The gut microbiota and the short chain fatty acids they produce may affect energy absorption and weight gain. Thus, the gut flora may have an impact on whether a person is fat or thin. Read on to learn more.<\/p>\n
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Short-chain fatty acids (SCFAs; acetic, propionic and butyric acid) are formed during bacterial fermentation of carbohydrates in the colon.<\/p>\n
SCFAs cause low intestinal pH from the ileum (end of the small intestine) to the cecum (beginning of large intestine), which prevents the overgrowth of bad bacteria (like Enterobacteriaceae and Clostridia) (R<\/a>).<\/p>\n SCFAs help fix ‘leaky gut’, strengthening the intestinal wall by increasing the secretion of mucin-2 (MUC-2), which then prevents LPS<\/a> from crossing the barrier (R<\/a>).<\/p>\n Out of the total SCFAs present in the colon, 90%-95% are acetate, propionate, and butyrate<\/a> in healthy people.<\/p>\n Most of the SCFAs are absorbed in the colon, being exchanged with bicarbonate (R<\/a>).<\/p>\n SCFAs are acidic, while bicarbonate is alkaline.<\/p>\n There is some conflicting information on SCFAs and weight. On the one hand, they increase caloric utilization. On the other hand, they have been inversely associated with obesity<\/a>. Overall, butyrate<\/a> seems to be broadly protective against obesity, propionate has mixed associations, and acetate is linked to weight gain (R<\/a>).<\/p>\n The fecal concentration of SCFAs is 20% higher in obese individuals than in their lean counterparts. According to some researchers, this may reflect a compensatory protective mechanism against obesity, in which a greater amount is eliminated from the stool (R<\/a>).<\/p>\n This would prevent the increased accumulation of SCFA in the intestines, which may cause weight gain (mainly from acetate) (R<\/a>).<\/p>\n SCFAs like butyrate and propionate increase the formation of the gut hormones glucagon<\/a>-like peptide-1 (GLP-1<\/a>) and polypeptide YY (PYY<\/a>). These reduce food intake by decreasing appetite (R<\/a>).<\/p>\n Butyrate<\/a> reduces food intake and has been linked to weight loss<\/a>.<\/p>\n Researchers are also investigating butyrate\u2019s potential to combat autoimmunity, cancer, and psychological disorders. Butyrate, which is primarily produced by Firmicutes<\/em> bacteria in the gut, appears to affect gene expression in the brain (R<\/a>, R<\/a>).<\/p>\n Butyrate is primarily used by colon cells as a major source of energy (R<\/a>).<\/p>\n Butyrate production is affected by the quantity of bacteria that produce butyrate and by the pH of the large intestine (R<\/a>).<\/p>\n Butyrate-producing bacteria seem to thrive in a more acidic environment (lower pH), whereas acetate and propionate bacteria seem to thrive in a more alkaline environment (higher pH) (R<\/a>).<\/p>\n In the mitochondria<\/a> of colon cells, 70% to 90% of butyrate is oxidized into acetyl-CoA, which is subsequently processed through the tricarboxylic acid cycle to generate a large quantity of ATP (R<\/a>).<\/p>\n Propionate also reaches the liver via portal circulation, where it is used to produce glucose<\/a>. Propionate has observed effects that may promote or suppress obesity, but overall it seems to be protective against obesity (R<\/a>).<\/p>\n Acetate and propionate are the main products of Bacteroidetes <\/em>(R<\/a>).<\/p>\n Of all the three SCFAs, acetate seems to cause the most weight gain. However, it also has some properties that are believed to protect against obesity. According to some researchers, it may act against weight gain in the hypothalamus<\/a> (arcuate nucleus) by increasing GABA<\/a> (R<\/a>).<\/p>\n A substantial proportion of acetate in the intestine is readily absorbed and reaches the liver (via portal circulation), where it\u2019s used to create cholesterol (R<\/a>, R<\/a>).<\/p>\n Human studies have shown that when lactulose (metabolized by microbiota<\/a> to produce high amounts of acetate) was administered to the diets of six volunteers for two weeks, there was a significant increase in both total and LDL<\/a> cholesterol, ApoB<\/a>, and blood levels of acetate (R<\/a>).<\/p>\n Acetate and propionate are the main products of Bacteroidetes (R<\/a>).<\/p>\n Obese animals and people have a lower microbiome diversity, a lower percentage of Bacteroidetes<\/em>, Verrucomicrobia<\/em>, Faecalibacterium prausnitzii <\/em>and a higher percentage of Firmicutes <\/em>and Actinobacteria<\/em>. Some of these results have not been reproduced in subsequent studies (R<\/a>).<\/p>\n<\/a>SCFAs In the Human Gut<\/strong><\/span><\/h2>\n
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<\/a>SCFAs and Obesity<\/strong><\/span><\/h2>\n
<\/a>Butyrate<\/strong><\/span><\/h3>\n
<\/a>Propionate<\/strong><\/span><\/h3>\n
<\/a>Acetate<\/strong><\/span><\/h3>\n
<\/a>Bacterial Species and Obesity<\/strong><\/span><\/h2>\n