**3.4 Relationship between obesity and the ratio of Bacteroides and Firmicutes in fecal samples**

Dysbiosis in obesity is often characterized by a decrease in microbial diversity, changes in the relative numbers of major enterotypes, such as Firmicutes and Bacteroidetes, and/or an increase in pathogenic microorganisms. In a study of 18 obese male volunteers, the percentage of total fecal bacteria identified as Bacteroides did not differ between obese subjects and a normal weight control group [57]. These results contrast with similar studies but are quite consistent taking into account significant inter-individual differences.

Despite the disagreement, the ratio of Firmicutes to Bacteroidetes was studied and associated with susceptibility to disease [60], particularly an increase in the number of Firmicutes and a decrease in Bacteroidetes were observed in obese patients and type 2 diabetics [61]. The ratio of Firmicutes and Bacteroidetes in the fecal samples of healthy adults was 10/1 and in obese patients was 100/1. Thus, obesity was shown to be associated with an increase in the number of Firmicutes and a decrease in fecal Bacteroidetes [62]. Also, the predominance of Firmicutes in the gut microbiota was constantly observed in obese subjects in the study of Lei et al. [60], and the number of Proteobacteria was

related to a large number of genera Bacteroides, Prevotella, and Ruminococcus that is positively correlated with a healthy intestinal microbiota. Some authors believe that an important factor associated with obesity is not the ratio of Bacteroidetes to Firmicutes in the gut microbiota, but the amount of short-chain fatty acids produced by it [63].
