RELATIONSHIP BETWEEN THE GUT MICROBIOTA COMPOSITION AND BODY MASS INDEX

Abstract

The gut microbiome is a key topic for current research since it is known that intestinal microbiota has a great metabolic potential and contains not only thousands of taxa of various bacteria, but also microbes, viruses, archaea and, most importantly, more than three million genes, which makes it our “second genome”. A wide amount of research proves that the gut microbiome contributes to the health of the host. The function of the human intestinal microbiota  involves the  absorption of nutrients and the synthesis of vitamins, energy harvesting from the food, immune response and reduction of the inflammatory process. Human gut microbiome also takes part in lipid and glucose metabolism and production of short chain fatty acids that may act as energy substrates. It also takes part in neural and hormonal energy regulation of the body since hormone ghrelin, which is also known as the “hunger hormone” and acts as a stimulus for food intake, fat deposition, and growth hormone secretion, is positively correlated with the genera Bacteroides and Prevotella and negatively correlated with Lactobacillus, Bifidobacterium, Blautia coccoides, and Eubacterium rectale. The short-chain fatty acids stimulate the secretion of glucagon-like peptide-1 (GLP 1). GLP-1, in turn, stimulates the secretion of insulin and reduces appetite. It is also known that pre-, pro- and synbiotics as well as fecal transplantation from normal weight individuals to obese individuals may contribute to the obesity treatment. Still the precise mechanisms of gut microbiome regulation for further weight correction have not yet been established. The purpose of our study was to establish the relationship between the body mass index and the gut microbial composition in adults. Thus we conducted a literature search with inclusion criteria of studies on adults only, the mandatory presence of at least two groups - one with BMI < 25 (n>15), the other ≥ 25 (n>15).
Most results found no differences in alpha diversity between groups. It has been shown that obesity can affect beta diversity of microbes, as there are changes in bacterial taxa, as well as in the number of microorganisms. In individuals with excess body weight or obesity the Firmicutes/Bacteroidetes ratio is higher with more abundant Firmicutes, while Bacteroidetes are more abundant in normal weight individuals. Firmicutes are believed to be efficient in harvesting energy and absorbing nutrients, making food as accessible as possible and thus increasing the availability of calories consumed. People with a normal weight are characterized by bacteria Flavonifractor plautii, Faecalibacterium prausnitzii, Bacteroides faecichinchillae, Bacteroides thetaiotaomicron, Blautia wexlerae, Clostridium bolteae, Flavonifractor plauti, Lachnospiraceae that are naturally found in people with a healthy profile. The amount of Dorea, Blautia, Coprococcus, Subdoligranulum, Eubacterium ventriosum, Ruminococcus bromii, Ruminococcus obeum, Streptococcus, Dialister was higher in obese or overweight individuals. The difference in the microbial composition may be due to the gender. Further studies with a larger number of samples and observation of weight changes in dynamics, taking into account dietary interventions, are needed to understand the mechanism of the effect of bacteria on body mass index.