bioRxiv · Feb 25, 2026
Fasting and re-feeding independently alter mouse gut microbiota during intermittent fasting
By Schell LD, Liow YJ, Carmody RN
Intermittent fasting (IF) elicits metabolic benefits that are partially driven by the gut microbiome. Studies have focused on endpoint IF-induced changes in the gut microbiome but have not explored whether the oscillating nature of IF elicits day-to-day microbiome changes that could independently affect health. To discriminate the long-term and short-term effects of IF on the gut microbiota, we fasted mice every other day (IF1:1) or every two days (IF1:2), measuring daily changes in body mass and composition, food intake, and gut microbiota composition. We show that short-term effects of fasting and re-feeding on gut microbiota composition outweigh longer-term effects of IF treatment, with composition responding differently to re-feeding and fasting. Re-feeding specifically promoted rapid expansion of Lactobacillus, a bacterial genus linked mechanistically to the metabolic benefits of IF. Our results highlight the plasticity of the gut microbiota, especially re-feeding effects, as a potential contributor to microbiome-mediated metabolic benefits of IF.