Conserved and variable responses of the gut microbiome to resistant starch type 2.

Resistant starch type 2 (RS2), a dietary fiber comprised solely of glucose, has been extensively studied in clinical trials and animal models for its capacity to improve metabolic and systemic health. Because the health modulatory effects of RS2 and other dietary fibers are thought to occur through modification of the gut microbiome, those studies frequently include assessments of RS2-mediated changes to intestinal microbial composition and function. In this review, we identify the conserved responses of the gut microbiome among 13 human and 35 animal RS2 intervention studies. Consistent outcomes of RS2 interventions include reductions in bacterial α-diversity; increased production of lumenal short-chain fatty acids; and enrichment of Ruminococcus bromii, Bifidobacterium adolescentis, and other gut taxa. Different taxa are usually responsive in animal models, and many RS2-mediated changes to the gut microbiome vary within and between studies. The root causes for this variation are examined with regard to methodological and analytical differences, host genetics and age, species differences (eg, human, animal), health status, intervention dose and duration, and baseline microbial composition. The significant variation found for this single dietary compound highlights the challenges in targeting the gut microbiome to improve health with dietary interventions. This knowledge on RS2 also provides opportunities to improve the design of nutrition studies targeting the gut microbiome and to ultimately identify the precise mechanisms via which dietary fiber benefits human health.