Dietary calcium impacts gut microbiome

Fructo-oligosaccharides (FOS), inulin and galacto-oligosaccharides (GOS) are widely recognized prebiotics that profoundly affect the intestinal microbiota, including stimulation of bifidobacteria and lactobacilli, and are reported to elicit several health benefits. The combination of dietary FOS and inulin with calcium-phosphate was reported to stimulate commensal Lactobacillus populations and protect the host against pathogenic Enterobacteriaceae, but little is known about the effects of GOS in diets with a different level of calcium. Here we investigate the microbiome changes elicited by dietary supplementation with GOS or inulin (40 g/kg) using diets with high (100 mmol/kg) and low (30 mmol/kg) calcium levels in adult Wistar rats. Feeding rats non-supplemented (no prebiotic-added) diets revealed that diets rich in calcium favored members of the Firmicutes and increased fecal lactic, succinic, acetic, propionic and butyric acid levels. In contrast, relatively low dietary calcium levels promoted the abundance of mucin degrading genera like Akkermansia and Bacteroides, and resulted in increased fecal propionic acid levels and modest increases in lactic and butyric acid levels. Irrespective of the calcium levels, supplementation with GOS or inulin strongly stimulated Bifidobacterium, while only high calcium diets increased the endogenous Faecalibaculum populations. Despite the prebiotic's substantial difference in chemical structure, sugar composition, oligomer size and the microbial degradation pathway involved in their utilization, inulin and GOS modulated the gut microbiota very similarly, in a manner that strongly depended on the dietary calcium level.