# A Review of the Relationship between Gut Microbiome and Obesity
###### Abstract  
Obesity is a rapidly growing problem of public health on a worldwide scale, responsible for more than 60% of deaths associated with high body mass index. Recent studies underpinned the augmenting importance of the gut microbiota in obesity. Gut microbiota alterations affect the energy balance of the host organism; namely, as a factor affecting energy production from the diet and as a factor affecting host genes regulating energy expenditure and storage. Gut microbiota composition is characterised by constant variability, and is affected by several dietary factors, suggesting the probability that manipulation of the gut microbiota may promote leaning or prevent obesity. Our narrative review summarizes the results of recent years that stress the effect of gut microbiota in the development of obesity. It investigates the factors (diet, dietary components, lifestyle, and environment) that might affect the gut microbiota composition. Possible strategies for the prevention and/or treatment of obesity include restoring or modifying the composition of the microbiota by consuming prebiotics and probiotics, fermented foods, fruits, vegetables, and avoiding foods of animal origin high in saturated fat and sugar.  
gut microbiome; obesity; weight loss +
Footnote †: journal: Medical  
of the human microbiome, with alternative terms for it including gut microbiome and gut flora, although the latter is now an obsolete term [1].  
Microbiome is the ecological community of microorganisms living in the human gut that evolved over thousands of years with the host body, forming complex and mutually beneficial relationships [3]. The number of microorganisms living in the gastrointestinal tract is close to \(10^{13}\), consisting predominantly of anaerobic bacteria and containing \(\approx\)500-1000 species (spp.), with a total genome estimated to have 100 times more genes than the human genome [4; 5]. Current studies of the gut microbiota focus mainly on bacteria. Other symbiotic microorganisms (e.g., virus, fungi, etc.) are basically ignored in gut microbiota analyses [2].  
Gut microbiota plays an important role in the physiology of the human body including the fermentation of water-soluble fibres to produce short-chain fatty acids and energy not available to the host and the synthesis of vitamins (e.g., vitamin B\({}_{2}\), folic acid, vitamin K, biotin). In addition, it metabolizes xenobiotics, preventing the colonization of pathogens, protecting the integrity of the intestinal epithelium, and promoting the development of a mature immune system [6; 7]. It also plays a key role in the regulation of intestinal transit, thereby influencing the amount of nutrients and energy absorbed from food [8]. When the composition of the gut microbiota is altered by a number of factors, the homeostasis of human health can be disturbed, resulting in the development of metabolic diseases (obesity, diabetes, non-alcoholic fatty liver disease (NAFLD), cardiovascular diseases, etc.) [9]. These and other functions shed light on the crucial role of the microbiome in weight gain and metabolism, discussed in more detail in this review [4; 5].