Central fat accretion and insulin sensitivity: differential relationships in parous and nulliparous women.

BACKGROUND/OBJECTIVES: Childbearing is associated with a disproportionate accumulation of visceral fat and an increased risk of metabolic disease. However, it is unknown whether the visceral fat accretion associated with pregnancy modifies a woman's risk for metabolic disease. The purpose of this study was to test whether the association between abdominal fat and insulin sensitivity differs by parity status in healthy overweight women. SUBJECTS/METHODS: Intra-abdominal adipose tissue (IAAT) via CT, body composition by DXA, insulin sensitivity via intravenous glucose tolerance test and minimal model (SI), HOMA-IR, and cardiorespiratory fitness (VO2max) were assessed in 212 non-diabetic, premenopausal, overweight non-Hispanic white and African-American women. RESULTS: Nulliparous women (n=98) were younger, had less IAAT and higher VO2max, but similar SI, HOMA-IR and leg fat, compared to parous (n=114). In nulliparous women, IAAT was negatively associated with SI, controlling for age, race and body fat mass (r=-0.40, P<0.001), but this relationship was attenuated in parous women (r=-0.15, P=0.16). In multiple linear regression analysis, leg fat and IAAT were significant predictors of SI in nulliparous, but not parous women. CONCLUSIONS: Results suggest that greater IAAT in parous women does not lead to greater insulin resistance; rather, transient insulin resistance during pregnancy may encourage intra-abdominal fat accumulation that is metabolically benign. This underscores the need to consider parity when assessing cardiometabolic risk.

The effects of weight loss approaches on bone mineral density in adults: a systematic review and meta-analysis of randomized controlled trials.

UNLABELLED: We assessed the impact of weight loss strategies including calorie restriction and exercise training on BMD in adults using a systematic review of randomized controlled trials. Weight reduction results in reduced BMD at the hip, but has less effect on the spine. Both calorie restriction and a combination of calorie restriction and exercise result in a decrease in hip bone density, whereas weight loss response to exercise training without dietary restriction leads to increased hip BMD. INTRODUCTION: Findings are not consistent on the effect of weight loss on bone mineral density (BMD). We conducted a systematic review on the randomized controlled trials to assess the effect of weight loss strategies, including calorie restriction and exercise programs on BMD in adults. METHODS: A structured and comprehensive search of MEDLINE and EMBASE databases was undertaken up to March 2016. Study-specific mean differences (MD) were pooled using a random-effects model. Subgroup analysis and meta-regression were used to find possible sources of between-study heterogeneity. RESULTS: Thirty-two randomized controlled trials met predetermined inclusion criteria. The meta-analysis revealed no significant difference on total BMD (MD 0.007, 95 % CI -0.020-0.034, p = 0.608). In contrast, the pooled data of studies showed a significant effect of weight loss on hip BMD (MD -0.008, 95 % CI -0.09 to -0.006 g/cm(2), p < 0.001) and also lumbar spine BMD (MD -0.018 g/cm(2), 95 % CI -0.019 to -0.017, p < 0.001). BMD in the hip site decreased after more than 4 months, especially in those who were obese. Moreover, calorie restriction interventions longer than 13 months showed a significant decreased in lumbar spine BMD. CONCLUSION: Weight loss led to significant decreases at the hip and lumbar spine BMD but not at the total. Weight loss response following calorie restriction resulted in a decrease in hip and lumbar spine bone density especially more than 1 year; whereas an exercise-induced weight loss did not.

Differences emerge in visceral adipose tissue accumulation after selection for innate cardiovascular fitness.

Cardiorespiratory fitness (CRF) has been reported to be inversely associated with visceral adipose tissue (VAT) accumulation, independent of body weight. However, the confounding effect of physical activity on the association between CRF and VAT remains inadequately addressed. On the basis of maximal oxygen uptake (VO(2 max)), 143 sedentary, overweight women were dichotomized into high-fit (HF) and low-fit (LF) groups. Body composition and VAT were measured using dual-energy X-ray absorptiometry and computed tomography, respectively, and activity-related energy expenditure (AEE) was calculated using the doubly labeled water technique. No differences were observed between HF and LF for body mass index (HF 28.2 ± 1.3; LF 28.3 ± 1.31 kg m(-2)), total body weight (HF 77.5 ± 6.8; LF 77.9 ± 7.3 kg), total fat mass (HF 33.5 ± 5.1; LF 33.9 ± 4.4 kg) or AEE (HF 439.9 ± 375.4; LF 517.9 ± 298.7 kcal day(-1)). Significant differences in visceral adiposity (HF 68.5 ± 30.4; LF 91.2 ± 31.8 cm(2); P<0.001) and insulin sensitivity (HF 5.1 ± 1.8; LF 3.1 ± 2.4 S(I) × 10(-4) min(-1) µIU(-1) ml(-1); P<0.01) were observed between the HF and LF groups, independent of age, race and AEE. This study affirms previous findings that CRF is an important determinant of the accumulation of VAT, and this relationship is independent of physical activity.

Metabolic predictors of obesity. Contribution of resting energy expenditure, thermic effect of food, and fuel utilization to four-year weight gain of post-obese and never-obese women.

This prospective study was designed to identify abnormalities of energy expenditure and fuel utilization which distinguish post-obese women from never-obese controls. 24 moderately obese, postmenopausal, nondiabetic women with a familial predisposition to obesity underwent assessments of body composition, fasting and postprandial energy expenditure, and fuel utilization in the obese state and after weight loss (mean 12.9 kg) to a post-obese, normal-weight state. The post-obese women were compared with 24 never-obese women of comparable age and body composition. Four years later, without intervention, body weight was reassessed in both groups. Results indicated that all parameters measured in the post-obese women were similar to the never-obese controls: mean resting energy expenditure, thermic effect of food, and fasting and postprandial substrate oxidation and insulin-glucose patterns. Four years later, post-obese women regained a mean of 10.9 kg while control subjects remained lean (mean gain 1.7 kg) (P < 0.001 between groups). Neither energy expenditure nor fuel oxidation correlated with 4-yr weight changes, whereas self-reported physical inactivity was associated with greater weight regain. The data suggest that weight gain in obesity-prone women may be due to maladaptive responses to the environment, such as physical inactivity or excess energy intake, rather than to reduced energy requirements.

Recombinant tyrosine aminotransferase from Trypanosoma cruzi: structural characterization and site directed mutagenesis of a broad substrate specificity enzyme.

The gene encoding tyrosine aminotransferase (TAT, EC 2.6.1.5) from the parasitic protozoan Trypanosoma cruzi was amplified from genomic DNA, cloned into the pET24a expression vector and functionally expressed as a C-terminally His-tagged protein in Escherichia coli BL21(DE3)pLysS. Purified recombinant TAT exhibited identical electrophoretic and enzymatic properties as the authentic enzyme from T. cruzi. Both recombinant and authentic T. cruzi TATs were highly resistant to limited tryptic cleavage and contained no disulfide bonds. Comprehensive analysis of its substrate specificity demonstrated TAT to be a broad substrate aminotransferase, with leucine, methionine as well as tyrosine, phenylalanine, tryptophan and alanine being utilized efficiently as amino donors. Valine, isoleucine and dicarboxylic amino acids served as poor substrates while polar aliphatic amino acids could not be transaminated. TAT also accepted several 2-oxoacids, including 2-oxoisocaproate and 2-oxomethiobutyrate, in addition to pyruvate, oxaloacetate and 2-oxoglutarate. The functionality of the expression system was confirmed by constructing two variants; one (Arg389) being a completely inactive enzyme; the other (Arg283) retaining its full activity, as predicted from the recently solved three-dimensional structure of T. cruzi TAT. Thus, only one of the two strictly conserved arginines which are essential for the enzymatic activity of subfamily Ialpha aspartate and aromatic aminotransferases is critical for T. cruzi's TAT activity.

Exercise over-stress and maximal muscle oxidative metabolism: a 31P magnetic resonance spectroscopy case report.

OBJECTIVE: 31P magnetic resonance spectroscopy (MRS) was used to document long lasting losses in muscle oxidative capacity after bouts of intense endurance exercise. METHODS: The subject was a 34 year old highly fit female cyclist (VO2MAX = 53.3 ml/kg/min). Over a five month period, she participated in three separate intense bouts of acute unaccustomed exercise. 31P MRS measurements were performed seven weeks after the first bout and every two weeks for 14 more weeks. In all cases, 31P MRS measurements followed three days after each bout. RESULTS: The subject showed a decreased ability to generate ATP from oxidative phosphorylation and an increased reliance on anaerobic ATP production during the 70% and 100% maximal voluntary contractions after the exercise bouts. Increased rates of fatigue and increased indicators of exercise difficulty also accompanied these reductions in muscle oxidative capacity. Increased oxidative and anaerobic ATP production were needed to maintain the work level during a submaximal 45% maximal voluntary contraction exercise. CONCLUSIONS: Acute increases in intensity accompanied by a change in exercise mode can influence the ability of muscle to generate ATP. The muscles were less economical and required more ATP to generate force during the submaximal exercises. During the maximal exercises, the muscle's mitochondria showed a reduced oxidative capacity. However, these reductions in oxidative capacity at the muscle level were not associated with changes in whole body maximal oxygen uptake. Finally, these reductions in muscular oxidative capacity were accompanied by increased rates of anaerobic ATP production, fatigue, and indicators of exercise difficulty.

Age-related decrease in resting energy expenditure in sedentary white women: effects of regional differences in lean and fat mass.

BACKGROUND: Lean mass and resting energy expenditure (REE) decrease with age. However, it is unknown whether age-related changes in regional lean and fat mass are responsible for the age-related decrease in REE. OBJECTIVE: Our objective was to determine how regional lean and fat mass vary with age and whether age is independently related to REE after adjustment for regional fat and lean mass. DESIGN: The study was a cross-sectional evaluation of 58 white women aged 23-77 y. Regional and whole-body lean and fat mass were measured by dual-energy X-ray absorptiometry, subcutaneous abdominal tissue (SAT) and intraabdominal adipose tissue (IAF) by computed tomography, and REE by ventilated-canopy indirect calorimetry. RESULTS: Independent of other significant correlates, age was significantly and independently associated with greater IAF (beta = 0.49) and less leg lean mass (beta = -0.35). IAF (r = -0.28) and IAF:SAT (r = -0.31) correlated negatively with REE. REE was negatively associated with greater age (beta = -0.42), independent of changes in lean and fat mass in different parts of the body. By contrast, trunk lean (beta = 0.27) and leg fat (beta = 0.27) mass were associated with greater REE independent of age and other body-composition variables. CONCLUSIONS: These results suggest that trunk lean mass (presumably primarily organ tissue) is relatively resistant to age-related changes in body composition, whereas muscle mass, especially leg muscle, tends to be lost. These data also suggest that the age-related decreases in REE are not fully explained by changes in body composition.

Estimating intraabdominal adipose tissue in women by dual-energy X-ray absorptiometry.

The purposes of this study were 1) to derive a prediction equation for estimating the intraabdominal adipose tissue (IAAT) by using dual-energy X-ray absorptiometry (DXA) with computed tomography (CT) scans as the criterion method, 2) to examine whether a smaller, more specific region was a better estimator of IAAT than the trunk alone by drawing three regions of interest (upper trunk, lower trunk, and pelvis) in the DXA scan, and 3) to cross-validate the newly developed equations and earlier equations by Svendsen. Body composition was measured in 206 pre- and postmenopausal women by anthropometry, DXA, and CT. Subjects were randomly divided into estimation (n = 151) and validation (n = 55) samples. Body-composition variables were analyzed by stepwise multiple regression to determine equations to estimate IAAT. The two equations developed to estimate IAAT both yielded an R2 of 0.81 when using the following variables: 1) sagittal diameter, age, waist circumference, and DXA trunk percent fat, and 2) sagittal diameter, age, waist circumference, and DXA pelvic percent fat. The R2 between the actual IAAT and estimates of IAAT for both equations was 0.81, whereas the R2 values were 0.63 and 0.71 for the Svendsen equations. In conclusion, we developed new equations using DXA and other simple measures that can be used to estimate IAAT in women of varying ages and body compositions.

A prospective study of weight maintenance in obese subjects reduced to normal body weight without weight-loss training.

We examined the pattern of weight maintenance in 24 obese women [body mass index (BMI; in kg/m2) 27.6 +/- 0.4 who were provided foods for a balanced deficit diet until each had lost > or = 10 kg and attained normal body weight (BMI 22.9 +/- 0.4). At 1 y subjects had regained a mean of 42% of their weight loss, which increased to 87% at 4 y. At 4 y 44% of patients had regained < 75%, whereas 37% had regained > or = 100% of the weight originally lost. The amount of weight gained was markedly different from that observed in 24 pair-matched never-obese control subjects over the same length of follow-up. Because the results reported herein were obtained without teaching the subjects weight-control skills, they may be regarded as reflective of the natural history of weight maintenance in this population and may serve as a reference for various weight-intervention programs. The pattern of weight rebound observed in this study is very similar to the pattern observed in combined results from published diet and behavioral-modification programs, which raises important questions regarding the efficacy of these approaches in long-term weight maintenance.

Regional fat distribution in women and risk of cardiovascular disease.

Improvements in technology have allowed more precise measurements of regional fat distribution and also present the opportunity to make a systematic evaluation of the various fat depots, including intraabdominal adipose tissue (IAF), subcutaneous adipose tissue (SAF), trunk fat, arm fat, and leg fat. The purpose of this study was to determine which of the fat distribution variables (arm fat, leg fat, trunk fat, IAF, or SAF) may have independent relations with cardiovascular (CVD) risk factors [serum triacylglycerol, serum cholesterol, high-density-lipoprotein (HDL) cholesterol, HDL2 cholesterol, HDL3 cholesterol, low-density-lipoprotein (LDL) cholesterol, very-low-density-lipoprotein (VLDL) cholesterol, VLDL3 cholesterol, lipoprotein(a), and systolic and diastolic blood pressure] in women after adjusting for age, menopause status, and other fat-distribution variables. Two hundred twenty-four (138 premenopausal and 86 postmenopausal) white females ranging in age from 17 to 77 y were sampled. Percentage body fat ranged from 8.8% to 48.1% and IAF cross sections ranged from 9.2 to 335 cm2. Simple zero-linear correlations and partial correlations were calculated. IAF and trunk fat were consistently positively related to CVD risk factors, whereas leg fat was consistently negatively related to CVD risk, indicating that IAF and trunk fat may put women at increased risk of developing CVD.

Racial differences in energy expenditure and aerobic fitness in premenopausal women.

BACKGROUND: Aerobic fitness, or maximal oxygen uptake (f1.gif" BORDER="0">O(2)max), and energy expenditure (EE) may be lower in African Americans than in whites. OBJECTIVE: The objective of this study was to compare sleeping EE (SEE), resting EE (REE), free-living total EE (TEE), and f1.gif" BORDER="0">O(2)max in African American and white women after adjustment for body composition and free-living activity-related energy expenditure (AEE). DESIGN: Eighteen African American and 17 white premenopausal women were matched for weight, percentage body fat, and age. SEE and REE were measured in a room calorimeter and f1.gif" BORDER="0">O(2)max was measured on a treadmill. Fat-free mass (FFM) and fat mass (FM) (4-compartment model), AEE (doubly labeled water and SEE), and regional lean tissue (dual-energy X-ray absorptiometry) were used as adjustment variables in SEE, REE, TEE, and f1.gif" BORDER="0">O(2)max comparisons. RESULTS: The African American women had significantly more limb lean tissue and significantly less trunk lean tissue than did the white women. The African American women also had significantly lower SEE (6.9%), REE (7.5%), TEE (9.6%), and f1.gif" BORDER="0">O(2)max (13.4%) than did the white women. Racial differences persisted after adjustment for f1.gif" BORDER="0">O(2)max, AEE, FFM, and limb lean tissue but disappeared after adjustment for trunk lean tissue. The f1.gif" BORDER="0">O(2)max difference was independent of all body-composition variables and of AEE. CONCLUSIONS: African American women had lower aerobic fitness than did white women, independent of differences in lean tissue or AEE. Diminished racial differences in SEE, REE, and TEE after adjustment for trunk lean tissue suggest that low EE in African American women is mediated by low volumes of metabolically active organ mass.

Electrical impedance in assessing human body composition: the BIA method.

Fundamental aspects of the body impedance analysis (BIA) method were investigated to determine limitations. This method measures body impedance with a low-level (800 microA) 50-KHz current conducted through the tissues. A linear regression equation was proposed to relate impedance measurements to total body fat. The hydrostatic densitometric method (underwater weighing) was used to validate the proposed mathematical expression. A correlation coefficient of 0.98 between these two methods was obtained. The overall results from this study indicate the usefulness of the BIA method in determining percent body fat in humans provided body fluids are not perturbed several hours before the measurements.

Lipid and insulin concentrations in obese postmenopausal women: separate effects of energy restriction and weight loss.

The separate effects of energy restriction and weight loss on serum lipids were studied in 24 postmenopausal moderately obese women before and after weight loss of greater than 10 kg to normal weight. Fasting serum triglycerides (TGs), total cholesterol (TC), high-density-lipoprotein (HDL) and low-density-lipoprotein (LDL) cholesterol, and insulin were measured at the end of four 10-d in-hospital phases, two before and two after weight loss: phase I, stable weight; phase II, 3350 kJ/d(800 kcal/d), followed by outpatient weight loss; phase III, 3350 kJ/d (800 kcal/d); and phase IV, stable weight. Diet composition and exercise were constant the entire study. Energy-restriction effect was determined by comparing average values in stable-weight phases (I and IV) with low-energy phases (II and III); weight-loss effect was determined by comparing values in obese phases (I and II) with reduced-weight phases (III and IV). Energy restriction lowered TG, TC, LDL cholesterol, the LDL-HDL cholesterol ratio, and insulin and raised HDL cholesterol (all P less than 0.05). Weight loss lowered TG, TC, LDL cholesterol, and insulin (all P less than 0.01) but did not change HDL cholesterol or the LDL-HDL cholesterol ratio. The results suggest that reduction to a weight-steady nonobese state significantly lowers TG, TC, and LDL cholesterol but does not improve HDL cholesterol or the LDL-HDL cholesterol ratio.

A longitudinal study of resting energy expenditure relative to body composition during puberty in African American and white children.

BACKGROUND: Body composition and resting energy expenditure (REE) have not been examined longitudinally during puberty. OBJECTIVE: The purpose of this longitudinal study was to examine the influence of pubertal maturation on REE relative to body composition in African American and white children. DESIGN: The study included 92 white and 64 African American children (mean age at baseline: 8.3 and 7.9 y, respectively) from Birmingham, AL. The children had 2-5 annual measurements of fat mass (FM), lean mass (LM), and REE. The Tanner stages of the children ranged from 1 to 5. Mixed-model repeated-measures analyses were used to test the change in REE relative to body composition with increasing Tanner stage among ethnic and sex groups. RESULTS: LM increased from Tanner stage 1 to subsequent stages. FM relative to LM decreased from Tanner stage 1 to stages 3, 4, and 5 but not from stage 1 to stage 2. The African American children had relatively higher limb LM and lower trunk LM than did the white children. REE declined with Tanner stage after adjustment for ethnicity, sex, FM, and LM. This decline was significant from Tanner stage 1 to stages 3, 4, and 5 but not to Tanner stage 2. After adjustment for age, Tanner stage, FM, and LM or LM distribution, REE was significantly higher in white than in African American children (by approximately 250 kJ/d). CONCLUSION: In a large sample of children at various Tanner stages, we found an ethnic difference in REE after adjustment for age, Tanner stage, FM, and LM that was not explained by the difference in LM distribution.

Body fat distribution in white and black women: different patterns of intraabdominal and subcutaneous abdominal adipose tissue utilization with weight loss.

BACKGROUND: Intraabdominal adipose tissue (IAAT) is the body fat depot most strongly related to disease risk. Weight reduction is advocated for overweight people to reduce total body fat and IAAT, although little is known about the effect of weight loss on abdominal fat distribution in different races. OBJECTIVE: We compared the effects of diet-induced weight loss on changes in abdominal fat distribution in white and black women. DESIGN: We studied 23 white and 23 black women, similar in age and body composition, in the overweight state [mean body mass index (BMI; in kg/m(2)): 28.8] and the normal-weight state (mean BMI: 24.0) and 38 never-overweight control women (mean BMI: 23.4). We measured total body fat by using a 4-compartment model, trunk fat by using dual-energy X-ray absorptiometry, and cross-sectional areas of IAAT (at the fourth and fifth lumbar vertebrae) and subcutaneous abdominal adipose tissue (SAAT) by using computed tomography. RESULTS: Weight loss was similar in white and black women (13.1 and 12.6 kg, respectively), as were losses of total fat, trunk fat, and waist circumference. However, white women lost more IAAT (P < 0.001) and less SAAT (P < 0.03) than did black women. Fat patterns regressed toward those of their respective control groups. Changes in waist circumference correlated with changes in IAAT in white women (r = 0.54, P < 0.05) but not in black women (r = 0.19, NS). CONCLUSIONS: Despite comparable decreases in total and trunk fat, white women lost more IAAT and less SAAT than did black women. Waist circumference was not a suitable surrogate marker for tracking changes in the visceral fat compartment in black women.

Do adaptive changes in metabolic rate favor weight regain in weight-reduced individuals? An examination of the set-point theory.

BACKGROUND: Obese persons generally regain lost weight, suggesting that adaptive metabolic changes favor return to a preset weight. OBJECTIVE: Our objective was to determine whether adaptive changes in resting metabolic rate (RMR) and thyroid hormones occur in weight-reduced persons, predisposing them to long-term weight gain. DESIGN: Twenty-four overweight, postmenopausal women were studied at a clinical research center in four 10-d study phases: the overweight state (phase 1, energy balance; phase 2, 3350 kJ/d) and after reduction to a normal-weight state (phase 3, 3350 kJ/d; phase 4, energy balance). Weight-reduced women were matched with 24 never-overweight control subjects. After each study phase, assessments included RMR (by indirect calorimetry), body composition (by hydrostatic weighing), serum triiodothyronine (T(3)), and reverse T(3) (rT(3)). Body weight was measured 4 y later, without intervention. RESULTS: Body composition-adjusted RMR and T(3):rT(3) fell during acute (phase 2) and chronic (phase 3) energy restriction (P: < 0.01), but returned to baseline in the normal-weight, energy-balanced state (phase 4; mean weight loss: 12.9 +/- 2.0 kg). RMR among weight-reduced women (4771 +/- 414 kJ/d) was not significantly different from that in control subjects (4955 +/- 414 kJ/d; P: = 0.14), and lower RMR did not predict greater 4-y weight regain (r = 0.27, NS). CONCLUSIONS: Energy restriction produces a transient hypothyroid-hypometabolic state that normalizes on return to energy-balanced conditions. Failure to establish energy balance after weight loss gives the misleading impression that weight-reduced persons are energy conservative and predisposed to weight regain. Our findings do not provide evidence in support of adaptive metabolic changes as an explanation for the tendency of weight-reduced persons to regain weight.

Dietary fat in relation to body fat and intraabdominal adipose tissue: a cross-sectional analysis.

Numerous studies report positive links between dietary fat and adiposity. However, the relation between fat intake and intraabdominal adipose tissue (IAAT), a risk factor for cardiovascular disease and diabetes, is not known. We therefore evaluated the association between dietary fat and adipose tissue stores in 135 white men aged 44 +/- 10 y (mean+/- SD: weight, 86 +/- 14 kg; body fat, 23 +/- 8%) and in 214 white women aged 45 +/- 14 y (weight, 64 +/- 12 kg; body fat, 33 +/- 10%). Dietary intake was estimated from 3-d food records, body composition from hydrostatic weighing, IAAT and subcutaneous abdominal adipose tissue (SCAAT) by computed tomography, and physical activity by using the Baecke Questionnaire. After adjustment for fat-free mass, sex, age, physical activity, and nonfat energy intake, fat intake was weakly correlated with fat mass, explaining only 2% of the variance (partial R2 = 0.018, P < 0.01). In a separate model that evaluated type of fat, saturated fat was positively related (partial R2 = 0.025, P < 0.01) to fat mass after adjustment for fat-free mass, sex, age, physical activity, and nonfat energy intake whereas polyunsaturated fat intake was negatively related (partial R2 = 0.007, P = 0.056). On the basis of partial correlation analyses, dietary fat was also associated with SCAAT adjusted for nonfat energy intake and IAAT (partial R2 = 0.014, P < 0.01), but not IAAT adjusted for nonfat energy intake and SCAAT. However, the association between dietary fat and adjusted SCAAT was not significant after further adjustment for sex, age, and physical activity. Thus, results of this cross-sectional analysis suggest that dietary fat independently plays a very minor role in increasing overall adiposity and does not specifically influence fat accretion in the intraabdominal region.

Energy expenditure and free-living physical activity in black and white women: comparison before and after weight loss.

BACKGROUND: The prevalence of obesity is higher in black than in white women. Differences in energy economy and physical activity may contribute to this difference. OBJECTIVE: The objective of this study was to compare free-living energy expenditure and physical activity in black and white women before and after weight loss. DESIGN: Participants were 18 white and 14 black women with body mass indexes (in kg/m(2)) between 27 and 30. Diet, without exercise, was used to achieve a weight loss of >/=10 kg and a body mass index <25. After 4 wk of energy balance in overweight and normal-weight states, body composition was assessed by using a 4-compartment model, sleeping and resting energy expenditures were assessed by using a chamber calorimeter, physiologic stress of exercise and exercise economy were measured by using standardized exercise tasks, and daily energy expenditure was assessed by using doubly labeled water. RESULTS: Weight loss averaged 12.8 kg. Sleeping and resting energy expenditures decreased in proportion to changes in body composition. Weight reduction significantly improved physiologic capacity for exercise in both groups of women, making it easier for them to be physically active. Black women had lower body composition-adjusted energy requirements than did white women-both before and after weight loss-during sleep (9% lower, 519 kJ/d; P < 0.001), at rest (14% lower, 879 kJ/d; P < 0.001), during exercise (6% lower; P < 0. 05), and as a daily total (9% lower, 862 kJ/d; P < 0.06). By contrast, free-living physical activity was similar between the groups. CONCLUSIONS: Weight-reduced women had metabolic rates appropriate for their body sizes. Black women had lower resting and nonresting energy requirements in both overweight and normal-weight states than did white women and did not compensate with greater physical activity, potentially predisposing them to greater weight regain.

The etiology of obesity: relative contribution of metabolic factors, diet, and physical activity.

Three major factors modulate body weight: metabolic factors, diet, and physical activity, each influenced by genetic traits. Despite recent advances in these areas, the prevalence of obesity in Westernized societies has increased. In contrast to monogenic animal models and rare human genetic syndromes, predisposition to common forms of obesity is probably influenced by numerous susceptibility genes, accounting for variations in energy requirements, fuel utilization, muscle metabolic characteristics, and taste preferences. Although recent increases in obesity prevalence cannot be explained by changes in the gene pool, previously "silent" genetic variants may now play important permissive roles in modern societies. Available data suggest that variations in resting energy expenditure, thermic effect of food, and fuel utilization exist but, by themselves, are unlikely to explain the onset of obesity. Regarding diet, the best available trend survey data indicate that fat and energy intake have fallen, in this and other Westernized countries. Diverging trends of decreasing energy intake and increasing body weight suggest that reduced physical activity may be the most important current factor explaining the rising prevalence of obesity. Subsistence in modern societies requires extreme adaptations in previously useful energy-conserving diet and exercise behaviors. Recognizing the difficulties in sustaining energy-restricted diets in the presence of fast foods and social feasts, the current trend toward increasing body weight is not likely to be reversed solely through recommendations for further reductions in energy intake. In all likelihood, activity levels will have to increase in response to an environment engineered to be more physically demanding.

Obesity-related hypertension: evaluation of the separate effects of energy restriction and weight reduction on hemodynamic and neuroendocrine status.

PURPOSE: Although weight reduction generally lowers blood pressure, it is unclear whether the response is due to concurrent dietary changes or to reduced body mass itself. In this study, the independent effects of energy restriction and weight reduction were examined prospectively in 24 obese, hypertensive, normoglycemic women whose dietary intake was tightly controlled. SUBJECTS AND METHODS: Sodium, potassium, and calcium intake, the polyunsaturated/saturated fat ratio, and the proportional composition of carbohydrate, fat, and protein were constant throughout the 5-month protocol. Hemodynamic and neuroendocrine status was evaluated in four 10-day hospital phases: two prior to weight loss (energy balance and then 800-kcal intake), and two after an average loss of 13 kg to normal body weight (800 kcal and then return to energy balance). RESULTS: Fasting serum insulin, triiodothyronine:reverse triiodothyronine ratio, resting metabolic rate, and heart rate declined, and sodium and potassium balances were negative during energy restriction. Catecholamines, renin, aldosterone, plasma volume, cardiac output, and blood pressure showed no consistent response to changes in energy intake. By contrast, weight reduction independently lowered blood pressure, plasma volume, cardiac output, and plasma renin activity. Body fat pattern remained unchanged. CONCLUSION: These results demonstrate that weight loss has a blood pressure-lowering effect that is distinct from energy restriction and that is related to changes in blood volume and cardiac output.