Assessment of obesity in children

Abstract

Obesity is usually defined on the basis of body composition measurements. Body composition can be assessed using elaborate methods or anthropometry. The choice of methods depends on the practical conditions of the study. Elaborate methods give accurate information, but they usually have high cost and high technical difficulty, and while considered precise, they still have limitations. They are often based on hypotheses established in adults, and usually in normal weight subjects. Their applicability to obese children is sometimes questionable. Anthropometric measurements are used either directly or as indices or in regression equations. As it is weakly correlated with height and highly correlated with body fat, the Weight/Height 2 Quetelet or Body Mass Index (BMI) is used as an index of adiposity. As opposed to traditional growth charts, the BMI charts simultaneously take weight, height and age into account. The BMI curve reflects the real changes of the child's body shape and fatness during growth. Early in life, it can be used as an indicator of later development. Measurement of weight and height should be augmented by skinfolds. The triceps skinfold is usually recommended and widely used, but trunk skinfolds, such as the subscapular, are better on many counts (e.g. association with body fat pattern or with risk factors, response to nutritional interventions etc.). Measurements can be expressed as a percentage of standard or as Z-score (SD unit). Both methods have limitations: the former does not take the changes of distribution with age into account, the latter does not take variations in prevalence of obesity with age into account. It is suggested here to use the latter method based on a selected healthy population or on a population presenting a low prevalence of obesity. Selecting a limited number of methodologies would improve inter-study comparisons and consequently research on obesity.