Abstract
There have been mixed results regarding the relationship among short chain fatty acids (SCFAs), microbiota, and obesity in human studies. We selected studies that provided data on SCFA levels or fecal microbiota abundance in obese and nonobese individuals and then combined the published estimates using a random-effects meta-analysis. Obese individuals had significantly higher fecal concentrations of acetate (SMD (standardized mean differences) = 0.87, 95% CI (confidence interva) = 0.24–1.50, I2 (I–squared) = 88.5), propionate (SMD = 0.86, 95% CI = 0.35–1.36, I2 = 82.3%), and butyrate (SMD = 0.78, 95% CI = 0.29–1.27, I2 = 81.7%) than nonobese controls. The subgroup analyses showed no evidence of heterogeneity among obese individuals with a BMI >30 kg/m2 (I2 = 0.0%). At the phylum level, the abundance of fecal microbiota was reduced in obese compared to nonobese individuals, but the difference was not statistically significant (Bacteroidetes phylum, SMD = −0.36, 95% CI = −0.73–0.01; Firmicutes phylum, SMD = −0.10, 95% CI = −0.31–0.10). The currently available human case-control studies show that obesity is associated with high levels of SCFA but not gut microbiota richness at the phylum level. Additional well-designed studies with a considerable sample size are needed to clarify whether this association is causal, but it is also necessary to identify additional contributors to SCFA production, absorption, and excretion in humans.
Highlights
Obesity is a state in which excess fat accumulates in the body due to an imbalance between energy intake and energy consumption [1]
Propionate, and acetate, which account for 90% to 95% of the Short chain fatty acids (SCFAs) present in the colon, act as signaling ligands between the gut microbiome and host metabolism at specific levels [2,3,4]
According to the random-effect meta-analysis results shown in Figure 2, obese individuals had significantly higher SCFA concentrations of acetate (SMD = 0.87, 95% confidence intervals (CIs) = 0.24–1.50) in the blood and feces, propionate (SMD = 0.86, 95% CI = 0.35–1.36) in feces, valerate (SMD = 0.32, 95% CI = 0.00–0.64) in feces, and butyrate (SMD = 0.78, 95% CI = 0.29–1.27) in feces than the nonobese individuals
Summary
Obesity is a state in which excess fat accumulates in the body due to an imbalance between energy intake and energy consumption [1]. Short chain fatty acids (SCFAs) are organic fatty acids with one to six carbon atoms and are the major anions produced by microbial fermentation of undigested carbohydrates, but the amount of SCFAs depends on various host, environmental, dietary, and gut microbiota factors [2]. Emerging evidence based on numerous animal studies has shown that the gut microbiota and its metabolites, SCFAs, play an important role in obesity [5,6,7].
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