Official Japanese reports significantly underestimate prevalence of overweight in school children: Inappropriate definition of standard weight and calculation of excess weight

Background: The obesity epidemic in Japan continues to increase. However, the prevalence and trends of obesity have not explicitly been determined in Japanese children. Aim: The study estimated the trend and prevalence of overweight in Japanese school children, 1980-2001. Subjects and methods: The 2001 cross-sectional national survey on 334,939 boys and 335,204 girls, 5-18 years of age was studied, using the 1978-1981 references. Main outcome measures were proportion of children with BMI ≥95th centile and those with ≥ + 20% excess body weight. Results: The prevalence of overweight increased 2.6 times (5.0% to 12.9%) in Japanese boys and 2.5 times (5.0% to 12.5%) in Japanese girls during the last two decades as assessed by using BMI, whereas the Japanese Ministry of Education, Culture, Sports and Science and Technology reported a much smaller increment in prevalence (5.8% to 9.2% in boys, 5.6% to 8.0% in girls, respectively) using the same data but based on a cut-off value of ≥ + 20% excess body weight. Conclusion: Official governmental reports significantly underestimate the current epidemic of obesity in Japan.