg (+50%, repeated-measures ANOVA P=0.03), and acetate rose from 27 to 34 mmol/kg (+26%, P=0.02); propionate did not change significantly. Exploratory k-means clustering of each participant’s before/during butyrate values identified 11 enhanced responders (median approximately 9 to 15 mmol/kg; paired t-test P=0.0003), three with high concentrations throughout, and six who remained low (P=0.14). The cohort summary therefore conceals a substantial low-response subgroup.
An OTU classified as Bifidobacterium adolescentis or one classified as Ruminococcus bromii generally expanded in enhanced/high responders; their combined relative abundance increased from roughly 2% to 9%, while remaining near 1.5% in low responders. Eubacterium rectale was more abundant in the high group, but that comparison rests on only three participants. Faecalibacterium prausnitzii did not significantly increase.
Interpretation
The study supports interindividual ecological response to the same RS2 exposure and the importance of primary starch degraders plus cross-feeding. It does not establish that these taxa predict response before treatment, diagnose symptoms, or cause health improvement. Fecal butyrate is not total production because most colonic SCFAs are absorbed, and the exploratory response categories risk overinterpretation. Participants were young, the intervention was brief and uncontrolled, and Procter & Gamble helped fund the work (the authors declared no competing interests). gap/needs-replication