Human body composition. Reference data and anthropometric equations. The metabolic syndrome and risk

Abstract

The determination of body composition is a key to the understanding of the relation between obesity and disease. In order to evaluate body composition data, reference values are needed. Since methods with high validity and reproducibility are expensive and often time consuming, simpler techniques based on anthropometry are needed. The prevalence of the metabolic syndrome is increasing. Consensus regarding a clinically useful definition of the syndrome predicting mortality and related morbidity is needed.Aims: 1) to establish population-based sex- and age-specific reference data with respect to dual energy x-ray absorptiometry (DEXA) determined body composition, 2) to examine if individual rather than fixed total body potassium/fat-free mass (TBK/FFM) ratios could improve FFM determinations, 3) to establish and validate optimal weight-for-height indices for prediction of body fat, and, 4) to analyse associations between definitions of the metabolic syndrome and mortality and atherosclerotic morbidity.Methods: 1135 men and women, 37-61 years of age from the Swedish Obese Subjects (SOS) reference study. In addition, 149 subjects aged 30-58 years from the intervention trail XENical in the prevention of Diabetes in Obese Subjects (XENDOS) were included in prediction of body fat. Body mass index (BMI) ranged from 17.6 to 46.1 kg/m2. Body composition was measured by DEXA, and TBK was determined by whole body counting. Anthropometric measurements: body weight, height, waist and hip circumferences and sagittal trunk diameter. Biochemistry: diabetes- and cardiovascular risk factors and hepatic function tests.Results: The prevalence of obesity in the SOS reference study was 10% in both men and women. At BMI 25 kg/m2, relative (absolute) body fat was 24% (19 kg) in men and 36% (25 kg) in women. Secular increases in abdominal fat distribution were observed in women but not in men. In sex-specific equations, TBK/FFM could be predicted from weight, height and age with errors <5%. Body fat in kg could be optimally and linearly predicted by weight/height (W/H) whereas percent body fat was optimally and curvilinearly predicted by BMI. Percent body fat asymptotically reached an upper maximal value of 56% in men and 52% in women. All-cause mortality was increased significantly in subjects with the metabolic syndrome according to WHO but not according to the EGIR (European Group for the study of Insulin Resistance) or the ATPIII (Adult Treatment Panel-III) definitions of the metabolic syndrome. Incident atherosclerotic morbidity was related to the WHO and EGIR definitions of the metabolic syndrome but not to the ATPIII definition.Conclusions: 1) Sex- and age-specific reference data on body composition has been provided. 2) In each sex, TBK/FFM can be predicted from age, weight and height. 3) Body fat in kg should be predicted from W/H rather than percent body fat from BMI. 4) Inclusion of glucose intolerance and/or insulin resistance as obligatory criteria in the definition of the metabolic syndrome seems to be important for the prediction of mortality and incident atherosclerotic morbidity.