Scientists have identified a "guild" of gut bacteria that helped alleviate symptoms of type 2 diabetes mellitus (T2DM) in patients eating a high-fiber diet. The authors say that promoting this exclusive microbial group via personalized nutrition may serve as a novel approach for maintaining the beneficial relationship between the body and its microbiome during T2DM. Past clinical trials have suggested eating a high-fiber diet can improve disease outcomes of T2DM, but responses to this treatment remain highly variable. To improve the efficacy of dietary interventions, it is critical to understand how the gut microbiome responds to dietary changes. Gut microbes play an array of protective roles in response to food intake; for example, hundreds of species can metabolize hard-to-digest carbohydrates to produce short-chain fatty acids (SCFAs), which provide energy to colon cells, mitigate inflammation and help regulate hunger. Now, Liping Zhao and colleagues suggest a select group of SCFA-producing microbes is responsible for the positive impact of high-fiber diets on patients with T2DM. In two T2DM patient cohorts, the researchers observed the group under a high-fiber diet exhibited greatly reduced blood sugar and body weight compared to the control group under standard care. Zhao et al. sequenced microbial genes in the patients' fecal samples, finding that the abundance of certain microbial species over others - as opposed to overall microbial diversity - seemed more closely correlated with health-related changes in the gut microbiota. Pursuing this hypothesis, the scientists identified 15 SCFA-producing strains that were specifically promoted by dietary fibers. Though belonging to different phyla, these bacteria acted as a guild to augment SCFA production, consequently supporting gut health by out-competing microbes that release compounds hindering effective metabolism.