Increased dietary protein stimulates amino acid catabolism via the gut microbiota and secondary bile acid productionOriginal paper
Karen Pendergrass is a microbiome researcher specializing in microbiome-targeted interventions (MBTIs). She systematically analyzes scientific literature to identify microbial patterns, develop hypotheses, and validate interventions. As the founder of the Microbiome Signatures Database, she bridges microbiome research with clinical practice. In 2012, based on her own investigative research, she became the first documented case of FMT for Celiac Disease, four years before the first published case study.
Read MoreWhat was studied?
Researchers examined whether gut microbiota composition changes with dietary protein intake, and whether those changes help regulate how the liver breaks down excess amino acids.
How was it studied?
Mice were fed low, adequate, or high protein diets (6%, 20%, or 50% protein) and assessed for colon oxygen conditions, microbiota taxonomy, bile acid levels, and pancreatic islet glucagon secretion, with some experiments repeated after antibiotic treatment. A parallel clinical study in healthy human adults (mean age 30.8 years, 57% female) tested whether an acute high-protein intake produced similar changes in gut bacteria, secondary bile acids, and circulating glucagon.
What did they find?
High-protein feeding increased colonic HIF-1α and mitochondrial activity, creating a more anaerobic colon environment linked to a shift toward gut bacterial species that produce secondary bile acids such as deoxycholic, lithocholic, and ursodeoxycholic acid. Rising secondary bile acids combined with amino acids like arginine synergistically stimulated glucagon release from pancreatic islets via the PC2 enzyme, and this glucagon rise induced hepatic amino acid degrading enzymes and urea cycle enzymes; antibiotics blunted these effects. Humans given a high-protein diet showed parallel increases in anaerobic bacterial species, fecal secondary bile acids, and serum glucagon.
Why it matters
The findings identify a gut microbiota to bile acid to glucagon to liver signaling pathway that helps the body safely dispose of excess amino acids from high-protein diets. This suggests gut bacteria and secondary bile acids are active partners in metabolic adaptation to dietary protein, not just bystanders.