Effects of obesity on QT, RR, and QTc intervals.
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Adult↗
Biomedical subjects
S B Heymsfield
Publications and source records attributed to S B Heymsfield.
Genetic, environmental, and phenotypic links between body mass index and blood pressure among women.
Greater relative weight is associated with higher blood pressure, but the reasons are unknown. The inability of current technology to induce sustained weight loss among overweight persons precludes experimental tests of whether this association is causal. We evaluated the degree to which the covariation between body mass index (BMI; kg/m2) and blood pressure (BP) among women is due to pleiotropic genetic factors, environmental factors, or phenotypic causation. The sample included 75 monozygotic (MZ) and 39 dizygotic (DZ) pairs of adult female twins. "BP" was calculated as the unit-weighted mean of systolic and diastolic. Data were analyzed through structural equation modeling. A model was specified stipulating that additive genetic effects (A) and unique environmental effects (E) each contributed to the covariance between BMI and BP, thus allowing for both pleiotropic and unique environmental influences on the covariance between BMI and BP. Dropping the pleiotropic influences significantly worsened the model (chi 2 = 4.62, df = 1, P = .032), suggesting significant pleiotropic effects. Dropping the environmental influences on the cross-phenotype covariance did not significantly worsen the model (chi 2 = 1.42, df = 1, P = .233). This indicates no significant effect of the environment on the covariance between BMI and BP. Finally, a model of phenotypic causation in which BMI directly influenced BP was fitted. This model provided the best single parameter explanation of the BP-BMI covariation. These data suggest that, among women, regardless of the source of variation, changes in BMI should lead to long-standing changes in BP.
Adult↗
Human body composition and the epidemiology of chronic disease.
Obesity and body fat distribution (FD) are established risk factors for chronic diseases. The body mass index (BMI) and the waist/hip circumference ratio (WHR) are used conventionally as indices of obesity and FD in epidemiological studies. Although some general limitations of these indices are recognized, others that affect their use in relative risks for disease are not well recognized. These include effects of sex, ethnicity, and especially age on the relationships between these indices and body composition, which can result in substantial misclassification of obesity and FD. There is considerable variability in body composition for any BMI, and some individuals with low BMIs have as much fat as those with high BMIs. This results in poor sensitivity for classifying levels of body fatness (e.g., too many "false negatives," or overweight individuals classified as not overweight), and relative risks are attenuated across all categories of BMI. A more serious problem, however, is that at different ages the same levels of BMI correspond to different amounts of fat and fat-free mass. Data from the Rosetta Study and the New Mexico Aging Process Study show that older adults have, on average, more fat than younger adults at any BMI, due to the loss of muscle mass with age. As a result, the sensitivity of BMI cutpoints with respect to body fatness decreases with age, and the use of a fixed cutpoint for all ages results in "differential misclassification bias." Taken together, these issues suggest that the increases with age in the prevalences of overweight and obesity, and in the risks for chronic diseases, may be mis-estimated using BMI. Similar issues may affect the use of WHR for estimating prevalences and associated risks of FD. New field methods for estimating body composition are available that can be applied in large, epidemiologic follow-up studies of chronic diseases. These methods will allow epidemiologists to consider, for example, whether it is increased fat, or the replacement of fat-free mass with fat, with age that is associated with risk for chronic disease.
Adipose Tissue↗
Bone mineral and body fat measurements by two absorptiometry systems: comparisons with neutron activation analysis.
In 185 adults (68 white and 31 black males, 66 white and 20 black females), total body bone mineral density and content and body fat% were measured by two dual energy X-ray absorptiometry (DXA) systems--Norland XR-26, software version 2.4, and Lunar DPX, software versions 3.4 and 3.6. In a subgroup of 18 males (10 white, 8 black), body fat% and total body calcium were also measured by in vivo neutron activation analysis (IVNA). For total body calcium, the DPX 3.4 system gave the highest (1239 g), IVNA the lowest (1195 g), and the XR-26 (1226 g) was not significantly different from the DPX 3.6 results. For fat%, the XR-26 system gave the highest estimate (23.5%), whereas measurements by the DPX 3.4 and 3.6 systems (17.4 and 18.2%) were similar to the IVNA measurements (18.3%). BMD and BMC measurements by the two DXA systems were highly correlated but significantly different for the entire studied population except in the case of BMC in black males.
Absorptiometry, Photon↗
Age-related changes in musculoskeletal mass between black and white women.
Earlier studies from our laboratory indicated that matched black and white women differ significantly in total body potassium (TBK), total body bone density (TBD), and total body bone mineral (TBBM). The aim of this investigation was to examine absolute levels and the kinetics of age-related changes in TBK, TBD, TBBM, and percent body fat in a cross-sectional cohort of 34 matched pairs (age +/- 4 years, weight +/- 2 kg, and height +/- 4 cm) of black and white healthy non-obese women. Black and white women had a similar percentage of body weight as fat, although adipose tissue distribution (ie, waist to hip circumference ratio [WHR]) differed significantly (P < .0007) between the two groups (WHR, mean +/- SD: black, 0.837 +/- 0.062; white, 0.788 +/- 0.043). TBBM and TBD were significantly (P < .0001) higher in young black women, and ethnic differences in total bone mineral mass persisted at all ages. TBK (P = 0.0482) and appendicular skeletal muscle mass (P < .0001) were higher in young black women; however, by ages 60 to 70 years, the two groups had similar TBK. Both groups of women lost musculoskeletal mass (ie, TBK and TBBM) and gained fat mass at similar rates. The results of this study suggest that black women have a greater appendicular muscle and skeletal mass, as well as upper-body fat distribution, than white women. These differences are independent of body weight, height, or percent fat, and the ethnic skeletal differences persist throughout the adult life span. The higher appendicular muscle mass, skeletal mass, and upper-body fat distribution suggest that black women may have greater androgenic activity than white women.
Adipose Tissue↗
Unexplained disturbance in body weight regulation: diagnostic outcome assessed by doubly labeled water and body composition analyses in obese patients reporting low energy intakes.
SUBJECTS: Ten patients who had long-term disturbances in body weight regulation, were referred over a 3-year period for obesity evaluation, and reported low energy intakes (< 1,200 kcal/day). OBJECTIVE: To ascertain whether these patients had a low energy expenditure and thus reduced energy requirement, and/or whether they were misreporting their energy intake. DESIGN: Comparison of outcome measures in referred patients and in obese control patients who did not report low energy intakes and disturbances in body weight regulation. MAIN OUTCOME MEASURES: Low energy expenditure was evaluated with serum thyroid hormone levels, resting metabolic rate (RMR), thermic effect of food (TEF), and total energy expenditure (TEE) by doubly labeled water technique. Misreporting of energy intake was evaluated by comparing patients' self-reported energy intake with energy intake estimated by doubly labeled water and body composition analyses over a 14-day period. STATISTICAL ANALYSES PERFORMED: Low energy expenditure was considered present in a patient if RMR or TEE was more than 15% below predicted values according to results from the control group. Patient group TEF was compared with TEF results observed in the control group. RESULTS: All patients had normal serum thyroid hormone levels. Eight patients had RMR and TEE values within 15% of predicted values and were substantially underreporting their energy intake. One patient had low TEE (-19%) and a normal RMR, a finding that implies a low level of physical activity. This patient also underreported energy intake as estimated by the doubly labeled water technique during the study (-38%). The 10th patient had a low RMR (-23.2%) and TEE (-25.0%), the mechanism of which was uncertain. This patient's reported food intake over the 14-day period was accurate but was less than her long-term intake over months or years as suggested by doubly labeled water TEE estimates. The TEF response in patients was not significantly different from that observed in the control group. CONCLUSIONS: Underreporting of energy intake from foods is a frequent finding in patients with disturbances in body weight regulation who are referred for obesity evaluation. Severe underreporting may be detectable by means of screening measures available to most dietitians. Low energy expenditure, due either to physical inactivity or to metabolic factors, is also observed. Modern evaluation methods provide new insights into patients with weight regulatory disturbances and at the same time stimulate important new research questions.
Adolescent↗
Systematic organization of body-composition methodology: an overview with emphasis on component-based methods.
The field of body-composition research currently lacks a systematic organization of methods used to quantitate components at the atomic, molecular, cellular, tissue-system, and whole-body levels of body composition. In this report we propose a classification system for body-composition methodology that proceeds in steps, beginning with division of methods into in vitro and in vivo categories, advances to organization by measurable quantity (property, component, or combined), and ends with grouping of methods by mathematical function (types I and II). Important characteristics of component-based methods are then developed, including a classification of component relationship types, the role of ratios and proportions in type II component-based methods, and the basis of simultaneous equations in multicomponent methods. This classification system, the first founded on a conceptual basis, explains similarities and differences between the many diverse methods, provides a framework for teaching body-composition methodology theories to students, and suggests future research opportunities.
Body Composition↗
The calorie: myth, measurement, and reality.
Few dietary components are surrounded by more misinformation and myths than the calorie. This confusion can be attributed in part to a lack of accurate and practical methods for assessing energy intake and thus requirements in humans over periods extending beyond several days. The availability of modern respiratory-chamber indirect calorimetry systems and results from human studies with doubly labeled water are now helping to clarify uncertainties surrounding energy requirements. We describe studies of patients with endogenous obesity as an example of how these research methods are resolving long-standing questions regarding energy requirements. The results of these investigations reveal some of the flaws in estimating energy requirements by self-report methods. Advances in accurately measuring energy expenditure are making important contributions to the study of human energy requirements and are providing new and important research opportunities.
Calorimetry↗
Measurement of skeletal muscle: laboratory and epidemiological methods.
Despite skeletal muscle's central role in the pathogenesis of sarcopenia, measurement methods remain underinvestigated and inadequately validated. Our review indicates that skeletal muscle (SM) measurement methods quantify different components and properties of muscle, ranging from the atomic to whole-body levels of body composition. Laboratory methods tend to measure whole body SM (e.g., total muscle protein, muscle cell mass, and adipose tissue-free SM components) while epidemiological methods tend to measure regional muscle (e.g., anatomic SM of an extremity). Advances in computerized axial tomography and magnetic resonance imaging methods now allow accurate estimates of whole body and regional SM and promise to finally permit comprehensive in vivo studies of SM biology and methodology. These imaging methods may help to resolve many of the confusing issues that surround the investigation of this major body composition component.
Adipose Tissue↗
Enteral solutions: is there a solution?
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Enteral Nutrition↗
Is the intra-uterine period really a critical period for the development of adiposity?
OBJECTIVE: The intra-uterine environment may be a critical period for the development of adiposity. Alternatively, most of the co-variance of relative weight from birth to adulthood may be genetic in origin. This study tested whether birth weight 'tracks' into adulthood, independent of genetic factors. DESIGN: Observational twin study. Birth weights and gestational ages from birth records of 8040 twins from the Minnesota Twin Registry including 699 monozygotic (MZ) male pairs, 609 dizygotic (DZ) male pairs, 939 MZ female pairs, 880 DZ female pairs, and 893 opposite sex DZ pairs ages (yrs) 28 to 52 (Mean = 40.3; s.d. = 6.2) were compared to self-reported adult height and weight. RESULTS: The correlation of birth weight with adult height was 0.236, with adult weight 0.188, and with adult body mass index 0.078 (all P-values < 0.0005). To test if this tracking was independent of genetic influences, we analyzed intra-pair differences for MZ twins. If differences in birth weight between members of a MZ twin pair correlate with adult relative weight, this association cannot be attributed to genetic influences. The correlation of intra-pair differences in birth weight with intra-pair differences in adult height was 0.316 (P < 0.0005), with adult weight 0.136 (P < 0.0005), and with adult BMI 0.026 (P = 0.331). Results were unchanged when multivariate regression modeling was employed. CONCLUSION: These data suggest that the intra-uterine environmental influences on birth weight have an enduring impact on adult height but not on adult relative weight. This suggests that the intra-uterine period is a critical period for the development of height but not for adiposity.
Adipose Tissue↗
Columbia respiratory-chamber indirect calorimeter: a new approach to air-flow modelling.
A new air-flow modelling approach for respiratory-chamber indirect calorimetry is introduced. Based on thermodynamic theory, differential equations describing the dynamics of the calorimeter are derived. These equations are then developed into a linear state space model that can be conceptualized as a modern control system. Furthermore, both the system/output noises and input/output delays are considered in the model in the context of real applications. Finally, system accuracy is analysed so that the parameters in the calorimeter can be selected to minimise the error in estimating energy expenditure in humans.
Basal Metabolism↗
The black American lifestyle intervention (BALI): the design of a weight loss program for working-class African-American women.
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Adult↗
Endogenous opioids and hypogonadism in human obesity.
Massively obese males often show symptoms of hypogonadism, but the mechanism for this is unclear. Increased endogenous opioid inhibition of the hypothalamic GnRH pulse generator resulting in insufficient stimulation of the pituitary gonadotroph has been proposed as a possible mechanism. If this hypothesis is correct, obese males should be more sensitive to the LH-elevating effects of the opiate antagonist, naloxone, than men of normal weight and gonadal status. This study investigated the etiology of obesity-related hypogonadism by examining luteinizing hormone (LH) and follicle stimulating hormone (FSH) responses to gonadotropin-releasing hormone (GnRH) and to infusions of saline or naloxone. Subjects were five obese (201 +/- 14% IBW) and five normal weight (control) (97 +/- 4% IBW) males. Before treatment, obese males had significantly (p < 0.05) lower testosterone levels than control subjects (307 +/- 72 vs. 597 +/- 49 ng/dl), whereas estradiol, androstenedione, and dehydroepiandrosterone levels were not different between the two groups. Both groups showed equivalent elevations in LH (fourfold to sixfold) in response to GnRH stimulation, but obese patients had significantly lower basal (p < 0.05) and GnRH-stimulated (p < 0.01) FSH levels. Infusions of naloxone (but not saline) led to significant (p < 0.01) increases in LH above preinfusion baseline levels (20.5 +/- 2.8% in obese and 28.6 +/- 6.3% in controls). In control subjects, integrated LH levels during naloxone infusion were not significantly elevated above those found during saline infusion, while obese subjects exhibited a 43% augmentation of integrated LH (31.0 +/- 5.3 ng/ml during naloxone vs. 21.7 +/- 1.8 ng/ml during saline, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Adult↗
A genetic analysis of relative weight among 4,020 twin pairs, with an emphasis on sex effects.
This study replicated previous findings showing a high heritability of obesity, as measured by body mass index (kg/m2), using a measure of relative weight that does not assume a constant regression of height on weight across different populations, and evaluated whether there are sex-limited genetic effects. Subjects were 4,020 adult twin pairs. Alternative causal structural equation models were fitted to variance-covariance matrices. The ADE model (additive genetic effects, dominant/nonadditive genetic effects, and unique environment) fit best. Allowing for sex-specific effects (common sex-limitation model) significantly improved the fit, X2(6) = 230.5, p < .001. The heritability of that portion of weight unrelated to height was large: .61 for men and .73 for women.
Adolescent↗
Gastric emptying in humans: influence of different regimens of parenteral nutrition.
Intravenous administration of nutrients can suppress oral food intake. Inhibition of gastric emptying (GE) is a potential explanation for this process. Inhibition of GE during parenteral nutrition (PN) and attenuation of this by parenteral nutrition enriched with branched-chain amino acids (BCAAs) was examined in nine healthy males maintained on standard liquid diets for 6 d before each of three GE studies. GE was measured by scintigraphy after ingestion of a liquid test meal, at weekly intervals, after a 6-h infusion of Ringer lactate solution (RL), peripheral PN, or PN with half the amino acids replaced with BCAAs (BCPN). With PN, gastric emptying during the first 50 min was delayed by 38% compared with RL infusion; BCPN attenuated the effect, suggesting that postabsorptive control of food intake may act through changes in GE. These findings have clinical potential to reduce interference with appetite and to optimize food intake during PN administration.
Adult↗
Reduced risk of liver-function-test abnormalities and new gallstone formation with weight loss on 3350-kJ (800-kcal) formula diets.
Weight loss in obese subjects ingesting very-low-energy (VLE; < 2510 kJ/d), low-fat (< or = 1 g/d) formula diets is associated with liver-function-test abnormalities and gallstone formation. It is unknown whether these abnormalities develop during treatment with diets higher in energy and fat. We prospectively studied liver-function tests and gallstone formation in 73 obese patients ingesting approximately 3500 kJ and 15-25 g fat daily for 10 wk. Two of 53 patients completing the protocol developed ultrasonographic gallstones during weight loss, a rate substantially lower than that observed with VLE diets. Trend analysis demonstrated significant increases in AST and ALT activities, but changes were less than those observed with VLE diets. Patients who developed gallstones had a significantly greater weight loss rate and larger increases in AST and ALT than did nonstone-forming patients. These results suggest that the risk of developing hepatobiliary abnormalities with dieting is lowered when subjects ingest greater amounts of energy and fat than that administered in earlier VLE-diet studies. Our results also highlight potential risk factors and markers of new gallstone formation.
Adult↗
Differences between young and old females in the five levels of body composition and their relevance to the two-compartment chemical model.
BACKGROUND: Body composition differs between young and old females, although the magnitude of these age-related changes remains uncertain. This uncertainty persists because methodology applied in earlier studies required assumptions that may be age-dependent and also because studies included young and old subjects who differed substantially in body size and health status. METHODS: To resolve these earlier concerns we examined components at the atomic, molecular, cellular, tissue-system, and whole body levels of body composition in 19 weight- and height-matched pairs of young (age 19-35 yrs) and old (age > 65 yrs) healthy White females. Isotope dilution, dual photon, whole-body counting, hydrodensitometry, and anthropometric methods were used either alone or in combination to produce multicomponent models. RESULTS: Old females had significantly more fat, greater truncal skinfolds and circumferences, and significantly less fat-free body mass (FFM), total body potassium (TBK), total body water (TBW), and bone mineral than did their young matched counterparts. Skeletal muscle mass was less in the old females, although the magnitude of the difference from young females varied between the three indices examined. The main assumptions (i.e., TBW/FFM = 0.73 kg/kg and density of FFM = 1.100 g/cc) which the widely used two-compartment TBW and hydrodensitometry methods are based on were not significantly different in young and old females. In contrast, the main assumed steady-state value for the two-compartment TBK method (TBK/FFM = 64.2 mmol/kg) was significantly lower (p < .001) in the old females. CONCLUSION: New approaches thus allow for a critical reexamination of body composition in elderly subjects, and these methods also give new insight into less complex widely used body composition techniques.
Adipose Tissue↗