Gut Microbiota Composition in Prediabetes and Newly Diagnosed Type 2 Diabetes: A Systematic Review of Observational Studies

Abstract

Evidence of gut microbiota involvement in regulating glucose metabolism and type 2 diabetes mellitus (T2DM) progression is accumulating. The understanding of microbial dysbiosis and specific alterations of gut microbiota composition that occur during the early stages of glucose intolerance, unperturbed by anti-diabetic medications, is especially essential. Hence, this systematic review was conducted to summarise the existing evidence related to microbiota composition and diversity in individuals with prediabetes (preDM) and individuals newly diagnosed with T2DM (newDM) in comparison to individuals with normal glucose tolerance (nonDM). A systematic search of the PubMed, MEDLINE and CINAHL databases were conducted from inception to February 2021 supplemented with manual searches of the list of references. The primary keywords of “type 2 diabetes”, “prediabetes”, “newly-diagnosed” and “gut microbiota” were used. Observational studies that conducted analysis of the gut microbiota of respondents with preDM and newDM were included. The quality of the studies was assessed using the modified Newcastle-Ottawa scale by independent reviewers. A total of 18 studies (5,489 participants) were included. Low gut microbial diversity was generally observed in preDM and newDM when compared to nonDM. Differences in gut microbiota composition between the disease groups and nonDM were inconsistent across the included studies. Four out of the 18 studies found increased abundance of phylum Firmicutes along with decreased abundance of Bacteroidetes in newDM. At the genus/species levels, decreased abundance of Faecalibacterium prausnitzii, Roseburia, Dialister, Flavonifractor, Alistipes, Haemophilus and Akkermansia muciniphila and increased abundance of Lactobacillus, Streptococcus, Escherichia, Veillonella and Collinsella were observed in the disease groups in at least two studies. Lactobacillus was also found to positively correlate with fasting plasma glucose (FPG), HbA1c and/or homeostatic assessment of insulin resistance (HOMA-IR) in four studies. This renders a need for further investigations on the species/strain-specific role of endogenously present Lactobacillus in glucose regulation mechanism and T2DM disease progression. Differences in dietary intake caused significant variation in specific bacterial abundances. More studies are needed to establish more consistent associations, between clinical biomarkers or dietary intake and specific gut bacterial composition in prediabetes and early T2DM.

The different trends in the burden of neurological and mental disorders following dietary transition in China, the USA, and the world: An extension analysis for the Global Burden of Disease Study 2019

“…Many studies showed that the patients with mental and neurological disorders including depressive disorders, schizophrenia, Alzheimer's disease, Parkinson's disease, autism spectrum disorders, attentiondeficit/hyperactivity disorder, and eating disorders also had a lower α-diversity in gut microbiota compared to healthy controls (16,(153)(154)(155)(156)(157). The patients with many chronic diseases such as cardiovascular diseases, cancers, and diabetes mellitus presented a lower α-diversity in gut microbiota, too (158)(159)(160)(161)(162). The abnormal gut microbiota could impair brain function through microbiota-gut-brain axis, making the host more susceptible to the above diseases (6)(7)(8)(9)163).…”

Regulatory effects of oral microbe on intestinal microbiota and the illness

“…When regarding IBD, the enrichment of adhesive bacteria (involving Veillonella ) increases Th17 cell activation and luminal secretory IgA ( Chen et al., 2020a ; Gonzalez-Soltero et al., 2020 ). In periodontitis-associated type 2 diabetes (T2D), Streptococcus and Veillonella are dominant in the symbiosis network, and microbial shifts may contribute to systemic inflammation and metabolic dysfunction ( Li et al., 2020 ; Letchumanan et al., 2022 ).…”

Addressing the Continuum of Dysglycaemia and Vascular Complications in Prediabetes and Type 2 Diabetes: Need for Early and Intensive Treatment

“…12 Systematic reviews have associated changes in the gut microbiome with insulin resistance, prediabetes and type 2 diabetes, with some evaluations of probiotics demonstrating improvements in glycaemic control. [13][14][15] These associations are variable, however, and this approach remains in the arena of research. Further study will be needed in this area before targeted modulation of the gut microbiome joins the evidence-based interventions for managing the diabetes continuum that are described later in this article.…”