Dietary Proteins Regulate Serotonin Biosynthesis and Catabolism by Specific Gut Microbes

More than 90% of serotonin is produced in the intestine. Previous studies have shown that different protein diets significantly affect serum serotonin levels. Here, the colonic microbiota and intestinal serotonin were measured to elaborate how protein diets affect serotonin production in a mouse model. The emulsion-type sausage protein and cooked pork protein diets increased the mRNA levels of tryptophan hydroxylase 1 (Tph1) and monoamine oxidase A (Maoa) and serotonin level as well but reduced the number of enterochromaffin cells. However, the soy protein diet increased the number of enterochromaffin cells and Tph1 mRNA level but decreased the Maoa mRNA level and the serotonin content. Specific gut microbes that responded to dietary changes and affected the content of short-chain fatty acids were significantly related to serotonin-associated biomarkers. These results suggest that dietary proteins may regulate serotonin biosynthesis and catabolism by altering specific gut microbes.