Obesity and gastrointestinal liver disorders in Japan.

In Japan, the prevalence of obesity in adult men has increased since the 1970s, while that in adult women has not changed. The prevalence of obesity in 5-, 8-, 11-, and 14-year-old boys and girls increased from the late 1980s to late 1990 s and has decreased since 2000, while that in 17-year-old girls increased in 2002, similar to that for boys, but has since decreased. In 2009, 33.3% of adult men and 25.0% of adult women were obese, and 8-10% of children (age, 5-17 years) were obese. The prevalence of visceral obesity in adults was 50.8% of men and 18.0% of women. Obesity, especially visceral obesity, affects insulin resistance and increases metabolic diseases (diabetes mellitus, dyslipidemia, hypertension, cardiovascular disease, and non-alcoholic fatty liver disease [NAFLD]) and various cancers. In Japan, with a body mass index (BMI) of 23-25 as the reference category, the hazard ratio of total mortality is 1.36 for a BMI of 30-40 in men and 1.37 with a BMI of 30-40 in women. The frequency of patients with NAFLD has gradually increased in proportion to the increase in the population with obesity. From recent studies in Japan, the number of NAFLD patients is estimated to be 10 million, and around 2 million are considered to have non-alcoholic steatohepatitis. Dietary and behavioral modification is effective for body weight loss and for improvement of obesity-related gastrointestinal liver diseases. If necessary, bariatric surgery is useful for obesity treatment.