The Role of Microbiome in Non-Alcoholic Fatty Liver Disease (NAFLD)

Gut microbiota (GM), or gut normal flora, is defined as the microorganisms, including bacteria, protozoa, fungi, archaea and viruses, that reside in the gastrointestinal tract of the human body. The gut microbiota consists of over 100 trillion bacteria along the gastrointestinal tract and has a 150-fold more complex genome than the human genome (Milosevic et al. 2019). GM plays a significant role in several physiological processes in the human body. For example, GM aids in the synthesis of vitamins, digestion, forming blood vessels (angiogenesis) and modulating the body’s immune system. Moreover, GM has a significant role in creating short-chain fatty acids (SCFA), providing energy to the body. However, any disruption of the GM balance, i.e., dysbiosis, can disturb systemic pathological processes, including the hepatic system through the gut-liver axis, the respiratory system, neurological system, endocrine system, and many other pathological diseases. Many factors contribute to the development of dysbiosis, such as host-related factors and, more importantly, environmental factors. Host-related factors include previous or current infections and inflammation, and genes. Environmental factors include high-fat and high-sugar diets, which are associated with the disruption of the barrier of the intestine, leading to more inflammation and eventually further damaging the functions of the gut, such as metabolism (Hrncir 2022).