Background: The association of trimethylamine-N-oxide (TMAO), a microbiota dependent metabolite from dietary choline and carnitine, with type 2 diabetes was inconsistent.

Objective: The investigators planned to investigate the association between plasma TMAO and newly diagnosed type 2 diabetes as well as whether the association could be modified by the TMAO-generating enzyme flavin monooxygenase 3 (FMO3) polymorphisms.

Design: This is an age- and sex-matched case-control study of 2694 participants: 1346 newly diagnosed cases of type 2 diabetes and 1348 controls. The patients of newly diagnosed type 2 diabetes were consecutively recruited from those attending for the first time the outpatient clinics of Department of Endocrinology, Tongji Medical College Hospital, Wuhan, China, from 2012 January to December 2014. Concomitantly, the investigators recruited healthy individuals who were frequency-matched by age (±5 years) and sex to patients from an unselected population undergoing a routine health check-up in the same hospital. The inclusion criteria for controls and newly diagnosed type 2 diabetes were: age ≥ 30 years, body mass index (BMI) < 40 kg/m2, no history of a diagnosis of diabetes and no history of receiving pharmacological treatment for hyperlipidaemia or hypertension. Patients with clinically significant neurological, endocrinological or other systemic diseases, as well as acute illness or chronic inflammatory or infective diseases, were excluded from the study. All the participants enrolled were of Chinese Han ethnicity. All the participants gave informed written consent to the study and did not take any medication known to affect glucose tolerance or insulin secretion before participation. The study was approved by the ethics committee of the Tongji Medical College. Concentrations of plasma TMAO were measured, and FMO3 E158K polymorphism (rs2266782) were genotyped.

Inclusion Criteria:

• Concomitantly, we recruited healthy individuals who were frequency-matched by age (±5 years) and sex to patients from an unselected population undergoing a routine health check-up in the same hospital.
• The inclusion criteria for controls and newly diagnosed type 2 diabetes were: age ≥ 30 years, body mass index (BMI) < 40 kg/m2, no history of a diagnosis of diabetes and no history of receiving pharmacological treatment for hyperlipidaemia or hypertension.

Exclusion Criteria:

• Patients with clinically significant neurological, endocrinological or other systemic diseases, as well as acute illness or chronic inflammatory or infective diseases, were excluded from the study.

All the participants enrolled were of Chinese Han ethnicity. They gave informed written consent to the study and did not take any medication known to affect glucose tolerance or insulin secretion before participation.