Differential gut microbiota composition between type 2 diabetes mellitus patients and healthy controls: A systematic review.

Aims: This systematic review summarised the latest findings on differential composition of gut microbiota in T2DM.

Methods: Literature search was performed using electronic databases. Relevant studies were identified, extracted and assessed for risk of bias. The primary outcome of this systematic review was the composition of gut microbiota in healthy controls and T2DM while the secondary outcomes included the correlation of gut microbiota with metabolic parameters.

Results: Thirteen case-control studies involving 575 T2DM and 840 healthy controls were included. T2DM patients exhibited a marked increase in lactobacilli. Six studies found lactobacilli to predominate the gut of T2DM patients; however, this could be confounded by the types of antihyperglyacemic medications. Conversely, butyrate producers dominate the gut of healthy controls. In T2DM patients, butyrate producers were surprisingly higher in those taking metformin intake than those not taking the drug. Whilst lactobacilli were found to be higher with increased plasma glucose, conflicting correlations were observed between various genera and anthropometric measurements, dietary intake, lipid profiles and inflammatory markers. There were moderate to strong significant positive correlations between the class Clostridia and phylum Firmicutes with pro-inflammatory IFN-γ as well as between Negativicutes and IL-6.

Conclusions: Altogether, butyrate-producing bacteria are negatively correlated to glycaemic parameters. Lactobacilli are higher in T2DM patients and Firmicutes is correlated with inflammation.