Anthropometry and Methods of Body Composition Measurement for Research and Field Application in the Elderly

European Journal of Clinical Nutrition (2000) 54, Suppl 3, S26±S32 ß 2000 Macmillan Publishers Ltd All rights reserved 0954±3007/00 $15.00 www.nature.com/ejcn Anthropometry and methods of body composition measurement for research and ®eld application in the elderly SB Heyms®eld1*, C NunÄez1, C Testolin1 and D Gallagher1 1Obesity Research Center, Department of Medicine, St Luke's-Roosevelt Hospital Center, Columbia University College of Physicians and Surgeons, New York, NY, USA Evaluation of body composition is important in the study of human energy and protein metabolism as methods are available for quantifying energy stores and protein content at a single point in time; energy ± protein balance can be monitored over time; and dynamic measures of energy and protein metabolism can be referenced to body mass and related measurable components for between-individual comparisons. This review emphasizes the need for considering subject age when developing body composition component prediction models that are applied in elderly populations. An overview of body composition research is provided that emphasizes compartment and level de®nitions and interrelations. Two broad method categories, mechanistic and descriptive, are then critically examined in relation to their role in energy-protein metabolism and aging research. Our collective review indicates that all major body composition components are now measurable using one or more methods that are based on non age-dependent assumptions. We also found that some methods, particularly descriptive ®eld methods (eg anthropometry), may be based on age-sensitive assumptions and measurements and suggestions for future development of these methods are provided. Lastly, as body composition differences between races, cultures, and countries are now recognized, it would be useful to create international cooperative groups with the aim of developing widely applicable descriptive ®eld methods based on simple available techniques such as anthropometry and bioimpedance analysis. Descriptors: anthropometry; body composition; aging European Journal of Clinical Nutrition (2000) 54, Suppl 3, S26±S32 `Science is fundamentally an exercise in measurement.' Human body components and their organization Dr Harold Varmus, NIH Director, 1999. The ®rst area, body composition rules, involves component and level de®nitions and also includes the study of quanti- tative component relationships. The 35 main body com- Overview position components are organized into ®ve levels of Evaluation of human body composition relates to the topic increasing complexity, atomic, molecular, cellular, tissue- of this workshop in two respects: methods are available for system, and whole body. The ®rst four levels and the quantifying energy stores and protein content at a single respective main components at each level are depicted in point in time and energy ± protein balance can be monitored Figure 2 (Heyms®eld et al, 1998). over time; and dynamic measures of energy and protein Subjects who are weight stable over short time periods metabolism can be referenced to body mass and related (ie several weeks) are in a body composition `steady state' measurable components for between-individual compari- in which component mass balance approaches zero. An sons. The speci®c aim of this review is to emphasize the important aspect of body composition research is establish- need for considering subject age when developing body ing the component relationships that exist under these composition component prediction models that are applied conditions. These include, for example, the water content in elderly populations. of fat-free body mass (ie total body water=fat-free body mass) and the potassium content of fat-free body mass (ie Human body composition research total body potassium=fat-free body mass). These relation- The study of human body composition dates back several ships are important and interesting because of their intrinsic centuries, although major research interest evolved in the scienti®c value (Wang et al, 2000) and because they are early years following World War II (Wang et al, 1999). The often the formative basis of body composition model modern study of body composition encompasses three development (Wang et al, 1995). This is a critical area in areas Ð body composition rules, methodology, and altera- the study of aging as component relationships may change tions (Figure 1). Each of these areas interacts with the other with senescence, physical activity, and nutritional status. two, and this is particularly important in the study of aging. Body composition models developed in young subjects Alterations in body composition that occur with aging may, may therefore not be accurate in older individuals. in turn, modify both component relationships or `rules' and body composition methods. Body composition method organization *Correspondence: SB Heyms®eld, Weight Control Unit, 1090 Amsterdam Body composition methods can be broadly classi®ed Avenue, 14th Floor, New York, NY 10025, USA. as in vitro and in vivo (Wang et al, 1995; Heyms®eld E-mail: [email protected] et al, 1996). This review only examines available in vivo Methods of body composition measurement SB Heyms®eld et al S27 Mechanistic methods are often based on models that have an underlying physical or biological basis. The typical form of mechanistic models is C b Q where b is usually a model relating Q to C. Some typical models are the ratios of total body water and potassium to fat-free body mass (ie TBW=FFM 0.73 and TBK= Figure 1 The study of human body composition: three research areas. FFM 60 mmol=kg) (Wang et al, 1995). As with descrip- From Wang et al (1995), with permission. tive methods, age should be considered when developing mechanistic methods. Available methods Mechanistic All of the methods in this category are presently formulated on mechanistic models. In vivo neutron activation. Nitrogen, carbon, hydrogen, phosphorus, sodium, chlorine, calcium and oxygen are all measurable in vivo by a group of methods referred to as neutron activation analysis. A source emits a neutron stream that interacts with subject tissues. The resulting decay products of activated elements can be counted by detectors and elemental mass established. By linking ele- Figure 2 Some of the main components at the ®rst four body composi- ments with molecular level components using simultaneous tion levels. From Heyms®eld et al (1998), with permission. equations, mechanistic models can be prepared for all major molecular level components (Heyms®eld et al, 1996). For example, C, N and Ca can be used to solve methods. In vivo methods can be further classi®ed accord- for total body fat, protein and bone mineral mass (Kehayias ing to any one of several descriptors: measurement location et al, 1991). Although limited in availability, neutron (laboratory=®eld); measurement frequency (static=dyna- activation analysis is extremely valuable in body composi- mic); mathematical function type (model=descriptive); tion research as there are no presently known age or and portion of the body evaluated (regional=whole-body). gender-dependencies of currently applied models. More- The primary organization paradigm applied in this review over, components such as total body protein are best is based upon mathematical function type. evaluated using neutron activation methods (Chettle & All in vivo methods are by necessity indirect (Wang Fremlin, 1984). et al, 1995). That is, some measurable somatic or physical Neutron activation methods thus afford the opportunity property is exploited in quantifying the component of to quantify molecular level components without potential interest. A useful and informative approach for organizing age-related bias in derived estimates. body composition methods is based on mathematical function type. The basic formula for estimating components (C) in vivo is Whole-body 40K counting. A small and constant percen- 40 C f Â Q tage of total body potassium (TBK) is radioactive ( K) and emits a characteristic g-ray. With appropriate shielding where f is mathematical function and Q is measurable from background, this g-ray can be counted using scintilla- quantity. Measurable quantities include various properties tion detectors. As the ratio of 40Kto39K is known and (eg tissue conductivity) and other components. Two broad constant, 39K and `total body potassium' can be estimated categories of mathematical function are recognized, accordingly. descriptive and mechanistic. All of the body's potassium is within the fat-free body Descriptive mathematical functions have the general mass component and the TBK=FFM ratio is reasonably form stable in the same subject over time and between different C a b Q subjects of the same gender. This allows development of mechanistic models based on assumed TBK ratios for sex where a and b are regression line intercepts and slopes, and potentially age (Forbes, 1987). respectively. A reference method is selected for measuring An example of the relationship between TBK and fat- the component of interest in a well-characterized subject free body mass is shown in Figure 3. The subjects are group. The property or predictor component (ie Q) is also healthy weight stable adults and TBK and fat-free body measured in the subjects and regression analysis is then mass were measured using 40K whole-body counting and used to develop the component estimation model. A key dual-energy X-ray absorptiometry (DXA), respectively. point is that descriptive models

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