Moderate energy restriction increases bone resorption in obese postmenopausal women

BACKGROUND

Weight reduction reduces bone mineral density (BMD) and increases the risk of osteoporosis.

OBJECTIVE

We investigated whether bone is mobilized in postmenopausal women during energy restriction and whether hormones regulate bone turnover and mass.

DESIGN

Twenty-seven obese postmenopausal women with a mean (+/-SD) age of 55.9 +/- 7.9 y and body mass index (in kg/m(2)) of 33.0 +/- 3.8 completed the 6-mo study. Fourteen women followed a moderate energy-restricted diet (WL group) and 13 control subjects maintained their body weight (WM group). Body weight, bone turnover markers, serum parathyroid hormone (PTH), and dietary intake were measured throughout the study. Total-body BMD, sex hormone binding globulin, leptin, and estrone were measured at baseline and at week 25.

RESULTS

In the WL group, body weight decreased by 10.2 +/- 5.5% (P < 0.001), body fat mass decreased by 18.7 +/- 11.3% (P < 0.001), and total-body BMD decreased by 1.2 +/- 1.2%; these changes were significantly different from those in the WM group (P < 0.05). Serial measurements showed chronically elevated rates of bone resorption and formation during energy restriction that were greater than in the WM group (P < 0.05). Serum sex hormone binding globulin increased and leptin decreased with weight loss (P < 0.05). Serum PTH tended to increase in the WL group but not in the WM group (P < 0.06). The reduction in fat mass with weight loss was directly associated with a decrease in serum estrone (P < 0.01, R(2) = 0.50).

CONCLUSIONS

Moderate energy restriction increases bone turnover in obese postmenopausal women and may be regulated in part by alterations in serum PTH and estrone.

Unreliable use of standard muscle hydration value in obesity

Intramuscular water content is assumed to be constant in humans independent of their anthropometric characteristics. To verify whether this assumption is correct, intramuscular water, proteins, glycogen, and both total and intramyocytic triglycerides were measured in 51 samples of rectus abdominis muscle obtained from 16 lean and 35 overweight and obese subjects (body mass index cutoff 24.9 kg/m2). Data (referred to as wet tissue) were analyzed by means of a composition model at the cellular level of the skeletal muscle (SM). The average SM water content was 76.3 +/- 3.3% in normal-weight individuals and 65.7 +/- 5.8% in obese subjects (P < 0.0001). Total triglycerides were 5.5 +/- 2.3% in controls and 19.0 +/- 7.0% in obese subjects (P < 0.0001). The intramyocytic triglyceride fraction was also increased in obese subjects. The composition model provides an explanation for the negative correlation between total triglycerides and intramuscular water, and some of the model parameters were determined from the experimental data. In conclusion, although the hydration of fat-free SM mass may be unchanged in obese subjects, the hydration of in toto muscle mass decreases as its lipid content increases.

Skeletal muscle mass and aging: regional and whole-body measurement methods

Skeletal muscle is a large compartment that can now be quantified using research and clinically applicable regional and whole-body methods. The most important advances are the two imaging methods, computed tomography (CT) and magnetic resonance imaging (MRI). Both CT and MRI can serve as regional and whole-body reference methods when evaluating other approaches for estimating skeletal muscle mass. Imaging methods also afford the opportunity to quantify both anatomic skeletal muscle and the smaller adipose-tissue free skeletal muscle component. Other available methods for estimating skeletal muscle, either regional or at the whole body level, include dual-energy x-ray absorptiometry, in vivo neutron activation analysis-whole body counting, anthropometry, ultrasound, bioimpedance analysis, and urinary metabolite markers. Each method is reviewed in the context of the aging process, cost, availability, practicality, and desired accuracy. New insights should be possible when skeletal muscle mass, measured using these methods, is combined with other descriptors of muscle biochemical and mechanical function.

Is body mass index a measure of adiposity in elderly women?

OBJECTIVE

To evaluate the accuracy of body mass index (BMI) as a predictor of body fat in elderly women.

RESEARCH METHODS AND PROCEDURES

A total of 1423 women aged 67 +/- 5 (mean +/- SD, range: 60 to 88) years were consecutively enrolled into the study. Fat mass (FM) was measured using DXA.

RESULTS

BMI explained 72.9% of FM variance (p < 0.0001), with a root mean square error of estimate (RMSE) of 3.5 kg. After standardization of RMSE on the dependent variable as RMSE%, the prediction error equaled 15%. BMI explained 54.8% of FM% variance (p < 0.0001), with an RMSE of 4.1%, corresponding to an RMSE% of 11%.

DISCUSSION

The relatively high RMSE% of the FM and FM%-BMI associations caution against the use of BMI as an adiposity index in individual elderly women. However, an error corresponding to 11% of FM% may be accepted for population studies of body fat in elderly women.

Alternative treatments for weight loss: a critical review

"Nontraditional" or "alternative" treatments are extremely popular, especially with respect to obesity and body composition. Although such treatments are widely used, it is not clear that these are supported by the existing data in the peer-reviewed literature. Herein, we review the data on 18 methods/products advocated as potential anti-obesity/fat-reducing agents. We have found that none have been convincingly demonstrated to be safe and effective in two or more peer-reviewed publications of randomized double-blind placebo-controlled trials conducted by at least two independent laboratories. Nevertheless, some have plausible mechanisms of action and encouraging preliminary data that are sufficiently provocative to merit further research.

Dual-energy X-ray absorptiometry: analysis of pediatric fat estimate errors due to tissue hydration effects

Dual-energy X-ray absorptiometry (DXA) percent (%) fat estimates may be inaccurate in young children, who typically have high tissue hydration levels. This study was designed to provide a comprehensive analysis of pediatric tissue hydration effects on DXA %fat estimates. Phase 1 was experimental and included three in vitro studies to establish the physical basis of DXA %fat-estimation models. Phase 2 extended phase 1 models and consisted of theoretical calculations to estimate the %fat errors emanating from previously reported pediatric hydration effects. Phase 1 experiments supported the two-compartment DXA soft tissue model and established that pixel ratio of low to high energy (R values) are a predictable function of tissue elemental content. In phase 2, modeling of reference body composition values from birth to age 120 mo revealed that %fat errors will arise if a "constant" adult lean soft tissue R value is applied to the pediatric population; the maximum %fat error, approximately 0.8%, would be present at birth. High tissue hydration, as observed in infants and young children, leads to errors in DXA %fat estimates. The magnitude of these errors based on theoretical calculations is small and may not be of clinical or research significance.

Lower limb skeletal muscle mass: development of dual-energy X-ray absorptiometry prediction model

Although magnetic resonance imaging (MRI) can accurately measure lower limb skeletal muscle (SM) mass, this method is complex and costly. A potential practical alternative is to estimate lower limb SM with dual-energy X-ray absorptiometry (DXA). The aim of the present study was to develop and validate DXA-SM prediction equations. Identical landmarks (i.e., inferior border of the ischial tuberosity) were selected for separating lower limb from trunk. Lower limb SM was measured by MRI, and lower limb fat-free soft tissue was measured by DXA. A total of 207 adults (104 men and 103 women) were evaluated [age 43 +/- 16 (SD) yr, body mass index (BMI) 24.6 +/- 3.7 kg/m(2)]. Strong correlations were observed between lower limb SM and lower limb fat-free soft tissue (R(2) = 0.89, P < 0.001); age and BMI were small but significant SM predictor variables. In the cross-validation sample, the differences between MRI-measured and DXA-predicted SM mass were small (-0.006 +/- 1.07 and -0.016 +/- 1.05 kg) for two different proposed prediction equations, one with fat-free soft tissue and the other with added age and BMI as predictor variables. DXA-measured lower limb fat-free soft tissue, along with other easily acquired measures, can be used to reliably predict lower limb skeletal muscle mass.

Interactions among sex, HIV infection, and fat redistribution

The interactions among sex, HIV infection, and body fat redistribution are uncertain. We retrospectively compared total, subcutaneous, and visceral adipose tissue (TAT, SAT, VAT) contents, as determined by whole body MRI, in 85 HIV-infected persons, including 48 HIV-positive persons with self-reported changes in body shape, and matched healthy controls. The effect of sex on regional fat contents differed among HIV-infected persons with and without self-reported changes in body shape. Women without changes had significantly less SAT and TAT than did controls, while men with changes had significantly less SAT and TAT than did controls. Higher contents of VAT were found in both men and women with self-reported changes in body shape.

Resting energy expenditure-fat-free mass relationship: new insights provided by body composition modeling

The relationship between resting energy expenditure (REE) and metabolically active fat-free mass (FFM) is a cornerstone in the study of physiological aspects of body weight regulation and human energy requirements. Important questions, however, remain unanswered regarding the observed linear REE-FFM association in adult humans. This led us to develop a series of REE-body composition models that provide insights into the widely used simple linear REE-FFM prediction model derived experimentally in adult humans. The new models suggest that the REE-FFM relationship in mammals as a whole is curvilinear, that a segment of this function within a FFM range characteristic of adult humans can be fit with a linear equation almost identical to that observed from a composite review of earlier human studies, and that mammals as a whole exhibit a decrease in the proportion of FFM as high metabolic rate organs with greater FFM. The present study thus provides a new approach for examining REE-FFM relationships, advances in a quantitative manner previously observed albeit incompletely formulated REE-body composition associations, and identifies areas in need of additional research.

Total-body skeletal muscle mass: development and cross-validation of anthropometric prediction models

BACKGROUND

Skeletal muscle (SM) is a large body compartment of biological importance, but it remains difficult to quantify SM with affordable and practical methods that can be applied in clinical and field settings.

OBJECTIVE

The objective of this study was to develop and cross-validate anthropometric SM mass prediction models in healthy adults.

DESIGN

SM mass, measured by using whole-body multislice magnetic resonance imaging, was set as the dependent variable in prediction models. Independent variables were organized into 2 separate formulas. One formula included mainly limb circumferences and skinfold thicknesses [model 1: height (in m) and skinfold-corrected upperarm, thigh, and calf girths (CAG, CTG, and CCG, respectively; in cm)]. The other formula included mainly body weight (in kg) and height (model 2). The models were developed and cross-validated in nonobese adults [body mass index (in kg/m(2)) < 30].

RESULTS

Two SM (in kg) models for nonobese subjects (n = 244) were developed as follows: SM = Ht x (0.00744 x CAG(2) + 0.00088 x CTG(2) + 0.00441 x CCG(2)) + 2.4 x sex - 0.048 x age + race + 7.8, where R:(2) = 0.91, P: < 0.0001, and SEE = 2.2 kg; sex = 0 for female and 1 for male, race = -2.0 for Asian, 1.1 for African American, and 0 for white and Hispanic, and SM = 0.244 x BW + 7.80 x Ht + 6.6 x sex - 0.098 x age + race - 3.3, where R:(2) = 0.86, P: < 0.0001, and SEE = 2.8 kg; sex = 0 for female and 1 for male, race = -1.2 for Asian, 1.4 for African American, and 0 for white and Hispanic.

CONCLUSION

These 2 anthropometric prediction models, the first developed in vivo by using state-of-the-art body-composition methods, are likely to prove useful in clinical evaluations and field studies of SM mass in nonobese adults.

Healthy percentage body fat ranges: an approach for developing guidelines based on body mass index

BACKGROUND

Although international interest in classifying subject health status according to adiposity is increasing, no accepted published ranges of percentage body fat currently exist. Empirically identified limits, population percentiles, and z scores have all been suggested as means of setting percentage body fat guidelines, although each has major limitations.

OBJECTIVE

The aim of this study was to examine a potential new approach for developing percentage body fat ranges. The approach taken was to link healthy body mass index (BMI; in kg/m(2)) guidelines established by the National Institutes of Health and the World Health Organization with predicted percentage body fat.

DESIGN

Body fat was measured in subjects from 3 ethnic groups (white, African American, and Asian) who were screened and evaluated at 3 universities [Cambridge (United Kingdom), Columbia (United States), and Jikei (Japan)] with use of reference body-composition methods [4-compartment model (4C) at 2 laboratories and dual-energy X-ray absorptiometry (DXA) at all 3 laboratories]. Percentage body fat prediction equations were developed based on BMI and other independent variables.

RESULTS

A convenient sample of 1626 adults with BMIs < or =35 was evaluated. Independent percentage body fat predictor variables in multiple regression models included 1/BMI, sex, age, and ethnic group (R: values from 0.74 to 0.92 and SEEs from 2.8 to 5.4% fat). The prediction formulas were then used to prepare provisional healthy percentage body fat ranges based on published BMI limits for underweight (<18.5), overweight (> or =25), and obesity (> or =30).

CONCLUSION

This proposed approach and initial findings provide the groundwork and stimulus for establishing international healthy body fat ranges.

Correlations between skeletal muscle mass and bone mass in children 6-18 years: influences of sex, ethnicity, and pubertal status

A constant sex-specific relationship between skeletal muscle mass and bone mass was observed in healthy adults based on TBK/TBCa, using TBK (total body potassium) by 40K counting and TBCa (total body calcium) by in-vivo neutron activation analysis (Ellis and Cohn, 1975). We revisited this topic in children by studying correlations between TBK and TBCa, and by comparing TBK/TBCa between sexes, pubertal groups (prepubertal and pubertal) and ethnic groups in 141 white, 101 black, and 62 Asian healthy children, aged 6 - 18 years, living in New York City. TBK was measured by 40K counting, and TBCa by dual energy x-ray absorptiometry. TBK and TBCa were significantly correlated from 6 to 18 years (r > 0.93), but the correlation equations varied by gender and ethnicity. Boys had significantly more TBK and greater TBK/TBCa than girls at a given age and weight, reflecting greater skeletal muscle mass in boys from 6 years, the age at which the study started. TBK/TBCa in blacks was significantly smaller than whites and Asians in both sexes in prepuberty and puberty, and pubertal black girls had the smallest mean TBK/TBCa. No significant differences were found between whites and Asians. TBK/TBCa decreased as body weight increased in prepubertal girls, and decreased as body weight and age increased in pubertal girls, but did not change with body weight or age in boys of any subgroup. The inverse relationship between TBK/TBCa and age in pubertal girls suggests greater increase in TBCa compared to TBK than in other groups, while the constant TBK/TBCa in boys reflects proportional increases in TBK and TBCa. Thus TBK/TBCa can be used as an index of relative growth in skeletal muscle mass and bone mass in white, black, and Asian children according to sex, age and pubertal status.

Estimation of skeletal muscle mass by bioelectrical impedance analysis

The purpose of this study was to develop and cross-validate predictive equations for estimating skeletal muscle (SM) mass using bioelectrical impedance analysis (BIA). Whole body SM mass, determined by magnetic resonance imaging, was compared with BIA measurements in a multiethnic sample of 388 men and women, aged 18-86 yr, at two different laboratories. Within each laboratory, equations for predicting SM mass from BIA measurements were derived using the data of the Caucasian subjects. These equations were then applied to the Caucasian subjects from the other laboratory to cross-validate the BIA method. Because the equations cross-validated (i.e., were not different), the data from both laboratories were pooled to generate the final regression equation SM mass (kg) = [(Ht<SUP>2</SUP>/ <IT>R</IT> x 0.401) + (gender x 3.825) + (age x -0. 071)] + 5.102 where Ht is height in centimeters; R is BIA resistance in ohms; for gender, men = 1 and women = 0; and age is in years. The r(2) and SE of estimate of the regression equation were 0.86 and 2.7 kg (9%), respectively. The Caucasian-derived equation was applicable to Hispanics and African-Americans, but it underestimated SM mass in Asians. These results suggest that the BIA equation provides valid estimates of SM mass in healthy adults varying in age and adiposity.

Weight stability masks sarcopenia in elderly men and women

Skeletal muscle loss or sarcopenia in aging has been suggested in cross-sectional studies but has not been shown in elderly subjects using appropriate measurement techniques combined with a longitudinal study design. Longitudinal skeletal muscle mass changes after age 60 yr were investigated in independently living, healthy men (n = 24) and women (n = 54; mean age 73 yr) with a mean +/- SD follow-up time of 4.7 +/- 2.3 yr. Measurements included regional skeletal muscle mass, four additional lean components (fat-free body mass, body cell mass, total body water, and bone mineral), and total body fat. Total appendicular skeletal muscle (TSM) mass decreased in men (-0.8 +/- 1.2 kg, P = 0.002), consisting of leg skeletal muscle (LSM) loss (-0.7 +/- 0.8 kg, P = 0.001) and a trend toward loss of arm skeletal muscle (ASM; -0.2 +/- 0.4 kg, P = 0.06). In women, TSM mass decreased (-0.4 +/- 1.2 kg, P = 0.006) and consisted of LSM loss (-0.3 +/- 0.8 kg, P = 0.005) and a tendency for a loss of ASM (-0.1 +/- 0.6 kg, P = 0.20). Multiple regression modeling indicates greater rates of LSM loss in men. Body weight in men at follow-up did not change significantly (-0.5 +/- 3.0 kg, P = 0.44) and fat mass increased (+1.2 +/- 2.4 kg, P = 0.03). Body weight and fat mass in women were nonsignificantly reduced (-0.8 +/- 3.9 kg, P = 0.15 and -0.8 +/- 3.5 kg, P = 0.12). These observations suggest that sarcopenia is a progressive process, particularly in elderly men, and occurs even in healthy independently living older adults who may not manifest weight loss.

Weight loss in postmenopausal obesity: no adverse alterations in body composition and protein metabolism

We sought to determine if decrements in the mass of fat-free body mass (FFM) and other lean tissue compartments, and related changes in protein metabolism, are appropriate for weight loss in obese older women. Subjects were 14 healthy weight-stable obese (BMI > or =30 kg/m(2)) postmenopausal women >55 yr who participated in a 16-wk, 1, 200 kcal/day nutritionally complete diet. Measures at baseline and 16 wk included FFM and appendicular lean soft tissue (LST) by dual-energy X-ray absorptiometry; body cell mass (BCM) by (40)K whole body counting; total body water (TBW) by tritium dilution; skeletal muscle (SM) by whole body MRI; and fasting whole body protein metabolism through L-[1-(13)C]leucine kinetics. Mean weight loss (+/-SD) was 9.6+/-3.0 kg (P<0.0001) or 10.7% of initial body weight. FFM decreased by 2.1+/-2.6 kg (P = 0.006), or 19.5% of weight loss, and did not differ from that reported (2.3+/-0.7 kg). Relative losses of SM, LST, TBW, and BCM were consistent with reductions in body weight and FFM. Changes in [(13)C]leucine flux, oxidation, and synthesis rates were not significant. Follow-up of 11 subjects at 23.7 +/-5.7 mo showed body weight and fat mass to be below baseline values; FFM was nonsignificantly reduced. Weight loss was accompanied by body composition and protein kinetic changes that appear appropriate for the magnitude of body mass change, thus failing to support the concern that diet-induced weight loss in obese postmenopausal women produces disproportionate LST losses.

Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr

We employed a whole body magnetic resonance imaging protocol to examine the influence of age, gender, body weight, and height on skeletal muscle (SM) mass and distribution in a large and heterogeneous sample of 468 men and women. Men had significantly (P < 0.001) more SM in comparison to women in both absolute terms (33.0 vs. 21.0 kg) and relative to body mass (38.4 vs. 30.6%). The gender differences were greater in the upper (40%) than lower (33%) body (P < 0.01). We observed a reduction in relative SM mass starting in the third decade; however, a noticeable decrease in absolute SM mass was not observed until the end of the fifth decade. This decrease was primarily attributed to a decrease in lower body SM. Weight and height explained approximately 50% of the variance in SM mass in men and women. Although a linear relationship existed between SM and height, the relationship between SM and body weight was curvilinear because the contribution of SM to weight gain decreased with increasing body weight. These findings indicate that men have more SM than women and that these gender differences are greater in the upper body. Independent of gender, aging is associated with a decrease in SM mass that is explained, in large measure, by a decrease in lower body SM occurring after the fifth decade.

Anthropometry and methods of body composition measurement for research and field application in the elderly

Evaluation of body composition is important in the study of human energy and protein metabolism as methods are available for quantifying energy stores and protein content at a single point in time; energy-protein balance can be monitored over time; and dynamic measures of energy and protein metabolism can be referenced to body mass and related measurable components for between-individual comparisons. This review emphasizes the need for considering subject age when developing body composition component prediction models that are applied in elderly populations. An overview of body composition research is provided that emphasizes compartment and level definitions and interrelations. Two broad method categories, mechanistic and descriptive, are then critically examined in relation to their role in energy-protein metabolism and aging research. Our collective review indicates that all major body composition components are now measurable using one or more methods that are based on non age-dependent assumptions. We also found that some methods, particularly descriptive field methods (eg anthropometry), may be based on age-sensitive assumptions and measurements and suggestions for future development of these methods are provided. Lastly, as body composition differences between races, cultures, and countries are now recognized, it would be useful to create international cooperative groups with the aim of developing widely applicable descriptive field methods based on simple available techniques such as anthropometry and bioimpedance analysis.

Effects of weight loss with orlistat on glucose tolerance and progression to type 2 diabetes in obese adults

BACKGROUND

Orlistat is a gastrointestinal lipase inhibitor that reduces dietary fat absorption by approximately 30%, promotes weight loss, and may reduce the risk of developing impaired glucose tolerance and type 2 diabetes in obese subjects.

OBJECTIVE

To test the hypothesis that orlistat combined with dietary intervention improves glucose tolerance status and prevents worsening of diabetes status more effectively than placebo.

METHODS

We pooled data from 675 obese (body mass index, 30-43 kg/m2) adults at 39 US and European research centers in 3 randomized, double-blind, placebo-controlled multicenter clinical trials. Subjects received placebo plus a low-energy diet during a 4-week lead-in period. On study day 1, the diet was continued, and subjects were randomized to receive placebo 3 times a day (n=316) or treatment with orlistat, 120 mg 3 times a day (n=359), for 104 weeks. A standard 3-hour oral glucose tolerance test was performed on day 1 and at the end of treatment.

MAIN OUTCOME MEASURES

The categorical assessment of glucose tolerance status (normal, impaired, diabetic) and changes in status from randomization to end of treatment were the primary efficacy measures. The secondary measures were fasting and postchallenge glucose and insulin levels.

RESULTS

The mean length of follow-up was 582 days. Subjects who were treated with orlistat lost more weight (mean +/- SEM, 6.72 +/- 0.41 kg from initial weight) than subjects who received placebo (3.79+/-0.38 kg; P<.001). A smaller percentage of subjects with impaired glucose tolerance at baseline progressed to diabetic status in the orlistat (3.0%) vs placebo (7.6%) group. Conversely, among subjects with impaired glucose tolerance at baseline, glucose levels normalized in more subjects after orlistat treatment (71.6%) vs placebo (49.1%; P=.04).

CONCLUSIONS

The addition of orlistat to a conventional weight loss regimen significantly improved oral glucose tolerance and diminished the rate of progression to the development of impaired glucose tolerance and type 2 diabetes.

Body composition modeling. Application to exploration of the resting energy expenditure fat-free mass relationship

There are now many published methods for predicting resting energy expenditure (REE) from measured body mass and composition. Although these published reports extend back almost a century, new related studies appear on a regular basis. It remains unclear what the similarities and differences are between these many methods and what, if any, advantages the newly introduced REE prediction models offer. These issues led us to develop an organizational system for REE prediction methods with the ultimate aim of clarifying prevailing ambiguities in the field. Our classification scheme is founded on the mathematical function type (descriptive and mechanistic) and body composition level (whole body-->molecular) used in REE prediction model development. The model is applied in an exploration of the well-established empirical relationship between REE and fat-free body mass (FFM). The developed relationships indicate that REE vs. FFM is a curvilinear relationship in mammals as a whole, that the relationship can be described as a linear function in humans, and that the simple linear regression line coefficients can be reconstructed from established tissue-system level component relationships. Our classification system, the first founded on a conceptual basis, highlights similarities and differences between the many diverse REE body composition prediction methods, provides a framework for teaching REE-body composition relationships to students, and suggests important future research opportunities.

Cellular-level body composition model. A new approach to studying fat-free mass hydration

Fat-free mass hydration, the ratio of total body water (TBW) to fat-free mass (FFM), is stable at approximately 0.73 in mammals, and this constancy provides a means of estimating total body fat in vivo. As there is no mechanistic theory to explain the magnitude and variability in TBW/FFM, the present investigation describes a cellular-level model indicating that FFM hydration is determined by four factors: body cell mass hydration, extracellular fluid hydration, ratio of extracellular solids to TBW, and ratio of extracellular water to intracellular water. According to the model, TBW/FFM can be predicted for adult humans as a mean of 0.73, and a variation range 0.69-0.77. The suggested modeling approach provides a conceptual framework for TBW-fat estimation method and identifies important areas that remain to be studied.