# A Review of the Relationship between Gut Microbiome and Obesity
## 6 Impact of Lifestyle and Environmental Factors on the Gut Microbiome
However, the correlation between obesity and short-chain fatty acids is not yet fully clarified. SCFAs are considered to contribute about 200 kcal/day to the human energy balance. Short-chain fatty acids are released into the bloodstream and then bind to G-protein-coupled receptors, participating in cellular signaling pathways including lipid, glucose, and cholesterol metabolism [85]. In high-carbohydrate diets and obesity, the binding of SCFAs as signal transduction molecules to G-protein-coupled receptors may be impaired, leading to increased intestinal energy storage and hepatic biogenesis. The acetate produced functions as a precursor for acetyl-CoA and fatty acids for de novo lipogenesis in the liver, thus, the overproduction of acetate may contribute to obesity [86]. Not all short-chain fatty acids have the same metabolic effects, as propionate is gluconeogenic in the liver, whereas butyrate and the previously mentioned acetate are lipogenic, but results from studies in humans are controversial [85]. [PERSON] et al. reported that obese children had more SCFA in their stools than non-obese children, and this was positively correlated with a higher BMI Z score, and a higher proportion of _Firmicutes_ and lower proportion of _Bacteroides_ in the gut [87]. The prebiotic found in nature is inulin, its dietary sources include asparagus, Jerusalem aritchokes, aritchokes, onions, garlic, bananas, oats, and soya. However, these dietary sources are not considered to be biologically valuable, as a daily intake of 4-8 g of fructoligosaccharide would significantly increase the _Bifidobacteria_[88; 32]. In overweight young children, after 16 weeks of supplementation with oligofructose-enriched inulin, body weight decreased by 3.1% and body fat by 2.4%, compared to children taking a placebo [89; 90]. The prebiotic selectively altered the gut microbiota by causing a significant increase in _Bifidobacterium spp._ and a decrease in _Bacteroides vulgaris_[90]. [PERSON] et. al. carried out a study based on broccoli consumption to investigate the effect of fibre on the gut microbiota. The study suggests that consuming broccoli decreases the relative abundance of _Firmicutes_ by 9%, while increasing the abundance of _Bacteroides_ by 10%, and increased the relative abundance of _Bacteroides_ by 8% compared to the control group [91]. In a randomised controlled trial, overweight or obese subjects were divided into three groups, with one group consuming wholegrain cereals, a second group consuming fruit and vegetables, and a control group consuming a diet of refined cereals for 6 weeks. Significant reductions in LPS were found in the group consuming whole grains and the group consuming fruits/vegetables. Fruit and vegetable consumption significantly reduced interleukin-6 (IL-6), whereas the whole grain diet significantly reduced tumor necrosis factor alpha (TNF-\(\alpha\)) levels [92; 93]. There is also a potential benefit to consuming probiotics in the form of fermented foods such as fermented vegetables, tempeh, miso, pickles, sauerkraut, kimchi, kombucha, and other beverages such as apple cider vinegar and fermented dairy products. These foods may be effective in maintaining body weight, balancing intestinal permeability and barrier functions, and controlling dysbiosis [94]. In a randomised clinical trial of obese Korean women, consumption of fermented kimchi for 8 weeks increased the relative abundance of _Bacteroides_ and _Prevotella_, and caused a non-significant reduction in body weight, waist circumference, and body fat percentage. Bacteroides show a negative correlation with obesity, and _Prevotella_ is the dominant genus in the microbiota of individuals who follow a low-fat, high-fibre diet [95]. Another clinical study proved the beneficial effects of kimchi on the gut microbiota; kimchi interventions resulted in higher abundance of SCFA-producing genera such as _Phascalorobacterium_, _Faecalibacterium_, and _Roseburia_[96]. During a 4 week weight-loss intervention, obese participants consumed 30 g of fermented cheese per day.