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Jack Wang

Publications and source records attributed to Jack Wang.

52 records · Page 3Linked to original sources
PubMed2003

Whole-body skeletal muscle mass: development and validation of total-body potassium prediction models.

BACKGROUND: A substantial proportion of total body potassium (TBK) in humans is found in skeletal muscle (SM), thus affording a means of predicting total-body SM from whole-body counter-measured (40)K. There are now > 30 whole-body counters worldwide that have large cross-sectional and longitudinal TBK databases. OBJECTIVE: We explored 2 SM prediction approaches, one based on the assumption that the ratio of TBK to SM is stable in healthy adults and the other on a multiple regression TBK-SM prediction equation. DESIGN: Healthy subjects aged >or= 20 y were recruited for body-composition evaluation. TBK and SM were measured by whole-body (40)K counting and multislice magnetic resonance imaging, respectively. A conceptual model with empirically derived data was developed to link TBK and adipose tissue-free SM as the ratio of TBK to SM. RESULTS: A total of 300 subjects (139 men and 161 women) of various ethnicities with a mean (+/- SD) body mass index (in kg/m(2)) of 25.1 +/- 5.4 met the study entry criteria. The mean conceptual model-derived TBK-SM ratio was 122 mmol/kg, which was comparable to the measurement-derived TBK-SM ratios in men and women (119.9 +/- 6.7 and 118.7 +/- 8.4 mmol/kg, respectively), although the ratio tended to be lower in subjects aged >or= 70 y. A strong linear correlation was observed between TBK and SM (r = 0.98, P < 0.001), with sex, race, and age as small but significant prediction model covariates. CONCLUSIONS: Two different types of prediction models were developed that provide validated approaches for estimating SM mass from (40)K measurements by whole-body counting. These methods afford an opportunity to predict SM mass from TBK data collected in healthy adults.

Absorptiometry, Photon↗
PubMed2003

Comparisons of waist circumferences measured at 4 sites.

BACKGROUND: Waist circumference (WC) is now accepted as a practical measure of adipose tissue distribution. Four body sites for WC measurements are commonly used, as follows: immediately below the lowest ribs (WC1), the narrowest waist (WC2), the midpoint between the lowest rib and the iliac crest (WC3), and immediately above the iliac crest (WC4). OBJECTIVE: We sought to compare the magnitude and reliability of WC measured at these 4 sites in males and females. DESIGN: WC was measured at each site 1 time in all subjects [49 males and 62 females, aged 7-83 y, with a body mass index (in kg/m(2)) of 9-43] and 3 times in a subgroup (n = 93) by one experienced observer using a heavy-duty inelastic tape. Body fat was measured in a subgroup (n = 74) with the use of dual-energy X-ray absorptiometry. RESULTS: The mean values of WC were WC2 < WC1 < WC3 < WC4 (P < 0.01) in females and WC2 < WC1, WC3, and WC4 (P < 0.01) in males. For all 4 sites, measurement reproducibility was high, with intraclass correlation (r) values > 0.99. WC values were significantly correlated with fatness; correlations with trunk fat were higher than correlations with total body fat in both sexes. CONCLUSIONS: WC values at the 4 commonly used anatomic sites differ in magnitude depending on sex, are highly reproducible, and are correlated with total body and trunk adiposity in a sex-dependent manner. These observations have implications for the use of WC measurements in clinical practice and patient-oriented research.

Abdomen↗
PubMed2003

Total body potassium differs by sex and race across the adult age span.

BACKGROUND: Total body potassium (TBK) is an index of fat-free mass. Data describing changes in TBK in African American, Asian, or Hispanic populations have not been reported. OBJECTIVE: The aim was to investigate possible sex and racial differences in TBK in adults over an age range of 70 y. DESIGN: The study used longitudinal and cross-sectional data collected in a body-composition unit from 973 men and 1368 women of African American, Asian, white, and Hispanic race-ethnicity. Random coefficient models in which baseline weight and height were taken into account were applied to estimate sex-specific changes in TBK among the 4 racial-ethnic groups. RESULTS: The ages of 30 and 31 y were identified for women and men, respectively, as the cutoffs after which TBK began to decline. Both sexes had similar racial-ethnic patterns for expected mean TBK at the age cutoffs: African Americans had the highest value, followed by whites, Hispanics, and Asians. After the age cutoffs, the decline in TBK differed by race and sex. In women, African Americans showed the most rapid decline, whereas Asians had the lowest. In men, Hispanics had the most rapid decline in TBK, followed by African Americans, whites, and Asians. CONCLUSION: Significant sex and racial differences exist in the rate of change in TBK with age. Further studies are needed to explore the associations of declining TBK with health risks.

Adult↗
PubMed2003

Magnitude and variation of fat-free mass density: a cellular-level body composition modeling study.

The mean density of fat-free mass (FFM) is remarkably stable at 1.10 g/cm(3) in healthy adult humans, and this stability is a cornerstone of the widely applied densitometry-based two-compartment model for estimating total body fat. At present, the usual means of exploring FFM density is by in vitro or in vivo experimental studies. The purpose of the present investigation was to develop a cellular-level body composition model that includes seven factors that determine FFM density. The model, when applied with available empirical coefficients, predicted an FFM density similar to that observed in vivo. An analysis of the seven model components indicates that the ratio of extracellular solids to total body water is a major determinant of individual variation in FFM density. The difference in FFM density across sex, race, and age groups was examined with the developed model. The present study thus provides a conceptual framework for the systematic study of FFM density in humans.

Adipose Tissue↗
PubMed2002

Effect of recombinant human growth hormone in the treatment of visceral fat accumulation in HIV infection.

HIV-associated lipodystrophy often includes excess accumulation of visceral fat. Recombinant human growth hormone (rhGH) is a potential treatment for the excess visceral fat. Prospective, open-label trials of 24 weeks of rhGH 6 mg/d and 24 weeks of 4 mg every other day were conducted with an intervening washout period of 12 weeks. Thirty HIV-positive participants (26 men and 4 women) with visceral adiposity were enrolled. The main outcome measure was change in visceral adipose tissue (VAT) on whole-body magnetic resonance imaging scan. Changes in whole-body subcutaneous adipose tissue and skeletal muscle, glucose metabolism, serum lipids, and quality of life were also assessed. Despite stable body weight, VAT decreased in evaluable subjects an average of 42% with rhGH 6 mg/d (n = 24; p <.001) and 15% with 4 mg every other day (n = 10; p <.01) after 12 weeks, with trends toward further decreases after an additional 12 weeks at each dose. Subcutaneous adipose tissue also decreased, but proportionately less and not significantly on the lower dose. Skeletal muscle increased. Body composition rebounded to or near baseline after the washout period. Effects on lipids were inconsistent. Total cholesterol levels fell on the higher dose only, whereas high-density lipoprotein cholesterol levels increased on the lower dose only, and there was no effect on triglyceride levels. Joint pain was the most common adverse event, and was reflected in subjective quality of life measurements as an increase in bodily pain. Insulin sensitivity fell, and 4 participants developed diabetes. Other adverse events included cancer of unknown relationship to treatment in 3 participants. Levels of distress decreased after 24 weeks on the higher dose. In conclusion, rhGH effectively reduces the excess visceral adipose tissue often associated with HIV fat redistribution/lipodystrophy. However, frequent adverse effects warrant controlled studies and careful patient monitoring, especially regarding glucose tolerance.

Adipose Tissue↗
PubMed2002

Bone mineral content is lower in prepubertal HIV-infected children.

Total body bone mineral content (TBBMC) was measured by dual energy x-ray absorptiometry in a cross-sectional study of 51 prepubertal HIV-infected children and 262 healthy prepubertal children aged 4.2 to 14.7 years. The mean TBBMC +/- SD was lower in HIV-positive children than in HIV-negative controls (955 +/- 325 vs. 1,106 +/- 273 g, respectively; p =.0006). Reductions in TBBMC remained in the HIV-positive group after adjusting for age, sex, and race by analysis of covariance (p <.001). Differences in TBBMC between HIV-positive and HIV-negative groups persisted when height and weight were also accounted for in the analysis (p =.027). The magnitude of the difference in TBBMC between the groups increased with age. In the HIV-positive group, no associations were observed between TBBMC and use of a protease inhibitor, duration of treatment with antiretroviral medications, viral load, or CD4 cell count. TBBMC is decreased in HIV-infected children. As a result of compromised bone mineral accrual, HIV-infected children may be at increased risk for osteoporosis and related complications.

Absorptiometry, Photon↗
PubMed2002

Trunk fat and blood pressure in children through puberty.

BACKGROUND: Fat distribution is well recognized as a cardiovascular risk factor in adults. The association between android fat distribution and cardiovascular risk factors, such as blood pressure (BP), was previously reported in an African-American and Caucasian pediatric population. The aim of the present study was to investigate the relationship between BP and body fat distribution in a large cross-sectional pediatric sample. The effects of race, sex, and puberty on this relationship were assessed. METHODS AND RESULTS: BP was measured in 920 healthy children and adolescents (African-American, Asian, and Caucasian, ages 5 to 18 years). Fat distribution was determined by skinfold thickness and dual-energy X-ray absorptiometry (DXA). Pubertal status was assessed by the criteria of Tanner. Regression analysis was used to explore the association between BP and fat distribution. Significant positive relationships between systolic and diastolic BP and trunk fat adjusted for total fat were seen in boys at all pubertal stages in all 3 races by both DXA and skinfold measurements. In girls, trunk fat was not a significant predictor of BP. CONCLUSIONS: Our results demonstrate a sex difference in the relationship between BP and trunk fat in that a significant positive relationship was present in boys only. These findings, based on 2 independent measures of fat distribution, may help identify the specific features of individuals at risk, allow earlier intervention, and suggest sex-specific determinants for BP.

Abdomen↗
PubMed2002

Regional subcutaneous-fat loss induced by caloric restriction in obese women.

OBJECTIVE: With anthropometric models using skinfolds and circumferences, we studied changes in the percentage of subcutaneous fat in the total cross-sectional area (SF%) at four body sites in obese women, before and after weight loss induced by 6 months of caloric restriction. RESEARCH METHODS AND PROCEDURES: In 61 obese women [31 African Americans and 30 whites; ages, 24 to 68 years; body mass index (BMI), > or =28 kg/m(2)], we measured SF% at the midpoint of the upper arm and thigh and the waistline and hipline, and we measured the percentage of total body fat by DXA before (Obs#1) and after (Obs#2) a 6-month nonintervention control period and then after 6 months on a 1200 kcal/d diet (Obs#3). RESULTS: The mean body weight and BMI increased (1.8 kg and 0.61 kg/m(2); p = 0.0001), but there were no significant changes in any other body composition measurements from Obs#1 to Obs#2. The means of Obs#3 for weight and BMI decreased by 11%, and the percentage of total body fat decreased by 13% of Obs#2 mean values (p = 0.0001). The mean SF% at each site decreased 7.6% to 18.0% of the Obs#2 mean values (p < 0.001). The SF% decreases were greater at mid-arm and mid-thigh than in the cross-sectional regions at the waistline and hipline (p = 0.05). There was no interaction between age or ethnicity (p > 0.2). CONCLUSIONS: In obese women, caloric restriction alone reduces anthropometrically measured subcutaneous fat proportionally more in peripheral than in central regions.

Absorptiometry, Photon↗
PubMed2002

Association of lean tissue and fat mass with bone mineral content in children and adolescents.

OBJECTIVES: There has been uncertainty in the adult body composition literature about whether fat mass (FM) or fat free mass is a better predictor of bone mineral content and bone mineral density. This issue has recently also been raised in the pediatric literature. Based on suggested skeletal muscle-bone relationships, this study tested the hypothesis that in children and adolescents lean tissue mass (LTM) is a better predictor of total bone mineral content (TBMC) than is FM. RESEARCH METHODS AND PROCEDURES: Subjects were 133 Italian children and adolescents, 5 to 17 years of age, undergoing a routine medical screen. FM (kilograms), LTM (kilograms), and TBMC (kilograms) were measured by DXA. Multiple regression analyses tested the independent association of FM and LTM with bone mineral content. RESULTS: Regression analyses, adjusting for pubertal status and other covariates, showed that FM and LTM were independently associated with TBMC. These associations were similar for boys and girls. TBMC was more strongly associated with LTM than FM. DISCUSSION: These observations support the hypothesis that in children and adolescents a close association exists between LTM, a measure of skeletal muscle, and skeletal characteristics.

Absorptiometry, Photon↗
PubMed2002

Use of a Durnin-Womersley formula to estimate change in subcutaneous fat content in HIV-infected subjects.

BACKGROUND: HIV-infected individuals may develop malnutrition or lipodystrophy, leading to losses of subcutaneous adipose tissue (SAT). OBJECTIVE: We compared the ability of a Durnin-Womersley formula for total adipose tissue (TAT) to estimate change in SAT with the use of whole-body magnetic resonance imaging (MRI) as a criterion measure. DESIGN: We analyzed data from 2 clinical trials: a prospective randomized trial of protein supplements, progressive resistance training, or combined treatment in 29 malnourished, HIV-positive women, and a prospective open-label trial of recombinant human growth hormone in 25 HIV-infected subjects with visceral adipose tissue (VAT) accumulation. Changes in fat by the Durnin-Womersley formula and in SAT, TAT, and VAT by MRI were compared by linear regression, and Bland-Altman analyses were used to assess the agreement between the prediction and criterion methods. The repeatability of the Durnin-Womersley measurement was evaluated in 14 weight-stable, healthy adults studied twice within 1 y. RESULTS: At baseline, Durnin-Womersley fat was significantly associated with SAT (r(2) = 0.75, P < 0.001) and TAT (r(2) = 0.79, P < 0.001) but not with VAT. Change in Durnin-Womersley fat was significantly associated with change in SAT (r(2) = 0.66, P < 0.001) and in TAT (r(2) = 0.57, P < 0.001) but not in VAT. The limits of agreement for the Durnin-Womersley estimation of change in SAT were -3.4 to 2.6 kg and the SEE was 1.5 kg. The SEE for repeated measures of SAT in healthy control subjects was 0.84. CONCLUSIONS: The Durnin-Womersley formula can be used to predict change in SAT. The limits of agreement and the SEE for predicting change in SAT by MRI are approximately twice as great as the error of repeated Durnin-Womersley measures in control subjects.

Adipose Tissue↗
PubMed2002

Bioelectrical impedance analysis models for prediction of total body water and fat-free mass in healthy and HIV-infected children and adolescents.

BACKGROUND: Bioelectrical impedance analysis (BIA) is an attractive method of measuring pediatric body composition in the field, but the applicability of existing equations to diverse populations has been questioned. OBJECTIVE: The objectives were to evaluate the performance of 13 published pediatric BIA-based predictive equations for total body water (TBW) and fat-free mass (FFM) and to refit the best-performing models. DESIGN: We used TBW by deuterium dilution, FFM by dual-energy X-ray absorptiometry, and BIA-derived variables to evaluate BIA models in a cross-sectional study of 1291 pediatric subjects aged 4-18 y, from several ethnic backgrounds, including 54 children with HIV infection and 627 females. The best-performing models were refitted according to criterion values from this population, cross-validated, and assessed for performance. Additional variables were added to improve the predictive accuracy of the equations. RESULTS: The correlation between predicted and criterion values was high for all models tested, but bias and precision improved with the refitted models. The 95% limits of agreement between predicted and criterion values were 16% and 11% for TBW and FFM, respectively. Bias was significant for some subgroups, and there was greater loss of precision in specific age groups and pubertal stages. The models with additional variables eliminated bias, but the limits of agreement and the loss of precision persisted. CONCLUSION: This study confirms that BIA prediction models may not be appropriate for individual evaluation but are suitable for population studies. Additional variables may be necessary to eliminate bias for specific subgroups.

Adolescent↗
PubMed2002

Prepubertal Asians have less limb skeletal muscle.

Skeletal muscle mass in prepubertal Asian children has not been examined previously. The aims of this study were to test the hypotheses that 1) prepubertal Asians have less appendicular skeletal muscle (ASM) mass compared with African-Americans and Caucasians, and 2) ASM is less in prepubertal Asian girls compared with Asian boys. ASM was estimated by using dual-energy X-ray absorptiometry in healthy prepubertal girls (n = 170) and boys (n = 166). The results showed that, after adjusting for age, height, and body weight, 1) Asian girls and boys had less amounts of ASM than African-Americans (P < 0.001); 2) Asian girls had less amounts of ASM than Caucasian girls (P = 0.004); 3) there was a trend towards less ASM in Asian compared with Caucasian boys (P = 0.07); 4) and Asian girls had significantly less ASM than Asian boys (P < 0.001). This study indicates that skeletal muscle mass as a fraction of body weight is smaller in Asian compared with African-American and Caucasian children.

Black or African American↗
PubMed2002

Sex and race differences in fat distribution among Asian, African-American, and Caucasian prepubertal children.

Sexual dimorphism in fat distribution is thought to emerge during puberty. Truncal or android body fat distribution is characteristic of adult males but is also recognized as a human cardiovascular risk factor. Race differences in truncal fat are clearly evident in adults and have been described in prepubertal children but not between Asians and other race groups. The aim of this study in African-American, Asian, and Caucasian prepubertal children was to evaluate sex differences and race differences in body fat distribution. Analysis of covariance was used to explore fat distribution in 358 prepubertal children (176 girls and 182 boys; 143 Asians, 95 African-Americans, and 120 Caucasians), measured by skinfold thickness and dual-energy x-ray absorptiometry (DXA) in a cross-sectional study. Extremity and gynoid fat masses were evaluated after adjustment for trunk or android fat, respectively, and for covariates including age, weight, height, and interactions. In Asian children, sex differences were present in models for gynoid fat by DXA only (P < 0.001), with girls having greater gynoid fat than boys. In African-American and Caucasian children, sex differences were present in models for extremity and gynoid fat masses, measured by both methods. Among girls, Asians had generally lower adjusted extremity and gynoid fat than Caucasians and African-Americans. Among boys, Asians had lower adjusted extremity fat by DXA than Caucasians (P < 0.01) but greater gynoid fat by skinfolds than African-Americans (P < 0.01). This study of prepubertal children demonstrates that: 1) sex differences in body fat distribution are present in prepubertal children but that the specific characteristics for Asians differ from African-Americans and Caucasians, and 2) differences in body fat distribution in Asian children, compared with African-Americans and Caucasians, are present but vary by sex. This comparison of African-American, Asian, and Caucasian prepubertal children suggests phenotypic differences. Additional studies are needed to explore the metabolic and health risk implications of these findings.

Abdomen↗
PubMed2002

Bone density and amenorrhea in ballet dancers are related to a decreased resting metabolic rate and lower leptin levels.

Osteopenia, which is correlated with amenorrhea and poor nutritional habits, has been well documented in elite ballet dancers. Estrogen replacement therapy and recovery from amenorrhea have not been associated with normalization of bone density. Thus, the osteopenia may be related to changes brought about by chronic dieting or other factors, such as a hypometabolic state induced by poor nutrition. The purpose of this study was to investigate the relationship of chronic dieting and resting metabolic rate (RMR) to amenorrhea and bone density. RMR, bone density, eating disorder assessments, leptin levels, and complete menstrual and medical histories were determined in 21 elite ballet dancers and in 27 nondancers (age, 20-30 yr). No significant correlations were found between high EAT26 scores, a measure of disordered eating, and RMR, bone densities, body weight, body fat, or fat-free mass. However, when RMR was adjusted for fat-free mass (FFM), a significant positive correlation was found between RMR/FFM and bone density in both the arms (P < 0.001) and spine (P < 0.05) in ballet dancers, but not in the normal controls. The dancers also demonstrated significantly higher EAT scores (22.9 +/- 10.3 vs. 4.1 +/- 2.4; P < 0.001) and lower RMR/FFM ratios (30.0 +/- 2.2 vs. 32.05 +/- 2.8; P < 0.01). The only variable to predict lower RMR/FFM in the entire sample was ever having had amenorrhea; this group had significantly higher EAT scores (18.0 +/- 13.5 vs. 10.3 +/- 10.2; P < 0.05), lower leptin levels (4.03 +/- 0.625 vs. 7.10 +/- 4.052; P < 0.05), and lower bone mineral density in the spine (0.984 +/- 0.11 vs. 1.10 +/- 0.13; P < 0.05) and arm (0.773 +/- 0.99 vs. 0.818 +/- 0.01; P < 0.05). We hypothesize that the correlation between low RMR and lower leptin levels and bone density may be more strongly related to nutritional habits in ballet dancers, causing significant depression of RMR, particularly for those with a history of amenorrhea.

Adult↗
PubMedDate not supplied

The relationship between energy expenditure and lean tissue in monozygotic twins discordant for spinal cord injury.

Energy expenditure and fat-free mass (FFM), as well as the relationships between these parameters, were investigated in thirteen pairs of monozygotic twins discordant for SCI. Basal energy expenditure (BEE) and resting energy expenditure (REE) were determined by indirect calorimetry. Measurements for FFM and fat mass were obtained by dual-energy x-ray absorptiometry. Total body potassium was determined by a 4-Pi whole-body counting chamber. Values are expressed as mean standard deviation. BEE and REE of the twins with SCI were significantly less than those of the able-bodied co-twins (1387 268 vs. 1660 324 kcal/d, p < 0.005, and 1682 388 vs. 1854 376 kcal/d, p < 0.05, respectively). Regardless of the group, direct and highly significant relationships were evident between BEE or REE and FFM or TBK. In summary, twins with SCI had lower energy expenditure than their able-bodied co-twins. Regardless of paralysis, direct linear relationships existed between energy expenditure and measures of lean mass.

Adult↗