Gut microbiota and metabolism

The intestine of a healthy human harbors over 100 trillion cells that have a symbiotic relationship with the host, and they play a part in important metabolic, systemic, and immunologic functions. The human gut microbiota begins to take shape in the fetal life, and it achieves adult-like properties by the age of 2–3 years after being influenced by the type of delivery, feeding with either breast milk or formula, antibiotic use, as well as many environmental factors leading to dysbiosis. The important role that the gut microbiota plays in human metabolism and health, as well as identification of specific microorganisms that play role in various metabolic processes have encouraged researchers to investigate metabolism of dietary components and some metabolites produced by the host in particular. Important metabolic functions of the gut microbiota include fermentation of complex carbohydrates that escape digestion; various polyphenols consumed in the diet; fats, amino acids, and proteins; deconjugation of bile acids; and synthesis of vitamin K and several components of vitamin B. This review aims to discuss the relationship between gut microbiota and metabolism of biochemically important macromolecules, flavonoids, and gases. In addition, a summary of the up-to-date information on this subject is presented with the aim of emphasizing the importance of microbiota.