Anthropometric and metabolic improvements in human type 2 diabetes after introduction of an Okinawan-based Nordic diet are not associated with changes in microbial diversity or SCFA concentrations

The Okinawan-based Nordic (O-BN) diet improves anthropometry and metabolism in type 2 diabetes mellitus (T2DM) patients. The aim of this study was to study mechanisms behind improvements by examining Enterobacteriaceae abundance, microbial diversity, and concentrations of short-chain fatty acids (SCFAs). A secondary aim was exploring if metformin treatment affects microbiota or SCFAs. Thirty T2DM patients received the O-BN diet for 12 weeks. Faecal and blood samples were collected at baseline, 12 and 28 weeks. Although patients experienced weight loss and improved metabolic parameters, there were no significant changes in Enterobacteriaceae abundance or microbial diversity. Patients on metformin displayed higher Enterobacteriaceae abundance throughout the study (p = .008, p = .038, and p = .001, respectively). Isovaleric acid was decreased after 12 weeks (p = .018). Butyric acid was decreased at follow-up (p = .007). Improved anthropometry and metabolism in T2DM after introduction of the O-BN diet is not associated with changes in Enterobacteriaceae abundance, microbial diversity or SCFA concentrations.