# A Review of the Relationship between Gut Microbiome and Obesity
## 6 Impact of Lifestyle and Environmental Factors on the Gut Microbiome
However, changes in the gut microbiota also depend on the type of fatty acids ingested. Omega-3 intake is directly related to the growth of _Lactobacillus_, whereas monounsaturated fatty acids (MUFA) and omega-6 polyunsaturated fatty acids (PUFA) are inversely related to the growth of Bifidobacteriumurium [47]. Furthermore, high-fat diets increase the overgrowth of Gram-negative pathogens, promoting the diffusion of bacterial fragments such as lipopolysaccharide (LPS) across the intestinal barrier. The LPS endotoxin can activate the nuclear factor kappa B (NF-\(\kappa\)B) pathway in the bloodstream. LPS can activate the NF-\(\kappa\)B pathway in the blood, and it functions as a ligand for Toll-like receptors with a proinflammatory cytokine CD14 (cluster of differentiation 14), causing an increased intestinal permeability, thereby facilitating the weight gain process. LPS translocation caused by a high-fat diet may be associated with low-grade chronic inflammation induced by obesity [81]. In high-protein diets, _Bacteroides_ and _Propionibacterium_ species convert dietary proteins into amino acids and their derivatives (ammonia, amines, phenols, and sulphides) [63]. Gut health may be compromised by increasing the protein content of the diet, but recent data are unclear about a probable link with obesity. A total of 40 overweight or obese individuals were randomized to high protein and calorie-restricted diets for 8 weeks. The dietary intervention changed the microbial composition and diversity, increased the relative abundance of _Akkermansia_ spp. and _Bifidobacterium_ spp., and decreased the enrichment of _Prerotella_-9 [82], which increases in obesity [83]. According to epidemiological data, a high intake of dietary fibre is beneficial for maintaining a normal body weight. Prebiotics are non-digestible oligosaccharides that can  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Lifestyle and Environment** & **Model** & \begin{tabular}{c} **Impact on** \\ **Microbiome** \\ \end{tabular}  & **Impact on Host** & **Reference** \\ \hline Birth by caesarean section & 6–12 month old infants & \(\uparrow\)_Staphylococcus_ & \(\uparrow\)Risk of obesity & [73; 74] \\  & & \(\downarrow\)_Bacteroides_ & \(\uparrow\)Risk of obesity & [73; 74] \\ \hline Maternal smoking & 3 month old infants & \(\uparrow\)_Firmicutes_ & \(\uparrow\)Risk of obesity & \\  & & & between 0–3 years & [75] \\ \hline Antibiotics consumption & Healthy children & \(\downarrow\)_Bifidobacterium_ & \\  & & \(\downarrow\)_Akkermansia_ & \(\uparrow\)Risk of obesity & [76] \\  & & _mucintiphilis_ & & \\ \hline Stress & Norwegian soldiers & \(\uparrow\)_Firmicutes_ & Increase in intestinal & \\  & & \(\downarrow\)_Bacteroides_ & permeability under stress & [77] \\ \hline Physical activity & \begin{tabular}{c} Subjects with \\ prediabetes and type 2 \\ diabetes \\ \end{tabular}  & \begin{tabular}{c} \(\downarrow\)_Firmicutes_ \\ \(\uparrow\)_Bacteroides_ \\ \(\uparrow\)Clostridium genus \\ \end{tabular}  & \(\downarrow\)Endotoxemia & [78] \\ \hline Alcohol & \ \begin{tabular}{c} Alcohol dependent \\ patients with high or \\ low intestinal \\ permeability \\ \end{tabular}  &
\begin{tabular}{c} \(\downarrow\)_Ruminococcus_ \\ \(\downarrow\)_Facallibacterium_ \\ \(\downarrow\)_Sublologarithmic_ \\ \(\downarrow\)_Oscill  
stimulate the growth of selective and beneficial intestinal bacteria, especially _Lactobacillus_ and _Bifidobacteria_[84]. From indigestible fibers, some bacteria species can produce metabolites and short-chain fatty acids (SCFA), including acetate, propionate, and butyrate, during fermentation, playing a metabolic role in the regulation of energy expenditure and may influence the pathogenesis of obesity [85]. High fibre intake is associated with an increase in the gut microbiome of _Prevotella_, _Lactobacillus_, and _Ruminococcus bromii_ species, among others, and a decrease in _Firmicutes_ strain members, and these characteristics are associated with lower body weight [49].