[Body mass index and tri-ponderal mass index of 1,453 healthy non-obese, non-undernourished millennial children. The Barcelona longitudinal growth study].

INTRODUCTION Body mass index-for age (BMI) and tri-ponderal mass index-for-age (TMI) values of healthy non-underweight, non-obese millennial children have not been reported until now. We aimed to obtain these values. SUBJECTS AND METHODS Longitudinal growth study (1995-2017) of 1,453 healthy non-underweight, non-obese millennial children, from birth (n = 477) or from 4 years of age (n = 976) to 18 years in girls and 19 years in boys (25,851 anthropometric measurements). RESULTS In each sex, mean BMI-for-age values increased from birth to one year, declined until 5and increased from then onwards. Mean TMI-for-age values decreased abruptly during the first 6years of age and slowly thereafter, in both sexes. Although, at some ages, mean BMI-for age values differed statistically between sexes, differences were scant and of poor clinical significance. The same occurred for TMI-for-age values. BMI-for-age cut-off values to define underweight status (-2 SD) were similar to those proposed by Cole and the WHO for both sexes. However, BMI-for-age cut-off values to define obesity (+2 SD) were lower in both sexes (1.0-5.3) than those proposed by Cole and similar to those proposed by the WHO until 12 in girls and 14 in boys and lower (1.0-4.8) from these ages onwards. CONCLUSIONS BMI-for-age and TMI-for-age values of healthy non-underweight, non-obese millennial children are provided. No clinically relevant differences were observed between sexes. These values may be used to measure underweight status and obesity in present pediatric populations and to evaluate the relationship between BMI-for-age and TMI-for-age in a clinical setting.