Proteins are indispensable components of living organisms, which are derived mainly from diet through metabolism. Dietary proteins are degraded by endogenous digestive enzymes to di- or tripeptides and free amino acids (AAs) in the small intestine lumen and then absorbed into blood and lymph through intestinal epithelial cells via diverse transporters. Microorganisms are involved not only in the proteins’ catabolism, but also the AAs, especially essential AAs, anabolism. Probiotics regulate these processes by providing exogenous proteases and AAs and peptide transporters, and reducing hazardous substances in the food and feed. But the core mechanism is modulating of the composition of intestinal microorganisms through their colonization and exclusion of pathogens. The other effects of probiotics are associated with normal intestinal morphology, which implies that the enterocytes secrete more enzymes to decompose dietary proteins and absorb more nutrients.

蛋白质是生命有机体不可或缺的组成部分，主要来自饮食，通过新陈代谢获得。膳食蛋白被内源性消化酶降解为小肠管腔中的二肽或三肽和游离氨基酸（AA），然后通过各种转运蛋白通过肠上皮细胞吸收到血液和淋巴液中。微生物不仅参与蛋白质的分解代谢，而且还参与AA，特别是必需的AA合成代谢。益生菌通过提供外源蛋白酶，AA和肽转运蛋白以及减少食品和饲料中的有害物质来调节这些过程。但是核心机制是通过肠道微生物的定殖和病原体排斥来调节其组成。益生菌的其他作用与正常的肠道形态有关，