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.     

Energy Expenditure in Lean and Obese Prepubertal Children

The relationship between energy expenditure and obesity was examined in prepubertal children. Consenting fifth graders underwent Tanner Staging, weight, height and skinfold measurements. Subjects were selected for further study to obtain equal numbers of girls and boys with a wide range of body composition. Weight, total daily energy expenditure (TDEE) by doubly labeled water (DLW), resting metabolic rate (RMR), and body composition were measured. Children were grouped into level of obesity based on tertiles of subscapular plus triceps skinfolds. The skinfold tertiles did quite well in grouping subjects by degree of obesity, as differences in percent fat in each tertile were significantly different. There were no differences in fat-free mass between the groups, while the highest tertile group weighed 14 kg more than the lowest. For DLW, energy expenditure was calculated using day 8 and day 9 urine samples as the final time point to examine precision. Mean energy expenditure using either day was nearly identical (2220 ± 400 vs. 2300 ± 370 kcal/d), with a CV of the difference of 5.5%. No differences in RMR, energy expended in activity, or TDEE between the three groups were observed. A reduction in RMR or TDEE could not explain differences in obesity in these prepubertal children. However, the fact that the heaviest children expended the same amount of energy in activity and had the same TDEE as the leanest, while weighing 14 kg more, indicates that the obese children had a reduced activity level.     

Longitudinal study of body weight changes in children: who is gaining and who is losing weight

Cross-sectional studies have reported significant temporal increases in prevalence of childhood obesity in both genders and various racial groups, but recently the rise has subsided. Childhood obesity prevention trials suggest that, on average, overweight/obese children lose body weight and nonoverweight children gain weight. This investigation tested the hypothesis that overweight children lose body weight/fat and nonoverweight children gain body weight/fat using a longitudinal research design that did not include an obesity prevention program. The participants were 451 children in 4th to 6th grades at baseline. Height, weight, and body fat were measured at month 0 and month 28. Each child's BMI percentile score was calculated specific for their age, gender and height. Higher BMI percentile scores and percent body fat at baseline were associated with larger decreases in BMI and percent body fat after 28 months. The BMI percentile mean for African-American girls increased whereas BMI percentile means for white boys and girls and African-American boys were stable over the 28-month study period. Estimates of obesity and overweight prevalence were stable because incidence and remission were similar. These findings support the hypothesis that overweight children tend to lose body weight and nonoverweight children tend to gain body weight.     

Risk ratios for obesity in families of obese African-American and Caucasian women

We examined age- and sex-standardized risk ratios (SRRs) in matched samples of 1,185 families of obese African-American and Caucasian women. Familial risk ratios increased with body mass index (BMI) of proband and BMI thresholds of relative. Ratios were higher in Caucasian than African-American families, apparently because Caucasian probands were more extreme relative to their population mean. Risk ratios for moderate obesity (BMI >/= 30) were around 2 for African-Americans and were a little higher in Caucasians. Ratios for extreme obesity (BMI >/= 40) ranged from 3 to 5 in African-Americans and from about 5 to 9 in Caucasians. Thin relatives were rare in families of both races. Risk ratios appear high enough in both racial groups to facilitate the identification of quantitative trait loci underlying common obesity phenotypes. The high population prevalence of obesity in African-American women will require particularly high selection thresholds to achieve risk ratios comparable to those for Caucasians. The scarcity of thin siblings in both groups will greatly increase the effort required in sample recruitment for discordant pair designs.     

Prediction models for insulin resistance in girls with premature adrenarche. The premature adrenarche insulin resistance score: PAIR score

AIM: The purpose of this study was to develop an accurate regression model to predict insulin resistance in girls with premature adrenarche. METHODS: The insulin sensitivity index was calculated from the frequently sampled intravenous glucose tolerance test with tolbutamide. Thirty-five prepubertal girls (23 Caribbean-Hispanic and 12 African-American; mean age 6.8 years) were studied. The insulin sensitivity index was compared to birth weight, body mass index (BMI), the presence of acanthosis nigricans (AN), insulin-like growth factor 1, insulin-like growth factor binding protein 1, sex hormone binding globulin, lipid profile, and adrenocorticotropic hormone stimulated androgens. RESULTS: The best prediction models included birth weight, BMI, and AN (model 1: R(2) = 0.78) and BMI, AN, and serum 17-OH pregnenolone (model 2: R(2) = 0.76). When viewed as screening tests, a cutoff value <5.5 (premature adrenarche insulin resistance score) in both equations showed a sensitivity of 100% and a specificity of 85%. CONCLUSION: Born small for gestational age, premature adrenarche, obesity, AN, and higher serum 17-OH pregnenolone levels may confer negative, but independent, health risks.     

Resting Metabolic Rate in Severely Obese Diabetic and Nondiabetic Subjects

Objectives : To compare the resting metabolic rate (RMR) between diabetic and nondiabetic obese subjects and to develop a predictive equation of RMR for these subjects. Research Methods and Procedures : Obese adults (1088; mean age = 44.9 ± 12.7 years) with BMI ≥ 35 kg/m² (mean BMI = 46.4 ± 8.4 kg/m²) were recruited. One hundred forty‐two subjects (61 men, 81 women) were diagnosed with type 2 diabetes (DM), giving the prevalence of DM in this clinic population as 13.7%. RMR was measured by indirect calorimetry, and several multivariate linear regression models were performed using age, gender, weight, height, BMI, fat mass, fat mass percentage, and fat‐free mass as independent variables. Results : The severely obese patients with DM had consistently higher RMR after adjustment for all other variables. The best predictive equation for the severely obese was RMR = 71.767 ? 2.337 × age + 257.293 × gender (women = 0 and men = 1) + 9.996 × weight (in kilograms) + 4.132 × height (in centimeters) + 145.959 × DM (nondiabetic = 0 and diabetic = 1). The age, weight, and height‐adjusted least square means of RMR between diabetic and nondiabetic groups were significantly different in both genders. Discussion : Severely obese patients with type 2 diabetes had higher RMR than those without diabetes. The RMR of severely obese subjects was best predicted by an equation using age, gender, weight, height, and DM as variables.     

Improved Equations for Estimating the Resting Metabolic Rate

New models were developed for predicting the resting metabolic rate (RMR) with sufficient accuracy for use in epidemiologic studies and for weight control of individuals. For this purpose, the RMR of 213 women and 76 men was measured, and physical measurements were taken. The RMR was regressed on correlates of RMR, avoiding harmful degrees of collinearity by rejecting interregressor correlations exceeding r=0.5. For women, the best model (R₂=0.71) included the regressors age, race, weight, pulse rate, smoking, and body temperature. The best model for males (R2 = 0.81) included age, race, weight, blood pressure, smoking, time (of day the RMR was measured), and whether subjects had a meal prior to calorimetry. The models were cross validated internally and also validated using an external database. In both cases, the mean estimated RMR did not differ significantly from the measured RMR. The accuracy of the models was compared with four models reported in the literature, three of which overestimated the RMR by up to 17%. In conclusion, improved RMR prediction models have been developed, more accurate than existing models, rendering them suitable for application to epidemiological databases and for individual weight control programs.     

Muscle fiber type is associated with obesity and weight loss

The purpose of this study was to test the hypothesis that muscle fiber type is related to obesity. Fiber type was compared 1) in lean and obese women, 2) in Caucasian (C) and African-American (AA) women, and 3) in obese individuals who lost weight after gastric bypass surgery. When lean (body mass index 24.0 +/- 0.9 kg/m(2), n = 28) and obese (34.8 +/- 0.9 kg/m(2), n = 25) women were compared, there were significant (P < 0.05) differences in muscle fiber type. The obese women possessed fewer type I (41.5 +/- 1.8 vs. 54.6 +/- 1.8%) and more type IIb (25.1 +/- 1.5 vs. 14.4 +/- 1.5%) fibers than the lean women. When ethnicity was accounted for, the percentage of type IIb fibers in obese AA was significantly higher than in obese C (31.0 +/- 2.4% vs. 19.2 +/- 1.9%); fewer type I fibers were also found in obese AA (34.5 +/- 2.8% vs. 48.6 +/- 2.2%). These data are consistent with the higher incidence of obesity and greater weight gain reported in AA women. With weight loss intervention, there was a positive relationship (r = 0.72, P < 0.005) between the percentage of excess weight loss and the percentage of type I fibers in morbidly obese patients. These findings indicate that there is a relationship between muscle fiber type and obesity.     

Pedometer-determined physical activity and indicators of health in Japanese adults

Recently, many cross-sectional studies observed that body mass index (BMI) and percentage of body fat (%BF) were inversely associated with pedometer-determined physical activities, but studies on Asian populations, including the Japanese, are sparse. Height, weight, body fat percentage (%BF, bioelectrical impedance analyzer), and waist circumference were measured on 117 women (62.8+/-4.5 years, 22.2+/-2.2 kg/m(2)) and 62 men (64.0+/-4.6 years, 23.6+/-2.5 kg/m(2)). Pearson correlations and partial correlation coefficients after controlling for age were calculated between steps/day and variables. Furthermore, participants were classified into four groups as follows: <5,000, 5,000-7,499, 7,500-9,999, and >or=10,000 steps/day, and analyzed using ANOVA across activity groups. In women, a significant correlation was found between steps/day and BMI (r=-0.217, p=0.018), %BF (r=-0.292, p=0.0014), and the relationship was still significant after controlling for age. The relationship between steps/day and waist circumference was not significant. In men, a significant relationship was not observed between steps/day and obesity indices. The correlations between steps/day and both BMI and %BF were significant in Japanese women, but weak compared with Caucasian and African-American women as reported previously. A possible cause is racial difference in degree of obesity and body shape. The effects of physical activity on body shape and composition may differ according to race.     

Age at Puberty and the Emerging Obesity Epidemic

Background

Recent studies have shown that puberty starts at younger ages than previously. It has been hypothesized that the increasing prevalence of childhood obesity is contributing to this trend. The purpose of this study was to analyze the association between prepubertal body mass index (BMI) and pubertal timing, as assessed by age at onset of pubertal growth spurt (OGS) and at peak height velocity (PHV), and the secular trend of pubertal timing given the prepubertal BMI.

Methodology/Principal Findings

Annual measurements of height and weight were available in all children born from 1930 to 1969 who attended primary school in the Copenhagen municipality; 156,835 children fulfilled the criteria for determining age at OGS and PHV. The effect of prepubertal BMI at age seven on these markers of pubertal development within and between birth cohorts was analyzed. BMI at seven years was significantly inversely associated with age at OGS and PHV. Dividing the children into five levels of prepubertal BMI, we found a similar secular trend toward earlier maturation in all BMI groups.

Conclusion/Significance

The heavier both boys and girls were at age seven, the earlier they entered puberty. Irrespective of level of BMI at age seven, there was a downward trend in the age at attaining puberty in both boys and girls, which suggests that the obesity epidemic is not solely responsible for the trend.     

Resistin levels are related to fat mass,but not to body mass index in children

The relationship of resistin levels with obesity remains unclear. The aim of this study was to determine resistin levels in prepubertal children and adolescents and evaluate their association with anthropometric parameters and body composition. The study population included 420 randomly selected 6–8-year-old children and 712 children aged 12–16 years. Anthropometric data were measured and body mass index (BMI) and waist-to-hip and waist-to-height ratios were calculated. Body composition was assessed using an impedance body composition analyzer. Serum resistin levels were determined using a multiplexed bead immunoassay. Resistin levels were not significantly different between sexes. No significant differences in serum resistin concentrations were found between obese, overweight, and normal weight children at any age, and no significant correlations were observed between resistin concentrations and weight or BMI. However, resistin levels showed a significant positive correlation with fat mass in 12–16-year-old children, particularly in girls. In addition to describing serum resistin levels in prepubertal children and adolescents, our study suggests that resistin is related to body fat rather than to BMI in adolescents.     

Lower than predicted resting metabolic rate is associated with severely impaired cardiorespiratory fitness in obese individuals

Obese individuals have reduced cardiorespiratory fitness as compared with leaner counterparts. Regular exercise maintains or increases fitness and lean body mass. Lean body mass, in turn, has a direct impact on resting metabolic rate (RMR). Given these relationships, we sought to evaluate the association between RMR and cardiorespiratory fitness in obese individuals. We evaluated 64 obese individuals (78% female) with direct assessment of RMR and cardiorespiratory fitness via breath‐by‐breath measurement of oxygen consumption and carbon dioxide production at rest and during exercise. The mean age and BMI were 47.4 ± 12.2 years and 47.2 ± 9.2 kg/m², respectively. The majority of subjects, 69%, had a measured RMR above that predicted by the Harris‐Benedict equation. Compared with the higher RMR group, those with a lower than predicted RMR had increased BMI, with values of 52.9 vs. 44.7 kg/m², P = 0.001, respectively. Analysis of those demonstrating significant effort during cardiopulmonary exercise testing (peak respiratory exchange ratio ≥1.10) revealed a significantly higher peak oxygen uptake (VO₂ peak) in the higher RMR group (17.3 ± 3.5 ml/min/kg) compared with the lower RMR group (13.6 ± 1.9 ml/min/kg), P = 0.003. In summary, a lower than predicted RMR was associated with a severely reduced VO₂ peak and a higher BMI in this cohort. These data suggest that morbid obesity may be a vicious cycle of increasing BMI, reduced cardiorespiratory fitness, muscle deconditioning, and lower RMR. Collectively, these responses may, over time, exacerbate the imbalance between energy intake and expenditure, resulting in progressive increases in body weight and fat stores.     

Waist Circumference is an Independent Correlate of Errors in Self‐Reported BMI

Although there are issues of reporting bias surrounding the use of self‐reported BMI, it is frequently the method employed to establish the prevalence of obesity. The goal of this study was to assess whether, independently of measured BMI, waist circumference (WC) was associated with the magnitude of the difference between self‐reported and measured BMI within a large sample of European‐American (EA) and African‐American (AA) adults. Self‐reported height and weight, and measured height, weight, and WC were collected on 12,809 adults (61% women, 66% EA) aged 18–65 years. Mean negative BMI differences (self‐reported minus measured BMI) were identified in all race‐by‐sex groups (AA men: ?0.55; EA men: ?0.63; AA women: ?0.91; EA women: ?0.67). WC was negatively associated with the BMI difference such that a higher WC was associated with greater under‐reporting of BMI. However, after adjusting for age and measured BMI, WC was positively associated with the BMI difference in all race‐by‐sex groups. These results suggest that WC could be useful in gaining an insight into people's awareness of their own body size and fatness.     

Cardiovascular regulation profile predicts developmental trajectory of BMI and pediatric obesity

The present study examined the role of cardiovascular regulation in predicting pediatric obesity. Participants for this study included 268 children (141 girls) obtained from a larger ongoing longitudinal study. To assess cardiac vagal regulation, resting measures of respiratory sinus arrhythmia (RSA) and RSA change (vagal withdrawal) to three cognitively challenging tasks were derived when children were 5.5 years of age. Heart period (HP) and HP change (heart rate (HR) acceleration) were also examined. Height and weight measures were collected when children were 5.5, 7.5, and 10.5 years of age. Results indicated that physiological regulation at age 5.5 was predictive of both normal variations in BMI development and pediatric obesity at age 10.5. Specifically, children with a cardiovascular regulation profile characterized by lower levels of RSA suppression and HP change experienced significantly greater levels of BMI growth and were more likely to be classified as overweight/at-risk for overweight at age 10.5 compared to children with a cardiovascular regulation profile characterized by high levels of RSA suppression and HP change. However, a significant interaction with racial status was found suggesting that the association between cardiovascular regulation profile and BMI growth and pediatric obesity was only significant for African-American children. An autonomic cardiovascular regulation profile consisting of low parasympathetic activity represents a significant individual risk factor for the development of pediatric obesity, but only for African-American children. Mechanisms by which early physiological regulation difficulties may contribute to the development of pediatric obesity are discussed.     

Factors influencing plasma zinc levels in low-income pregnant women

Plasma zinc (Zn) concentrations were measured in 4376 indigent women (86% African-American), at a mean (±SD) gestational age of 15 (±7.8) wk to determine the relationship between various maternal characteristics and plasma Zn levels during pregnancy. Mean plasma Zn levels were lower in African-American women than in Caucasian women, in multiparous women than in primiparous women, and in women with body weight >69.9 kg than in those with body weight ≤69.9 kg (p≤0.001 for each comparison). There were no significant differences related to maternal age, marital status, education, or smoking habit. Multiple regression analysis, including maternal prepregnancy weight, race, age, parity, smoking habit, education, and marital status indicated that race, parity, and pregnancy weight were significantly associated with maternal plasma Zn levels, adjusted for gestational age. Maternal race was the best predictor of plasma Zn concentrations among the population of pregnant women studied A significant proportion of variance in maternal plasma Zn levels remained unexplained after taking into account various maternal characteristics. The reasons for lower plasma Zn levels in African-American women, compared to Caucasian women, during pregnancy are unknown.     

Alternative Methods for Measuring Obesity in African American Women

The use of body mass index (BMI) may not be the most appropriate measurement tool in determining obesity in diverse populations. We studied a convenience sample of 108 African American (AA) women to determine the best method for measuring obesity in this at-risk population. The purpose of this study was to determine if percent body fat (PBF) and percent body water (PBW) could be used as alternatives to BMI in predicting obesity and risk for hypertension (HTN) among AA women.After accounting for age, BMI, and the use of anti-hypertensive medication, PBF (p = 0.0125) and PBW (p = 0.0297) were significantly associated with systolic blood pressure, while BMI was not. Likewise, PBF (p = 0.0316) was significantly associated with diastolic blood pressure, while PBW and BMI were not. Thus, health care practitioners should consider alternative anthropometric measurements such as PBF when assessing obesity in AA women.     

Weight loss and race modulate nitric oxide metabolism in overweight women

Weight reduction is associated with a decrease in the risk of developing cardiovascular disease. We hypothesized that, given the central role of reactive oxygen and nitrogen species in vascular biology, changes in nitric oxide (NO) metabolism contribute to benefits of weight loss. In a controlled weight loss trial involving overweight (body mass index (BMI) = 27-30 kg/m(2)), otherwise healthy premenopausal Caucasian and African-American women, serum levels of nitrite and nitrate, as an index of NO production, and protein 3-nitrotyrosine and myeloperoxidase (MPO), as markers of inflammation, were determined. Testing was performed before and after reduction to normal body weight (BMI < 25) under standardized conditions, with controlled diet, and following 1 month of weight maintenance. After weight loss there was an increase in nitrite and nitrate, and levels were higher among African-American women relative to Caucasian counterparts. Whereas weight loss was associated with a decrease in 3-nitrotyrosine in Caucasian women, no change was observed among African-Americans. Furthermore, MPO levels increased in response to weight loss for African-Americans, but did not change in Caucasian women. These data indicate that vascular production of reactive nitrogen species can be modulated by race and weight loss and highlight important racial differences in these responses and are discussed in the context of risk for developing vascular disease.     

Associations of Body Mass and Body Fat Distribution with Parity Among African-American and Caucasian Women: The CARDIA Study

Associations of parity with body fat and its distribution are poorly understood; therefore, we examined the relationships between parity and obesity in young adult women. Body mass index (BMI), skin folds, and waist-hip ratio were compared in 1452 African-American and 1268 Caucasian nonpregnant women aged 18 to 30, adjusting for age (where no age-parity interactions were present), education, physical activity (assessed by questionnaire) and fitness (assessed by graded exercise test), dietary fat intake, alcohol and smoking. Adjusted mean BMI was significantly higher in African-American women aged 25–30 years with three or more children (28.5 kg/m²) than in those with two (27.0 kg/m²), one (26.2 kg/m²), or no children (26.3 kg/m²). Similar trends were found in Caucasians (BMI = 23.3, 23.4, 23.7, 25.0 kg/m² for parity = 0,1, 2, ≥ 3, respectively), but the mean BMI was significantly higher in African Americans in each parity group. The association between BMI and parity was not present among women 18–24 years of age. Skinfolds were directly associated with parity in African Americans only. Waist-hip ratios were generally lower among nulliparous than parous women in both ethnic groups; race differences were present only among nulliparas. In conclusion, parity was associated with BMI in women aged 25 to 30 years but did not explain ethnicity-related differences in body mass.     

Toward an early marker of metabolic dysfunction: omentin-1 in prepubertal children

Omentin-1 is a recently recognized adipokine primarily originating in visceral adipose tissue. We posited that circulating omentin-1 could be an early marker of metabolic dysfunction. To this end, we examined the associations between circulating omentin-1, body fat (bioelectric impedance), an endocrine-metabolic profile (homeostasis model assessment for insulin resistance (HOMA(IR)), serum lipids, high-molecular-weight (HMW) adiponectin and blood pressure (BP)) and family history of obesity and diabetes in asymptomatic prepubertal children (n = 161; 77 boys and 84 girls; age 7 ± 1 year) with a normal distribution of height and weight. Increased circulating omentin-1 was associated with a poorer metabolic profile, with relatively higher HOMA(IR), fasting triacylglycerol, BP and familial prevalence of diabetes (all P < 0.005 to P < 0.0001), and relatively lower fraction of HMW adiponectin (P < 0.005), whereas no relationship was found with body weight or fat or with family history of obesity. All these associations were independent of age, gender and fat mass. In conclusion, circulating omentin-1 may become a marker of metabolic dysfunction integrating insulin sensitivity, markers of adipose-tissue metabolism and BP as early as in prepubertal childhood.     

Racial Differences in Metabolic Predictors of Obesity among Postmenopausal Women

NICKLAS, BARBARA S., DORA M. BERMAN, DAWN C. DAVIS, C. LYNNE DOBROVOLNY, AND KAREN E. DENNIS. Racial differences in metabolic predictors of obesity among postmenopausal women. Ober Res. Objective: This study determined whether there are racial differences in resting metabolic rate (RMR), fat oxidation, and maximal oxygen consumption (VO,max) in obese [body mass index (BMI = 34±2 kg/m²)], postmenopausal (58±2 years) women. Research Methods and Procedures: Twenty black and 20 white women were matched for fat mass and lean mass (LM), as determined by dual energy X-ray absorptiometry. RMR and fat oxidation were measured by indirect calorimetry in the early morning after a 12-hour fast using the ventilated hood technique. VO₂max was measured on a treadmill during a progressive exercise test to voluntary exhaustion. Results: RMR, adjusted for differences in LM, was 5% higher in white than black women (1566±27 and 1490±26 kcal/day, respectively; p<0. 05); and fat oxidation rate was 17% higher in white than black women (87±4 and 72±3 g/day, respectively; p<0. 01). VO₂max (L/minute) was 150 mL per minute (8%) higher (p<0. 05) in white than black women. VO₂max correlated with LM in black (r = 0. 44, p = 0. 05) and white (r=0. 53, p<0. 05) women, but the intercept of the regression line was higher in white than black women (p<0. 05), with no significant difference in slopes. In a multiple regression model including race, body weight, LM, and age, LM was the only independent predictor of RMR (r² = 0. 46, p<0. 0001), whereas race was the only independent predictor of fat oxidation (r² = 0. 18,p<0. 05). The best predictors of VO,max were LM (r² = 0. 22, p<0. 05) and race (cumulative r² = 0. 30, p<0. 05). Discussion: These results show there are racial differences in metabolic predictors of obesity. Determination of whether these ethnic differences lead to, or are an effect of, obesity status or other lifestyle factors requires further study.