9 Though underweight, energy intake is not itself constraining their growth. This paradox can be attributed to extremely low levels of lean mass. Despite extremely low BMI SDS, the patients have body fat levels higher than the average in healthy children. 9 This may be important for their nutritional management, as the low BMI may lead to inappropriate overfeeding.įigure 1 Data from infant patients with congenital myasthenia, a condition in which the development of connective tissue is impaired. 8 BMI may be particularly misleading in hospital patients, where children apparently “malnourished” in terms of BMI actually have an increase in relative body fat and a severe decrease in lean tissue (fig 1 1 ). BMI is a global index of nutritional status-used, for example, to categorise both overweight/obesity, 4 and eating disorders in combination with psychological criteria 5-but its relation with body composition per se is controversial.Īlthough correlated with per cent fat, 6, 7 BMI cannot distinguish fat and lean masses, and there is a twofold range of variation in fatness for a given BMI value in individual children. 3 In adults, BMI is predictive of clinical outcomes such as type 2 diabetes however, its predictive value for children and adolescents is less clear. Such data would therefore represent a “reference” (what exists), but not a “standard” (what should exist).īody mass index (BMI, calculated as weight/height 2) is also widely used as an index of relative weight, often expressed as SDS to take into account age and sex. Although the contemporary epidemic of obesity presents challenges for body composition reference data, whether individual patients are becoming more or less fat over time can only be assessed through comparison with a reference population. However, publication of contemporary children's skinfold reference data remains a current research priority for assessment of relative fatness in patients. They can be converted into standard deviation score (SDS) format for longitudinal evaluations. The best use of skinfold thickness data is as raw values, where they act as reliable indices of regional fatness. In general, intraobserver and interobserver error are low compared to between‐subject variability, but in obese children accuracy and precision are poorer. 2 Measurements are quick and simple to obtain in most age groups including young infants.
Traditionally, skinfold thickness measurements have been used to rank individuals in terms of relative “fatness” or to assess the size of specific subcutaneous fat depots. For more information, readers are strongly encouraged to read the more detailed e‐version of this article on the journal website ( ). The aim of this review is to discuss the theoretical basis, assumptions, and advantages and disadvantages of available techniques. The relative magnitude of these errors varies between techniques. Thus all techniques suffer from two types of error: methodological error when collecting raw data, and error in the assumptions by which raw data are converted to final values.
In vivo techniques do not measure body composition directly, but rather predict it from measurements of body properties. A further important issue is that of the difficulty of validating techniques in humans. A single technique is unlikely to be optimal in all circumstances. Several techniques are available, varying in complexity and ease of use, and each making assumptions that may affect its suitability for different conditions. As discussed below, only multicomponent models are now considered sufficiently accurate to act as reference or criterion methods for the molecular approach to measuring body composition (distinguishing fat and fat‐free masses), against which other methods should be evaluated. The gold standard for body composition analysis is cadaver analysis, so no in vivo technique may be considered to meet the highest criteria of accuracy. 1 However, other components of body composition also influence health outcomes, and its measurement is increasingly considered valuable in clinical practice. The ongoing epidemic of obesity in children and adults has highlighted the importance of body fat for short term and long term health. Body composition and growth are key components of health in both individuals and populations.
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