Co-authors J. A. Krumbeck and M. X. Maldonado-Gomez contributed equally to this work. Purpose of review -A wide range of dietary carbohydrates, including prebiotic food ingredients, fermentable fibers, and milk oligosaccharides, are able to produce significant changes in the intestinal microbiota. These shifts in the microbial community are often characterized by increased levels of bifidobacteria and lactobacilli. More recent studies have revealed that species of Faecalibacterium, Akkermansia,

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... and other less well studied members may also be enriched. We review the implications of these recent studies on future design of prebiotics and synbiotics to promote gastrointestinal health. Recent findings -Investigations assessing the clinical outcomes associated with dietary modification of the gut microbiota have shown systemic as well as specific health benefits. Both prebiotic oligosaccharides comprised of a linear arrangement of simple sugars, as well as fiber-rich foods containing complex carbohydrates, have been used in these trials. However, individual variability and nonresponding study participants can make the outcome of dietary interventions less predictable. In contrast, synergistic synbiotics containing prebiotics that specifically stimulate a cognate probiotic provide additional options for personalized gut therapies. Summary -This review describes recent research on how prebiotics and fermentable fibers can influence the gut microbiota and result in improvements to human health.