Validity of methods of body composition assessment in young and older men and women

Resting energy expenditure is not increased in mildly hyperglycaemic obese diabetic patients

Resting energy expenditure (REE) is believed to be increased in type 2 diabetes, an increase that is associated with deteriorating glucose tolerance during its development. Meanwhile, insulin resistance, a state linked to obesity and observed in all type 2 diabetic patients, is associated with reduced REE. Our aim was to compare REE in obese patients with and without diabetes. REE, body composition (total body water, density, percentage fat and fat-free mass: 3-compartment model) and metabolic control were assessed in fifty obese Caucasian patients with diabetes (glycated haemoglobin level 7.6 (SD 1.5) %) and fifty obese patients who were non-diabetic. Despite being more overweight and younger, obese non-diabetic patients had an absolute REE (7.73 (SD 1.44) v. 8.12 (SD 1.37) MJ; P=0.17) and percentage fat-free mass similar to those of obese diabetic patients. Even when adjusted for differences in body composition, REE remained similar in both groups. Furthermore, REE (absolute and adjusted) was unaffected by both glucose level and control (glycated haemoglobin), with fat-free mass being the only determinant of REE. We conclude that REE is not necessarily increased by the presence of diabetes in obese people.

Indicadores antropométricos de excesso de gordura corporal em mulheres

O objetivo deste estudo foi determinar a sensibilidade, a especificidade e a concordância entre dois indicadores de excesso de gordura em mulheres. Foram avaliadas 65 mulheres (50-77 anos de idade), com massa corporal média de 70,3 ± 11kg, estatura de 158,0 ± 5,5cm, permitindo o cálculo do índice de massa corporal (IMC) e do recíproco do índice ponderal (RIP). O percentual de gordura, mensurado através da absortometria radiológica de dupla energia (%G DEXA), foi utilizado como o método de referência. A estatística descritiva, a correlação de linear de Pearson (r) e o índice de Kappa (k) foram utilizados para análise dos dados. O IMC, o RIP e o %G DEXA apresentaram escores médios de 28 ± 4,2kg.m-2; 38 ± 1,9cm.kg-1/3; e 38,1 ± 6,0%, respectivamente. A prevalência de excesso de gordura foi de 89,2% para o %G DEXA. O RIP e o IMC apresentaram prevalências de excesso de gordura de 83,1% e 73,8%, respectivamente. Os coeficientes de correlação linear de Pearson entre %G DEXA e o RIP (r = -0,76) e entre %G DEXA e o IMC (r = 0,72) foram significativos (p < 0,01). O índice de Kappa identificou associação de k = 0,31 entre as medidas de %G DEXA e IMC, e de k = 0,48 entre %G DEXA e RIP. Os indicadores antropométricos apresentaram índices de sensibilidade e especificidade altos (IMC = 79,3% e 71,4%; RIP = 90% e 71,4% respectivamente). A análise através da curva ROC (receiver operator characteristic curve) apresentou áreas sobre a curva de 0,80 para o IMC e de 0,83 para o RIP que não diferiram significativamente (p < 0,05). Os pontos de corte de 26,2kg.m-2 para o IMC e 39,3cm.kg-1/3 para o RIP demonstraram a melhor relação entre sensibilidade e especificidade na identificação de excesso de gordura. Assim, conclui-se que os indicadores antropométricos analisados não diferem em relação à identificação de excesso de gordura e que ambos apresentam valores de sensibilidade e especificidade altos na avaliação do excesso de gordura em mulheres acima de 50 anos de idade.

Aplicabilidade de equações na avaliação da composição corporal da população brasileira

O excesso de gordura corporal está, freqüentemente, associado a alterações metabólicas importantes e às doenças crônicas, como diabetes, hipertensão arterial e dislipidemias. A disponibilidade de métodos que permitam estimar a composição corporal é fundamental para avaliação de atletas e do estado de saúde de indivíduos. Entre os métodos existentes, as medidas de dobras cutâneas são habitualmente utilizadas na população brasileira, devido à sua facilidade e relativa precisão em estimar a gordura corporal. Entretanto, existem limitações quanto à utilização desse método, que podem implicar em erros de estimativas da gordura corporal importantes. A proposta deste trabalho é descrever os estudos que validaram essas equações e os principais fatores que influenciam a acurácia das mesmas na população em geral. Também são discutidos aspectos quanto à aplicabilidade dessas equações na população brasileira.

Evaluation of Lunar Prodigy dual-energy X-ray absorptiometry for assessing body composition in healthy persons and patients by comparison with the criterion 4-component model

BACKGROUND

Dual-energy X-ray absorptiometry (DXA) is widely used to assess body composition in research and clinical practice. Several studies have evaluated its accuracy in healthy persons; however, little attention has been directed to the same issue in patients.

OBJECTIVE

The objective was to compare the accuracy of the Lunar Prodigy DXA for body-composition analysis with that of the reference 4-component (4C) model in healthy subjects and in patients with 1 of 3 disease states.

DESIGN

A total of 215 subjects aged 5.0-21.3 y (n = 122 healthy nonobese subjects, n = 55 obese patients, n = 26 cystic fibrosis patients, and n = 12 patients with glycogen storage disease). Fat mass (FM), fat-free mass (FFM), and weight were measured by DXA and the 4C model.

RESULTS

The accuracy of DXA-measured body-composition outcomes differed significantly between groups. Factors independently predicting bias in weight, FM, FFM, and percentage body fat in multivariate models included age, sex, size, and disease state. Biases in FFM were not mirrored by equivalent opposite biases in FM because of confounding biases in weight.

CONCLUSIONS

The bias of DXA varies according to the sex, size, fatness, and disease state of the subjects, which indicates that DXA is unreliable for patient case-control studies and for longitudinal studies of persons who undergo significant changes in nutritional status between measurements. A single correction factor cannot adjust for inconsistent biases.

'Glucose control-related' and 'non-glucose control-related' effects of insulin on weight gain in newly insulin-treated type 2 diabetic patients

Insulin use is common in type 2 diabetes and is frequently accompanied by weight gain, the composition of which is poorly understood. The present study evaluates insulin-induced body composition changes. Body weight and composition of thirty-two type 2 diabetic patients undergoing their first 12 months of insulin therapy were compared with those observed in thirty-two type 2 diabetic patients previously treated on insulin (minimum 1 year). Body composition was determined by simultaneous body water spaces (bioelectrical impedance analysis) and body density measurements. After 6 months, glycosylated Hb (HbA1c) significantly improved in the newly treated group (P<0.0001), but remained stable in those treated previously. HbA1c did not differ between 6 and 12 months in the two groups. Body weight significantly (P=0.04) changed over 12 months in those newly treated only (+2.8 kg), essentially comprising fat-free mass (P=0.044). Fat mass remained unchanged (P=0.85) as did total body water, while extracellular: total body water ratio tended to increase in those newly treated (P=0.059). Weight changes correlated with HbA1c changes (R2 0.134, P=0.002) in the initial 6 months only. Insulin therapy leads to weight gain (2.8 kg), predominantly fat-free mass, over 12 months. After 6 months, newly treated patients continued gaining weight despite an unchanged HbA1c, suggesting the potential anabolic role of insulin in subsequent gains. Therefore, in the initial 6 months, weight gain can be attributed to a 'glucose control-related effect' and further gain appears to be due to a 'non-glucose control-related' effect of insulin treatment.

Prediction of DXA-determined whole body fat from skinfolds: importance of including skinfolds from the thigh and calf in young, healthy men and women

OBJECTIVE

To investigate the relationship of percent body fat (%fat), assessed by dual energy-X-ray absorptiometry (DXA) or a four-compartment model, with upper body and lower limb skinfolds.

DESIGN

Cross-sectional design involving forward stepwise and hierarchical multiple regression analyses to assess the relationship of %fat with skinfolds and a combination of four commonly used upper body skinfolds (biceps, triceps, subscapular and iliac crest) with the calf and thigh skinfolds.

SETTING

University research laboratory.

SUBJECTS

In all, 31 females, mean age 20.9 (+/-2.0) y, and 21 males, mean age 22.3 (+/-5.5) y volunteered for this study, which was approved by the Ethics Committee of the School of Sport, Health and Exercise Sciences, University of Wales, Bangor.

MEASUREMENTS

%fat from DXA in both groups, and %fat from a four-compartment (water, bone mineral mass, fat and residual) model (%fat4C) in females only. Skinfolds were measured at the abdomen, iliac crest, biceps, triceps, subscapular, calf and thigh.

RESULTS

All skinfolds were positively associated with DXA estimates of %fat (P < 0.01). In males and females, the thigh skinfold had the highest correlation with %fat. This was also observed when %fat4C was used as the criterion in females. Stepwise multiple regression analysis using %fatDXA as the criterion selected the thigh (R(2) = 0.82), calf (R(2) change 0.04) and iliac crest (R(2) change = 0.03) for females, and the thigh (R(2) = 0.79), iliac crest (R(2) change = 0.11) and abdomen (R(2) change = 0.03) for males (all P < 0.01). When %fat4C was used as the criterion in the females, only the thigh was selected as a significant predictor (R(2) = 0.76). Independent prediction factors were created from the sum of biceps, triceps, subscapular and iliac crest (sigma4skf) and from the sum of the thigh and calf (sigmathigh + calf). These factors were then entered into a hierarchical multiple linear regression analysis to predict percent fat. Order of entry was varied to allow the assessment of unique variance accounted for by each predictor. The sum of the thigh and calf explained more variance in %fatDXA than that explained by the sigma4skf alone, irrespective of the order of entry in both males and females. This was also observed when %fat4C was used as the criterion in the females.

CONCLUSIONS

The results of this study confirm that lower body skinfolds are highly related to percent body fat in fit and healthy young men and women, and uphold current recommendations by the British Olympic Association to include the thigh skinfold with sigma4skf. Conventional use of the sigma4skf to estimate percent body fat is significantly enhanced by the inclusion of the thigh and calf skinfolds, either independently or in combination. In this group of males and females, the sum of the thigh and calf skinfolds accounted for the most variance in percent fat.

Comparison of anthropometry to DXA: a new prediction equation for men

OBJECTIVE

This study compared three professionally recommended anthropometric body composition prediction equations for men to dual energy X-ray absorptiometry (DXA), and then developed an updated equation, DXA Criterion (DC) from DXA.

DESIGN

Cross-sectional.

SETTING

Exercise Physiology Lab. University of Missouri-Columbia, USA.

SUBJECTS

A total of 160 men aged 18-62 y old.

INTERVENTIONS

Percent body fat (%BF) by anthropometry was compared to DXA on the same day.

RESULTS

Although %BF was significantly correlated (r=0.923-0.942) (P<0.01) with DXA for all three equations, each equation underestimated %BF (range=3.1-3.3%) (P<0.01) compared to DXA. The following DC equation for men was created: %BF=0.465+0.180(Sigma7SF)-0.0002406(Sigma7SF)(2)+0.06619(age); (Sigma7SF=sum of chest, midaxillary, triceps, subscapular, abdomen, suprailiac, thigh; age=years). The predicted residual sum of squares (PRESS) R(2) was high (0.90) and the PRESS standard error of estimates was excellent (2.2% at the mean) for the DC equation when applied to our sample of 160 men.

CONCLUSIONS

The currently recommended anthropometric equations for men underestimate %BF compared to DXA. The DC equation yields a more accurate estimation of %BF in men aged 18-62 y old. The results from this study support the need for the current %BF standards and norms for men to be adjusted upward.

Endocrine control of body composition in infancy, childhood, and puberty

Body composition exhibits marked variations across the early human lifetime. The precise physiological mechanisms that drive such developmental adaptations are difficult to establish. This clinical challenge reflects an array of potentially confounding factors, such as marked intersubject differences in tissue compartments; the incremental nature of longitudinal intrasubject variations in body composition; technical limitations in quantitating the unobserved mass of mineral, fat, water, and muscle ad seriatim; and the multifold contributions of genetic, dietary, environmental, hormonal, nutritional, and behavioral signals to physical and sexual maturation. From an endocrine perspective (reviewed here), gonadal sex steroids and GH/IGF-I constitute prime determinants of evolving body composition. The present critical review examines hormonal regulation of body composition in infancy, childhood, and puberty.

Comparison of the Bod Pod and dual energy x-ray absorptiometry in men

The majority of studies investigating the accuracy of the Bod Pod have compared it to hydrostatic weighing (HW), the long held, and perhaps outdated 'gold standard' method of body composition analysis. Much less research has compared the Bod Pod to dual energy x-ray absorptiometry (DXA), a technique that is becoming popular as an alternative reference method. The purpose of this study was to compare per cent fat estimates by the Bod Pod to those of DXA in a large number of men. Participants were 160 men (32 +/- 11 years). Per cent body fat was estimated to be 19.4 +/- 6.8 and 21.6 +/- 8.4 for DXA and the Bod Pod, respectively. Although the two methods were highly correlated (0.94), the mean difference of 2.2% was significant (p < 0.01). The amount of difference increased as body fatness increased (p < 0.0001). The results of this study indicate that a difference between methods existed for our sample of men. It is uncertain exactly where the difference lies. Practitioners should be aware that even with the use of technologically sophisticated methods (i.e., Bod Pod, DXA), differences between methods exist and the determination of body composition is at best, an estimation.

Can body volume be determined by PET?

PURPOSE

To avoid dependence on body weight, the standardised uptake value (SUV) in positron emission tomography (PET) can instead be normalised to the lean body mass (LBM), which can be determined from body volume and mass. This study was designed to answer the following questions: Firstly, can the total body volume in principle be determined using PET? Secondly, is the precision of this measurement comparable to that achieved using an established standard method.

METHODS

Ten patients were examined during oncological whole-body PET examinations. The whole-body volume of the patients was determined from the transmission scan in PET. Air displacement plethysmography with BOD POD was used for comparison as the standard method of volume determination.

RESULTS

In all patients, the whole-body volumes could be determined using PET and the standard method. Bland and Altman [23] analysis for agreement between the volumes determined by the two methods (presentation of differences vs means) revealed a very small difference of -0.14 l. With a mean patient volume of 71.81+/-15.93 l, the relative systematic error is only <0.1%. On this basis, equality of the volume values determined by the two methods can be assumed.

CONCLUSION

PET can be used as a supplementary method for experimental determination of whole-body volume and total body fat in tumour patients. The fat content can be used to calculate the LBM and to determine body weight-independent SUVs (SUV(LBM)).

Effect of insulin treatment on the body composition of Type 2 diabetic patients

OBJECTIVE

Insulin is used commonly in Type 2 diabetes and is often accompanied by weight gain. The composition of this weight gain is poorly understood. Predominant increases in fat mass could increase cardiovascular risks. The aim of the study was to evaluate insulin-induced body composition changes.

RESEARCH DESIGN AND METHODS

Body weight and composition of 35 Type 2 diabetic patients during their first 6 months of insulin therapy was compared with those in 34 Type 2 diabetic individuals treated with insulin for at least 1 year prior to commencing the study. Body composition was determined by the simultaneous measurement of body water spaces and body density.

RESULTS

Over 6 months, glycaemic control improved in the new treatment group only (HbA(1c): 7.26 +/- 0.81 vs. 9.66 +/- 1.60%; P < 0.0001), remaining stable in the previously treated group (7.67 +/- 1.25 vs. 7.76 +/- 1.26%; P = NS). Weight significantly increased over time in the newly treated group (+1.7 kg; P = 0.04), but not in the previously treated group (-0.3 kg). It comprised of both fat (+0.85 kg) and fat-free mass (+0.55 kg). Total body water remained unchanged. Using bioelectrical impedance analysis, the gain in fat mass was +2.2 kg; P = 0.048.

CONCLUSIONS

Over 6 months, insulin therapy leads to a weight gain of 1.7 kg because of an increase in both fat and fat-free mass. When body composition is determined by bioelectrical impedance analysis, the results are biased by fluctuations in hydration.

Comparison of anthropometry to dual energy X-ray absorptiometry: a new prediction equation for women

The purpose of this study was to assess the accuracy of three recommended anthropometric equations for women and then develop an updated prediction equation using dual energy x-ray absorptiometry (DXA). The percentage of body fat (%BF) by anthropometry was significantly correlated (r = .896-.929; p < .01) with DXA, but each equation underestimated %BF (3.2-5.6 %BF; p < .01). The following DXA criterion (DC) equation was created: %BF= -6.40665 + 0.41946(S3SF) - 0.00126(S3SF)2 + 0.12515(hip) + 0.06473 (age); (S3SF = sum of triceps, suprailiac, thigh; hip = circumference in cm; age = years). The predicted residual sum of squares (PRESS) R2 was high (0.86), and the PRESS standard error of estimate (SEE) was low (2.5 %BF) for our sample of 150 women. The DC equation was further crosschecked on a separate sample of women (n = 25) and again showed excellent agreement. The DC equation appears to be a more accurate estimation of %BF in women.

Celiac disease as a cause of growth retardation in childhood

PURPOSE OF REVIEW

Celiac disease is a syndrome characterized by damage of the small intestinal mucosa caused by the gluten fraction of wheat proteins and similar alcohol-soluble proteins (prolamines) of barley and rye in genetically susceptible subjects. The presence of gluten in these subjects leads to a self- perpetuating mucosal damage, and the elimination of gluten results in full mucosal recovery. The clinical manifestations of celiac disease are protean in nature and vary markedly with the age of the patient, the duration and extent of disease, and the presence of extraintestinal pathologic changes. In addition to the classic gastrointestinal form, a variety of other clinical manifestations of the disease have been described, including atypical and asymptomatic forms. Although the typical form of celiac disease, characterized by failure to thrive, is still the most frequent presentation in the pediatric age group, severe growth delay is less commonly seen in developed countries.

RECENT FINDINGS

Recent epidemiologic studies suggest that celiac disease-associated growth retardation is becoming a tangible health problem in developing countries, where the problem has been historically overlooked. Given the protean nature of the clinical presentation of celiac disease, the diagnosis is extremely challenging and relies on a sensitive and specific algorithm that allows the identification of different manifestations of the disease. Serologic tests developed in the past decade provide a noninvasive tool for screening individuals at risk for the disease as well as the general population.

SUMMARY

The current gold standard for the diagnosis of celiac disease remains histologic confirmation of the intestinal damage in serologically positive individuals. The keystone treatment of celiac disease patients is a lifelong elimination diet in which food products containing gluten are avoided.

Áreas de secção transversa do braço: implicações técnicas e aplicações para avaliação da composição corporal e da força dinâmica máxima

As áreas do tecido muscular (A MB) e do anel de gordura do braço (A GB), podem ser estimadas por medidas antropométricas. OBJETIVO: Investigar a validade e o erro intertestador da antropometria para inferência A MB e do A GB. Secundariamente, estudou-se a previsão da força dos membros superiores e tronco através da A MB. MÉTODOS: Foram voluntários para este estudo 40 adultos masculinos jovens (25 ± 6 anos; 72,6 ± 9,4kg), divididos aleatoriamente nos grupos de validade interna (VI, n = 30) e validade externa (VE, n = 10). Determinou-se para VI, através de conceitos geométricos, a área total do braço (A TB), A MB, A GB e área percentual de gordura do braço. O somatório de oito dobras cutâneas (S DC8) foi empregado como índice da adiposidade corporal. A força dos membros superiores e do tronco foi medida através da carga máxima alcançada no exercício supino reto livre (1-RM). As medidas antropométricas foram realizadas por dois avaliadores independentes. Os dados foram tratados por meio da análise de regressão, coeficiente de correlação intraclasse (ICC) e teste t de Student pareado (a < 0,05). RESULTADOS: A variância do S DC8 pode ser explicada em 93% (EPE = 14,6mm) a partir da A GB e do peso corporal. A A MB explicou em 66,1% (EPE = 9kg) a 1-RM. Não se observou diferença significativa, para o grupo VE, entre os valores medidos (84,2 ± 16,2kg) e preditos (78,4 ± 14,2kg) de 1-RM. Observou-se pouca variação entre os avaliadores para A MB (ICC = 0,99), A GB (ICC = 0,96) e A TB (ICC = 0,99). CONCLUSÃO: A antropometria pode ser empregada para inferência da A MB e do A GB, com boa concordância entre avaliadores, para estimativa da adiposidade corporal e da força dos membros superiores e tronco.

Impact of indexing resting metabolic rate against fat-free mass determined by different body composition models

OBJECTIVE

To examine the differences arising from indexing resting metabolic rate (RMR) against fat-free mass (FFM) determined using two-, three- and four-compartment body composition models.

DESIGN

All RMR and body composition measurements were conducted on the same day for each subject following compliance with premeasurement protocols.

SUBJECTS

Data were generated from measurements on 104 males (age 32.1+/-12.1 y (mean+/-s.d.); body mass 81.15+/-12.85 kg; height 179.5+/-6.5 cm; body fat 20.6+/-7.6%).

INTERVENTIONS

Body density (BD), total body water (TBW) and bone mineral mass (BMM) were measured by hydrodensitometry, deuterium dilution and dual energy X-ray absorptiometry (DXA), respectively. These measures were used to determine two (hydrodensitometry: BD; hydrometry: TBW)-, three (BD and TBW)- and four- compartment (BD, TBW and BMM) FFM values. DXA also provided three compartment derived FFM values. RMR was measured using open circuit indirect calorimetry.

RESULTS

Three (body fat group: lean, moderate, high) x five (body composition determination: hydrodensitometry, hydrometry, three-compartment, DXA, four-compartment) ANOVAs were conducted on FFM and RMR kJ.kg FFM(-1).d(-1). Within-group comparisons revealed that hydrodensitometry and DXA were associated with significant (P<0.001) overestimations and underestimations of FFM and RMR kJ.kg FFM(-1).d(-1), respectively, compared with four-compartment-derived criterion values. A significant interaction (P<0.001) resulted from DXA's greater deviations from criterion values in lean subjects. While hydrometric means were not significantly (P> or =0.68) different from criterion values intraindividual differences were large (FFM: -1.5 to 2.9 kg; RMR: -6.0 to 3.2 kJ.kg FFM(-1).d(-1)).

CONCLUSION

The relationship between RMR kJ.kg FFM(-1).d(-1) and exercise status would best be investigated using three (BD, TBW)- or four (BD, TBW, BMM)-compartment body composition models to determine FFM. Other models either significantly underestimate indexed RMR (hydrodensitometry, DXA) or display large intraindividual differences (hydrometry) compared with four-compartment derived criterion values.

SPONSORSHIP

Australian Research Council (small grants scheme).

Comparison of body composition methods in overweight and obese children

The objective of the present study was to investigate the accuracy of percent body fat (%fat) estimates from dual-energy X-ray absorptiometry, air-displacement plethysmography (ADP), and total body water (TBW) against a criterion four-compartment (4C) model in overweight and obese children. A volunteer sample of 30 children (18 male and 12 female), age of (mean ± SD) 14.10 ± 1.83 yr, body mass index of 31.6 ± 5.5 kg/m, and %fat (4C model) of 41.2 ± 8.2%, was assessed. Body density measurements were converted to %fat estimates by using the general equation of Siri (ADPSiri) (Siri WE. Techniques for Measuring Body Composition. 1961) and the age- and gender-specific constants of Lohman (ADPLoh) (Lohman TG. Exercise and Sport Sciences Reviews. 1986). TBW measurements were converted to %fat estimates by assuming that water accounts for 73% of fat-free mass (TBW73) and by utilizing the age- and gender-specific water contents of Lohman (TBWLoh). All estimates of %fat were highly correlated with those of the 4C model ( r ≥ 0.95, P < 0.001; SE ≤ 2.14). For %fat, the total error and mean difference ± 95% limits of agreement compared with the 4C model were 2.50, 1.8 ± 3.5 (ADPSiri); 1.82, -0.04 ± 3.6 (ADPLoh); 2.86, -2.0 ± 4.1 (TBW73); 1.90, -0.3 ± 3.8 (TBWLoh); and 2.74, 1.9 ± 4.0 DXA (dual-energy X-ray absorptiometry), respectively. In conclusion, in overweight and obese children, ADPLoh and TBWLoh were the most accurate methods of measuring %fat compared with a 4C model. However, all methods under consideration produced similar limits of agreement.

Personality characteristics as predictors of underreporting of energy intake on 24-hour dietary recall interviews

OBJECTIVE

To identify characteristics associated with misreporting of energy intake during 24-hour dietary recalls (24 HR).

DESIGN

Ninety-eight subjects were administered two 24 HRs. Energy expenditure was determined by doubly labeled water (44 subjects) or intake balance (54 subjects). Data on subjects' physical, lifestyle, and psychosocial characteristics were also collected. Subjects/setting At the Beltsville Human Nutrition Research Center 52 women and 46 men were administered 24HR and completed lifestyle and personality questionnaires and a memory test. Physical characteristics such as weight, percent body fat, and total energy expenditure were measured. Statistical analysis The influences of subject parameters on energy misreporting were assessed by linear regression and Pearson product-moment correlation analysis for continuous variables and by ANOVA for discrete variables. Stepwise regression was used to identify key factors in underreporting.

RESULTS

Factors particularly important in predicting underreporting of energy intake include factors indicating dissatisfaction with body image; for example, a 398 kcal/day underreport in subjects attempting weight loss during the past year with a nearly 500 kcal/day underreport in women. Overall, women underreported by 393 kcal/day relative to men and women evinced a social desirability bias amounting to a 26 kcal underreport for each point on the social desirability scale. Gender differences also were evident in the effect of percent body fat (with men underreporting about 16 kcal/day/percent body fat) and in departure from self-reported ideal body weight (with women underreporting about 21 kcal/day/kg).

APPLICATIONS/CONCLUSIONS

Body image and fatness are key factors on which health professionals should focus when seeking predictors of underreporting of dietary intake. Dietary interviews must be conducted to minimize bias related to subjects' tendencies to win approval and avoid censure by the interviewer. In addition, dissatisfaction with body image may lead to underestimation of food intake, therefore reducing likelihood of success in weight loss. Thus, health care professionals involved in weight loss counseling may achieve better success if treatment includes generating a more positive body image.

Development and validation of skinfold-thickness prediction equations with a 4-compartment model

BACKGROUND

Skinfold-thickness measurements are commonly obtained for the indirect assessment of body composition.

OBJECTIVE

We developed new skinfold-thickness equations by using a 4-compartment model as the reference. Additionally, we compared our new equations with the Durnin and Womersley and Jackson and Pollock skinfold-thickness equations to evaluate each equation's validity and precision.

DESIGN

Data from 681 healthy, white adults were used. Percentage body fat (%BF) values were calculated by using the 4-compartment model. The cohort was then divided into validation and cross-validation groups. Equations were developed by using regression analyses and the 4-compartment model. All equations were then tested by using the cross-validation group. Tests for accuracy included mean differences, R(2), and Bland-Altman plots. Precision was evaluated by comparing root mean squared errors.

RESULTS

Our new equations' estimated means for %BF in men and women (22.7% and 32.6%, respectively) were closest to the corresponding 4-compartment values (22.8% and 32.8%). The Durnin and Womersley equation means in men and women (20.0% and 31.0%, respectively) and the Jackson and Pollock mean in women (26.2%) underestimated %BF. All equations showed a tendency toward underestimation in subjects with higher %BF. Bland-Altman plots showed limited agreement between Durnin and Wormersley, Jackson and Pollock, and the 4-compartment model. Precision was similar among all the equations.

CONCLUSIONS

We developed accurate and precise skinfold-thickness equations by using a 4-compartment model as the method of reference. Additionally, we found that the skinfold-thickness equations frequently used by clinicians and practitioners underestimate %BF.

Validation of bioelectrical impedance analysis in patients with amyotrophic lateral sclerosis

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a neurologic disease with an unfavorable prognosis that may be accompanied by malnutrition or overweight. Nutritional status is difficult to evaluate in these patients because of their physical limitations and the asymmetry of their disease involvement. Bioelectrical impedance analysis (BIA), which enables bedside analysis of body compartments, has not been adequately validated for use in patients with ALS.

OBJECTIVE

We compared reference measures of fat-free mass (FFM(a)), obtained by dual-energy X-ray absorptiometry, with FFM obtained by BIA and by the skinfold-thickness technique.

DESIGN

We measured FFM(a) in 32 ALS patients. Anthropometric measures included weight, height, skinfold thickness, and arm and wrist circumferences. The fat mass obtained from the skinfold-thickness measures enabled us to calculate FFM. BIA was performed by measuring the bioimpedances at 5, 50, and 100 kHz of each side of the body and from one side to the other. FFM was calculated by using the instrument's internal software and by using 3 standard equations. The concordance between the methods was evaluated by the Bland-Altman test.

RESULTS

Two of the 16 measured FFM values were not significantly different from FFM(a). However, the risk of dispersion was too high to be acceptable in practice. An equation was then developed by using multivariate analysis, with impedance at 50 kHz. This equation was validated in a second population of 15 ALS patients and with the use of 2 successive measurements performed on 18 patients.

CONCLUSION

BIA is a simple technique that is valid for use in ALS patients, both for a single exam measure and for longitudinal monitoring, with the use of an adapted equation and a frequency of 50 kHz.

Growth hormone treatment improves body composition in adults with Prader-Willi syndrome

OBJECTIVE

Low growth hormone (GH) secretion and hypogonadism are common in patients with Prader-Willi syndrome (PWS). In this study we present the effects of GH treatment on body composition and metabolism in adults with PWS.

PATIENTS AND MEASUREMENTS

Nineteen patients with clinical PWS were recruited, 13 had PWS genotype. They were randomised to treatment with placebo or GH (Genotropin, Pharmacia Corporation, Sweden) 0.8 IU (0.2 mg) daily for 1 month and then 1.6 IU (0.5 mg) daily for 5 months. Thereafter patients received open label treatment so that all had 12 months of active GH treatment. Doses were individually titrated to keep serum IGF-I within the normal range for age. Body composition using dual energy X-ray absorptiometry (DXA), metabolic and endocrinological parameters, including oral glucose tolerance test (OGTT), were studied every 6 months. Seventeen patients, nine men and eight women, 17-32 years of age, with a mean body mass index (BMI) of 35 +/- 3.2 kg/m2 completed the study.

RESULTS

Compared to placebo, GH treatment increased IGF-I (P < 0.01) levels and decreased body fat (P = 0.04). When all patients recieved GH treatment a mean reduction in body fat of 2.5% (P < 0.01) concomitant with a mean increase in lean body mass of 2.2 kg (P < 0.05) was seen. Significant changes in body composition were only seen in the patients with the PWS genotype. Lipid profiles were normal in most patients before treatment and did not change. OGTT was impaired in five patients at 12 months, but two of these patients increased in fat mass. Insulin levels were unchanged. According to homeostasis model assessment (HOMA), insulin resistance did not change. Side-effects attributed to water retention occurred in three patients, one of whom had to be given increased diuretic therapy.

CONCLUSION

This study shows beneficial effects of GH treatment on body composition in adult PWS patients without significant side-effects. Consequently, further studies are encouraged.

Percent body fat via DEXA: comparison with a four-compartment model

This study compared body composition by dual-energy X-ray absorptiometry (DEXA; Lunar DPX-L) with that via a four-compartment (4C; water, bone mineral mass, fat, and residual) model. Relative body fat was determined for 152 healthy adults [30.0 +/- 11.1 (SD) yr; 75.10 +/- 14.88 kg; 176.3 +/- 8.7 cm] aged from 18 to 59 yr. The 4C approach [20.7% body fat (%BF)] resulted in a significantly (P < 0.001) higher mean %BF compared with DEXA (18.9% BF), with intraindividual variations ranging from -2.6 to 7.3% BF. Linear regression and a Bland and Altman plot demonstrated the tendency for DEXA to progressively underestimate the %BF of leaner individuals compared with the criterion 4C model (4C %BF = 0.862 x DEXA %BF + 4.417; r(2) = 0.952, standard error of estimate = 1.6% BF). This bias was not attributable to variations in fat-free mass hydration but may have been due to beam-hardening errors that resulted from differences in anterior-posterior tissue thickness.

Impact of abdominal visceral fat, growth hormone, fitness, and insulin on lipids and lipoproteins in older adults

We examined the relationship between abdominal visceral fat (AVF) and plasma concentrations of lipids and lipoproteins in 19 females (F) (not on estrogen) and 31 males (M) over the age of 60 (age = 66.8 years). In addition, the effects of growth hormone (GH) release, fitness (Vo(2) peak), insulin, and glucose concentrations (both fasting and in response to an oral glucose tolerance test) on lipids were examined. Subjects were categorized by low (L) and high (H) AVF (L < 130 cm(2), H > 130 cm(2)), fat mass (FM) (above or below median value), and AVF corrected for fat mass. Factorial analysis of variance (ANOVA) showed that when subjects were divided by AVF and FM, similar results were observed with H > L (P <.05) for very-low-density lipoprotein-cholesterol (VLDL-C), triglycerides (TG), VLDL-TG, apolipoprotein (apo)-B, apo-B VLDL, cholesterol (Chol)/high-density lipoprotein (HDL), LDL/HDL, apoB/A1 and L > H for HDL, HDL(2), HDL(3), apo A1, and LDL/apo-B LDL. Gender differences were also observed with F > M for Chol, LDL, HDL, and HDL(2). When AVF was corrected for FM, these gender differences were still present. After correcting for FM, differences remained between H and L AVF groups for VLDL, TG, VLDL-TG, apo-B, apo-B LDL, apo-B VLDL, apoB/A1 (P <.05). Twenty-four hour integrated GH concentration (IGHC) was inversely related to VLDL, TG, VLDL TG, LDL TG, apoB, apoB VLDL, apoB LDL, Chol/HDL, LDL/HDL, and apoB/A1 in F, but not M (P <.05). Vo(2) peak was directly related to Chol, LDL, HDL(3), and apoB LDL with stronger relationships observed in F. Fasting insulin was related to lipids and lipoproteins in both men and women. These data suggest that, in older adults, elevated levels of AVF, FM, and AVF corrected for FM are associated with unfavorable lipid-lipoprotein profiles and extend similar findings reported in younger males and females with elevated AVF. These data also support previous findings indicating that AVF is a primary determinant of GH release.

Assessing the validity of body mass index standards in early postmenopausal women

OBJECTIVE

To examine the relationship between percentage of total body fat (%Fat) and body mass index (BMI) in early postmenopausal women and to evaluate the validity of the BMI standards for obesity established by the NIH.

RESEARCH METHODS AND PROCEDURES

Three hundred seventeen healthy, sedentary, postmenopausal women (ages, 40 to 66 years; BMI, 18 to 35 kg/m(2); 3 to 10 years postmenopausal) participated in the study. Height, weight, BMI, and %Fat, as assessed by DXA, were measured. Receiver operating characteristic analysis was performed to evaluate the ability of BMI to discriminate obesity from non-obesity using 38%Fat as the criterion value.

RESULTS

A moderately high relationship was observed between BMI and %Fat (r = 0.81; y = 1.41x + 2.65) with a SE of estimate of 3.9%. Eighty-one percent of other studies examined fell within 1 SE of estimate as derived from our study. Receiver operating characteristic analysis showed that BMI is a good diagnostic test for obesity. The cutoff for BMI corresponding to the criterion value of 38%Fat that maximized the sum of the sensitivity and specificity was 24.9 kg/m(2). The true-positive (sensitivity) and false-positive (1--specificity) rates were 84.4% and 14.6%, respectively. The area under the curve estimate for BMI was 0.914.

DISCUSSION

There is a strong association between %Fat and BMI in postmenopausal women. Current NIH BMI-based classifications for obesity may be misleading based on currently proposed %Fat standards. BMI >25 kg/m(2) rather than BMI >30 kg/m(2) may be superior for diagnosing obesity in postmenopausal women.

Effect of 6-month adherence to a very low carbohydrate diet program

To determine the effect of a 6-month very low carbohydrate diet program on body weight and other metabolic parameters.Fifty-one overweight or obese healthy volunteers who wanted to lose weight were placed on a very low carbohydrate diet (<25 g/d), with no limit on caloric intake. They also received nutritional supplementation and recommendations about exercise, and attended group meetings at a research clinic. The outcomes were body weight, body mass index, percentage of body fat (estimated by skinfold thickness), serum chemistry and lipid values, 24-hour urine measurements, and subjective adverse effects.Forty-one (80%) of the 51 subjects attended visits through 6 months. In these subjects, the mean (+/- SD) body weight decreased 10.3% +/- 5.9% (P <0.001) from baseline to 6 months (body weight reduction of 9.0 +/- 5.3 kg and body mass index reduction of 3.2 +/- 1.9 kg/m(2)). The mean percentage of body weight that was fat decreased 2.9% +/- 3.2% from baseline to 6 months (P <0.001). The mean serum bicarbonate level decreased 2 +/- 2.4 mmol/L (P <0.001) and blood urea nitrogen level increased 2 +/- 4 mg/dL (P <0.001). Serum total cholesterol level decreased 11 +/- 26 mg/dL (P = 0.006), low-density lipoprotein cholesterol level decreased 10 +/- 25 mg/dL (P = 0.01), triglyceride level decreased 56 +/- 45 mg/dL (P <0.001), high-density lipoprotein (HDL) cholesterol level increased 10 +/- 8 mg/dL (P <0.001), and the cholesterol/HDL cholesterol ratio decreased 0.9 +/- 0.6 units (P <0.001). There were no serious adverse effects, but the possibility of adverse effects in the 10 subjects who did not adhere to the program cannot be eliminated.A very low carbohydrate diet program led to sustained weight loss during a 6-month period. Further controlled research is warranted.

Regional muscle and adipose tissue amino acid metabolism in lean and obese women

The effect of obesity on regional skeletal muscle and adipose tissue amino acid metabolism is not known. We evaluated systemic and regional (forearm and abdominal subcutaneous adipose tissue) amino acid metabolism, by use of a combination of stable isotope tracer and arteriovenous balance methods, in five lean women [body mass index (BMI) <25 kg/m(2)] and five women with abdominal obesity (BMI 35.0-39.9 kg/m(2); waist circumference >100 cm) who were matched on fat-free mass (FFM). All subjects were studied at 22 h of fasting to ensure that the subjects were in net protein breakdown during this early phase of starvation. Leucine rate of appearance in plasma (an index of whole body proteolysis), expressed per unit of FFM, was not significantly different between lean and obese groups (2.05 +/- 0.18 and 2.34 +/- 0.04 micromol x kg FFM(-1) x min(-1), respectively). However, the rate of leucine release from forearm and adipose tissues in obese women (24.0 +/- 4.8 and 16.6 +/- 6.5 nmol x 100 g(-1) x min(-1), respectively) was lower than in lean women (66.8 +/- 10.6 and 38.6 +/- 7.0 nmol x 100 g(-1) x min(-1), respectively; P < 0.05). Approximately 5-10% of total whole body leucine release into plasma was derived from adipose tissue in lean and obese women. The results of this study demonstrate that the rate of release of amino acids per unit of forearm and adipose tissue at 22 h of fasting is lower in women with abdominal obesity than in lean women, which may help obese women decrease body protein losses during fasting. In addition, adipose tissue is a quantitatively important site for proteolysis in both lean and obese subjects.

Peak VO2 correction for fat-free mass estimated by anthropometry and DEXA

PURPOSE

Anthropometric (ANTHRO) and dual-energy x-ray absorptiometric (DEXA) estimates of total body and leg fat-free masses (FFM) were obtained in 77 randomly selected sedentary men and women, aged 20-80: intermethod limits of agreement and their clinical significance, as inferred from the differences on peak VO2 corrected for FFMANTHRO and FFMDEXA, were determined.

METHODS

Limits of agreement were calculated as mean bias +/- 95% confidence intervals: peak VO2 at maximum cycle ergometry was related to FFMANTHRO and FFMDEXA by using both standard (y x x(-1)) and power function ratios (allometry).

RESULTS

Data distribution of the ANTHRO-DEXA differences presented significant heteroscedasticity in both sexes, i.e., differences were proportional to the mean (P < 0.05). After logarithmic transformation, the mean bias +/- 95% limits of agreement were expressed as ratios (ANTHRO x DEXA(-1) x// error ratio): these corresponded to 0.95 x// 1.11 or 0.99 x// 1.15 for total body FFM and 0.90 x// 1.10 or 1.02 x// 1.07 for leg FFM in men and women, respectively. In addition, we found different allometric exponents for FFMANTHRO and FFMDEXA: the intermethod differences, therefore, increased after power function expression (P < 0.05).

CONCLUSION

Discrepancies between ANTHRO and DEXA measurements of FFM depend on the magnitude of the estimate: differences are typically within 10 to 15%. Importantly, FFM-corrected peak VO2 values can vary according to the method chosen for body composition assessment, especially when allometry is used for peak VO2 correction. These results demonstrate that ANTHRO-DEXA differences in FFM estimation do have relevant practical consequences for the analysis of maximum aerobic capacity in nontrained humans.

Comparison of the BOD POD with the four-compartment model in adult females

PURPOSE

This study was designed to compare the accuracy and bias in estimates of total body density (Db) by hydrostatic weighing (HW) and the BOD POD, and percent body fat (%fat) by the BOD POD with the four-compartment model (4C model) in 42 adult females. Furthermore, the role of the aqueous and mineral fractions in the estimation of body fat by the BOD POD was examined.

METHODS

Total body water was determined by isotope dilution ((2)H(2)0) and bone mineral was determined by dual-energy x-ray absorptiometry. Db and %fat were determined by the BOD POD and HW. The 4C model of Baumgartner was used as the criterion measure of body fat.

RESULTS

HW Db (1.0352 g x cm(-3)) was not statistically different (P = 0.35) from BOD POD Db (1.0349 g x cm(-3)). The regression between Db by HW and the BOD POD significantly deviated from the line of identity (Db by HW = 0.90 x Db by BOD POD + 0.099; R(2) = 0.94). BOD POD %fat (28.8%) was significantly lower (P < 0.01) than %fat by the 4C model (30.6%). The regression between %fat by the 4C model and the BOD POD significantly deviated from the line of identity (%fat by 4C model = 0.88 x %fat by BOD POD + 5.41%; R(2) = 0.92). BOD POD Db and %fat showed no bias across the range of fatness. Only the aqueous fraction of the fat-free mass (FFM) had a significant correlation with the difference in %fat between the 4C model and the BOD POD.

CONCLUSION

These data indicate that the BOD POD underpredicted body fat as compared with the 4C model, and the aqueous fraction of the FFM had a significant effect on estimates of %fat by the BOD POD.

Bioelectrical impedance analysis estimation of water compartments in elderly diseased patients: the source study

BACKGROUND

This study validates, in geriatric patients, bioelectrical impedance analysis (BIA) equations that had been derived to estimate total body water (TBW) and extracellular water (ECW) in healthy elderly subjects.

METHODS

We performed a multicentric trial in six geriatric wards. We studied 169 patients with varying degrees of hydration: dehydrated, euvolemic, and overhydrated. BIA estimates of TBW and of ECW were compared with the measurement of TBW with (18)O dilution and of ECW with bromide (Br) dilution.

RESULTS

BIA estimated TBW with a difference of 0.48 +/- 2.3 l (mean +/- SD) (50 kHz; p = .01) and 0.69 +/- 2.2 l (100 kHz; p < 0.001) compared with (18)O dilution. The difference was not affected by the hydration status. Estimates of ECW with BIA were systematically biased compared with Br dilution: 4.6 +/- 3.1 l (equation from Segal and colleagues; p < .001) and 3.4 +/- 2.9 l (equation from Visser and colleagues; p < .001). We propose a new, cross-validated equation. Conclusions. Body water spaces can be estimated accurately in geriatric patients with BIA.

Chronic cellular dehydration in the aged patient

BACKGROUND

As a reduction of water spaces is expected in the elderly because of fat-free mass loss, disease is often associated with increased hydration. The present study compared water spaces and cellular hydration in adults, healthy and diseased aged patients.

METHODS

An open study was conducted in 6 geriatric wards and a nutrition laboratory involving 85 aged diseased persons, 68 healthy elderly adults, and 35 adults. Total body water (TBW, H(2)(18)O dilution), extracellular water (ECW, Bromide dilution), and fat-free mass (FFM, body density and Siri's equation) were measured directly whereas intracellular water (ICW = TBW - ECW) and body cell mass (FFM - ECW) were obtained by calculations.

RESULTS

FFM, TBW, and ICW were higher in adults than in the 2 other groups and in the elderly than in aged patients. ECW was higher in aged patients than in healthy elderly participants. The proportion of TBW made of ECW or ICW was the same in adults and in healthy elderly persons. A higher proportion of TBW was composed of ECW, and a lower proportion of TBW was composed of ICW, in diseased patients compared with the 2 other groups. The proportion of ICW in body cell mass was also lower in diseased patients.

CONCLUSIONS

Diseased elderly persons display reduced ICW and expanded ECW. A cellular dehydration is suggested.

Elevated plasma cholecystokinin at high altitude: metabolic implications for the anorexia of acute mountain sickness

The aims of the present study were to measure the satiety neuropeptide cholecystokinin (CCK) in humans at terrestrial high altitude to investigate its possible role in the pathophysiology of anorexia, cachexia, and acute mountain sickness (AMS). Nineteen male mountaineers aged 38 +/- 12 years participated in a 20 +/- 5 day trek to Mt. Kanchenjunga basecamp (BC) located at 5,100 m, where they remained for 7 +/- 5 days. Subjects were examined at rest and during a maximal exercise test at sea-level before/after the expedition (SL1/SL2) and during the BC sojourn. There was a mild increase in Lake Louise AMS score from 1.1 +/- 1.2 points at SL1 to 2.3 +/- 2.3 points by the end of the first day at BC (P < 0.05). A marked increase in resting plasma CCK was observed on the morning of the second day at BC relative to sea-level control values (62.9 +/- 42.2 pmol/L(-1) vs. SL1: 4.3 +/- 8.3 pmol/L(-1), P < 0.05 vs. SL2: 26.5 +/- 25.2 pmol/L(-1), P < 0.05). Maximal exercise increased CCK by 78.5 +/- 24.8 pmol/L(-1), (P < 0.05 vs. resting value) during the SL1 test and increased the plasma concentration of non-esterified fatty acids and glycerol at BC (P < 0.05 vs. SL1/SL2). The CCK response was not different in five subjects who presented with anorexia on Day 2 compared with those with a normal appetite. While there was no relationship between the increase in CCK and AMS score at BC, a more pronounced increase in resting CCK was observed in subjects with AMS (> or =3 points at the end of Day 1 at BC) compared with those without (+98.9 +/- 1.4 pmol/L(-1) vs. +67.6 +/- 37.2 pmol/L(-1), P < 0.05). Caloric intake remained remarkably low during the stay at BC (8.9 +/- 1.4 MJ.d(-1)) despite a progressive decrease in total body mass (-4.5 +/- 2.1 kg after 31 +/- 13 h at BC, P < 0.05 vs. SL1/SL2), which appeared to be due to a selective loss of torso adipose tissue. These findings suggest that the satiogenic effects of CCK may have contributed to the observed caloric deficit and subsequent cachexia at high altitude despite adequate availability of palatable foods. The metabolic implications of elevated CCK in AMS remain to be elucidated.

The interrelationship between body topology and body composition varies with age among women

The purpose of this analysis was to evaluate the relationship between age and the size and distribution of the fat and lean tissue compartments in a population-based sample of women. The study population consisted of the 875 women aged 18-94 y in the Iowa Bone Health Study who reported never smoking. Fat mass and lean mass were measured using dual X-ray absorptiometry. Hip and waist circumference and height were measured using standardized protocols. Regression was used to model the associations among age, composition and topology measures. When fat mass was modeled as a function of hip and waist circumference as well as age, age(2) and height, the age x height and age x waist circumference interaction terms remained in the fitted model and collectively accounted for 91% of the variance. In contrast, the quadratic model of age alone accounted for 8% of the observed variance in fat mass. Lean mass was modeled in two segments, with age dichotomized at 58 y. Age alone did not predict lean mass in women <58 y but did predict lean mass in women >/=58 y, with the modeled relationship including interactions with waist circumference and height. These models accounted for 70% of observed variance in lean mass. Age is associated with body composition but explains <10% of variation. When measures of height and circumferences are available, amounts of lean and fat mass are highly predictable. This is particularly important for lean mass because no other surrogate measures exist for lean mass, whereas there are surrogates for fat mass, including body mass index.

Total body water and percentage fat mass measurements using bioelectrical impedance analysis and anthropometry in spinal cord-injured patients

BACKGROUND AND AIMS

Spinal cord injured patients may be adversely affected by disturbances of nutritional status, particularly malnutrition and fat mass overload. Malnutrition increases the risk for development of pressure sores, and fat mass excess increases the cardiovascular and respiratory risks of these patients, as well as predisposing to the development of diabetes mellitus, pressures sores and bony fractures. Body impedance analysis and anthopometry are easy bedside methods for body composition assessment. The aims of the study were to validate, in 20 spinal cord injured patients, body impedance analysis as a means to estimate total body water, and to validate a skinfold measurement of percentage fat independent of hydration of fat-free mass in the same population.

METHODS

Total body water was measured by (18)O dilution as a reference method. Impedance and anthropometric measurements (four different skinfolds) were obtained. The results of total body water given by impedance analysis and calculated with three formulas were compared to the reference method. The fat mass percentage obtained with each of the skinfolds using the 3-compartment Siri's formula was compared to a reference value using the sum of the skinfolds.

RESULTS AND CONCLUSION

The formula using 100 kHz resistance, height, weight and gender overestimated total body water by only 0.76 +/- 1.85 L, with an acceptable concordance with labeled water results. The formula with 50 kHz resistance was less accurate and concordant. Each skinfold may be used for assessing percentage fat mass. Based on these findings, we feel that the triceps skinfold, whose the variability is the lowest compared to the reference values, can be used alone in clinical practice.

Assessing body composition and changes in body composition. Another look at dual-energy X-ray absorptiometry

Dual-energy X-ray absorptiometry (DXA) is selected with increasing frequency as a method for both assessing body composition and measuring the changes in body composition. Issues have been raised about hydration, software version, hardware (fan beam vs. pencil beam), and the subject population in relation to the validity of DXA-derived estimates of body composition. This paper reviews validation studies of DXA to assess the impact of recent developments in its technology. Studies by Prior et al., Kohrt et al., Salamone et al., Going et al., and Pietrobelli et al. demonstrate the effectiveness of DXA estimates of changes in body composition. By contrast, Clasey et al., Nelson et al., and Friedl et al. found limitations in DXA estimates of body composition and its changes. These contradictory conclusions were explored for threats to internal validity in each research study. From this analysis, two validation guidelines are recommended for use when evaluating estimates of body composition. When multicomponent models are used, it is essential that estimates of body water as a fraction of fat-free mass fall in the expected range (71 to 75%) and have a relatively small standard deviation (2 to 3%). For measuring changes in body composition, DXA estimates of total body mass must accurately reflect both baseline and posttreatment scale body weight estimates. Failure to meet these guidelines threatens the internal validity of the study and raises the likelihood of methodological discrepancies. Applying these criteria to DXA studies of body composition under review accounts for much of the contradictory conclusions among investigations.