New evidence has emerged in recent years to suggest a strong link between the human gut microbiota, its metabolites, and various physiological aspects of hosts along with important pathophysiological dimensions of diseases. The research indicates that the gut microbiota can facilitate metabolite production in two ways: first, the resident species of the gut microbiota use the amino acids produced from food or the host as elements for protein synthesis, and second, conversion or fermentation are used to drive nutrient metabolism. Additionally, the gut microbiota can synthesize several nutritionally essential amino acids de novo, which is a potential regulatory factor in amino acid homeostasis. The primary objective of this review is to summarize the current literature relating to the ways in which microbial amino acids contribute to host amino acid homeostasis.