Enterotypes

Enterotypes are proposed discrete clusters of human gut microbial community composition, originally defined by Arumugam et al. (2011, Nature; n = 39 metagenomes, six nationalities) using Jensen-Shannon divergence and PAM clustering on shotgun-sequenced fecal samples. Three clusters were described, each distinguished by a dominant genus: Enterotype 1 (Bacteroides, enriched in carbohydrate and protein fermentation), Enterotype 2 (Prevotella, mucin degradation, plant-rich diets), Enterotype 3 (Ruminococcus/Akkermansia, also mucin-degrading). The clusters were reported as independent of age, sex, and geography, though long-term diet — animal protein and fat toward Bacteroides, carbohydrates toward Prevotella — associates with enterotype membership. The concept was rapidly contested. Knights et al. (2014, Cell Host & Microbe) showed enterotype assignment shifts within individuals over time, suggesting compositional gradients rather than sharp boundaries. Costea et al. (2018, Nature Microbiology) reconciled both views across multiple large cohorts: Prevotella-dominated communities consistently separate from Bacteroides-dominated ones, while intermediate and Firmicutes-driven communities grade continuously, yielding two, three, or four clusters depending on method. Aging relevance is indirect: centenarian cohorts report Bacteroides-dominant profiles resembling younger adults; Prevotella and Faecalibacterium decline in oldest-old groups. As of 2026, enterotypes remain useful stratification variables in diet-intervention studies but are not validated biomarkers of biological age.