In a proof-of-concept study, Patrice Cani and colleagues report that treatment with live or pasteurized A. muciniphila is safe and well-tolerated in humans. A total of 32 volunteers received either placebo or A. muciniphila as a dietary supplement for 3 months. Only the participants who received the pasteurized bacteria preparation presented with improved insulin sensitivity, reduced levels of insulin, signs of a better gut barrier, and cholesterol in the blood, as compared with individuals who received a placebo.