Prevalence of and risk factors for non-alcoholic fatty liver disease in a non-obese Japanese population, 2011-2012

Non-alcoholic fatty liver disease (NAFLD) in non-obese subjects is not rare in Japan, but it has not been clearly described. To clarify its prevalence and risk factors, we investigated the clinical characteristics of NAFLD in non-obese subjects in comparison with NAFLD in obese subjects in the Japanese general population. A cross-sectional study was performed with 5433 subjects who received health checkups from 2011 to 2012. Subjects consuming more than 20 g of alcohol per day and those with autoimmune liver disease, viral hepatitis, uncontrolled biliary disease and insufficient data were excluded. Subjects with a body mass index (BMI) a parts per thousand yen25 kg/m(2) were considered obese, and subjects with a BMI < 25 kg/m(2) were considered non-obese. A total of 3271 subjects were enrolled. The overall prevalence of NAFLD was 24.6 %: 68.5 % in obese subjects and 15.2 % in non-obese subjects. The multivariate logistic regression analysis revealed that a parts per thousand yen10 kg of weight gain since the age of 20 was significantly associated with NAFLD in non-obese subjects of both genders, and eating an evening meal within 2 h before going to bed 3 days or more per week and drinking < 20 g of alcohol per day were negatively associated in non-obese females. Metabolic factors such as waist circumference and triglycerides were predictors of NAFLD in non-obese subjects, and body fat percentage was a predictor in non-obese males. Lifestyle as well as metabolic factors may play crucial roles in the pathogenesis of NAFLD, even in the non-obese Japanese population.