Body mass index is associated with fat mass in normal, overweight/obese, and stunted preschool children in central Thailand

Background and Objectives: Body mass index (BMI) is widely used as a surrogate measure of adiposity. The relationship between BMI and body fatness varies by race, sex, and age and more variations have been found among children. This study investigated the relationship between BMI and fat mass among 3-5 year old children having different nutritional status. Methods and Study Design: A cross-sectional study was conducted in 15 daycare centers in central Thailand. 137 healthy preschool children were recruited according to their nutritional status: thin [BMI for age Z scores, (BAZ) <-2 SD], normal BMI (-2 SD <= BAZ <=+/- 2 SD), overweight/obese (BAZ >+2 SD), and stunted [height for age Z scores <-2 SD]. Fat-free mass was determined by deuterium dilution technique. Fat mass (FM) in kilograms (TFM) and in percentage (FM%), and fat mass index (FMI, FM/height(2)) were calculated. Results: FM and FMI were the highest in the overweight/obese groups. In the thin group, girls had higher FMI compared to boys (3.2 vs 2.8 kg/m(2), p<0.05). The relationship between BMI with FMI and FM differed by nutritional status. BMI was more strongly associated with FMI, TFM, and FM% in the overweight/obese (r=0.97, 0.95, 0.80, p<0.05) and the normal (r=0.88, 0.84, 0.68, p<0.05) groups but not in the stunted group, and inconsistent in the thin group. Conclusions: The inconsistency in the relationship between BMI and body fatness suggests that BMI is appropriate for reflecting adiposity in normal and overweight/obese children, but not undernourished preschool children.