# A Review of the Relationship between Gut Microbiome and Obesity
## 6 Impact of Lifestyle and Environmental Factors on the Gut Microbiome
The natural probiotic intake increased the abundance of _Lactobacillus_, _Streptococcaceae_, _Lactococcus_, and _Streptococcus_, as well as SCFA-producing _Phascalorctobacterium_ and _Butyricinomas_[97]. Interestingly, the excessive use of food additives such as emulsifiers may be connected to the obesity crisis. These substances can alter the gut microbiome and cause dysbiosis, and these changes contribute to many undesirable conditions such as obesity, inflammation, and metabolic syndrome inflammatory bowel diseases [98; 99; 100]. Animal studies show an association between prenatal and perinatal antibiotic use and an increased risk of childhood obesity [101]. Mice treated with low-dose penicillin at birth had a greater increase in body weight at weaning compared to control mice. Following 4 weeks of antibiotic administration, adult mice showed increased body weight and fat mass from 20 weeks of age. According to the authors, this was not a consequence of prolonged dysbiosis, as the microbiota recovered 4 weeks after treatment was stopped, but they believe that a long-term effect of a temporary disruption of the gut microbiota may be responsible. Other studies report that antibiotic use can increase the risk of obesity in healthy children associated with a decrease in _Bifidobacterium_, _Akkermansia muciniphilia_, while abnormal obesity has been reported in patients with Q-fever endocarditis with a decrease in _Bacteroidetes_ and _Lactobacillus_ and an increase in _Firmicutes_[76; 102]. Physical activity has an impact on the gastrointestinal system, as it can reduce the transit time of faeces, increase the number of beneficial microbial species, and enrich its diversity [103]. Both moderate intensity and intense physical activity can reduce endotoxemia and improve insulin sensitivity and _Firmicutes/Bacteroidetes_ ratio [78]. Moreover, athletes tend to have more _Akkermansia muciniphilia_, associated with a lower BMI, compared to non-athletes [104]. For many years, the infant's gut was considered sterile and was thought to be colonized after birth by the maternal microbiota, diet, and environment. Recent research suggests that microbial colonization of the infant starts before birth because the womb is not sterile [105]. Several researchers question the evidence for the \"intrauterine colonisation hypothesis\" due to the controversial results. However, this area of research is currently under debate [106]. Earlier findings suggest that microbial exposure can start during pregnancy, and colonization with microbes from the maternal microbiota and the environment begins immediately after birth [107]. The mode of delivery influences differences in the composition of the gut microbiome of infants, which persist for at least 6 months after birth [108]. There is a link between caesarean delivery and childhood obesity, suspected to affect later body weight [74; 109; 110; 111; 112]. Birth by caesarean section, especially if the mother was overweight or obese, increases the risk of overweight or obesity in the first 3 years of life [74; 112]. The main difference is that vaginally born infants typically have higher concentrations of _Bacteroides_, _Bifidobacteria_, and _Lactobacillus_ in the first days of life and greater microbial variability in the following weeks. The microbiome of infants born by caesarean section, similar to the maternal skin and the hospital environment, is mainly composed of _Staphylococcus_, _Streptococcus_, and _Clostridium_[113]. A cohort study monitoring the body mass of 943 infants born vaginally and 362 by caesarean section found that the mean BMI of infants born by caesarean section was significantly higher than that of infants born vaginally six months after birth. However, no significant differences were found in the BMI of the children at either 2 or 5 years of age, thus, it is suggested that the method of birth has no long-term effect on the children's BMI [114].