The Quételet index revisited in children and adults / El índice de Quételet reevaluado en niños y adultos

BACKGROUND: The body mass index (BMI) is based on the original concept that body weight increases as a function of height squared. As an indicator of obesity the modern BMI assumption postulates that adiposity also increases as a function of height in states of positive energy balance. OBJECTIVE: To evaluate the BMI concept across different adiposity magnitudes, in both children and adults. METHODS: We studied 975 individuals who underwent anthropometric evaluation: 474 children and 501 adults. Tetrapolar bioimpedance analysis was used to assess body fat and lean mass. RESULTS: BMI significantly correlated with percentage of body fat (%BF; children: r = 0.893; adults: r = 0.878) and with total fat mass (children: r = 0.967; adults: r = 0.953). In children, body weight, fat mass, %BF and waist circumference progressively increased as a function of height squared. In adults body weight increased as a function of height squared, but %BF actually decreased with increasing height both in men (r = −0.406; p < 0.001) and women (r = −0.413; p < 0.001). Most of the BMI variance in adults was explained by a positive correlation of total lean mass with height squared (r2 = 0.709), and by a negative correlation of BMI with total fat mass (r = −0.193). CONCLUSIONS: Body weight increases as a function of height squared. However, adiposity progressively increases as a function of height only in children. BMI is not an ideal indicator of obesity in adults since it is significantly influenced by the lean mass, even in obese individuals

ANTECEDENTES: El índice de masa corporal (IMC) se basa en el concepto original de que el peso corporal aumenta en función de la talla al cuadrado. Como indicador de obesidad, el supuesto actual sobre el IMC es que la adiposidad corporal también aumenta en función de la talla en estados de balance energético positivo. OBJETIVO: Evaluar el concepto del IMC en diferentes magnitudes de adiposidad, tanto en niños como adultos. MÉTODOS: Estudiamos a 975 individuos sometidos a evaluación antropométrica: 474 niños y 501 adultos. Se usó bioimpedancia tetrapolar para evaluar la masa grasa y magra corporal. RESULTADOS: Había una correlación significativa de IMC con el porcentaje de grasa corporal (%GC; niños: r = 0,893, adultos: r = 0,878) y con la masa grasa total (niños: r = 0,967; adultos: r = 0,953). En los niños, el peso corporal, la masa grasa, el %GC y el perímetro de la cintura aumentaban progresivamente en función de la talla al cuadrado. En los adultos, el peso corporal aumentaba en función de la talla al cuadrado, pero el %GC disminuía al aumentar la talla tanto en varones (r = −0,406; p < 0,001) como en mujeres (r = −0,413; p < 0,001). La mayor parte de la varianza del IMC en adultos se explicaba por una correlación positiva de la masa magra total con la talla al cuadrado (r2 = 0,709) y por una correlación negativa del IMC con la masa grasa total (r = −0,193). CONCLUSIONES: El peso corporal aumenta progresivamente en función de la talla al cuadrado. Sin embargo, sólo en los niños la grasa corporal aumenta progresivamente en función de la talla. El IMC no es un indicador ideal de obesidad en los adultos, ya que está significativamente influido por la masa magra, aún en los obesos

The Quételet index revisited in children and adults.

BACKGROUND: The body mass index (BMI) is based on the original concept that body weight increases as a function of height squared. As an indicator of obesity the modern BMI assumption postulates that adiposity also increases as a function of height in states of positive energy balance. OBJECTIVE: To evaluate the BMI concept across different adiposity magnitudes, in both children and adults. METHODS: We studied 975 individuals who underwent anthropometric evaluation: 474 children and 501 adults. Tetrapolar bioimpedance analysis was used to assess body fat and lean mass. RESULTS: BMI significantly correlated with percentage of body fat (%BF; children: r=0.893; adults: r=0.878) and with total fat mass (children: r=0.967; adults: r=0.953). In children, body weight, fat mass, %BF and waist circumference progressively increased as a function of height squared. In adults body weight increased as a function of height squared, but %BF actually decreased with increasing height both in men (r=-0.406; p<0.001) and women (r=-0.413; p<0.001). Most of the BMI variance in adults was explained by a positive correlation of total lean mass with height squared (r(2)=0.709), and by a negative correlation of BMI with total fat mass (r=-0.193). CONCLUSIONS: Body weight increases as a function of height squared. However, adiposity progressively increases as a function of height only in children. BMI is not an ideal indicator of obesity in adults since it is significantly influenced by the lean mass, even in obese individuals.