Features of annual changes in body fat distribution in Japanese children

During the last two decades, the prevalence of obesity and being overweight among children has tended to increase in developed countries. Accumulation of internal fat mass may cause metabolic problems to a greater extent than accumulation of subcutaneous fat mass. This is a lifestyle-related medical condition. In children, internal fat has a greater metabolic effect than in adults. Therefore, changes in morbidity due to obesity and being overweight in childhood need to be investigated by observing changes in body fat distribution such as internal fat mass and subcutaneous fat mass. This study investigated changes in body weight and body fat distribution in Japanese children. Height and weight were measured once a year for two years in 3-4-year-olds (72 boys and 59 girls) and for three years in 6-9-year-olds (60 boys and 93 girls). Body mass index (BMI) was calculated as weight/stature². Fat free mass (FFM) and fat mass (FM) were calculated by bioelectrical impedance analysis. Internal fat mass (IFM) and subcutaneous fat mass (SFM) were estimated using the equation of Komiya. Subjects were categorized into groups [underweight (<25th percentile), standard (25-75th percentile), or overweight (>75th percentile)] for each sex-age group by BMI percentile and investigated for changes in body fat distribution. BMI decreased in the standard group for both boys and girls by 5 and 6 years of age, and then increased from 6 to 12 years. FMI increased from about 6 years of age. This result suggested that the increase of BMI was attributable to an increase of FMI. BMI did not change in more than 60% of the subjects in each group. Comparing those who maintained a standard weight with those who became overweight, the increase in weight in the latter was significant. In the latter group, both FFM and FM increased in boys, whereas only FM increased in girls, and there was a significant increase of SFM in both sexes. However, the increase in IFM did not differ much between those who maintained a standard weight and those who became overweight. This suggests that the increase in FM was attributable to an increase of SFM in this cohort of children. These findings show that obesity and being overweight in childhood persists into adulthood. It is necessary to improve health education for early prevention of obesity and improvement of lifestyle.