The role of the gut mycobiota in regulating lipid absorption and obesity

This study investigates how the small intestinal microbiota regulate host digestive and absorptive adaptive responses to dietary lipids and how those interactions influence susceptibility to diet-induced obesity. Using germ-free (GF) and specific pathogen-free (SPF) mice, the authors show that GF mice are resistant to diet-induced obesity and exhibit malabsorption of fat, with specific impairments in lipid digestion and absorption localized to the small intestine. The work demonstrates that small bowel microbes are essential for host adaptation to dietary lipid changes by regulating gut epithelial processes involved in lipid digestion and absorption.

Mechanistically, the study provides evidence that proximal small intestinal microbes modify both digestive and absorptive phases of lipid handling: GF mice conventionalized with jejunal microbiota from high-fat diet–fed animals display increased lipid absorption even when later fed a low-fat diet, indicating that microbial communities induced by high-fat feeding can confer a host phenotype of enhanced lipid uptake. The authors further show that conditioned media from defined bacterial strains can directly upregulate lipid absorption genes in murine proximal small intestinal epithelial organoids, implicating microbially derived soluble factors in modulation of epithelial gene expression. Experimental approaches described include dietary interventions (low-fat versus high-fat diets), radiolabeled lipid gavage ([3H]triolein and [14C]cholesterol) with and without tyloxapol to assess absorption dynamics, and measurements of systemic and portal lipid parameters such as triglycerides (TG), low-density lipoprotein (LDL), non-esterified fatty acids (NEFA), fasting serum glucose and markers of insulin resistance.

Stool measurements of TG, NEFA, bile, and total cholesterol are reported, and results are pooled across multiple independent experiments. Figures referenced illustrate that GF mice remain resistant to weight gain under high-fat feeding and have altered fat pad weights relative to SPF controls, as well as impaired radiolabeled lipid uptake into intestinal epithelium and metabolic tissues. Together the findings identify the proximal gut microbiota as key regulators of host adaptability to dietary lipid variations through both digestive and absorptive mechanisms and suggest that microbial regulation of epithelial lipid metabolism can contribute to states of overnutrition and undernutrition. The study highlights the small intestine, and specifically jejunal microbial communities and their secreted products, as important determinants of host lipid handling and metabolic phenotype.

By integrating in vivo germ-free animal models, dietary manipulation, radiolabeled lipid tracing, and ex vivo organoid assays, Martinez-Guryn et al. provide a coherent framework linking small intestinal microbial composition and activity to host lipid absorption and obesity-related outcomes.