The present study demonstrated that dietary supplementation of synbiotics prevented excessive weigh gain in obese mice when compared to controls, modulated the GM and reduced the gene expression of beta-catenin expression. The last mentioned is an important gene involved in tight junction signaling, inflammation and obesity .
The mechanism by which synbiotic supplementation could influence the loss of weight has not been fully elucidated. However, corroborating our results, studies have demonstrated that dietary supplementation with probiotics and prebiotics combination is able to modulate the GM of mice and obesity humans, which leads to significant changes in the prevalence of specific intestinal bacteria. These population with dietary supplementation may benefit from the decrease of energy harvest capacity from diet and thus reduce weight gain [19, 20].
In the present study the intragroups analyses of alpha and beta diversities were differ between all treated groups and control group. Addicionaly, the intergroups analyses also showed a significant difference between lean and obese treated and control groups. Our data demosntrate that the richness and evenness of the GM in lean and obese animals were different before treatment and this difference became more evident after synbiotic supplementation. Corroboring our findings, studies with probiotics supplementation in human and mice may change GM richness and diversity for conditions such as obesity and metabolic disorders [21, 22]. Lower diversity in the GM has been linked to obesity, higher IR, higher visceral fat and numerous inflammatory conditions . Thus, GM diversity could be linked to body weight.
The gut microbiota is mainly composed by bacteria from the Bacteroidetes and Firmicutes phylum. Proteobacteria, Verrucomicrobia, Actinobacteria, Fusobacteria, and Cyanobacteria are present in minor proportions . Adequate amounts of Cyanobacteria are considered beneficial for the host to diminish inflammation through NF-κB inhibition, and, consequently, reduce proinflammatory cytokines, protecting the host against oxidative stress . However, increased Cyanobacteria have been associated with obesity  and recent study published by Shao et al. showed that after weight loss the abundance of these bacteria decreases . Our findings showed Cyanobacteria phylum reduction in the OT group after supplementation associated with weight loss, similarly to Shao et al .
Turicibacter is a genus in the Firmicutes phylum of bacteria that has been found most commonly in the gut . Although this bacteria has been related to greater energy extraction from the diet and that would be related to obesity , the data on the literature are conflicting. There are studies that also show a negative correlation between the amount of Turicibacter and NF-κB and associate a lower amount of this bacteria with the most inflamed individuals with obesity and steatosis . In our study, the analyzes of fecal microbiota of ob/ob mice treated (obese and lean) after synbiotics supplementation demonstrated a decrease of Turicibacter genus when compared to control groups, which could be a interesting finding, responsible for reducing the energy extraction from the diet. Besides, we observed an increase of Enterobacteriaceae family in relation to the control groups. This family is a group of bacteria considered beneficial either by promoting protection of the intestinal barrier or regulating the growth of other bacteria that promote gastrointestinal disorders .
The other relevant finding of our study was the decrease in Clostridiaceae family, and Coprococcus genus in the OT group and a reduction in the abundance of Sutterella genus in LT group. Clostridiaceae family is the group of bacteria present mainly in obese and in T2DM animals  and is associated with dysbiosis in adults and children ) and inflammatory bowel disease in adults . In consonance with our findings, a recent study demonstrated that probiotic supplementation (Lactobacillus paracasei) is able to reduce the abundance of Clostridiaceae . On the other hand, Coprococcus, a genus in the Firmicutes phylum, when increased has been associated with a high-fat diet in mice . Bacteria of the genus Sutterella have been often associated with inflammatory bowel disease and disrupt of the intestinal epithelial homeostasis . It is evident that the consumption of high-protein and high-sugar diets increase Sutterella in the gut  and that probiotics supplementation reduces their abundance , which corroborates our findings in the LT group.
In our study, a significant increase in the following groups of gut bacteria was observed in the LT group: Bacteroides and Lactococcus genus, Enterobacteriales order, Bacteroidaceae, Prevotelaceae and Enterobacteriaceae family. The abundance of some of these bacteria is linked to the improvement of the integrity of the intestinal barrier .
The main role of the intestinal barrier is to separate the internal environment from the luminal content, and the complex system of intercellular junctions, including tight junctions, seals together the epithelial cells to form a continuous layer . In our study we observed a lower expression of intestinal beta-catenin in OT and LT groups compared to control groups. There was no difference in cadherin, occludin and ZO-1. The beta-catenin is one of the proteins that compose the tight junctions which are primarily responsible for maintenance of the intestinal permeability barrier, regulating the passage of ions and solutes between cells by the paracellular pathway . However, when beta-catenin expression is increased it would enter the cell nucleus and would induce the activation of NF-kB, pro-inflammatory genes and the expression of others oncogenes, which are important for development of some intestinal diseases [41, 42] and hepatocellular carcinoma (HCC) . Evidence about the effect of synbiotic supplementation on beta-catenin modulation is scarce. Our results are consistent with Kuugbee et al. that has shown an inhibition of beta-catenin signaling pathway after probiotic  and synbiotic supplementation . Based on these results we can infer that the reduction in beta-catenin expression improves the permeability of the intestinal barrier, preventing the passage of endotoxins from the intestinal lumen through the intestinal barrier and consequently not triggering inflammatory cytokines, which are important for the development of obesity. On the other hand, there are studies showing increased expression of tight junction after synbiotic administration, highlighting ZO-1, occludin and claudin, but not evaluating beta-catenin [19, 45]. Apparently, modulation of intestinal tight junctions happens with prolonged use of symbiotic, which perhaps justifies no difference in gene expression of cadherin, occludin and ZO-1 in our study.
There were strengths and limitations in our study that should be considered. The strengths of our study were the combination of four different probiotics strains, the choice of isogenic mice, the microbial sequencing techniques and the rigorous evaluation of gene expression and liver histology performed by a specialist. However, our study also had some limitations. First, we only chose one probiotic fiber to include in the synbiotic supplementation and the treatment period has lasted only 8 weeks. Perhaps for these reasons, we have not observed more consistent results in gene expression in these animals. Despite these limitations, we believe that our results are encouraging and support the consideration of larger, well-designed studies to evaluate synbiotics supplementation as obesity prevention.
In conclusion, our experimental study with animal model shows that synbiotics supplementation is effective to prevent excessive weigh gain, positively modulates the gut microbiota, reduces beta-catenin expression, but was not able to improve other tight junctions gene expressions. Our data support the evidence of beneficial effects of synbiotics supplementation on prevention of obesity. Nonetheless, more randomized controlled trials are needed.