Body composition in Pima Indians: validation of bioelectrical resistance

Validity of Body-Composition Methods across Racial and Ethnic Populations

Multi-compartment body-composition models that divide the body into its multiple constituents are the criterion method for measuring body fat percentage, fat mass, and fat-free mass. However, 2- and 3-compartment body-composition devices such as air displacement plethysmography (ADP), DXA, and bioelectrical impedance devices [bioelectrical impedance analysis (BIA)] are more commonly used. Accurate measures depend on several assumptions, including constant hydration, body proportion, fat-free body density, and population characteristics. Investigations evaluating body composition in racial and ethnic minorities have observed differences in the aforementioned components between cohorts. Consequently, for racial/ethnic minority populations, estimates of body composition may not be valid. The purpose of this review was to comprehensively examine the validity of common body-composition devices in multi-ethnic samples (samples including >1 race/ethnicity) and in African-American, Hispanic, Asian, and Native American populations. Based on the literature, DXA produces valid results in multi-ethnic samples and ADP is valid for Hispanic and African American males when utilizing race-specific equations. However, for DXA and ADP, there is a need for validity investigations that include larger, more racially diverse samples, specifically including Hispanic/Latinx, Asian, Native American adults, and African-American females. Technology has advanced significantly since initial validity studies were conducted; therefore, conclusions are based on outdated models and software. For BIA, body-composition measures may be valid in a multi-ethnic sample, but the literature demonstrates disparate results between races/ethnicities. For BIA and ADP, the majority of studies have utilized DXA or hydrostatic weighing as the criterion to determine validity; additional studies utilizing a multi-compartment model criterion are essential to evaluate accuracy. Validity studies evaluating more recent technology in larger, more racially/ethnically diverse samples may improve our ability to select the appropriate method to accurately assess body composition in each racial/ethnic population.

DNA methylation and adiposity phenotypes: an epigenome-wide association study among adults in the Strong Heart Study

BACKGROUND

Elevated adiposity is often posited by medical and public health researchers to be a risk factor associated with cardiovascular disease, diabetes, and other diseases. These health challenges are now thought to be reflected in epigenetic modifications to DNA molecules, such as DNA methylation, which can alter gene expression.

METHODS

Here we report the results of three Epigenome Wide Association Studies (EWAS) in which we assessed the differential methylation of DNA (obtained from peripheral blood) associated with three adiposity phenotypes (BMI, waist circumference, and impedance-measured percent body fat) among American Indian adult participants in the Strong Heart Study.

RESULTS

We found differential methylation at 8264 CpG sites associated with at least one of our three response variables. Of the three adiposity proxies we measured, waist circumference had the highest number of associated differentially methylated CpGs, while percent body fat was associated with the lowest. Because both waist circumference and percent body fat relate to physiology, we focused interpretations on these variables. We found a low degree of overlap between these two variables in our gene ontology enrichment and Differentially Methylated Region analyses, supporting that waist circumference and percent body fat measurements represent biologically distinct concepts.

CONCLUSIONS

We interpret these general findings to indicate that highly significant regions of the genome (DMR) and synthesis pathways (GO) in waist circumference analyses are more likely to be associated with the presence of visceral/abdominal fat than more general measures of adiposity. Our findings confirmed numerous CpG sites previously found to be differentially methylated in association with adiposity phenotypes, while we also found new differentially methylated CpG sites and regions not previously identified.

Effectiveness of the Healthy Lifestyle Promotion Program for Yaquis with Obesity and Risk of Diabetes in the Short and Medium Term: A Translational Study

Type 2 diabetes (T2D) is a public health problem worldwide, and the main risk factor for its development is obesity. The Yaqui ethnic group of Sonora has serious obesity problems, resulting in an increased risk of T2D in its inhabitants. The objective of this study was to evaluate the effectiveness of a health promotion program on obesity parameters and cardiovascular risk factors in short- (6 months) and medium-term periods (12 months) in indigenous Yaquis of Sonora. The design is a translational clinical study of a single cohort with prepost intervention measurements in a sample of 93 subjects. The effectiveness of the program was evaluated by comparing obesity parameters, metabolic markers, and physical activity 6 and 12 months with those measured under basal conditions using a paired t-test or Wilcoxon rank-sum test. The short-term retention percentage was 58.0%. There was a decrease in body weight (Δ = -3.9 kg, p ≤ 0.05) and other obesity parameters, and an increase in physical activity and improvements in metabolic markers (p ≤ 0.05) was observed. Similar findings were obtained for the medium-term period; body weight loss was also -3.9 kg (p ≤ 0.05). The short and medium-term results of the program showed improvements in the obesity parameters and other cardiovascular risk factors of the participants. These results support the effectiveness of the program and its translation in this ethnic group.

Study design of the Maycoba Project: obesity and diabetes in Mexican Pimas

OBJECTIVE

To focus on the rationale and methods of the Maycoba Project.

METHODS

Study population included Mexican Pima Indians (MPI) and Blancos aged ≥20-years, living in the village of Maycoba and surrounding area. Surveys in 1995 and 2010 included a medical history, biochemical and anthropomet- ric measurements. Additionally, socio- economic, physical activity, and dietary interviews were conducted. The 2010 study incorporated investigations on type 2 diabetes (T2D) and obesity-associated genetic alleles and human-envi- ronment changes.

RESULTS

The study results are limited to demographic data and description of the eligible and ex- amined sample.

CONCLUSIONS

This study may yield important information on T2D and obesity etiology in a traditional population exposed to environmental changes.

Body composition and arsenic metabolism: a cross-sectional analysis in the Strong Heart Study

OBJECTIVE

The objective of this study was to evaluate the association between measures of body composition and patterns of urine arsenic metabolites in the 1989-1991 baseline visit of the Strong Heart Study, a cardiovascular disease cohort of adults recruited from rural communities in Arizona, Oklahoma, North Dakota and South Dakota.

METHODS

We evaluated 3,663 Strong Heart Study participants with urine arsenic species above the limit of detection and no missing data on body mass index, % body fat and fat free mass measured by bioelectrical impedance, waist circumference and other variables. We summarized urine arsenic species patterns as the relative contribution of inorganic (iAs), methylarsonate (MMA) and dimethylarsinate (DMA) species to their sum. We modeled the associations of % arsenic species biomarkers with body mass index, % body fat, fat free mass, and waist circumference categories in unadjusted regression models and in models including all measures of body composition. We also considered adjustment for arsenic exposure and demographics.

RESULTS

Increasing body mass index was associated with higher mean % DMA and lower mean % MMA before and after adjustment for sociodemographic variables, arsenic exposure, and for other measures of body composition. In unadjusted linear regression models, % DMA was 2.4 (2.1, 2.6) % higher per increase in body mass index category (< 25, ≥25 & <30, ≥30 & <35, ≥35 kg/m2), and % MMA was 1.6 (1.4, 1.7) % lower. Similar patterns were observed for % body fat, fat free mass, and waist circumference measures in unadjusted models and in models adjusted for potential confounders, but the associations were largely attenuated or disappeared when adjusted for body mass index.

CONCLUSION

Measures of body size, especially body mass index, are associated with arsenic metabolism biomarkers. The association may be related to adiposity, fat free mass or body size. Future epidemiologic studies of arsenic should consider body mass index as a potential modifier for arsenic-related health effects.

Perfil nutricional dos indígenas Xukuru-Kariri, Minas Gerais, de acordo com diferentes indicadores antropométricos e de composição corporal

O objetivo deste artigo foi avaliar o perfil nutricional dos indígenas Xukuru-Kariri entre 7 anos e 78 anos aldeados em Minas Gerais de acordo com os diferentes indicadores antropométricos e de composição corporal . As medidas aferidas foram: peso, estatura, circunferência da cintura (CC) e percentual de gordura corporal (%GC). Foram calculadas a sensibilidade e a especificidade para os índices antropométricos com intervalo de confiança de 95% e o valor preditivo positivo (VPP) e negativo (VPN). A população foi constituída por 58 indivíduos, sendo 56,9% (n = 33) do sexo masculino e 43,1% (n = 25) do sexo feminino. A especificidade foi superior à sensibilidade em relação a todos os índices. Observou-se que 29% dos indivíduos foram classificados com excesso de adiposidade corporal quando avaliados pelo IMC e pela bioimpedância mão a mão e 50% dos indivíduos apresentaram alta adiposidade corporal em relação ao IMC e a CC. É necessário que sejam realizados estudos com diferentes etnias a fim de se construir indicadores nutricionais específicos para orientação de serviços de saúde indígenas.

Sex differences in obesity-related changes in left ventricular morphology: the Strong Heart Study

OBJECTIVES

It is unclear whether there are sex differences in the relations of left ventricular mass to body composition and fat distribution in nonobese or obese hypertensive and nonhypertensive individuals and whether the obesity-related increase in left ventricular mass is similar in men and women.

METHODS

We examined sex differences in the relations between left ventricular mass and both body composition and fat distribution, in the presence or absence of obesity in 1068 men and 1851 women (65%) of the Strong Heart Study cohort, without prevalent cardiovascular disease or severe chronic kidney disease. Fat-free mass (FFM) and adipose mass were estimated by bioelectric impedance analysis and fat distribution by waist-to-hip ratio (WHR).

RESULTS

Adipose mass was significantly higher in women than in men for any weight category (P < 0.0001). After adjusting for age, hypertension, systolic blood pressure (BP) and diabetes, both left ventricular mass/height (LVMi) and left ventricular mass (LVM)/FFM were greater in obese women than obese men (P < 0.0001). Relative wall thickness was also greater in women than in men (P < 0.0001). LVM was independently related to Doppler-stroke volume, FFM and systolic BP in both sexes, with WHR and adipose mass contributing to variance of LVM in women but not in men (both P < 0.03).

CONCLUSION

Obesity influences left ventricular geometry substantially more in women than in men, possibly due to biological factors specifically associated with female adiposity.

Differences in insulin resistance in Mexican and U.S. Pima Indians with normal glucose tolerance

CONTEXT

Insulin resistance is a major risk factor for the development of type 2 diabetes in Pima Indians, a population with the highest prevalence of type 2 diabetes mellitus in the world. Their Mexican counterpart, living a traditional lifestyle in the mountains of Sonora, have at least 5 times less diabetes than the U.S. Pima Indians.

OBJECTIVE

We evaluated whether Mexican Pima Indians had lower insulin resistance than U.S. Pima Indians.

DESIGN AND PATIENTS

We compared fasting insulin and homeostasis model assessment for insulin resistance (HOMA-IR) in 194 Mexican Pima Indians (100 females, 94 males) and 449 U.S. Pima Indians (246 females, 203 males) with normal glucose tolerance from a cross-sectional study. Adjusted differences of log-transformed outcomes (fasting insulin and HOMA-IR) between groups were evaluated using multiple linear regression models and paired t test in a matched subset.

RESULTS

Unadjusted fasting insulin and HOMA-IR were much lower in the Mexican Pima Indians than in their U.S. counterparts. After adjusting by obesity, age, and sex, mean (95% confidence interval) for fasting insulin was 6.22 (5.34-7.24) vs. 13.56 μU/ml (12.27-14.97) and for HOMA-IR 1.40 (1.20-1.64) vs. 3.07 (2.77-3.40), respectively, for Mexican Pima and U.S. Pima Indians. Results were confirmed in subset matched for age, sex, and body fat.

CONCLUSION

Our results indicate that Mexican Pima Indians have lower insulin resistance in comparison with their genetically related U.S. counterparts, even after controlling for differences in obesity, age, and sex. This finding underscores the importance of lifestyle factors as protecting factors against insulin resistance in individuals with a high propensity to develop diabetes.

The effect of acute fluid consumption on measures of impedance and percent body fat estimated using segmental bioelectrical impedance analysis

BACKGROUND/OBJECTIVES

To determine the effect of acute fluid consumption on measures of impedance and percent body fat (%BF) estimated using segmental bioelectrical impedance analysis (SBIA).

SUBJECTS/METHODS

Seventy-six healthy, recreationally active adults (41 women; 35 men) volunteered to participate in this study (mean+/-s.d.; age, 21.0+/-1.6 years; body mass index, 25.0+/-3.2 kg/m2). Subjects had their body composition assessed on three separate occasions. After a baseline measurement, subjects consumed 591 ml of water (H2O), a carbohydrate/electrolyte drink (CHOE) or received nothing (CON). Subjects were reassessed 20, 40 and 60 min following (POST) the baseline measure in each fluid condition.

RESULTS

Twenty minutes after drinking a H2O or CHOE beverage, %BF (1.1 and 1.2%), impedance (12 and 14 Omega) and body mass increased significantly (P<0.001). During the CON trial, %BF (0.3 and 0.5%) and impedance (7 and 11 Omega) also increased significantly above baseline values at 40 and 60 min POST. However, the normal hourly variability was significantly (P<0.009) less than the observed fluid-induced %BF alterations. The greatest %BF increases were observed in the lightest subjects, who were women. Fluid type had no effect on the magnitude of change POST.

CONCLUSIONS

Twenty minutes after drinking, %BF estimates increased approximately 1.0% due to elevations in impedance and body mass. As such, we recommend adhering to the pretest fluid restriction guideline to avoid fluid-induced alterations in SBIA body composition measures. In addition, use of a consistent testing schedule may minimize normal %BF variation over time.

Cardiac markers of pre-clinical disease in adolescents with the metabolic syndrome: the strong heart study

OBJECTIVES

Our aim was to evaluate the impact of metabolic syndrome (MetS) on cardiac phenotype in adolescents.

BACKGROUND

A high prevalence of MetS has been reported in adolescents.

METHODS

Four hundred forty-six nondiabetic American Indian adolescents (age 14 to 20 years, 238 girls) underwent clinical evaluation, laboratory testing, and Doppler echocardiography. Age- and gender-specific partition values were used to define obesity and hypertension. Metabolic syndrome was defined according to Adult Treatment Panel III criteria, modified for adolescents. Left ventricular (LV) hypertrophy and left atrial (LA) dilation were identified using age- and gender-specific partition values.

RESULTS

One hundred eleven participants met criteria for MetS. They had a similar age and gender distribution as non-MetS participants. Analysis of covariance, controlling for relevant confounders, demonstrated that participants with MetS had higher LV, LA, and aortic root diameters, higher LV relative wall thickness, and greater LV mass index. Accordingly, MetS participants showed higher prevalences of LV hypertrophy (43.2% vs. 11.7%) and LA dilation (63.1% vs. 21.9%, both p < 0.001) compared with non-MetS participants. In addition, MetS was associated with a reduction in midwall shortening, lower transmitral mitral early to atrial peak velocity ratio, and mildly prolonged mitral early deceleration time (all p < 0.05). In multiple regression analysis, independently of demographics, obesity, blood pressure, and single metabolic components of MetS, clustered MetS was associated with a 2.6-fold higher likelihood of LV hypertrophy and a 2.3-fold higher likelihood of LA dilation (both p < or = 0.02).

CONCLUSIONS

In a population sample of adolescents, MetS is associated with higher prevalences of LV hypertrophy and LA dilation and with reduced LV systolic and diastolic function, independently of individual MetS components.

Body fat measurement by bioelectrical impedance and air displacement plethysmography: a cross-validation study to design bioelectrical impedance equations in Mexican adults

BACKGROUND

The study of body composition in specific populations by techniques such as bio-impedance analysis (BIA) requires validation based on standard reference methods. The aim of this study was to develop and cross-validate a predictive equation for bioelectrical impedance using air displacement plethysmography (ADP) as standard method to measure body composition in Mexican adult men and women.

METHODS

This study included 155 male and female subjects from northern Mexico, 20-50 years of age, from low, middle, and upper income levels. Body composition was measured by ADP. Body weight (BW, kg) and height (Ht, cm) were obtained by standard anthropometric techniques. Resistance, R (ohms) and reactance, Xc (ohms) were also measured. A random-split method was used to obtain two samples: one was used to derive the equation by the "all possible regressions" procedure and was cross-validated in the other sample to test predicted versus measured values of fat-free mass (FFM).

RESULTS AND DISCUSSION

The final model was: FFM (kg) = 0.7374 * (Ht2 /R) + 0.1763 * (BW) - 0.1773 * (Age) + 0.1198 * (Xc) - 2.4658. R2 was 0.97; the square root of the mean square error (SRMSE) was 1.99 kg, and the pure error (PE) was 2.96. There was no difference between FFM predicted by the new equation (48.57 +/- 10.9 kg) and that measured by ADP (48.43 +/- 11.3 kg). The new equation did not differ from the line of identity, had a high R2 and a low SRMSE, and showed no significant bias (0.87 +/- 2.84 kg).

CONCLUSION

The new bioelectrical impedance equation based on the two-compartment model (2C) was accurate, precise, and free of bias. This equation can be used to assess body composition and nutritional status in populations similar in anthropometric and physical characteristics to this sample.

Cardiac and systemic hemodynamic characteristics of hypertension and prehypertension in adolescents and young adults: the Strong Heart Study

BACKGROUND

The epidemic of overweight is increasing the prevalence of both prehypertension and early-onset hypertension, but few population-based data exist on their impact on cardiac structure and function in adolescents and young adults.

METHODS AND RESULTS

We analyzed clinical characteristics, hemodynamic parameters, and left ventricular structure and function in 1940 participants, 14 to 39 years of age, in the Strong Heart Study. Hypertension occurred in 294 participants (15%), who were more often men (70% versus 30%), older (age, 31+/-7 versus 25+/-8 years), and more commonly diabetic (23% versus 4.5%; all P<0.001) than their normotensive counterparts. Prehypertension occurred in 675 (35%) of participants with similar trends in gender, age, and diabetes status. After adjustment for covariates, both hypertensive and prehypertensive participants had higher left ventricular wall thickness (0.83 and 0.78 versus 0.72 cm), left ventricular mass (182 and 161 versus 137 g), and relative wall thickness (0.30 and 0.29 versus 0.28 cm) and 3- and 2-fold-higher prevalences of left ventricular hypertrophy than their normotensive counterparts (all P<0.001). Hypertension and prehypertension also were associated with higher mean pulse pressure/stroke volume index (1.24 and 1.15 versus 1.02 mm Hg/mL x m2) and total peripheral resistance index (3027 and 2805 versus 2566 dynes x s x cm(-5) x m2; all P<0.001).

CONCLUSIONS

In a population with high prevalences of obesity and diabetes, hypertension and prehypertension are associated with increases in both cardiac output and peripheral resistance index. Despite the young age of participants with hypertension and prehypertension, they had prognostically adverse preclinical cardiovascular disease, including left ventricular hypertrophy and evidence of increased arterial stiffness.

Gender differences in left ventricular systolic function in American Indians (from the Strong Heart Study)

Data from population-based studies indicate that men have a higher incidence and worse prognoses of congestive heart failure than women. Echocardiography was used to compare left ventricular (LV) myocardial and chamber contractility between 490 male and 861 female American Indian participants in the second Strong Heart Study examination. After adjusting for fat-free mass, baseline hypertension, diabetes mellitus, coronary heart disease, and alcohol consumption, LV ejection fractions were higher in women than men (66 +/- 8% vs 63 +/- 9%, p = 0.002), as were stress-corrected mid-wall shortening (106 +/- 13% vs 104+/-15%, p = 0.006) and the circumferential end-systolic stress/end-systolic volume index (7.1 x 10(4) +/- 1.9 x 10(4) vs 6.5 x 10(4) +/- 2.1 x 10(4) kdyne/cm3, all p values <0.001). LV ejection fractions were less than the predefined partition value in 4.7% of women and in 16.7% of men (odds ratio 0.25, 95% confidence interval 0.18 to 0.34, p <0.001). Stress-corrected mid-wall shortening was less than the predetermined lower limit of normal in 2.9% of women and in 6.2% of men (odds ratio 0.45, 95% confidence interval 0.29 to 0.70, p <0.001). There was no significant gender difference in supranormal function by either measure of LV systolic function. Estimated mean independent effects of female gender were a 3% greater ejection fraction, 2.7% greater stress-corrected mid-wall shortening, and a 0.4 x 10(4) kdyne/cm3 greater circumferential end-systolic stress/end-systolic volume index. In conclusion, in a population-based sample aged 45 to 74 years, women had greater LV myocardial and chamber function than men. Gender-specific partition values for measures of LV systolic function may be necessary to detect abnormal contractility in clinical and epidemiologic studies.

Effects of traditional and western environments on prevalence of type 2 diabetes in Pima Indians in Mexico and the U.S

OBJECTIVE

Type 2 diabetes and obesity have genetic and environmental determinants. We studied the effects of different environments on these diseases in Pima Indians in Mexico and the U.S.

RESEARCH DESIGN AND METHODS

Adult Pima-Indian and non-Pima populations in the Sierra Madre mountains of Mexico were examined using oral glucose tolerance tests and assessments for obesity, physical activity, and other risk factors. Results were compared with those from Pima Indians in Arizona. Both Pima populations were typed for DNA polymorphisms to establish their genetic similarity.

RESULTS

The age- and sex-adjusted prevalence of type 2 diabetes in the Mexican Pima Indians (6.9%) was less than one-fifth that in the U.S. Pima Indians (38%) and similar to that of non-Pima Mexicans (2.6%). The prevalence of obesity was similar in the Mexican Pima Indians (7% in men and 20% in women) and non-Pima Mexicans (9% in men and 27% in women) but was much lower than in the U.S. Pima Indians. Levels of physical activity were much higher in both Mexican groups than in the U.S. Pima Indians. The two Pima groups share considerable genetic similarity relative to other Native Americans.

CONCLUSIONS

The much lower prevalence of type 2 diabetes and obesity in the Pima Indians in Mexico than in the U.S. indicates that even in populations genetically prone to these conditions, their development is determined mostly by environmental circumstances, thereby suggesting that type 2 diabetes is largely preventable. This study provides compelling evidence that changes in lifestyle associated with Westernization play a major role in the global epidemic of type 2 diabetes.

Prediction of fat-free mass by bioimpedance analysis in migrant Asian Indian men and women: a cross validation study

BACKGROUND

Bioimpedance analysis (BIA) is a fast and convenient field technique for estimation of total body fat-free mass (FFM). However, bioimpedance-based prediction equations have been developed in predominantly white populations and little information is available on their usefulness in Asian Indian populations.

OBJECTIVE

To develop a prediction equation for FFM based on BIA measurements applicable to a migrant population of Asian Indians and to investigate the predictive accuracy of published BIA-based equations in this ethnic group.

DESIGN

FFM was measured by dual-energy X-ray absorptiometry in 211 healthy adults (110 men, 101 women; age ranges 19-74 year) of Asian Indian ethnicity and used as the reference measure to develop prediction equations based on single-frequency BIA measurements of resistance and reactance. A cross-validation technique was applied. Predictive accuracy of published BIA-based equations was assessed in this sample.

RESULTS

Sex-specific equations developed in the entire group included height2/resistance and body weight as predictors (R2=0.84 and 0.70 and standard errors of estimate of 2.8 and 2.0 kg for males and females, respectively; CV: 6%). Of published equations examined, one predicted FFM satisfactorily in men with nonsignificant bias and may be applicable to Asian Indian populations. None of the published equations tested performed satisfactorily in women.

CONCLUSIONS

Bioimpedance-based equations for predicting FFM developed specifically in Asian Indians are recommended for field studies designed to measure body composition of this ethnic group.

Body composition in underweight elderly subjects: reliability of bioelectrical impedance analysis

BACKGROUND AND AIMS

In underweight elderly subjects it is important to estimate body composition and particularly fat-free mass (FFM). Bioelectrical impedance analysis (BIA) is a non-invasive method in determining FFM, but its usefulness in these frail subjects should be verified. The aim of this study is to verify in underweight elderly people the reliability of previously published BIA formulas in detecting FFM.

METHODS

Fifty-seven hospitalized elderly subjects (27 males and 30 females) with body mass index <20 kg/m(2) were selected. In all subjects, FFM was detected by dual energy X-ray absorptiometry. Moreover, BIA measurements were performed at standard frequency (50 kHz and 800 microA) and FFM was derived using the main previous published BIA equations.

RESULTS

In men, Kyle and Rising equations gave acceptable estimates of FFM with a mean error, respectively, of 1+/-1.9 and 1.4+/-1.7 kg. Also RJL formula could be used after adjusting for a correction factor. In women, no equation seemed sufficiently reliable to estimate FFM.

CONCLUSIONS

BIA method seems useful to evaluate body composition in underweight elderly men but it seems to have intrinsic limits in women. Nevertheless, the variability in behavior of the different equations suggests to be careful in adopting BIA equations.

Guidelines for using body composition measurement in patients with human immunodeficiency virus infection

Wasting remains a significant condition of human immunodeficiency virus (HIV) infection despite antiretroviral treatment. Early identification requires the measurement of various body composition parameters, particularly body cell mass (BCM). Anthropometry may provide some useful information. Cost and complexity issues make many body composition techniques unsuitable for the clinical setting. Bioelectrical impedance analysis (BIA) may be the best method available to caregivers for monitoring serial changes in BCM over time and for determining the occurrence of wasting. It is not useful, however, for detecting body composition changes in patients with fat redistribution syndromes. Portability, low cost, ease of use, and patient acceptance make anthropometry and BIA ideally suited for the clinical setting.

New equations for calculating the components of energy expenditure in infants

OBJECTIVES

To derive new equations for 24-hour energy expenditure (24-h EE; kcal/d) and resting (RMR; kcal/d) and sleeping metabolic rates (SMR; kcal/d) in young infants by using the Enhanced Metabolic Testing Activity Chamber (EMTAC).

METHODS

Data from 50 (25 male/25 female) healthy normally growing infants (4.9 +/- 1.6 months, 7.1 +/- 1.4 kg, 65 +/- 5 cm) who had 24-h EE, RMR, and SMR extrapolated from 4- to 6-hour metabolic measurements in the EMTAC were used to derive new equations for 24-h EE, RMR, and SMR. Equations were derived by means of multiple regression analysis (SPSS 8.0), with weight alone or with length and weight entered as independent variables. Similar data from 10 additional test infants (4 male/6 female, 5.1 +/- 0.6 months, 7.5 +/- 1.0 kg, 65 +/- 5 cm) were used to cross-validate the new equations.

RESULTS

Twenty-four-hour EE, RMR, and SMR were 79.6 +/- 19.2, 66.8 +/- 15.1, and 62.3 +/- 10.3 kcal/kg per day, respectively. No differences existed in RMR (kcal/kg per day) from the 10 test infants between the weight (68.6 +/- 1.9) and height-weight based equations (68.4 +/- 6.1) or that measured by the EMTAC (67.6 +/- 10.2). Weight was the major predictor of 24-h EE, RMR, and SMR. The WHO, Schofield-weight and weight-height equations underestimated (P <.05) by 19%, whereas the new equations were within 4% of RMR obtained from the EMTAC.

CONCLUSIONS

The new equations for assessing energy requirements in healthy infants are more accurate than those previously published that underestimated 24-h EE by 15 kcal/kg per day.

Separate and joint effects of systemic hypertension and diabetes mellitus on left ventricular structure and function in American Indians (the Strong Heart Study)

Although the association of systemic hypertension (SH) with diabetes mellitus (DM) is well established, the cardiac features and hemodynamic profile of patients with SH and DM diagnosed by American Diabetes Association criteria have not been elucidated. To address this issue, echocardiograms were analyzed in 1,025 American Indian participants of the Strong Heart Study with neither DM nor SH, 642 with DM alone, 614 with SH alone, and 874 with SH and DM. In analyses that adjusted for age, gender, body mass index, and heart rate, DM and SH were associated with increased left ventricular (LV) wall thicknesses, with the greatest impact of DM on LV relative wall thickness and of the combination of DM and SH on LV mass (both p <0.001). LV fractional shortening was reduced with SH and SH + DM, midwall shortening was reduced with DM, SH, and their combination, and was reduced in both diabetic groups compared with their nondiabetic counterparts (p <0.001). DM alone was associated with lower measures of LV pump performance (stroke volume, cardiac output, and their indexes) than SH alone. Pulse pressure/stroke index, an indirect measure of arterial stiffness, was elevated in participants with DM or SH alone and most in those with both conditions. There were progressive increases from the reference group to DM alone, SH alone, and DM + SH with regard to prevalences of LV hypertrophy (12% to 19%, 29% and 38%) and subnormal LV myocardial function (7% to 10%, 11% and 18%, both p <0.001). In conclusion, DM and SH each have adverse effects on LV geometry and function, and the combination of SH and DM results in the greatest degree of LV hypertrophy, myocardial dysfunction, and arterial stiffness.

Nutritional status after short-term dietary supplementation in hospitalized malnourished geriatric patients

AIM

To examine the evolution of different parameters of the nutritional status after short-term oral protein-energy supplementation in moderately malnourished geriatric patients.

METHODS

Seventeen hospitalized malnourished elderly patients and 12 healthy adults received dietary supplements for 10 days. A group of six malnourished elderly subjects served as controls. Spontaneous oral intakes, biological and biophysical markers of the nutritional status were measured. Fat-free mass (FFM) was assessed using Dual energy X-ray absorptiometry (DXA), bio-impedance analysis (BIA) and anthropometry.

RESULTS

In elderly subjects, the supplementation significantly increased both dietary intake (energy +32%, protein +65%) and FFM (+1.3 kg, P<0.001) as assessed using DXA. BIA and anthropometric data correlated with DXA measurements in the elderly (BIA: r=0.68--0.80, anthropometry: r=0.80--0.89), but failed to reflect accurately the changes measured in FFM. Supplementation had no notable effect on biological markers in any of the groups. IGF-I and hand-grip strength were not significantly influenced by the supplementation despite trends towards an improvement.

CONCLUSIONS

Monitoring short-term changes in nutritional status in malnourished elderly individuals is a problem in routine clinical management. Our data put in the limelight the changes in IGF-I values related to dietary supplementation, and, chiefly, suggest a prime role for the assessment of dietary intake and FFM, as assessed by DXA, as indicators of short-term efficacy of refeeding. Nevertheless larger studies are necessary to confirm the clinical and prognostic significance of the changes.

Insulin sensitivity regulates autonomic control of heart rate variation independent of body weight in normal subjects

It is unclear whether insulin sensitivity independent of body weight regulates control of heart rate variation (HRV) by the autonomic nervous system. Insulin action on whole-body glucose uptake (M-value) and heart rate variability were measured in 21 normal men. The subjects were divided into 2 groups [normally insulin sensitive (IS, 8.0 +/- 0.4 mg/kg.min) and less insulin sensitive (IR, 5.1 +/- 0.3 mg/kg.min)] based on their median M-value (6.2 mg/kg x min). Spectral power analysis of heart rate variability was performed in the basal state and every 30 min during the insulin infusion. The IS and IR groups were comparable, with respect to age (27 +/- 2 vs. 26 +/- 2 yr), body mass index (22 +/- 1 vs. 23 +/- 1 kg/m(2)), body fat (13 +/- 1 vs. 13 +/- 1%), systolic (121 +/- 16 vs. 117 +/- 14 mm Hg) and diastolic (74 +/- 11 vs. 73 +/- 11 mm Hg) blood pressures, and fasting plasma glucose (5.4 +/- 0.1 vs. 5.5 +/- 0.1 mmol/L) concentrations. Fasting plasma insulin was significantly higher in the IR (30 +/- 4 pmol/L) than in the IS (17 +/- 3 pmol/L, P < 0.05) group. In the IS group, insulin significantly increased the normalized low-frequency (LFn) component, a measure of predominantly sympathetic nervous system activity, from 36 +/- 5 to 48 +/- 4 normalized units (nu; 0 vs. 30-120 min, P < 0.001); whereas the normalized high-frequency (HFn) component, a measure of vagal control of HRV, decreased from 66 +/- 9 to 48 +/- 5 nu (P < 0.001). No changes were observed in either the normalized LF component [35 +/- 5 vs. 36 +/- 2 nu, not significant (NS)] or the normalized HF component (52 +/- 6 vs. 51 +/- 4 nu, NS) in the IR group. The ratio LF/HF, a measure of sympathovagal balance, increased significantly in the IS group (0.92 +/- 0.04 vs. 1.01 +/- 0.04, P < 0.01) but remained unchanged in the IR group (0.91 +/- 0.04 vs. 0.92 +/- 0.03, NS). Heart rate and systolic and diastolic blood pressures remained unchanged during the insulin infusion in both groups. We conclude that insulin acutely shifts sympathovagal control of HRV toward sympathetic dominance in insulin-sensitive, but not in resistant, subjects. These data suggest that sympathetic overactivity is not a consequence of hyperinsulinemia.

Relations of stroke volume and cardiac output to body composition: the strong heart study

BACKGROUND

Although cardiac output (CO) plays the vital role of delivering nutrients to body tissues, few data are available concerning the relations of stroke volume (SV) and CO to body composition in large population samples.

METHODS AND RESULTS

Doppler and 2D echocardiography and bioelectric impedance in 2744 Strong Heart Study participants were used to calculate SV and CO and to relate them to fat-free body mass (FFM), adipose mass, and demographic variables. Both SV and CO were higher in men than women and in overweight than normal-weight individuals, but these differences were diminished or even reversed by normalization for FFM or body surface area. In both sexes, SV and CO were more strongly related to FFM than adipose mass, other body habitus measures, arterial pressure, diabetes, or age. In multivariate analyses using the average of Doppler and left ventricular SV to minimize measurement variability, FFM was the strongest correlate of SV and CO; other independent correlates were adipose mass, systolic pressure, diabetes, age, and use of digoxin and calcium channel and beta-blockers.

CONCLUSIONS

In a population-based sample, SV and CO are more strongly related to FFM than other variables; increased FFM may be the primary determinant of increased SV and CO in obesity.

Estimation of body fat from anthropometry and bioelectrical impedance in Native American children

OBJECTIVE

Obesity, as measured by body mass index, is highly prevalent in Native American children, yet there are no valid equations to estimate total body fatness for this population. This study was designed to develop equations to estimate percentage body fat from anthropometry and bioelectrical impedance as a critical part of Pathways, a multi-site study of primary prevention of obesity in Native American children.

DESIGN

Percentage fat was estimated from deuterium oxide dilution in 98 Native American children (Pima/Maricopa, Tohono O'odham and White Mountain Apache tribes) between 8 and 11 y of age. The mean fat content (38.4%+/-8. 1%) was calculated assuming the water content of the fat-free body was 76%. Initial independent variables were height, weight, waist circumference, six skinfolds and whole-body resistance and reactance from bioelectrical impedance (BIA).

RESULTS

Using all-possible-subsets regressions with the Mallows C (p) criterion, and with age and sex included in each regression model, waist circumference, calf and biceps skinfolds contributed least to the multiple regression analysis. The combination of weight, two skinfolds (any two out of the four best: triceps, suprailiac, subscapular and abdomen) and bioelectrical impedance variables provided excellent predictability. Equations without BIA variables yielded r2 almost as high as those with BIA variables. The recommended equation predicts percentage fat with a root mean square error=3.2% fat and an adjusted r2=0.840.

CONCLUSION

The combination of anthropometry and BIA variables can be used to estimate total body fat in field studies of Native American children. The derived equation yields considerably higher percentage fat values than other skinfold equations in children.

Validation of near-infrared interactance and skinfold methods for estimating body composition of American Indian women

PURPOSE

This study tested the predictive accuracy of the Jackson et al. skinfold (SKF) equations (sigma7SKF and sigma3SKF), a multi-site near-infrared interactance (NIR) prediction equation, and the Futrex-5000 NMR equation in estimating body composition of American Indian women (N = 151, aged 18-60 yr).

METHODS

Criterion body density (Db) was obtained from hydrodensitometry at residual lung volume.

RESULTS

Sigma7SKF significantly underestimated Db (P < 0.05). Sigma3SKF and Heyward's NIR equations significantly overestimated Db (P < 0.05). The Futrex-5000 NIR equation significantly underestimated percent of body fat (%BF) (P < 0.05). Prediction errors for SKF and multi-site NIR exceeded 0.0080 g x cc(-1). The SEE for Futrex-5000 was 5.5%BF. Thus, ethnic-specific SKF and NIR equations were developed. For the SKF model, the sigma3SKF (triceps, axilla, and suprailium) and age explained 67.3% of the variance in Db:Db = 1.06198316 -0.00038496(sigma3SKF) -0.00020362(age). Cross-validation analysis yielded r = 0.88, SEE = 0.0068 g x cc(-1), E = 0.0070 g x cc(-1), and no significant difference between predicted and criterion Db. For the NIR model, the hip circumference, sigma2AdeltaOD2 (biceps and chest), FIT index, age, and height explained 73.9% of the variance in Db:Db = 1.0707606 -0.0009865(hip circumference) -0.0369861(sigma2deltaOD2) + 0.0004167(height) + 0.0000866(FIT index) -0.0001894(age). Cross-validation yielded r = 0.85, SEE = 0.0076 g x cc(-1), E = 0.0079 g x cc(-1), and a small, but significant, difference between predicted and criterion Db.

CONCLUSIONS

We recommend using the ethnic-specific SKF and NIR equations developed in this study to estimate Db of American Indian women.

Daily energy expenditure in Mexican and USA Pima indians: low physical activity as a possible cause of obesity

BACKGROUND

Obesity is caused by an imbalance between energy intake and energy expenditure. However, it is unknown whether increased physical activity protects susceptible populations against the development of obesity and type 2 diabetes.

OBJECTIVE

To investigate the potential protective role of environment and physical activity against obesity by measuring total energy expenditure in Mexican and USA Pima Indians.

METHODS

We compared the physical activity level of 40 (17 female and 23 male; 37+/-11 y, 66+/-13 kg) Mexican Pima Indians from a remote, mountainous area of Northwest Mexico, with 40 age-and-sex matched (17 female and 23 male; 37+/-12 y, 93+/-22 kg) Pima Indians from the Gila River Indian Community in Arizona, USA. We measured total energy expenditure (TEE) by doubly labeled water and calculated physical activity by different methods: physical activity level (PAL) as the ratio of TEE on resting metabolic rate (RMR), TEE adjusted for RMR by linear regression, activity energy expenditure adjusted for body weight (AEE), and activity questionnaire.

RESULTS

Physical activity was higher in Mexican Pima Indians when compared with USA Pima Indians as assessed by PAL (1.97+/-0.34 vs 1.57+/-0.16, P<0.0001), TEE adjusted for RMR (3289+/-454 vs 2671+/-454 kcal/day, P<0.0001) and AEE adjusted for body weight (1243+/-415 vs 711+/-415 kcal/day, P<0. 0001). Questionnaires revealed more time spent on occupational activities among Mexican Pima compared with USA Pima (23.9+/-13.3 vs 12.6+/-13.9 h/week, P<0.001).

CONCLUSION

These data support a significant role for physical activity in the prevention of obesity in genetically susceptible populations. International Journal of Obesity (2000)24, 55-59

Effect of heparin-stimulated plasma lipolytic activity on VLDL APO B subclass metabolism in normal subjects

Heparin given intravenously enhances lipolysis, although fasting lipids are not markedly altered in long-term administration. In the present study we investigated heparin-induced acute perturbation of VLDL subclass metabolism. Eight men were examined during a control study and during an 8.5 h infusion of heparin. 2H3-leucine was used as tracer and kinetic constants derived using a non-steady-state model. Heparin infusion increased both plasma lipoprotein and hepatic lipase activity and raised plasma FFAs two-fold (P < 0.001). The fractional catabolic rate (FCR) of VLDL1 apo B increased on heparin (25.7 +/- 4.2 and 10.8 +/- 1.7 pools/d, heparin vs. control, P < 0.02). The FCR of VLDL2 apo B increased to 12.6 +/- 1.9 pools/d on heparin vs. 8.8 +/- 1.1 pools/d during the control (NS). Total VLDL apo B production was not significantly changed (824 +/- 45 and 692 +/- 91 mg/d, heparin vs. control, NS). We conclude that during heparin infusion, the catabolism of especially large triglyceride-rich VLDL1 apo B is greatly increased. However, although the FFA levels were high during the heparin study, the production of total VLDL apo B did not rise. These findings are consistent with the known action of heparin on lipoprotein lipase but indicate that acute increase in plasma FFA levels does not lead to a rise in VLDL apo B production.

Use of the leg-to-leg bioelectrical impedance method in assessing body-composition change in obese women

BACKGROUND

There is little information on whether bioelectrical impedance analysis (BIA) accurately predicts changes in body composition associated with energy restriction, exercise, or both.

OBJECTIVE

We had 2 objectives: to determine the validity of the leg-to-leg BIA system in 1) estimating body composition in obese and nonobese women, with a cross-sectional design, and 2) assessing changes in body composition in obese women in response to 12 wk of energy restriction, exercise training, or both.

DESIGN

Subjects were 98 moderately obese women (43.2 +/- 0.6% body fat, 45.0 +/- 1.1 y of age) and 27 nonobese control subjects (24.0 +/- 1.5% body fat, 43.5 +/- 2.5 y of age). Obese subjects were randomly divided into 1 of 4 groups, with fat-free mass, fat mass, and percentage body fat estimated with BIA and underwater weighing before and after 12 wk of intervention. The 4 groups were diet only (4.19-5.44 MJ/d), exercise only (five, 45-min sessions/wk at 78.5 +/- 0.5% of maximum heart rate), both exercise and diet, and control (no diet or exercise).

RESULTS

No significant difference was found between underwater weighing and BIA in estimating the fat-free mass of the obese and nonobese women (all subjects combined, r = 0.78, P < 0.001, SEE = 3.7 kg) or in estimating decreases in fat mass during 12 wk of energy restriction, exercise, or both in obese subjects (F[3.85] = 1.45, P = 0.233).

CONCLUSIONS

The leg-to-leg BIA system accurately assessed fat-free mass in obese and nonobese women, and changes in fat mass with diet alone or when combined with exercise.

Relations of left ventricular mass to fat-free and adipose body mass: the strong heart study. The Strong Heart Study Investigators

BACKGROUND

It is unclear whether increased left ventricular (LV) mass in overweight individuals is related to their adiposity or to greater fat-free mass (FFM).

METHODS AND RESULTS

We compared echocardiographic LV mass to FFM and adipose body mass by bioelectric impedance and to anthropometric measurements in 3107 American Indian participants in the Strong Heart Study. In men and women, the relations of LV mass and FFM (r=0.37 and 0.38, P<0.001) were closer (P<0.05 to <0.001) than they were with adipose mass, waist/hip ratio, body mass index, systolic blood pressure, height, or height2.7. Regression analyses showed that in men LV mass had the strongest independent relation with FFM, followed by systolic blood pressure and age (all P<0.001); in women, LV mass was related to FFM more strongly than it was to systolic blood pressure, age (all P<0. 001), and diabetes (P=0.012). Adipose mass had no independent relation to LV mass. When waist/hip ratio or body mass index were substituted for adipose mass, LV mass was independently related to FFM (P<0.001) and body mass index (P=0.02) but not to waist/hip ratio in men and was independently related to FFM and waist/hip ratio (both P<0.001) but not to body mass index in women. Using 97.5 percentile gender-specific partitions for LV mass/FFM in reference individuals, we found that LV hypertrophy occurred in 20.8% of Strong Heart Study participants with hypertension, overweight, or diabetes compared with 10.5% and 16.7% by LV mass indexed for body surface area or height2.7.

CONCLUSIONS

LV mass is more strongly related to FFM than to adipose mass, waist/hip ratio, body mass index, or height-based surrogates for lean body weight; LV mass/FFM criteria may increase sensitivity to detect LV hypertrophy.

Serum total renin, an independent marker of the activity and severity of retinopathy in patients with IDDM

BACKGROUND/AIMS

Recent studies have demonstrated marked renin and prorenin concentration gradients between ocular tissues and blood, and local expression of the renin-angiotensin system (RAS) in the eye. The authors determined whether serum total renin, which mostly consists of prorenin, is a marker of the activity and severity of diabetic retinopathy independent of other microvascular complications.

METHODS

Total renin concentrations (TRC) were measured with a time resolved immunofluorometric assay in 38 patients with IDDM (age 34 (SD 7) years, duration of disease 22 (7) years, serum creatinine 95 (15) mumol/l, urinary albumin excretion rate (UAER) 207 (829) micrograms/min, HbA1c 8.5% (1.2%)), and in 13 matched normal subjects. All subjects were carefully characterised with respect to the presence and severity of retinopathy (RP score), nephropathy, and neuropathy using seven different tests of autonomic neuropathy.

RESULTS

Serum TRC was on average twofold higher in IDDM (396 (SE 211) ng/l) than in normal subjects (201 (88) ng/l, p < 0.001). It was nearly twofold higher in patients with preproliferative or active proliferative retinopathy requiring careful follow up or therapy (TRC 596 (268) ng/l, n = 11) compared with those with quiescent proliferative retinopathy after laser treatment (TRC 338 (183) ng/l, p < 0.01, n = 5); moderately severe non-proliferative retinopathy (337 (106) ng/l, p < 0.01, n = 13), no retinopathy, or only minimal non-proliferative retinopathy (270 (43) ng/l, p < 0.001, n = 9). In multiple linear regression analysis, RP score (p < 0.01), but not the UAER or any index of autonomic neuropathy, was an independent determinant of serum TRC, and explained 32% of its variation (R = 0.57, p < 0.005).

CONCLUSIONS

Serum TRC in patients with diabetic retinopathy is increased independent of renal function and autonomic neuropathy especially in those with severe active changes requiring careful follow up or treatment. These findings support the idea that diabetic retinopathy is the most important determinant of serum TRC in patients with IDDM, and that TRC is produced when retinopathy is active.

Effects of hydration changes on bioelectrical impedance in endurance trained individuals

PURPOSE

The purpose of this study was to determine how differences in hydration states and ion content of hydrating fluids affected bioelectrical impedance (BI) and hydrostatic weighing (HW) measurements.

METHODS

Fifteen athletic subjects aged 19-56 yr were recruited. Relative body fat (%), fat-weight (FW), and fat-free weight (FFW) were assessed using BI and HW under normal conditions (N), hypohydration (HPO), rehydration (RHY), and superhydration (SHY) states. During the RHY and SHY trial periods, subjects were hydrated with either distilled water or an electrolyte solution (ELS). HPO and SHY levels were set at 3% of each person's normally hydrated body weight.

RESULTS

Comparison between the distilled water and the ELS trials indicated that hydration solution had no effect on BI or HW. Thus, the results presented are the trial means of both hydration solutions combined. Both BI and HW were shown to be highly test-retest reliable (r-values: 0.96 and 0.99, respectively). The effects of exercise induced HPO followed by RHY on body composition values indicated that HW was very stable across measurement periods while BI was not. From N to the HPO state, BI %BF declined from 14.4 +/- 5.3% to 12.3 +/- 5.3%, respectively. After RHY, BIA %BF increased to 15.5 +/- 5.8%. Similar findings occurred when subjects were superhydrated (N-BI = 13.2 +/- 5.3%; SHY-BI = 15.4 +/- 5.6%). With a comparison of the intercepts and slopes of HW and BIA for the N and SHY states, it was clear hydration status significantly affected the intercepts (HW: 0.37 vs. BI: 1.85) and not the slopes (HW: 1.00 vs BI: 0.99). As a result, a majority of all fluid changes were interpreted as FW by BI. During HPO, 82% of the weight loss was considered FW while during RHY or SHY, 128% and 85% of the water weight regain/gain was considered FW.

CONCLUSION

These results indicate that BI is not a valid technique in athletes, especially when wanting to determine body composition effects of training/detraining. This study indicates that even small fluid changes such as those that occur with endurance training may be interpreted incorrectly as changes in an athlete's body fat content.

Predictive accuracy of BIA equations for estimating fat-free mass of black men

This study assessed the predictive accuracy of previously published bioelectrical impedence analysis (BIA) equations in estimating the fat-free mass (FFM) of black men, 19 to 50 years. The reference method was hydrostatic weighing (HW) at residual lung volume. Body density (Db) was converted to relative body fat (%BF) for calculation of FFMHW using the Schutte et al. equation. Resistance and reactance were measured with a Valhalla bioimpedance analyzer. Age-specific, generalized, and fatness-specific BIA equations were cross validated using regression analysis. The Segal fatness-specific equations were modified using a method recommended by Stolarczyk. All of the equations significantly (P < 0.05) underestimated the average reference measure of FFMHW. However, the underestimation of FFM for the modified Segal fatness-specific equation was relatively small (-1.8 kg) and not likely to have much clinical significance. Furthermore, this equation had a high correlation with reference FFMHW (ry,y' = 0.97), low prediction errors (SEE = 2.1 kg; E = 2.7 kg), and accurately estimated the FFM within +/- 3.5 kg for 78% of the individuals in the sample. Thus, we recommend using the modified fatness-specific BIA equation for estimating the FFM of black men.

Body composition of spinal cord injured adults

The prevalence of diseases associated with obesity, such as cardiovascular disease and diabetes mellitus, is higher in the spinal cord injury (SCI) population. Specifically, the mortality rate for cardiovascular disease is 228% higher in the SCI population. In addition, 100% of SCI individuals have osteoporosis in the paralysed extremities. These diseases are related to physical activity level, the level of the spinal cord lesion, and time post injury. Physically active SCI men and women have above-average fat mass (16 to 24% and 24 to 32%, respectively, compared with 15% for able-bodied men and 23% for able-bodied women), while sedentary SCI individuals have 'at-risk' levels of body fat (above 25% and 32%, respectively). The proportions and densities of the 3 main constituents comprising the fat-free body (mineral, protein and water) are altered following SCI. Bone mineral content decreases by 25 to 50%, and the magnitude of reduction is dependent on the level, completeness and duration of SCI. Because of denervation resulting in skeletal muscle atrophy, total body protein reduces by 30%, and total body water relative to bodyweight decreases by 15% following SCI. Indirect methods based on 2-component body composition models assume constant proportions and densities of mineral, protein, and water in the fat-free body. As a result, prediction equations based on 2-component models yield invalid estimates of fat and fat-free mass in the SCI population. Therefore, future research needs to directly quantify the proportions and densities of the constituents of the fat-free body in the SCI population relative to age, sex, physical activity level, level of the spinal cord lesion and time post injury, and to develop equations based on multicomponent body composition models.

Chronic hyperglycemia impairs endothelial function and insulin sensitivity via different mechanisms in insulin-dependent diabetes mellitus

BACKGROUND

We explored whether chronic hyperglycemia is associated with defects in endothelium-dependent vasodilatation in vivo and whether defects in the hemodynamic effects of insulin explain insulin resistance.

METHODS AND RESULTS

Vasodilator responses to brachial artery infusions of acetylcholine, sodium nitroprusside, and NG-monomethyl-L-arginine and, on another occasion, in vivo insulin sensitivity (euglycemic insulin clamp combined with the forearm catheterization technique) were determined in 18 patients with insulin-dependent diabetes mellitus (IDDM) and 9 normal subjects. At identical glucose and insulin levels, insulin stimulation of whole-body and forearm glucose uptake was 57% reduced in the IDDM patients compared with normal subjects (P < .001). The defect in forearm glucose uptake was attributable to a defect in glucose extraction (glucose AV difference, 1.1 +/- 0.2 versus 1.9 +/- 0.2 mmol/L, P < .001, IDDM versus normal subjects), not blood flow. Within the group of IDDM patients, hemoglobin A1c was inversely correlated with forearm blood flow during administration of acetylcholine (r = -.50, P < .02) but not sodium nitroprusside (r = .07). The ratio of endothelium-dependent to endothelium-independent blood flow was approximately 40% lower in patients with poor glycemic control than in normal subjects or patients with good or moderate glycemic control.

CONCLUSIONS

We conclude that chronic hyperglycemia is associated with impaired endothelium-dependent vasodilatation in vivo and with a glucose extraction defect during insulin stimulation. These data imply that chronic hyperglycemia impairs vascular function and insulin action via distinct mechanisms. The defect in endothelium-dependent vasodilatation could contribute to the increased cardiovascular risk in diabetes.

Cross-validation of fat-free mass estimated from body density against bioelectrical resistance: effects of obesity and gender

The major purpose of this study was to examine whether estimates of body composition from bioelectrical resistance were systematically biased by obesity and/or gender (using hydrodensitometry as a comparison method). We compared fat-free mass (FFM) by bioelectrical resistance (BR) using 5 equations (Lukaski, Kushner, Rising, Khaled, and Segal) to FFM by hydrodensitometry (HD) in 20 lean men, 30 lean women, 33 obese men and 22 obese women. None of the BR equations was successfully cross-validated against FFM by HD in all 4 sub-groups. The Lukaski equation significantly underestimated FFM in all 4 groups by 2.7 to 4.7 kg; the Kushner equation significantly underestimated FFM by 2.0 to 2.9 kg except in obese women; the Rising equation significantly overestimated FFM in obese women (5.3 kg) and men (2.9 kg); the Khaled equation successfully predicted FFM in all groups except obese men; and the Segal equation successfully predicted FFM in all groups except lean men. In some groups, a portion of the discrepancy could be explained by bias originating from body fat. Analysis of our data by forward regression analysis demonstrated that height2/resistance, body weight, gender and suprailiac skinfold thickness provide the most accurate estimates of FFM (R2 = 0.92; SEE = 3.58 kg) that are free of bias originating from gender and body fat. We conclude that the estimation of fat-free mass by BR is significantly influenced by gender and obesity. An alternative equation is proposed for estimating fat-free mass based on measurement of height2/resistance, body weight, gender and suprailiac skinfold thickness.

The prediction of extracellular and total body water from bioelectric impedance in a non-Caucasian population from central Asia

The availability of only a small number of studies on bioelectric impedance analysis (BIA) in non-Caucasian ethnic groups appears to limit reliable utilization of this method in anthropological field studies. In this study, 28 male Turkish-Mongolian subjects native of Kazakhstan (Central Asia) underwent total body water (TBW) and extracellular water (ECW) assessment by deuterium oxide (D2O) and sodium bromide (NaBr) dilution respectively. Bioelectric impedance (BI) was recorded at multiple frequencies. ECW and TBW were calculated from BI at 1 and 100 kHz respectively by applying formulae developed on a sample of Caucasian subjects with a hydration status similar to that of the study population. TBW predicted from BI at 1 and 100 kHz (37.5 +/- 3.31) was highly correlated and not significantly different from that obtained by D2O dilution (39.0 +/- 4.11, r = 0.894, p < 0.0001, SEE = 1.91). Similarly, ECW predicted from BI at 1 kHz (15.1 +/- 1.21) was highly correlated and not significantly different from that obtained by NaBr dilution (15.0 +/- 1.61, r = 0.847, p < 0.0001, SEE = 0.81). It is concluded that selected predictive formulae developed on Caucasian subjects may provide a precise and accurate assessment of ECW and TBW in Turkish-Mongolian populations.

Predicting body fatness: the body mass index vs estimation by bioelectrical impedance

The body mass index (weight in kilograms/height in square meters) is a common surrogate for fatness. With the advent of bioelectrical impedance analysis, more precise measurement of fatness in populations is now possible. We measured height, weight, and percentage that is fat by bioelectrical impedance analysis in 2032 adults, ages 31 to 92, participating in the Framingham studies. Body mass index was a poor predictor of fatness in women (R2 = 0.55) and men (R2 = 0.38), and was imprecise (standard error of estimate = 5 percentage points). The relationship between percentage fat and body mass index was quadratic in both sexes, and was altered by age in women (P < .0001) and, to a lesser extent, in men (P < .027). These data suggest that body mass index is an imprecise measurement of fatness compared with bioelectrical impedance.

Bioelectrical impedance and body composition: present status and future directions

Single-frequency bioelectrical impedance analyzers used to assess body composition are being replaced by multiple-frequency analyzers. At low frequencies, the current flows primarily through extracellular fluids; at high frequencies, it completely penetrates all body tissues. Measures of bioelectrical impedance at multiple frequencies can differentiate total and extracellular fluid compartments in the body. This has considerable value for assessing clinical and nutritional status. Impedance measures at a single frequency contain only a small window of the available impedance spectrum information, which may explain the difficulty in discriminating among individuals. The impedance spectrum and its analysis may provide a much clearer picture of individual differences in body water and body composition. With increasing clinical uses of bioelectrical impedance in individuals and sample populations, the use of multiple-frequency impedance may help to elucidate differences that are not discernible with single-frequency impedance.

Body composition following hemodialysis: studies using dual-energy X-ray absorptiometry and bioelectrical impedance analysis

The detection, prevention and treatment of disease is greatly facilitated by the availability of accurate and non-invasive techniques for measuring the amount and regional distribution of fat mass and fat-free mass. As differing degrees of hydration may influence these measurements, we used dual-energy X-ray absorptiometry (DXA) and bioelectrical impedance analysis (BIA) to detect changes in hydration following hemodialysis, and to determine whether fat mass, fat-free mass and bone density measurements were affected by these fluid changes. Ten subjects (7 men, 3 women) mean age 46.2 years (range 25-68 years), with renal failure had bone density, fat-free mass and fat mass measured by DXA, and total body water and fat-free mass measured by BIA, before and after hemodialysis. Thirty-two subjects had fat-free mass measured by DXA and BIA in an attempt to derive new equations (using fat-free mass measured by DXA as the reference standard) to improve the predictive value of BIA. The new equations were then used to derive the changes in fat-free mass following hemodialysis measured using BIA. In absolute terms, total tissue measured by DXA (r = 0.99, p = 0.01) and total body water measured by BIA (r = 0.91, p = 0.01) correlated with gravimetric weight. Following hemodialysis, fat mass and bone density measured by DXA were unaffected by the fluid changes. The change in gravimetric weight was 1.8 +/- 0.3 kg, p = 0.01 (mean +/- SEM). This change was measured as 1.9 +/- 0.3 kg by DXA, -0.9 +/- 1.0 kg by BIA using the published equation for fat-free mass, and 3.2 +/- 0.4 kg using the new equation for fat-free mass.(ABSTRACT TRUNCATED AT 250 WORDS)