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9: Body size (Chapter 10)

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    Abstract

    Body size can be assessed from measurements of stature (height or length), weight, and head circumference using stan­dard­ized procedures described here. When height cannot be measured, published equations based on knee height, lower leg length, arm span or demi-span are used. To interpret the measurements, indices such as weight-for-age, body-mass-index-for-age, stature-for age, weight-for stature, and body mass index (BMI, weight / height2) are constructed.

    To evaluate the anthropometric indices, they can be compared with appropriate growth reference data using Z‑scores or per­cent­iles. For international use, the WHO prescriptive Child Growth Standard for children (0–5y) and the WHO growth reference for school-age children and adolescents (5–19y) should be used. Statistically determined reference limits or cutoffs can also be applied to generate “anthropometric indicators” such as stunting (stature-for-age < −2 Z‑score), wasting (weight-for-stature < −2 Z‑score), over­weight (weight-for-stature > +2 Z‑score), and thinness, over­weight, and obesity based on BMI-for-age < −2, > +2, and > +3 Z‑scores, respectively. Both stature-for-age at < − Z‑score and weight-for-stature at < −2 Z‑score are recommended by WHO because together they can distinguish between stunting and wasting. To assess changes in stature over time, however, use of stature-for-age difference rather than stature-for-age Z‑score is now preferred.

    To assess and compare the severity of malnutrition across countries, five prevalence thresholds for wasting, over­weight, and stunting can be used. Recognition of an elevated mortality risk for children suffering from multiple anthropometric deficits simultaneously has led to the development of the Composite Index of Anthropometric Growth Failure (CIAF). This is used to characterize the overall burden of under‑ and ‑over-nutrition in children age < 5y so they can be identified and prioritized for intervention.

    Changes in body weight over time are used in both clinical and public health settings. In clinical settings lack of weight gain and weight loss are used identify pediatric undernutrition, whereas weekly weight gain is used to monitor response of children with severe acute malnutrition (SAM) to feeding programs. In public health, changes in body weight over time are often monitored because of their increased risk of mortality. New U.S guidelines for gestational weight gain are now available which have been adopted by WHO for low-income populations until specific country cutoffs are available.

    BMI is currently the indicator of choice for defining under­weight, over­weight, and obesity in adults and children. However, the limitations of BMI alone has led to the use of both BMI and waist circumference because the distribution of abdominal visceral fat has an even greater cardio­metabolic risk than excess body fat per se. The BMI cutoffs used to classify adults as under­weight (BMI < 18.5kg/m2), over­weight (BMI > 25kg/m2), and obese (BMI > 30kg/m2) are based on adverse health risks and sometimes risk of mortality. In adults, WHO recommends the use of universal BMI cutoffs for over­weight (BMI > 25kg/m2) and obesity (BMI > 30kg/m2); three classes of obesity are also defined. This classification has been adopted by several countries, including Canada and the United States, with the highest class indicative of severe obesity (i.e., BMI > 40kg/m2). Cutoffs to define grades of low BMI values indicative of under­weight in adults are also recommended together with a classification to identify populations with a public health problem. Increasingly, low- and middle-income countries are impacted by both under- and over-nutrition, a condition termed the “double burden of malnutrition”.

    In children, no simple cutoff to define thinness, over­weight, or obesity can be used because BMI has a characteristic curvilinear shape with age. Instead, countries have compiled their own ways of defining thinness, over­weight, and obesity in children. Three classification schemes are described with cutoffs defined by BMI-for-age Z‑scores or per­cent­iles based on international or national growth reference data. They include those set by the International Obesity Task Force (IOTF), the new WHO classification based on their international growth standard and growth reference, and the U.S classification based on the 2000 CDC growth charts. Clearly, there is an urgent need for consensus on BMI cutoffs for thinness, over­weight, and obesity in childhood that are defined by adverse health risks. Only in this way can valid international comparisons across countries on the prevalence of thinness, over­weight, and obesity in childhood be made.

    • 9.1: Anthro­pometric assess­ment of body size (10.0)
      This page discusses the importance of anthropometric measurements, such as stature and body weight, for health assessment in low-income countries. It highlights standardized procedures that lead to key indices, like weight-for-stature and stature-for-age, endorsed by the WHO to differentiate stunting from wasting.
    • 9.2: Measure­ments of body size (10.1)
      This page outlines the importance of various growth measurements, such as head circumference, recumbent length, standing height, weight, and elbow breadth, crucial for assessing children's health. It emphasizes standardized protocols, proper positioning, and the use of trained personnel to ensure accuracy. Techniques like knemometry for lower leg length and the use of precision scales for weight measurement are highlighted, along with the significance of population-specific equations.
    • 9.3: Growth indices, indicators, and recom­mended growth refer­ence data (10.2)
      This page covers the significance of anthropometric indices and growth standards in evaluating child nutrition, highlighting distinctions between WHO and NCHS references and their impacts on malnutrition rates. It discusses various growth metrics, challenges in interpretation, and the dual burden of malnutrition. Key targets by WHO/UNICEF aim to reduce stunting and improve nutritional health by 2030.
    • 9.4: Body mass index in adults (10.3)
      This page discusses the limitations of Body Mass Index (BMI) in assessing overweight and obesity, including misclassifications and the need for waist circumference as a complementary measure for health risks. It highlights age, race, and economic factors impacting body composition, particularly in low- and middle-income countries where obesity is on the rise.
    • 9.5: BMI in children and adolescents (10.4)
      This page outlines the complexities of using Body Mass Index (BMI) to classify overweight, obesity, and thinness in children and adolescents. It discusses varying BMI standards from the International Obesity Task Force (IOTF) and WHO, as well as U.S. CDC methodologies. Challenges arise from age dependency, ethnic differences, and varying national standards, complicating international comparisons.

    This page titled 9: Body size (Chapter 10) is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Rosalind S. Gibson via source content that was edited to the style and standards of the LibreTexts platform.