Dympna Gallagher

Body mass index as a measure of adiposity among children and adolescents: A validation study☆☆☆★★★

OBJECTIVES To test the hypothesis that in a healthy pediatric population body mass index (BMI) (kilograms per meter square) is a valid measure of fatness that is independent of age for both sexes. METHODS Total body fat (TBF) (in kilograms) and percent of body weight as fat (PBF) were estimated by dual energy x-ray absorptiometry (DXA) in 198 healthy Italian children and adolescents between 5 and 19 years of age. We developed multiple regression analysis models with TBF and percent body fat as dependent variables and BMI, age, and interaction terms as independent variables. Separate analyses were conducted for boys and girls. RESULTS BMI was strongly associated with TBF (R2 = 0.85 and 0.89 for boys and girls, respectively) and PBF (R2 =0.63 and 0.69 for boys and girls, respectively). Confidence limits on BMI-fatness association were wide, with individuals of similar BMI showing large differences in TBF and in PBF. Age was a significant covariate in all regression models. Addition of nonlinear terms for BMI did not substantially increase the R2 for TBF and PBF models in boys and girls. CONCLUSION Our results support the use of BMI as a fatness measure in groups of children and adolescents, although interpretation should be cautious when comparing BMI across groups that differ in age or when predicting a specific individuals TBF or PBF.

Predictors of skeletal muscle mass in elderly men and women.

BACKGROUND Elderly men and women lose muscle mass and strength with increasing age. Decreased physical activity, hormones, malnutrition and chronic disease have been identified as factors contributing to this loss. There are few data, however, for their multivariate associations with muscle mass and strength. This study analyzes these associations in a cross-sectional sample of elderly people from the New Mexico Aging Process Study. METHODS Data collected in 1994 for 121 male and 180 female volunteers aged 65-97 years of age enrolled in The New Mexico Aging Process Study were analyzed. Body composition was measured using dual energy X-ray absorptiometry; dietary intake from 3 day food records; usual physical activity by questionnaire; health status from annual physical examinations; and serum testosterone, estrone, sex-hormone binding globulin (SHBG), and insulin-like growth factor (IGF1) from radioimmunoassays of fasting blood samples. Statistical analyses included partial correlation and stepwise multiple regression. RESULTS The muscle mass and strength (adjusted for knee height) decreased with increasing age in both sexes. The muscle mass was significantly associated with serum free-testosterone, physical activity, cardiovascular disease, and IGF1 in the men. In the women, the muscle mass was significantly associated with total fat mass and physical activity. Age was not associated significantly with muscle mass after controlling for these variables. Grip strength was associated with age independent of muscle mass in both sexes. Estrogen (endogenous and exogenous) was not associated with muscle mass or strength in women. CONCLUSIONS Age-related loss of muscle mass and strength occurs in relatively healthy, well-nourished elderly men and women and has a multifactorial basis. Sex hormone status is an important factor in men but not in women. Physical activity is an important predictor of muscle mass in both sexes.

Organ-tissue mass measurement allows modeling of REE and metabolically active tissue mass.

Investigators have expressed interest in the associations between resting energy expenditure (REE) and body mass for over a century. Traditionally, descriptive models using regression analysis are applied, linking REE with metabolically active compartments such as body cell mass (BCM) and fat-free body mass (FFM). Recently developed whole body magnetic resonance imaging (MRI) and echocardiography methods now allow estimation of all major organs and tissue volumes in vivo. Because measured values are available for REE, BCM, and FFM content of individual organs and tissues, it should now be possible to develop energy expenditure-body composition estimation models based on MRI-measured organ-tissue volumes. Specifically, the present investigation tested the hypothesis that in vivo estimation of whole body REE, BCM, and FFM is possible using MRI- and echocardiography-derived organ volumes combined with previously reported organ-tissue metabolic rates and chemical composition. Thirteen subjects (5 females, 8 males) had REE, BCM, and FFM measured by indirect calorimetry, whole body40K counting, and dual-energy X-ray absorptiometry, respectively. Models developed from estimated and measured variables were highly correlated, with no significant differences between those estimated and measured [e.g., calculated vs. measured REE: r = 0.92, P < 0.001; (mean ± SD) 6,962 ± 1,455 and 7,045 ± 1,450 kJ/day, respectively ( P = not significant)]. Strong associations were observed between REE, individual or combined organ weights, BCM, and FFM that provide new insights into earlier observed metabolic phenomona. The present approach, the first to establish an energy expenditure-body composition link with a mechanistic model in vivo, has the potential to greatly expand our knowledge of energy expenditure-body size relationships in humans.Investigators have expressed interest in the associations between resting energy expenditure (REE) and body mass for over a century. Traditionally, descriptive models using regression analysis are applied, linking REE with metabolically active compartments such as body cell mass (BCM) and fat-free body mass (FFM). Recently developed whole body magnetic resonance imaging (MRI) and echocardiography methods now allow estimation of all major organs and tissue volumes in vivo. Because measured values are available for REE, BCM, and FFM content of individual organs and tissues, it should now be possible to develop energy expenditure-body composition estimation models based on MRI-measured organ-tissue volumes. Specifically, the present investigation tested the hypothesis that in vivo estimation of whole body REE, BCM, and FFM is possible using MRI- and echocardiography-derived organ volumes combined with previously reported organ-tissue metabolic rates and chemical composition. Thirteen subjects (5 females, 8 males) had REE, BCM, and FFM measured by indirect calorimetry, whole body 40K counting, and dual-energy X-ray absorptiometry, respectively. Models developed from estimated and measured variables were highly correlated, with no significant differences between those estimated and measured [e.g., calculated vs. measured REE: r = 0.92, P < 0. 001; (mean +/- SD) 6,962 +/- 1,455 and 7,045 +/- 1,450 kJ/day, respectively (P = not significant)]. Strong associations were observed between REE, individual or combined organ weights, BCM, and FFM that provide new insights into earlier observed metabolic phenomona. The present approach, the first to establish an energy expenditure-body composition link with a mechanistic model in vivo, has the potential to greatly expand our knowledge of energy expenditure-body size relationships in humans.

Bioimpedance analysis : evaluation of leg-to-leg system based on pressure contact foot-pad electrodes

Conventional single frequency bioimpedance analysis (BIA) systems require technician placement of arm and leg gel electrodes, a suitable location for recumbent measurements, and a separate measurement of body weight. The aim of this study was to evaluate a new single frequency 50 KHz leg-to-leg bioimpedance analysis (BIA) system combined with a digital scale that employs stainless steel pressure-contact foot pad electrodes for standing impedance and body weight measurements. Healthy adults were evaluated for 1) electrode validity and 2) potential for body component estimation. Pressure-contact foot-pad electrode measured impedance was highly correlated with (N = 9, r = 0.99, P < 0.001) impedance measured using conventional gel electrodes applied to the plantar surface of both lower extremities; mean (+/-SD) impedance was systematically higher by about 15 ohms for pressure contact electrodes (526 +/- 56 ohms vs 511 +/- 59 ohms; P < 0.001). Second, the relationship between stature-adjusted leg-to-leg impedance (H2/Z) measured by the new system and two body composition components (total body water by 3H2O dilution (N = 144); and fat-free body mass, by underwater weighing and dual x-ray absorptiometry (N = 231)) was modeled using multiple regression analysis. Correlation coefficients for H2/Z alone versus body composition components were lower for leg-to-leg BIA than for arm-to-leg BIA; correlation coefficients and SEEs became similar for the leg-to-leg and arm-to-leg BIA systems with addition of three covariates (age, gender, and waist/hip circumference ratio) to regression models. The leg-to-leg pressure contact electrode BIA system has overall performance characteristics for impedance measurement and body composition analysis similar to conventional arm-to-leg gel electrode BIA and offers the advantage of increased speed and ease of measurement.

Are dual-energy X-ray absorptiometry regional estimates associated with visceral adipose tissue mass?

Objective: Recent studies support the possibility of estimating abdominal fat using a region of interest (ROI) selected by conventional whole body dual-energy X-ray absorptiometry (DXA). This is an important observation as DXA ROI estimates have some advantages over waist circumference or computed tomography/magnetic resonance imaging (MRI) as a means of assessing visceral adipose tissue (VAT) and adipose tissue distribution. The aim of this study was to evaluate the usefulness of DXA abdominal ROI estimates in assessing VAT among non-obese men.Design: Observational, cross-sectional study comparing correlations between MRI-measured total VAT and surrogate measures including DXA ROIs. A stepwise multiple regression model was applied to derive a predictive equation with total VAT mass.Subjects: Ninety non-obese healthy men between the ages of 18 and 44 y with BMI<30 kg/m2.Measurements: Abdominal adipose tissue and total VAT were measured by whole body MRI; VAT area by single-slice MRI at the L4–5 level; specific DXA ROIs for abdominal regional fat defined as ROI A (L2–4), B (L2-upper iliac), C (lower costal-upper iliac), and D (ROI C excluding spine); and simple anthropometric measures.Results: Correlations between total VAT and ROIs A (r=0.85) and B (r=0.84) were not significantly different from that of VAT area at L4–5 (r=0.87), but significantly higher (P <0.01) than that of waist circumference (r=0.77). The highest correlations with total abdominal adipose tissue were for DXA ROIs and conventional DXA trunk fat (r=0.95–0.97). A stepwise multiple regression analysis revealed that 86% of the variance in total VAT was predicted by VAT area at L4–5, ROI A, and waist-hip ratio.Conclusions: DXA ROIs (L2–4, L2-upper iliac) were associated with total VAT as well as MRI-derived VAT area at L4–5 in non-obese men. DXA ROI fat distribution estimates may be useful in the early detection of men with abdominal/visceral obesity.

Waist Circumference Correlates with Metabolic Syndrome Indicators Better Than Percentage Fat

Objective: Percent fat is often considered the reference for establishing the magnitude of adipose tissue accumulation and the risk of excess adiposity. However, the increasing recognition of a strong link between central adiposity and metabolic disturbances led us to test whether waist circumference (WC) is more highly correlated with metabolic syndrome components than percent fat and other related anthropometric measures such as BMI.

Body mass index and all-cause mortality among people age 70 and over: the Longitudinal Study of Aging

OBJECTIVES: To assess the relationship between body mass index (BMI; kg/m2) and mortality in a large nationally representative sample of US adults over age 70 years. DESIGN: Prospective longitudinal cohort study, the Longitudinal Study of Aging (LSOA). Subjects were all those 7260 black and white people (2769 men, 4491 women) initially interviewed in 1984 for whom height and weight were available. These subjects were followed through to 1990. MEASUREMENTS: Measurements included self-reported height and weight, date of death if subjects died, sex, age, race, measures of socio-economic status, number of living first degree relatives, and responses to questions asking whether the subject had retired due to poor health, had difficulty eating, worried about their health, and felt their health was worse than during the prior year. Smoking status was not assessed. RESULTS: When analyzed via Cox proportional hazard regression, the relationship between BMI and mortality, represented by means of hazard ratio, was clearly U-shaped for both men and women. The base of the curves was fairly wide suggesting that a broad range of BMIs are well tolerated by older adults. The minimum mortality (estimated from the fitted proportional hazard models) occurred at a BMI of approximately 31.7 for women and 28.8 for men. The results were essentially unchanged, if analyses were weighted, if various disease states were controlled for, and if apparently unhealthy subjects were excluded. CONCLUSIONS: The finding of the relatively high BMI (27–30 for men, 30–35 for women) associated with minimum hazard in persons older than seventy years supports some previously documented findings and opposes others and, if confirmed in future research, has implications for public health and clinical recommendations.

Adipose tissue distribution is different in type 2 diabetes

BACKGROUND The extent to which adipose tissue (AT) distribution is different between persons with type 2 diabetes (T2DM) and nondiabetic control subjects remains unclear. OBJECTIVE The aim of this study was to establish whether total body adiposity and its distribution, quantified by using state-of-the-art whole-body magnetic resonance imaging, differs between these 2 groups. DESIGN This cross-sectional evaluation included 93 participants (n = 56 women and 37 men) in the Look AHEAD (Action for HEAlth in Diabetes) Trial with T2DM who had a mean (+/-SD) age of 58.3 +/- 6.6 y and body mass index (in kg/m(2)) of 31.6 +/- 3.1 and 93 healthy non-T2DM control subjects (n = 64 women and 29 men) who had a mean (+/-SD) age of 60.6 +/- 17.1 y and body mass index of 29.6 +/- 3.0. All participants self-reported being of African American or white ancestry. Magnetic resonance imaging-derived in vivo measures of total-body AT (TAT) and its distribution, subcutaneous AT (SAT), visceral AT (VAT), and intermuscular AT (IMAT) were acquired. Linear regression models were developed for each AT compartment to adjust for important covariates of race, sex, age, height, and weight and to examine potential interactions of covariates. RESULTS These models showed significantly less SAT (African American: -1.2 kg; white: -2.4 kg; both P = 0.001), including less femoral-gluteal SAT, more VAT (African American: 0.7 kg, P < 0.001; white: 1.8 kg, P = 0.007), and more IMAT (0.5 kg, P = 0.001) in the T2DM group. CONCLUSION We concluded that AT distribution is significantly altered in T2DM, ie, more VAT and IMAT--2 depots known to exacerbate insulin resistance--and less SAT in persons with T2DM than in healthy control subjects, a novel finding that we posit may compound the risk of insulin resistance.

Body composition changes with aging: The cause or the result of alterations in metabolic rate and macronutrient oxidation?

It has been well documented that as individuals age, body composition changes, even in the absence of changes in body weight. Studies have shown that fat mass increases and muscle mass decreases with age. However, it is unclear why such changes occur. Resting metabolic rate (RMR) and substrate oxidation rates have been examined with aging. It has been proposed that reductions in RMR and fat oxidation may lead to changes in body composition. Alternatively, changes in body composition with aging may lead to reductions in RMR. The purpose of this review is to provide an overview of the literature surrounding the impact of aging on RMR and substrate oxidation. Although long-term longitudinal studies are lacking, most cross-sectional studies or short-term longitudinal studies show a reduction in RMR with aging that cannot be explained by changes in body composition including loss in fat-free mass, where the latter includes atrophy or decreases in the mass of high metabolic rate organs. There is indirect evidence suggesting that the metabolic rate of individual organs is lower in older compared with younger individuals. With aging, we conclude that reductions in the mass of individual organs/tissues and in tissue-specific organ metabolic rate contribute to a reduction in RMR that in turn promotes changes in body composition favoring increased fat mass and reduced fat-free mass.

Body composition changes in stable-weight elderly subjects: the effect of sex.

Background and aims: Although cross-sectional and longitudinal studies have shown age-related changes in body composition and fat distribution, they may be related to body weight changes. The aim of this study was to evaluate yearly age-related changes in body composition and fat distribution, over a two-year period, in 101 women and 60 men (age range: 68 to 78 years at baseline). Methods: Body composition was evaluated by dual energy X-ray absorptiometry (DXA), and fat distribution by waist and hip circumferences and waist-to-hip circumference ratio. Baseline free testosterone, IGF-1 and serum albumin were evaluated in all subjects, as well as physical activity. Clinical evaluation was performed at baseline and yearly in order to exclude subjects with any condition inducing pathological changes in body composition or fat distribution. Subjects with a weight change >5% of their baseline body weight during the study period, were excluded. Results: Significant increases occurred in Body Mass Index (BMI) (1.18% in women, 1.13% in men), waist (1.75% in women, 1.39% in men), and hip circumference (1.06% in women, 1.31% in men), whereas height decreased significantly in both men (0A2%) and women (0.55%). Significant increases in total body fat (1.31%) and percent body fat (1.27%) were observed in women but not in men. Lean body mass did not change significantly throughout the study in either sex. Significant losses in leg muscle mass and appendicular skeletal muscle mass (ASM), calculated as the sum of arm and leg fat-free soft tissue, were observed in men (respectively 3.56 and 2.77%) and women (respectively 2A1 and 1.59%). A significant decrease in ASM adjusted by stature (ASM/height2), a proposed proxy for sarcopenia, was found in men only (1.97%). The rates of loss in leg muscle mass and appendicular muscle mass were significantly higher in men than in women, even after adjusting for free testosterone, IGF-1, physical activity and serum albumin. Conclusions: These data demonstrate significant changes in body composition and fat distribution in independently living, weight-stable elderly men and women. These changes are dependent on sex and independent of physical activity, hormones or serum albumin.