# A Review of the Relationship between Gut Microbiome and Obesity
## 4 The Role of Certain Bacterial Phylum and Species
The authors suggest _Prevotella_ as a potential biomarker in the management of obesity [30]. Probiotics regulate the gut microecosystem, host energy metabolism, and reduce low grade inflammation and oxidative stress, and may, therefore, influence the prevention and management of obesity by regulating the gut microbiota [31; 32]. The composition of gut microbiota also varies depending on the severity of obesity. With obesity, the genera Bacteroidales, such as a _Lactobacillus spp._, _Bifidobacterium spp._, _Bacteroidetes_ spp., and _Enterococcus_ spp., as well as _Firmicutes_ and _Bacteroidetes_ and _Enterobacteriaceae_ species increased, while the proportion of Clostridia, including _Costidrium septum_ and _Enterobacter_ spp. decreased [33; 34]. Particularly, a significant decrease in the composition of bacterial genus _Akkermansia_, _Faccalibacterium_, _Oscillibacter_ and _Alistiyes_ has been shown in obese people compared to normal weight people [35; 36]. Higher levels of _Lactobacillus reuteri_ and lower levels of _Methanobrevibacter smithii_ are associated with obesity leading to significant weight gain, while _Bifidobacterium animalis_ and _Methanobrevibacter smithii_ and other _Lactobacillus species_ are found in higher abundance in normal weight individuals [37]. Several studies confirm that _Akkermansia muciniphila_ abundance is negatively correlated with being overweight, obesity, metabolic syndrome, and untreated type 2 diabetes in mice [38; 39]. In animal models, a study showed that _Christensenella minuta_ inhibited weight gain and altered the gut microbiome pattern of the recipient mice. The exact mechanism of action of the bacteria in human models is not yet clear, but it has the potential to be effective in reducing body weight including via the production of SCFA (acetic acid, butyric acid) and via the strong inhibition of de novo lipogenesis in the regulation of hepatic lipid metabolism [40; 41]. Dietary interventions with probiotics, prebiotics, or synbiotics may be effective in reversing the disturbances observed in the gut microbiota during obesity or unbalanced diets, as they may be able to reduce and maintain body weight [42; 43]. In a randomised controlled clinical trial, a symbiotic was administered to individuals participating in a weight loss program. The probiotics used were _Lactobacillus acidophilus_, _Bifidobacterium lactis_, _Bifidobacterium longum_, and _Bifidobacterium bifidum_ and the prebiotic component was a mixture of galactooligosaccharides. No significant differences in body weight and body composition were found between the placebo and the symbiotic groups during the 3 month intervention. However, symbiotic supplementation increased the abundance of _Bifidobacterium_ and _Lactobacillus_, which have been associated with positive health effects [43; 44]. In addition, supplementation with probiotics may be associated with an increase in appetite, and it should be considered ineffective without adequate diet, and can only be used as a supplement [45]. There is some evidence that probiotics can regulate not only the balance of the gut microbiota but also hormones related to appetite. However, a systematic review has found that probiotics have minimal influence on hormone levels playing a role in appetite regulation (e.g., leptin, fasting insulin, resistin) in overweight/obese individuals [46].