Sex differences in the association between fatty liver and type 2 diabetes incidence in non‐obese Japanese: A retrospective cohort study

AIMS/INTRODUCTION: Asians develop type 2 diabetes at a lower body mass index (BMI) compared with other races, which is partly because of Asian‐specific fat depots. Sex plays a role in fat deposition, regardless of race. This retrospective cohort study aimed to investigate the association among fatty liver, sex and type 2 diabetes in non‐obese Japanese. MATERIALS AND METHODS: The participants in this study (13,596 men and 6,037 women) were aged 30–64 years, and had undergone health checkups between 2013 and 2015, in Aichi, Japan. Baseline BMI was categorized as follows: <18.5, 18.5–19.9, 20–22.9, 23–24.9, 25–27.4 and ≥27.5 kg/m(2). Fatty liver was diagnosed by abdominal ultrasonography. The joint effect of BMI and fatty liver on the incidence of type 2 diabetes was assessed, stratified by sex. RESULTS: During follow up, 738 men and 138 women developed type 2 diabetes. Compared with the BMI of 20–22.9 kg/m(2) without fatty liver group, the BMI of 20–22.9 kg/m(2) with fatty liver was associated with a higher risk of type 2 diabetes in men, but not in women. Furthermore, men with a BMI of 23–24.9 and 25–27.4 kg/m(2) without fatty liver had no significant type 2 diabetes risk, whereas women with a BMI of 23–24.9 and 25–27.4 kg/m(2), regardless of fatty liver, had an increased risk. CONCLUSIONS: These results suggest the association between fatty liver and type 2 diabetes in non‐obese Asians is different by sex; fatty liver increases diabetes risk among male, not female, non‐obese Asians.