Type 2 diabetes is a common complex metabolic disorder. Currently, more than 380 million people live with type 2 diabetes globally, and this number is expected to increase to more than 550 million by 2030.
1 Recently, studies
2-5 have indicated a role of gut microbiome in type 2 diabetes. Differences in gut microbiome composition with type 2 diabetes status may comprise pathways on how dietary and other environmental factors affect development of insulin resistance and type 2 diabetes. Several studies
2-4 have indicated that, compared with healthy participants, patients with type 2 diabetes have a lower overall α diversity of gut microbiome composition. More specifically, lower abundance of certain butyrate-producing bacteria, such as class Clostridia and genus
Faecalibacterium, have been observed in patients with type 2 diabetes.
2-5 For example, Larsen et al
3 reported a lower abundance of Clostridia in patients with type 2 diabetes, and Qin et al
5 observed that patients with type 2 diabetes had lower abundance of
Faecalibacterium. In addition, some nonbutyrate bacteria, such as
Haemophilus parainfluenzae, have also been reported to be associated with type 2 diabetes.
5 However, these associations were not very strong, and most of these specific bacteria have not been reproduced in other cohorts.
6 Furthermore, these previous studies
2-6 had several limitations. They were limited in sample sizes, ranging from 20
3 to 784
2 participants. Larger samples with more statistical power may be required to detect true associations. Moreover, in most of these previous observational studies,
2-5 key confounders, such as lifestyle and socioeconomic status, that are known to be determinants of gut microbiome and type 2 diabetes
7 were not controlled for. Finally, because almost all these previous studies
2-5 were conducted in patient populations or case-control settings, it is unclear whether associations are also relevant on a population level and whether type 2 diabetes–associated bacteria are associated to key subclinical parameters, such as insulin resistance and fasting glucose, among groups without diabetes. Examining associations for gut microbiome and such subclinical parameters will help investigators infer potential pathways behind gut microbiome and type 2 diabetes risk. Acquiring and updating this knowledge are particularly relevant, considering the increasing recognition that gut microbiome may play an important role in the development of type 2 diabetes and could be a promising target for prevention and treatment of type 2 diabetes. Therefore, we aimed to investigate the associations between gut microbiome composition with insulin resistance and type 2 diabetes in 2 large population-based cohorts, using a microbiome-wide approach and taking into account various sociodemographic and lifestyle factors.