Body size and pubertal development explain ethnic differences in structural geometry at the femur in Asian, Hispanic, and white early adolescent girls living in the U.S

Variation in structural geometry is present in adulthood, but when this variation arises and what influences this variation prior to adulthood remains poorly understood. Ethnicity is commonly the focus of research of skeletal integrity and appears to explain some of the variation in quantification of bone tissue. However, why ethnicity explains variation in skeletal integrity is unclear.

METHODS

Here we examine predictors of bone cross sectional area (CSA) and section modulus (Z), measured using dual-energy X-ray absorptiometry (DXA) and the Advanced Hip Analysis (AHA) program at the narrow neck of the femur in adolescent (9-14 years) girls (n=479) living in the United States who were classified as Asian, Hispanic, or white if the subject was 75% of a given group based on parental reported ethnicity. Protocols for measuring height and weight follow standardized procedures. Total body lean mass (LM) and total body fat mass (FM) were quantified in kilograms using DXA. Total dietary and total dairy calcium intakes from the previous month were estimated by the use of an electronic semi-quantitative food frequency questionnaire (eFFQ). Physical activity was estimated for the previous year by a validated self-administered modifiable activity questionnaire for adolescents with energy expenditure calculated from the metabolic equivalent (MET) values from the Compendium of Physical Activities. Multiple regression models were developed to predict CSA and Z.

RESULTS

Age, time from menarche, total body lean mass (LM), total body fat mass (FM), height, total calcium, and total dairy calcium all shared a significant (p<0.05), positive relationship with CSA. Age, time from menarche, LM, FM, and height shared significant (p<0.05), positive relationships with Z. For both CSA and Z, LM was the most important covariate. Physical activity was not a significant predictor of geometry at the femoral neck (p≥0.339), even after removing LM as a covariate. After adjusting for covariates, ethnicity was not a significant predictor in regression models for CSA and Z.

CONCLUSION

Variability in bone geometry at the narrow neck of the femur is best explained by body size and pubertal maturation. After controlling for these covariates there were no differences in bone geometry between ethnic groups.

Androidal fat dominates in predicting cardiometabolic risk in postmenopausal women

We hypothesized that soy isoflavones would attenuate the anticipated increase in androidal fat mass in postmenopausal women during the 36-month treatment, and thereby favorably modify the circulating cardiometabolic risk factors: triacylglycerol, LDL-C, HDL-C, glucose, insulin, uric acid, C-reactive protein, fibrinogen, and homocysteine. We collected data on 224 healthy postmenopausal women at risk for osteoporosis (45.8–65 y, median BMI 24.5) who consumed placebo or soy isoflavones (80 or 120 mg/d) for 36 months and used longitudinal analysis to examine the contribution of isoflavone treatment, androidal fat mass, other biologic factors, and dietary quality to cardiometabolic outcomes. Except for homocysteine, each cardiometabolic outcome model was significant (overall P-values from ≤.0001 to .0028). Androidal fat mass was typically the strongest covariate in each model. Isoflavone treatment did not influence any of the outcomes. Thus, androidal fat mass, but not isoflavonetreatment, is likely to alter the cardiometabolic profile in healthy postmenopausal women.

Contribution of serum inflammatory markers to changes in bone mineral content and density in postmenopausal women: a 1-year investigation

Bone formation and resorption are influenced by inflammatory processes. We examined the relationships among inflammatory markers and bone mineral content (BMC) and density (BMD) and determined the contribution of inflammatory markers to 1-yr changes in BMC and BMD in healthy postmenopausal women. This analysis included 242 women at baseline from our parent Soy Isoflavones for Reducing Bone Loss project who were randomly assigned to 1 of 3 treatment groups: placebo, 80 mg/d soy isoflavones, or 120 mg/d soy isoflavones. BMD and BMC from the lumbar spine (LS), total proximal femur (hip), and whole body were measured by dual energy X-ray absorptiometry and the 4% distal tibia by peripheral quantitative computed tomography. Serum inflammatory markers (C-reactive protein, interleukin [IL]-1 beta, IL-6, tumor necrosis factor-alpha [TNF-alpha], and white blood cell count [WBC]) were measured at baseline, 6, and 12 mo. Because of attrition or missing values, data analysis at 12 mo includes only 235 women. Significant associations among IL-6, TNF-alpha, and WBC were observed with percent change in LS, hip, and whole body BMC and BMD. Multiple regression analysis indicated that in combination inflammatory markers accounted for 1.1-6.1% of the variance to the observed 12-mo changes in BMC and BMD. Our results suggest that modifying inflammatory markers, even in healthy postmenopausal women, may possibly reduce bone loss.

Longitudinal changes in pancreatic and adipocyte hormones following Roux-en-Y gastric bypass surgery

AIMS/HYPOTHESIS

Bariatric surgery is an effective treatment for severe obesity, as in addition to dramatic weight loss, co-morbidities such as type 2 diabetes are frequently resolved. Although altered gastrointestinal peptide hormone secretion and its relationship with post-surgical improvements in insulin sensitivity has been studied, much less is known about long-term changes in pancreatic and adipose tissue-derived hormones. Our objective was to conduct a comprehensive longitudinal investigation of the endocrine changes following Roux-en-Y gastric bypass surgery (RYGBP), focusing on pancreatic and adipocyte hormones and systemic markers of inflammation.

METHODS

Nineteen severely obese women (BMI 45.6 +/- 1.6 kg/m(2)) were studied prior to RYGBP, and at 1, 3, 6, and 12 months after RYGBP. Body composition was assessed before surgery and at 1 and 12 months.

RESULTS

Pre-surgical adiposity was correlated with circulating adipocyte hormones (leptin, visfatin) and inflammatory molecules (IL-6, high sensitivity C-reactive protein [hsCRP], monocyte chemoattractant protein-1). As expected, RYGBP reduced fat mass and fasting insulin and glucose concentrations. In addition, reductions of fasting pancreatic polypeptide (PP) and glucagon concentrations were observed at 1 and 3 months, respectively. In the 12 months following RYGBP, concentrations of most adipocyte hormones (leptin, acylation-stimulating hormone and visfatin, but not retinol-binding hormone-4) and inflammatory molecules (IL-6, hsCRP and soluble intracellular adhesion molecule-1) were significantly reduced. Reductions of insulin resistance (measured by homeostasis model assessment of insulin resistance) were independently associated with changes of glucagon, visfatin and PP. Pre-surgical HMW adiponectin concentrations independently predicted losses of body weight and fat mass.

CONCLUSIONS/INTERPRETATION

These results suggest that pancreatic and adipocyte hormones may contribute to the long-term resolution of insulin resistance after RYGBP.

Circulating concentrations of high-molecular-weight adiponectin are increased following Roux-en-Y gastric bypass surgery

AIMS/HYPOTHESIS

In addition to weight loss, bariatric surgery for severe obesity dramatically alleviates insulin resistance. In this study, we investigated whether circulating concentrations of the high-molecular-weight (HMW) form of adiponectin are increased following gastric bypass surgery. The HMW form is implicated as the multimer responsible for adiponectin's hepatic insulin-sensitising actions.

SUBJECTS AND METHODS

We studied 19 women who were undergoing Roux-en-Y gastric bypass surgery. Studies were conducted prior to, and 1 and 12 months after surgery.

RESULTS

One month after surgery, total plasma adiponectin concentrations were unchanged. Nevertheless, increases in both HMW (by 40+/-15%, p=0.006) and the proportion of adiponectin in the HMW form (from 40+/-2 to 50+/-2%, p<0.0001) were observed. At 12 months, total and HMW adiponectin concentrations were increased by 58+/-8% and 118+/-21%, respectively (both p<0.001). The majority (80%) of the increase of total adiponectin was due to an increase of the HMW form. After adjustment for covariates, increases of HMW and total adiponectin at 12 months were correlated with the decrease of fat mass (HMW, p=0.0076; total, p=0.0302). In subjects with improved insulin sensitivity at 12 months after surgery (n=18), the increase of HMW, but not that of total adiponectin, predicted the relative decrease of insulin resistance (HMW: p=0.0044; total: p=0.0775, after adjustment for covariates).

CONCLUSIONS/INTERPRETATION

These data suggest that the reduction of fat mass following gastric bypass surgery is an important determinant of the increase of HMW adiponectin concentrations, which in turn is associated with and may contribute to the resulting improvement of insulin sensitivity.

Validation of fan beam dual energy x ray absorptiometry for body composition assessment in adults aged 18-45 years

BACKGROUND

Pencil beam dual energy x ray absorptiometry (DXA) has been shown to provide valid estimates of body fat (%BF), but DXA fan beam technology has not been adequately tested to determine its validity.

OBJECTIVE

To compare %BF estimated from fan beam DXA with %BF determined using two and three compartment (2C, 3C) models.

METHODS

Men (n = 25) and women (n = 31), aged 18-41 years, participated in the study. Body density, from hydrostatic weighing, was used in the 2C estimate of %BF; DXA was used to determine bone mineral content (BMC) for the 3C estimate of %BF calculated using body density and BMC (3C(BMC)). DXA was also used to determine %BF. Analysis of variance was used to test for significant differences in %BF between sexes and among methods.

RESULTS

Women were significantly shorter, weighed less, had less fat free mass, and a higher %BF than men. No significant differences were found among methods (2C, 3C(BMC), DXA) for determination of %BF in either sex. Although not significant, Bland-Altman plots showed that DXA gave higher values for %BF than the 2C and 3C(BMC) methods.

CONCLUSION

DXA determination of %BF was not different from that of the 2C and 3C(BMC) models in this group of young adults. However, to validate fan beam DXA fully as a method for body composition assessment in a wide range of individuals and populations, comparisons are needed that use a 4C model with a measure of total body water and BMC.

Low bone mass in premenopausal chronic dieting obese women

BACKGROUND

Obese premenopausal women are thought to be at low risk for osteoporosis due to increased body weight and effects of estrogen on weight-bearing bone.

OBJECTIVE

To examine the effect of restrained eating on obese women, we examined bone mineral density (BMD) and content (BMC) of the spine and femur in obese women who were restrained eaters, with emphasis on the relationship between BMC and determinants of bone mass, and current eating behaviors, dietary intake, physical activity, and indices of calcium regulation, bone metabolism, stress and inflammation.

DESIGN

A total of 78 obese, Caucasian, female, restrained eaters, ages 30-45 y, were enrolled in a weight lose program. Height, weight, bone turnover markers, serum parathyroid hormone (PTH), cortisol, c-reactive protein (CRP), dietary intake, eating behaviors, physical activity, and BMD and BMC were measured.

SETTING

This study was conducted at the University of California, in Davis, CA, USA.

RESULTS

In all, 31% of women had osteopenia or osteoporosis (OSTEO). In the OSTEO group, 87.5% of women had osteoporosis or osteopenia of the lumbar spine and 12.5% of the women had osteoporosis or osteopenia in femur. A significant positive correlation between BMC and energy expenditure (r=0.256), and a significant negative correlation between BMC and number of times on a weight loss diet (r=-0.250) and cognitive restraint (r=-0.239) were observed. No significant differences were observed between OSTEO women and nonosteoporotic women for current eating behaviors, dietary intake, physical activity habits, bone turnover, calcium regulation, stress, or inflammation.

CONCLUSIONS

Obese restrained eaters are at risk for low bone mass. Prior dieting may be responsible. Chronic dieters should be encouraged to decrease their dietary restraint, develop healthy eating habits and increase physical activity.

Body composition in disease: what can we measure and how can we measure it?

This manuscript presents a brief overview of the topic of body composition in disease. The purpose of this paper is threefold: (1). to present examples of diseases in which body composition assessment might provide valuable information to physicians and other clinical personnel in patient care; (2). provide basic information on the types of methodologies available for various aspects of body composition assessment; and (3). give a brief review of some of the research literature available on the topic of body composition use in disease. Materials in this paper should not be interpreted as providing all the relevant information in this area of research, but the paper does represent a limited overview of the topic.

Evaluating a 'non-diet' wellness intervention for improvement of metabolic fitness, psychological well-being and eating and activity behaviors

CONTEXT

Current public health policy recommends weight loss for obese individuals, and encourages energy-restricted diets. Others advocate an alternative, 'non-diet' approach which emphasizes eating in response to physiological cues (eg hunger and satiety) and enhancing body acceptance.

OBJECTIVE

To evaluate the effects of a 'health-centered' non-diet wellness program, and to compare this program to a traditional 'weight loss-centered' diet program.

DESIGN

Six-month, randomized clinical trial.

SETTING

Free-living, general community.

PARTICIPANTS

Obese, Caucasian, female, chronic dieters, ages 30-45 y (n=78).

INTERVENTIONS

Six months of weekly group intervention in a non-diet wellness program or a traditional diet program, followed by 6 months of monthly after-care group support.

OUTCOME MEASURES

Anthropometry (weight, body mass index); metabolic fitness (blood pressure, blood lipids); energy expenditure; eating behavior (restraint, eating disorder pathology); psychology (self-esteem, depression, body image); attrition and attendance; and participant evaluations of treatment helpfulness. Measures obtained at baseline, 3 months, 6 months and 1 y.

RESULTS

(1 y after program initiation): Cognitive restraint increased in the diet group and decreased in the non-diet group. Both groups demonstrated significant improvement in many metabolic fitness, psychological and eating behavior variables. There was high attrition in the diet group (41%), compared to 8% in the non-diet group. Weight significantly decreased in the diet group (5.9+/-6.3 kg) while there was no significant change in the non-diet group (-0.1+/-4.8 kg).

CONCLUSIONS

Over a 1 y period, a diet approach results in weight loss for those who complete the intervention, while a non-diet approach does not. However, a non-diet approach can produce similar improvements in metabolic fitness, psychology and eating behavior, while at the same time effectively minimizing the attrition common in diet programs.

Influence of cognitive eating restraint on total-body measurements of bone mineral density and bone mineral content in premenopausal women aged 18-45 y: a cross-sectional study

BACKGROUND

We examined the relation between cognitive eating restraint (CER) and total-body measurements of bone mineral density (BMD) and bone mineral content (BMC).

OBJECTIVE

Our objective was to determine whether women with CER had lower total-body BMD and BMC than did other women.

DESIGN

Premenopausal women, 90-150% of ideal weight, had measurements of their BMD and BMC made and completed questionnaires on physical activity, weight history, body size satisfaction, dieting history, eating behavior, and childbearing history. Bone measurements were examined for differences between groups with low and high CER scores by using analysis of covariance and quartiles of body weight to adjust for body size differences. CER was assessed by using the Three-Factor Eating Inventory and was defined as a score > or =9; normal eating restraint (NER) was defined by a score <9. Total-body BMC, BMD, and fat and lean masses were measured by dual-energy X-ray absorptiometry.

RESULTS

Fifty-two percent of the women were classified as having CER. Women with CER were significantly more dissatisfied with their bodies. Analysis of covariance, with weight as the covariate, indicated a significant difference in BMC between women in preplanned pairs from the 5 lowest and 5 highest CER levels. No significant differences in BMD were observed between groups. Significantly lower BMC was found in women with high CER scores and body weights <71 kg than in those with high CER scores and weights > or =71 kg.

CONCLUSIONS

BMC was significantly differently between women with low and high CER scores. BMC was significantly lower in women with body weights <71 kg and classified with CER. Lower BMC in women with high CER scores may indicate an increased risk of osteoporosis.

Conjugated linoleic acid supplementation in humans: effects on body composition and energy expenditure

Recent animal studies have demonstrated that dietary conjugated linoleic acid (CLA) reduces body fat and that this decrease may be due to a change in energy expenditure. The present study examined the effect of CLA supplementation on body composition and energy expenditure in healthy, adult women. Seventeen women were fed either a CLA capsule (3 g/d) or a sunflower oil placebo for 64 d following a baseline period of 30 d. The subjects were confined to a metabolic suite for the entire 94 d study where diet and activity were controlled and held constant. Change in fat-free mass, fat mass, and percentage body fat were unaffected by CLA supplementation (0.18+/-0.43 vs. 0.09+/-0.35 kg; 0.01+/-0.64 vs. -0.19+/-0.53 kg; 0.05+/-0.62 vs. -0.67+/-0.51%, placebo vs. CLA, respectively). Likewise, body weight was not significantly different in the placebo vs. the CLA group (0.48+/-0.55 vs. -0.24+/-0.46 kg change). Energy expenditure (kcal/min), fat oxidation, and respiratory exchange ratio were measured once during the baseline period and during weeks 4 and 8 of the intervention period. At all three times, measurements were taken while resting and walking. CLA had no significant effect on energy expenditure, fat oxidation, or respiratory exchange ratio at rest or during exercise. When dietary intake was controlled, 64 d of CLA supplementation at 3 g/d had no significant effect on body composition or energy expenditure in adult women, which contrasts with previous findings in animals.

The effects of zinc depletion on peak force and total work of knee and shoulder extensor and flexor muscles

In this study we tested the effect of zinc (Zn) on muscle function in human. After receiving 12 mg Zn/day for 17 days, 8 male subjects received 0.3 mg Zn/day for either 33 or 41 days. Subjects were divided into two groups for repletion. Group A subjects received overnight infusions of 66 mg Zn on Days 1 and 10 and then were fed 12 mg Zn/day for another 16 days. Group B subjects were fed 12 mg Zn/day for 3 weeks. Peak force and total work capacity of the knee and shoulder extensor and flexor muscle groups were assessed using an isokinetic dynamometer at baseline, at two points during depletion, and at repletion. Plasma Zn declined significantly during depletion and remained below baseline levels after repletion. The peak force of the muscle groups tested was not affected by acute Zn depletion, however, total work capacity for the knee extensor muscles and shoulder extensor and flexor muscles declined significantly. The data suggest that acute Zn depletion alters the total work capacity of skeletal muscle.

Monitoring changes in fat-free mass in HIV-positive men with hypotestosteronemia and AIDS wasting syndrome treated with gonadal hormone replacement therapy

OBJECTIVE

To compare methods for assessing changes in body composition during gonadal hormone replacement therapy in a group of HIV-positive men with AIDS wasting syndrome.

DESIGN

The study included a 21-day, double-blind, randomized, placebo-controlled inpatient intervention and a 12-week open-label intervention. The inpatient intervention included 18 men who were confined to a metabolic ward. Days 1-7 comprised weight stabilization and body composition measures followed by 14 days of nandrolone decanoate at either 65 or 195 mg weekly, or placebo, and repeat testing. The open-label intervention comprised 12 weeks of 200 mg nandrolone decanoate fortnightly with measurements of fat-free mass at 6 and 12 weeks.

METHODS

The inpatient intervention measured nitrogen balance from 24 h urine and fecal collections and fat-free mass by dual energy x-ray absorptiometry (DEXA), bioimpedance spectroscopy (BIS) and D2O dilution. Nitrogen balance was calculated as the difference between dietary intake and urinary and fecal nitrogen excretion. Nitrogen was converted to fat-free mass using the constant of 32.5 g. Repeated measures analysis of variance was used to determine which methods were significantly different from the reference nitrogen balance technique.

RESULTS

Nitrogen accretion of lean tissue was 0.55 and 0.85 kg weekly for low and high-dose groups, respectively. Estimated nitrogen retention during the open-label study was 0.42 kg weekly. Body weight increased with the estimated lean tissue accretion. DEXA, BIS and D2O methods demonstrated improvements in fat-free mass, although the BIS estimate of fat-free mass most closely matched the results of the nitrogen retention method.

CONCLUSION

DEXA, BIS and D2O techniques demonstrated increases in fat-free mass. The BIS method is less costly, more convenient to use, and had results that more closely matched those from nitrogen balance and retention methods. BIS may be the preferred method to monitor changes in fat-free mass in AIDS patients and patients with malnutrition.

Comparison of different techniques to measure body composition in moderately active adolescents

OBJECTIVE

To evaluate the differences in the estimate of body fat percentage (%FM) and the amount (kg) of fat free mass (FFM) by different methods in 26 moderately active adolescents very similar in age, body fatness, and training status.

METHODS

Mean (SD) age was 16.7 (0.9) years, height was 177.0 (5.1) cm, and weight 68.0 (5.2) kg. %FM was assessed using dual-energy x ray absorptiometry (DXA) and two skinfold prediction equations: that of Slaughter et al (%FM Sla) and that of Deurenberg et al (%FM Deu). In the same way, FFM was measured using DXA and different impedance equations: those of Suprasongsin et al (FFM Sup), Schaefer et al (FFM Sch), Houtkooper et al (FFM Hou), and Deurenberg et al (FFM Deu). To determine the interchangeability of the different methods of measuring %FM and FFM, one way analysis of variance, standard error (SE), and coefficient of variation (CV%) ((SD/mean) x 100) were used.

RESULTS

On average, no significant statistical differences were observed between the values determined for %FM: DXA value, 11.7 (5.4%); %FM Sla, 10.9 (4.0)%; %FM Deu, 11.5 (2.3)%. On the other hand, SE and CV% between each pair of the three methods used showed very large variability. With regard to the measurement or prediction of FFM, the mean value measured by DXA was significantly higher than that predicted by the equation of Sch (+7.2 kg, p < 0.001), Deu (+3.2 kg, p < 0.001), and Hou (+2.6 kg, p < 0.001), whereas it was lower than that predicted by the equation of Sup (-1.6 kg, p < 0.05). The Hou and Deu values were the only two that, on average, did not differ in a statistically significant way, although they showed the highest CV%.

CONCLUSIONS

In our sample of moderately active adolescents the estimated values for %FM and FFM appear to be highly dependent on method.

Estimates of fat-free mass (FFM) by densitometry, dual energy X-ray absorptiometry (DXA), and bioimpedance spectroscopy (BIS) in caucasian and Chinese-American women

Estimates of fat-free mass (FFM) from dual energy X-ray absorptiometry and bioelectrical impedance spectroscopy (BIS) were compared to results obtained by densitometry in a group of Caucasian and Chinese-American women. Each group included 38 women between the ages of 18 and 24 years. The Chinese-American women were significantly shorter in stature, had lower body weights, and lower values for FFM compared to the Caucasian women. DXA estimates of FFM were consistently lower than those obtained from densitometry; BIS estimates were similar to densitometry results.

Effect of weight loss on bone mineral content and bone mineral density in obese women

Studies of body-composition changes during weight loss have had conflicting results with regard to changes in bone mineral content (BMC) and bone mineral density (BMD). We examined BMC and BMD for changes during weight loss. Fourteen women enrolled in a 15-wk weight loss program. Dual-energy X-ray absorptiometry (DXA) measures of the total body were made at baseline (T1), the midpoint of weight loss (T2), and at the end of weight loss (T3). Body weight changed significantly throughout the 15 wk, declining from a high of 89.7+/-3.6 to 74.1+/-3.2 kg. Fat-free mass declined initially (47.8+/-1.7 kg at T1, 45.7+/-1.4 kg at T2, and 46.0+/-1.5 kg at T3) and then stabilized. Fat mass changed significantly during the study (39.2 kg at T1, 32.4 kg at T2, and 29.3 kg at T3). No significant differences were observed in BMC or bone areal measurement during the study. However, BMD declined significantly from baseline (1.217 g/cm2 at T1, 1.197 g/cm2 at T2, and 1.200 g/cm2 at T3). The changes in BMC and BA were in opposite directions, resulting in a significant decline in BMD without a loss of BMC. These data suggest that changes in BMD observed with weight loss may be the result of a lack of instrument sensitivity when body weight and composition change and are simply an artifact and not a physiologic change in BMD. Further research is needed to determine the full effect of weight loss on BMC, bone area, and BMD.

A longitudinal study of calcium homeostasis during human pregnancy and lactation and after resumption of menses

To clarify the role of the intestine, kidney, and bone in maintaining calcium homeostasis during pregnancy and lactation and after the resumption of menses, a longitudinal comparison was undertaken of 14 well-nourished women consuming approximately 1200 mg Ca/d. Measurements were made before conception (prepregnancy), once during each trimester of pregnancy (T1, T2, and T3), early in lactation at 2 mo postpartum (EL), and 5 mo after resumption of menses. Intestinal calcium absorption was determined from the enrichment of the first 24-h urine sample collected after administration of stable calcium isotopes. Bone mineral of the total body and lumbar spine was measured by dual-energy X-ray absorptiometry and quantitative computerized tomography, respectively. Twenty-four-hour urine and fasting serum samples were analyzed for calcium, calcitropic hormones, and biochemical markers of bone turnover. Despite an increase in calcium intake during pregnancy, true percentage absorption of calcium increased from 32.9+/-9.1% at prepregnancy to 49.9+/-10.2% at T2 and 53.8+/-11.3% at T3 (P < 0.001). Urinary calcium increased from 4.32+/-2.20 mmol/d at prepregnancy to 6.21+/-3.72 mmol/d at T3 (P < 0.001), but only minor changes in maternal bone mineral were detected. At EL, dietary calcium and calcium absorption were not significantly different from that at prepregnancy, but urinary calcium decreased to 1.87+/-1.22 mmol/d (P < 0.001) and trabecular bone mineral density of the spine decreased to 147.7+/-21.2 mg/cm3 from 162.9+/-25.0 mg/cm3 at prepregnancy (P < 0.001). Calcium absorption postmenses increased nonsignificantly to 36.0+/-8.1% whereas urinary calcium decreased to 2.72+/-1.52 mmol/d (P < 0.001). We concluded that fetal calcium demand was met by increased maternal intestinal absorption; early breast-milk calcium was provided by maternal renal calcium conservation and loss of spinal trabecular bone, a loss that was recovered postmenses.

Effects of physical activity, body weight and composition, and muscular strength on bone density in young women

OBJECTIVE

The purpose of this study was to examine the relationship between body weight and composition, muscular strength, physical activity, and bone mineral density (BMD) in eumenorrheic college-aged women.

METHODS

BMD and bone mineral content (BMC) of the total body, and BMD of the lumbar spine (L2-L4) and femoral neck (via dual energy x-ray absorptiometry), as well as body composition and muscular strength, were measured in 60 college-aged women. The women were divided into three groups: 1) low body weight athletes involved in weight-bearing, collegiate sports (N = 20), 2) matched low body weight and sedentary (N = 20), and 3) average body weight and sedentary (N = 20). All groups were matched for height, age, and age at menarche.

RESULTS

The athletes had significantly greater (P < 0.05) (mean +/- SD) total body BMD (1.164 +/- 0.06 g x cm[-2]), L2-L4 BMD (1.240 +/- 0.13 g x cm[-2]), femoral neck BMD (1.144 +/- 0.13 g x cm[-2]) and total body BMC (2.44 +/- 0.30 kg) than the low body weight, sedentary (LWS) group, but were only greater than the average body weight sedentary group (AWS) for femoral neck BMD. Significant correlations were found between lean body mass (LBM) and all BMD variables (P < 0.001). A significant correlation (P < 0.01) was found between fat mass and all BMD variables in the sedentary subjects alone (N = 40), but with inclusion of the athletes (N = 60), none of the correlations between fat mass and BMD were significant. Arm and leg strength isometric torque values corrected for muscle + bone cross-sectional area (M + B CSA) were not significantly different between the athletes and LWS group, but the athletes were greater (P < 0.05) than the AWS group for both arm and leg strength/M + B CSA. No significant, site-specific correlations were found between strength/M + B and BMD.

CONCLUSIONS

In summary, the athletes had significantly greater BMD, BMC, and LBM than the LWS group and, except for a greater femoral neck BMD, similar BMD, BMC, and LBM as the AWS group. These results suggest that LBM and weight-bearing exercise both enhance BMD in eumenorrheic young adult women.

The fatness-specific bioelectrical impedance analysis equations of Segal et al: are they generalizable and practical?

The fatness-specific bioelectrical impedance analysis (BIA) equations of Segal et al (Am J Clin Ntr 1988;47: 7-14; Segal equations) have been shown to be generalizable across sex, ethnicity, age, and degrees of adiposity. However, these fatness-specific equations require an a priori determination of percentage body fat (%BF) by using a skinfold equation or densitometry to categorize subjects into obese or nonobese groups. These procedures negate the use of BIA as a fast and simple method. It was hypothesized that the average of the Segal nonobese and obese fatness-specific equations (BIA average method) could be used in lieu of the skinfold method for categorizing subjects who are not obviously lean or obese. In phase 1 these three methods were compared for a subsample of 59 women who were not obviously lean or obese. The %BF of 75% of these subjects was accurately estimated within 3.5%BF by using the BIA average method whereas only 71% and 46% were accurately estimated by fusing the densitometric and skinfold methods, respectively. In phase 2, the predictive accuracy of the Segal fatness-specific equations, used in combination with the BIA average method, was compared with other BIA equations published previously for 602 American Indian, Hispanic, and white women and men. The Segal fatness-specific equations yielded the smallest prediction error (SEE = 2.22 kg for women and 3.59 kg for men) and the %BF of 70% of the subjects was accurately estimated within 3.5%BF compared with 24-59% for other BIA equations. Therefore, we recommend using the Segal fatness-specific and average equations to assess body composition in heterogeneous populations.

Weight loss is greater with consumption of large morning meals and fat-free mass is preserved with large evening meals in women on a controlled weight reduction regimen

The purpose of this study was to determine whether meal ingestion pattern [large morning meals (AM) vs. large evening meals (PM)] affects changes in body weight, body composition or energy utilization during weight loss. Ten women completed a metabolic ward study of 3-wk weight stabilization followed by 12 wk of weight loss with a moderately energy restricted diet [mean energy intake +/- SD = 107 +/- 6 kJ/(kg.d)] and regular exercise. The weight loss phase was divided into two 6-wk periods. During period 1, 70% of daily energy intake was taken as two meals in the AM (n = 4) or in the PM (n = 6). Subjects crossed over to the alternate meal time in period 2. Both weight loss and fat-free mass loss were greater with the AM than the PM meal pattern: 3.90 +/- 0.19 vs. 3.27 +/- 0.26 kg/6 wk, P < 0.05, and 1.28 +/- 0.14 vs. 0.25 +/- 0.16 kg/6 wk, P < 0.001, respectively. Change in fat mass and loss of body energy were affected by order of meal pattern ingestion. The PM pattern resulted in greater loss of fat mass in period 1 (P < 0.01) but not in period 2. Likewise, resting mid-afternoon fat oxidation rate was higher with the PM pattern in period 1 (P < 0.05) but not in period 2, corresponding with the fat mass changes. To conclude, ingestion of larger AM meals resulted in slightly greater weight loss, but ingestion of larger PM meals resulted in better maintenance of fat-free mass. Thus, incorporation of larger PM meals in a weight loss regimen may be important in minimizing the loss of fat-free mass.

Evaluation of body composition by dual energy x-ray absorptiometry and two different software packages

Dual energy x-ray absorptiometry (DXA) measures body composition, tissue distribution, bone mineral content (BMC), and bone mineral density (BMD). Differences are possible due to software versions. This investigation examined body composition, tissue distribution, BMC, and BMD measurements using a DXA (Lunar Corp., Madison, WI) with different software packages (versions 3.4 and 3.6R). Fifteen women, ages 20-40 yr, enrolled in a weight-loss study (body mass index = 28) and volunteered for body composition assessment by densitometry. BMC, BMD, and tissue distribution measurements were made using DXA. Results were analyzed once each with software versions 3.4 and 3.6R. BMC + total soft tissue, measured using DXA, was comparable to measured body weight (3.4 = 76.3 kg; 3.6R = 76.5 kg; weight = 76.5 kg). Lower BMC and BMD (5.5% and 1.8%, P < 0.01) were observed with 3.6R. Arm tissue mass was lower (1,530 g; P < 0.01) and fat declined (1,069 g; P < 0.01) with 3.6R. Leg tissue mass decreased 487 g (P < 0.01), but fat tissue increased (526 g, P < 0.01) with 3.6R. A larger fat mass (1,492 g) and lower lean mass (1,115 g) were observed with 3.6R compared with 3.4. Percent fat values by densitometry using DXA 3.4 and 3.6R were 38.1%, 39.9, and 41.9%, respectively. These results demonstrated differences in total body composition, lean and fat tissue distribution, and bone measurements from DXA software versions.

Fluid changes during pregnancy: use of bioimpedance spectroscopy

The increase in body water during pregnancy is responsible for the largest portion of weight gain and is of interest of clinical practitioners. However, assessing changes in body fluids is not easily accomplished during pregnancy. The purpose of this study was to examine the accuracy of bioelectrical impedance spectroscopy for estimating fluid volumes before, during, and after pregnancy. Ten healthy adult women were recruited for the study. Total body water (TBW) and extracellular fluid (ECF) volume were measured at baseline (preconception); 8-10, 24-26, and 34-36 wk of gestation; and 4-6 wk postpartum by deuterium oxide and NaBr dilution, respectively. Estimates of TBW and ECF were also obtained by bioimpedance spectroscopy (BIS). At baseline, mean values for dilution and BIS estimates of TBW and ECF were 33.2 +/- 4.6 (SD) vs. 31.6 +/- 6.2 liters and 15.2 +/- 1.3 vs. 16.9 +/- 2.3 liters, respectively. TBW and ECF estimated by BIS were not significantly different from the dilution values at any time point. These results suggest that BIS may be useful in estimating volumes of ECF and TBW during pregnancy.

The effects of endurance exercise with and without a reduction of energy intake on fat-free mass and the composition of fat-free mass in obese women

OBJECTIVE

The objective of this study was to evaluate the effects of endurance exercise on fat-free mass and nitrogen balance, with energy restriction or with energy intake to meet non-exercise needs in obese women.

DESIGN

The study was a 14-week metabolic control study with a 2-week baseline period for dietary stabilization followed by a 12-week period of exercise (E) with or without energy restriction (D), E or D+E.

SETTING

Metabolic research unit of the Western Human Nutrition Research Center.

SUBJECTS

Ten obese women between the ages of 19 and 37 years volunteered as subjects. Body weight ranged from 19% to 41% IBW and body fat was 31-40% of body weight.

INTERVENTION

Women were assigned to either an energy-restricted or energy-'adequate' group so that group means for weight, body fat, FFM, predicted VO2max and RMR were similar. Data were polled for the 2-week baseline period and in 3-week intervals during the intervention period.

RESULTS

The data indicated that E had a slower rate of weight loss and a lower loss of FFM than D+E. Nitrogen balance was more positive in E than D+E. Negative N balance occurred in the D+E group when blood was drawn. There was no decrease in N excretion to compensate for blood losses. N balance for E was positive throughout the study.

CONCLUSION

Changes in FFM, assessed by total body electrical conductivity, were different from the results obtained by classic nitrogen balance. This suggests that losses were due to fluid losses, which were confirmed by deuterium dilution procedures. This study demonstrated that body protein stores remained intact during periods of increased energy expenditure and dietary restriction in obese women.

Brief communication: changes in thermogenesis and caloric efficiency with high and normal protein-reducing diets in women

A pilot study with four women (40-60% above ideal weight, 32-42 years old) was conducted for 6 weeks of weight maintenance, 12 weeks at 50% calories (1000 and 1200 kcal/day) and 6 weeks of weight maintenance after weight loss. Two women consumed 17% and two 32% of their calories from protein during restriction; their energy metabolism and body composition changes were examined. The use of doubly labeled water for measuring energy expenditure during weight loss was evaluated. Although the 32% protein diet did not reduce lean body tissue loss, the apparent increased efficiency of calorie utilization compared to the 17% protein diet is worthy of further investigation. Thermic effect of a meal was greatly reduced in these women compared to previously reported responses. Further refinements of the doubly labeled water method are needed prior to application in weight loss studies.

Body composition assessment: dual-energy X-ray absorptiometry (DEXA) compared to reference methods

The use of dual energy X-ray absorptiometry (DEXA) for the assessment of body composition was examined in 55 adults (26 male & 29 female) ranging in age from 19 to 65 years. DEXA measures of bone mineral content (BMC, g), bone mineral density (BMD, g/cm2) and soft tissue (ST) were based on differential energy attenuation at dual energy levels of 40 and 70 keV. The ratio of the low- to high-energy attenuation in ST was used to quantify fat (%FatDEXA) and fat-free mass minus the bone component (FFMDEXA). BMC and BMD were significantly correlated (r = 0.82 and 0.60) with densitometric fat-free mass (FFMD). No significant differences were observed between the sum of FFMDEXA + BMC versus FFMD for either the males or females (males: FFMDEXA + BMC = 61.7 kg; FFMD = 59.1 kg; females: FFMDEXA + BMC = 43.8 kg; FFMD = 42.8 kg). Percentage body fat from DEXA for the women was equivalent to percentage fat from density (%FatDEXA = 30.8 versus %FatD = 32.2); however, significant differences were observed for the men (%FatDEXA = 19.4 versus %FatD = 23.5). Percentage fat differences for the men may be due to classification of individual soft tissue pixels. DEXA is reliable, easy to use, and appears to give accurate values for the estimation of FFM for both men and women. Additional research is needed to ascertain the cause of the differences in the estimation of percent body fat for men.

Use of multi-frequency bioelectrical impedance analysis for the estimation of extracellular fluid

Thomasset (Lyon Medicine (1962): 207, 107-118; (1963): 209, 1325-1350; (1965): 214, 131-143) and others suggested that low-frequency impedance measurements could be used to estimate extracellular fluid and that high-frequency measurements could be used for the assessment of total body water. It was the purpose of this study to examine the relationship between body fluid compartments and multi-frequency bioelectrical impedance analysis (MF-BIA). Total body water (TBW) and extracellular fluid (ECF) were measured using deuterium and sodium bromide dilution procedures. Intracellular fluid volume (ICF) was calculated as the difference between TBW and ECF. A tetrapolar arrangement of surface electrodes was used to measure whole-body resistance (R), reactance (Xc), impedance (Z), and phase angle (P) at 25 frequencies ranging from 1 kHz to 1.35 MHz. Subjects (n = 60; 40 male and 20 female) were between the ages of 19 and 65 years. Mean ratios (+/- SEM) of ECF/ICF and ECF/TBW were 0.83 +/- 0.021 and 0.45 +/- 0.011, respectively. Individuals with the largest fat-free mass (FFM) had the highest ECF value. Whole-body resistive index values most correlated to ECF were at 224, 300, 400, 548 and 1 kHz with correlations ranging from 0.93 to 0.84. All possible subset regression analysis was used to develop a prediction equation for ECF: R2 = 0.924 and SEE = 1.061: ECF = 5.17753 + (0.09989*RI224) + (0.09322*WT) - (1.3962*SEX), where RI = resistive index (HT2/R) at the specific frequency of 224kHz; WT = weight in kilograms; sex was dummy-coded, males = 0, females = 1.

Assessment of fat-free mass in teen-agers: use of TOBEC methodology

The accuracy of total-body electrical conductivity (TOBEC) for body composition assessment was examined in 50 teen-agers (33 males and 17 females) aged 11-19 y. Body composition measures included densitometry, hydrometry, bone mineral density of the one-third distal radius, and TOBEC. Fat-free mass (FFM) was calculated by using one-, two-, and three-compartment models: densitometry, FFMd; densitometry and hydrometry, FFMdw; and densitometry, hydrometry, and bone mineral density, FFMdwb. Correlations between TOBEC variables and the three calculations of FFM were highly significant (r = 0.88-0.95; P less than 0.01). No significant differences were observed (ANOVA) between the TOBEC estimate of FFM (FFMT) and FFMd, FFMdw, and FFMdwb. Similar results were observed when the data were analyzed by gender. The TOBEC estimate of FFM was equivalent to the estimates of FFM derived from one-, two-, and three-component models. Its ease of measurement and its prediction accuracy (R2 = 0.933; SEE = 2.45 kg) in teen-agers make it a preferred technique for body composition assessment.

Energy expenditure and physical performance in overweight women: response to training with and without caloric restriction

The metabolic effects of exercise training and the influence of a moderate calorie restriction on the training response were examined in overweight women. Ten healthy women, 119% to 141% of desirable weight, completed the 14-week study. After a 2-week stabilization period, in which diets were designed to maintain body weight (BW), five women were assigned to a 12-week experimental program of diet and exercise (D + EX) that included a 50% reduction in energy intake and a program of moderate intensity aerobic exercise 6 days per week. The other five women were assigned to the same daily exercise (EX) and continued to consume the stabilization diet. Periodic measurements of resting metabolic rate (RMR), thermic effect of food (TEF), energy cost of exercise, and predicted maximal aerobic capacity (VO2 max) were obtained, and the respiratory quotient (RQ) was determined during rest and exercise. Body composition was monitored weekly. Tests of strength and anaerobic capacity were conducted. D + EX lost an average of approximately 1.1 kg/wk, which was 67% fat, 33% lean. EX lost approximately 0.5 kg/wk, which was 86% fat, 14% lean. In both groups, the exercise program resulted in an 11% to 13% improvement in VO2 max and an 8% to 16% decrease in energy expenditure at submaximal workloads. The caloric restriction significantly increased fat utilization during exercise. The RMR declined 9% in D + EX, from 1,550 to 1,411 kcal/d, whereas it was maintained in EX, 1,608 to 1,626 kcal/d. The decrease in RMR observed in D + EX was consistent with the loss of fat-free mass (FFM).(ABSTRACT TRUNCATED AT 250 WORDS)

Use of total-body electrical conductivity for the assessment of body composition in middle-aged and elderly individuals

Body composition was predicted for 114 middle-aged and elderly individuals aged 35-90 y by using total-body electrical conductivity (TOBEC), densitometry, and hydrometry. Highly significant correlations were achieved between the TOBEC Phase value and fat-free mass (FFM) determined by densitometry (FFMd) and hydrometry (FFMdw) with values ranging from 0.713 to 0.981. TOBEC predicted FFM (FFMT) was consistently higher than either FFMd or FFMdw for both men and women in all age groups. A theoretical calculation of percent body fat was performed with a three-component model with body density, total body water, and bone mineral content. The recalculation of fat was used to estimate a new FFM (FFMnew). These calculations resulted in a decrease in fat and an increase in FFMnew. Because the TOBEC signal is unaffected by bone mineralization, FFMT may provide a more accurate estimation of body composition than do FFMd or FFMdw in this group of individuals.

Age as a factor in the hemodynamic responses to isometric exercise

This study was designed to determine the effect of isometric contractions of the finger flexors and leg extensor muscle groups on the cardiovascular responses of men 18-31 and 50-71 years of age. A 2X2X4 split-plot design was carried out with men representing two age groups, using two muscle groups and performing isometric contractions at four different intensities. Analysis of variance indicated significant differences for all main effects. The systolic and diastolic blood pressures were found to be (1) higher for the leg extension contractions compared to the finger flexion contractions, (2) higher for each increment in %MVC workload, and (3) higher for the older individuals. Heart rate responses were found to be (1) higher for the leg extension exercises, (2) higher with each increase in %MVC, and (3) higher for the younger subjects. Stroke volumes demonstrated (1) higher values for the young men at each workload, (2) lower values for leg extension exercises, and (3) a greater decline with longer contraction times. The older individuals had higher pressor responses than did the younger subjects, higher pressor and heart rate responses were observed with isometric leg extension exercises and increasing %MVC levels, and the older subjects had lower stroke volume responses compared to the younger subjects.

Comparison of physiological responses to maximal arm exercise among able-bodied, paraplegics and quadriplegics

A comparison of pulmonary, cardiovascular and metabolic responses was made in 32 subjects consisting of 11 able-bodied, 8 paraplegics (T4-L3 lesions) and 13 quadriplegics (C5-C8 lesions) during maximal arm cranking exercise. A progressive continuous arm cranking test, modified for each group, was employed to elicit maximal responses with pulmonary and metabolic determinations made with open circuit spirometry and selected cardiovascular measurements made by impedance cardiography. Additionally, non-exercise static and dynamic lung function assessments were made. Quadriplegics had significantly lower (p less than 0.05) tidal volumes, vital capacities, forced expiratory volumes at 1 seconds, and maximal breathing capacities than the other two groups. The mean peak VO2 during maximal arm cranking was 28.2, 25.3 and 12.0 ml/kg.min for the able-bodied (AB), paraplegics (PP) and quadriplegics (QP), respectively. Furthermore, reduced cardiovascular function was observed in the QP as evident in the low peak HR (109 b/min), peak SV (52 ml/b) and peak Q (5.7 l/min). Values for the QP were 64% and 64% peak HR, 89% and 50% peak SV and 54% and 33% peak Q of values observed for the PP and AB groups, respectively. The peak SV and Q values were significantly lower (P less than 0.05) for the PP group when compared with the AB group. Although not statistically significant the estimated a-v O2 difference was higher for both spinal cord injured groups (14.0 and 14.6 ml O2/100 ml, PP and QP respectively). The impaired work capacity and reduced oxygen transport and utilisation of the QP group can be attributed to impaired sympathetic cardiac stimulation and a smaller available active muscle mass.

Use of total-body electrical conductivity for monitoring body composition changes during weight reduction

The ability of a new total-body electrical conductivity instrument (TOBEC) to monitor changes in body composition during weight reduction was examined. Twelve moderately overweight women were confined to a metabolic unit for a period of 8 wk, 2-wk baseline and 6-wk reduction periods, during which changes in body composition were assessed by densitometry and hydrometry. Additionally, TOBEC measures were taken to predict lean body mass (LBM) changes. A total of 6.6 kg body weight was lost during the 6-wk reduction period. A decline in LBM was observed during the first 3 wk of reduction, from 47.4 to 45.7 kg, with no further LBM decline observed. Changes observed in the TOBEC phase value corresponded to the observed changes in LBM and total body water (TBW) during baseline and reduction periods. TOBEC was sensitive to small changes in LBM and TBW and may be useful for monitoring composition changes during nutritional intervention programs.

TOBEC methodology for body composition assessment: a cross-validation study

The accuracy of prediction equations for estimating lean body mass (LBM) from total-body electrical conductivity (TOBEC) was examined by cross-validation. Two samples of adults, aged 18-35 yr, were drawn from separate geographic locations. LBM was determined by densitometry and TOBEC was measured with TOBEC II instrument. LBM and TOBEC were highly correlated in both samples (r = 0.96 and 0.97). Cross-validation of LBM prediction equations was accomplished by exchanging equations and comparing predicted LBM values. There was a mean difference of 0.974 kg LBM between the two equations (p less than 0.0001). Thus, data from 157 subjects were pooled and one equation was developed that incorporated height (cm), sex (males = 0, females = 1), and the zero-, first-, and second-order Fourier coefficients (FC0, FC1, and FC2) of the TOBEC phase value: LBM, kg = -36.410 + (-1.324 X sex) + (0.01185 X (FC1(0.5)xht)) + (12.347 X FC2(0.5)) + (0.0627 X FC0)-(0.9232 X FC2) This equation, developed from 157 subjects, accounted for 96% of the variability in LBM and had a standard error of estimate of 2.17 kg LBM.