Body composition by DEXA in older adults: accuracy and influence of scan mode

Myths and Methodologies: Understanding the health impact of head down bedrest for the benefit of older adults and astronauts. Study protocol of the Canadian Bedrest Study

Weightlessness during spaceflight can harm various bodily systems, including bone density, muscle mass, strength and cognitive functions. Exercise appears to somewhat counteract these effects. A terrestrial model for this is head-down bedrest (HDBR), simulating gravity loss. This mirrors challenges faced by older adults in extended bedrest and space environments. The first Canadian study, backed by the Canadian Space Agency, Canadian Institutes of Health Research, and Canadian Frailty Network, aims to explore these issues. The study seeks to: (1) scrutinize the impact of 14-day HDBR on physiological, psychological and neurocognitive systems, and (2) assess the benefits of exercise during HDBR. Eight teams developed distinct protocols, harmonized in three videoconferences, at the McGill University Health Center. Over 26 days, 23 participants aged 55-65 underwent baseline measurements, 14 days of -6° HDBR, and 7 days of recovery. Half did prescribed exercise thrice daily combining resistance and endurance exercise for a total duration of 1 h. Assessments included demographics, cardiorespiratory fitness, bone health, body composition, quality of life, mental health, cognition, muscle health and biomarkers. This study has yielded some published outcomes, with more forthcoming. Findings will enrich our comprehension of HDBR effects, guiding future strategies for astronaut well-being and aiding bedrest-bound older adults. By outlining evidence-based interventions, this research supports both space travellers and those enduring prolonged bedrest.

Skinfold-based-equations to assess longitudinal body composition in children from birth to age 5 years

BACKGROUND & AIMS

In order to identify children at risk for excess adiposity, it is important to determine body composition longitudinally throughout childhood. However, most frequently used techniques in research are expensive and time-consuming and, therefore, not feasible for use in general clinical practice. Skinfold measurements can be used as proxy for adiposity, but current anthropometry-based-equations have random and systematic errors, especially when used longitudinally in pre-pubertal children. We developed and validated skinfold-based-equations to estimate total fat mass (FM) longitudinally in children aged 0-5 years.

METHODS

This study was embedded in the Sophia Pluto study, a prospective birth cohort. In 998 healthy term-born children, we longitudinally measured anthropometrics, including skinfolds and determined FM using Air Displacement Plethysmography (ADP) by PEA POD and Dual energy X-ray Absorptiometry (DXA) from birth to age 5 years. Of each child one random measurement was used in the determination cohort, others for validation. Linear regression was used to determine the best fitting FM-prediction model based on anthropometric measurements using ADP and DXA as reference methods. For validation, we used calibration plots to determine predictive value and agreement between measured and predicted FM.

RESULTS

Three skinfold-based-equations were developed for adjoined age ranges (0-6 months, 6-24 months and 2-5 years), based on FM-trajectories. Validation of these prediction equations showed significant correlations between measured and predicted FM (R: 0.921, 0.779 and 0.893, respectively) and good agreement with small mean prediction errors of 1, 24 and -96 g, respectively.

CONCLUSIONS

We developed and validated reliable skinfold-based-equations which may be used longitudinally from birth to age 5 years in general practice and large epidemiological studies.

Body composition and bone mineral density by Dual Energy X-ray Absorptiometry: Reference values for young children

BACKGROUND & AIMS

Childhood obesity is a global public health threat, with an alarming rise in incidence. Obesity at young age has short-term and long-term morbidity. It is, therefore, important to accurately assess body composition throughout infancy and childhood to identify excess adiposity. However, reference values for age 2-5 years, needed to interpret measurements and identify young children at risk, are lacking. Our primary objective was to fill the current gap in reference values by constructing sex-specific body composition reference values and charts for fat mass (FM), fat mass percentage (FM%), fat mass index (FMI), lean body mass (LBM), lean body mass index (LBMI) and total body less head bone mineral density (BMD_TBLH) for children aged 2-5 years using Dual-Energy X-ray Absorptiometry (DXA).

METHODS

We performed 599 accurate DXA-measurements in 340 term-born children aged 2-5 years, using Lunar Prodigy with Encore software (V14.1). Using GAMLSS, sex-specific reference values and charts were created for FM, FM%, FMI, LBM, LBMI and BMD_TBLH.

RESULTS

Sex-specific body composition reference values and charts for age 2-5 years were constructed. In boys and girls, FM and LBM increased from age 2-5 years (all p ≤ 0.001), but body size-corrected FM% and FMI decreased (all p ≤ 0.023). LBMI remained similar between 2 and 5 years of age. Girls had higher FM, FM% and FMI and lower LBM and LBMI compared to boys. BMC and BMD_TBLH increased with age between 2 and 5 years of age (all p < 0.001) and were similar for boys and girls.

CONCLUSIONS

We present sex-specific reference values and charts for body composition and total body bone mineral density measured by DXA, based on a large cohort of healthy children aged 2-5 years. These longitudinal references can be used for clinical practice and research purposes to monitor body composition and bone mineral density development and identify children at risk for excess adiposity.

High baseline fat mass, but not lean tissue mass, is associated with high intensity low back pain and disability in community-based adults

Objectives

Low back pain is the largest contributor to disability worldwide. The role of body composition as a risk factor for back pain remains unclear. Our aim was to examine the relationship between fat mass and fat distribution on back pain intensity and disability using validated tools over 3 years.

Methods

Participants (aged 25–60 years) were assessed at baseline using dual-energy X-ray absorptiometry (DXA) to measure body composition. All participants completed the Chronic Pain Grade Scale at baseline and 3-year follow-up. Of the 150 participants, 123 (82%) completed the follow-up.

Results

Higher baseline body mass index (BMI) and fat mass (total, trunk, upper limb, lower limb, android, and gynoid) were all associated with high intensity back pain at either baseline and/or follow-up (total fat mass: multivariable OR 1.05, 95% CI 1.01–1.09, p < 0.001). There were similar findings for all fat mass measures and high levels of back disability. A higher android to gynoid ratio was associated with high intensity back pain (multivariable OR 1.04, 95% CI 1.01–1.08, p = 0.009). There were no associations between lean mass and back pain.

Conclusions

This cohort study provides evidence for the important role of fat mass, specifically android fat relative to gynoid fat, on back pain and disability.

The Use of a Stem and Leaf Aqueous Extract of Cissus quadrangularis (CQR-300) to Reduce Body Fat and Other Components of Metabolic Syndrome in Overweight Participants

BACKGROUND

Previous work had shown the ability of an aqueous leaf and stem extract of Cissus quandrangularis (300 mg of CQR, CQR-300) to improve components of metabolic syndrome (MS) in overweight individuals.

OBJECTIVE

This small pilot study aimed to confirm the efficacy of CQR-300 in reducing the percentage body fat measured using two different methods-bioelectrical impedance assay versus dual-energy X-ray absorptiometry (DEXA).

DESIGN

The study was an 8-week double-blind, placebo-controlled pilot trial on 67 individuals who were requested by a dietary counselor to maintain their normal exercise and dietary routines. Participants were randomly divided into two groups, placebo (32 participants) and the CQR-300 group (35 participants), and received 300 mg of corn starch or CQR-300 daily.

METHODS

Body fat was measured by bioelectrical impedance using a TANITA impedance meter and by DEXA, with blood samples taken at baseline and at 8 weeks for the measurement of lipid parameters.

RESULTS

After 8 weeks of treatment, participants of the placebo group showed a 1.05% decrease in body fat as determined by bioelectrical impedance analysis, but no difference using DEXA. In the same time period, the CQR-300 group had an 8.9% and 12.8% decreases in the body fat as measured by impedance and DEXA, respectively. These values were significantly (p < 0.05) lower than the placebo. Compared with the placebo, the CQR-300 group demonstrated significant (p < 0.05) decreases in the waist and hip circumferences, systolic and diastolic blood pressures, total cholesterol, triglycerides, fasting blood glucose, as well as leptin levels. On the contrary, there were significant (p < 0.05) increases in HDL-cholesterol and adiponectin levels.

CONCLUSION

CQR-300 administered as a single 300 mg dose daily was effective in reducing body fat as well as improving blood parameters associated with MS.

Fluid balance concepts in medicine: Principles and practice

The regulation of body fluid balance is a key concern in health and disease and comprises three concepts. The first concept pertains to the relationship between total body water (TBW) and total effective solute and is expressed in terms of the tonicity of the body fluids. Disturbances in tonicity are the main factor responsible for changes in cell volume, which can critically affect brain cell function and survival. Solutes distributed almost exclusively in the extracellular compartment (mainly sodium salts) and in the intracellular compartment (mainly potassium salts) contribute to tonicity, while solutes distributed in TBW have no effect on tonicity. The second body fluid balance concept relates to the regulation and measurement of abnormalities of sodium salt balance and extracellular volume. Estimation of extracellular volume is more complex and error prone than measurement of TBW. A key function of extracellular volume, which is defined as the effective arterial blood volume (EABV), is to ensure adequate perfusion of cells and organs. Other factors, including cardiac output, total and regional capacity of both arteries and veins, Starling forces in the capillaries, and gravity also affect the EABV. Collectively, these factors interact closely with extracellular volume and some of them undergo substantial changes in certain acute and chronic severe illnesses. Their changes result not only in extracellular volume expansion, but in the need for a larger extracellular volume compared with that of healthy individuals. Assessing extracellular volume in severe illness is challenging because the estimates of this volume by commonly used methods are prone to large errors in many illnesses. In addition, the optimal extracellular volume may vary from illness to illness, is only partially based on volume measurements by traditional methods, and has not been determined for each illness. Further research is needed to determine optimal extracellular volume levels in several illnesses. For these reasons, extracellular volume in severe illness merits a separate third concept of body fluid balance.

Early body composition, but not body mass, is associated with future accelerated decline in muscle quality

BACKGROUND

Muscle quality (MQ) or strength-to-mass ratio declines with aging, but the rate of MQ change with aging is highly heterogeneous across individuals. The identification of risk factors for accelerated MQ decline may offer clues to identity the underpinning physiological mechanisms and indicate targets for prevention and treatment. Using data from the Baltimore Longitudinal Study of Aging, we tested whether measures of body mass and body composition are associated with differential rates of changes in MQ with aging.

METHODS

Participants included 511 men and women, aged 50 years or older, followed for an average of 4 years (range: 1-8). MQ was operationalized as ratio between knee-extension isokinetic strength and CT-thigh muscle cross-sectional area. Predictors included body mass and body composition measures: weight (kg), body mass index (BMI, kg/m² ), dual-energy x-ray absorptiometry-measured total body fat mass (TFM, kg) and lean mass (TLM, kg), and body fatness (TFM/weight). Covariates were baseline age, sex, race, and body height.

RESULTS

Muscle quality showed a significant linear decline over the time of the follow up (average rate of decline 0.02 Nm/cm² per year, P < .001). Independent of covariates, neither baseline body weight (P = .756) nor BMI (P = .777) was predictive of longitudinal rate of decline in MQ. Instead, higher TFM and lower TLM at baseline predicted steeper longitudinal decline in MQ (P = .036 and P < .001, respectively). In particular, participants with both high TFM and low TLM at baseline experienced the most dramatic decline compared with those with low TFM and high TLM (about 3% per year vs. 0.5% per year, respectively). Participants in the higher tertile of baseline body fatness presented a significantly faster decline of MQ than the rest of the population (P = .021). Similar results were observed when body mass, TFM, and TLM were modeled as time-dependent predictors.

CONCLUSIONS

Body composition, but not weight nor BMI, is associated with future MQ decline, suggesting that preventive strategies aimed at maintaining good MQ with aging should specifically target body composition features.

Body mass index, body fat, and nutritional status of patients with heart failure: The PLICA study

BACKGROUND & AIMS

Nutritional assessment may help to explain the incompletely understood obesity paradox in patients with heart failure (HF). Currently, obesity is usually identified by body mass index (BMI). Our objective was to assess the prognostic influence of undernourishment in HF outpatients.

METHODS

Two published definitions of undernourishment were used to assess 214 ambulatory HF patients. Definition 1 included albumin, total lymphocyte count, tricipital skinfold (TS), subscapular skinfold, and arm muscle circumference (AMC) measurements (≥2 below normal considered undernourishment). Definition 2 included TS, AMC, and albumin (≥1 below normal considered undernourishment). Patients were also stratified by BMI and body fat percentage and followed for 2 years. All-cause death or HF hospitalization was the primary endpoint.

RESULTS

Based on BMI strata, among underweight patients, 60% and 100% were undernourished by Definitions 1 and 2, respectively (31% and 44% among normal-weight, 4% and 11% among overweight, and 0% and 3% among obese patients, respectively, according to the two definitions). The most prevalent undernourishment type was marasmus-like (18% of the total cohort). Undernourishment by both definitions was significantly associated with lower event-free survival. Following multivariable analysis, age, NYHA functional class, NTproBNP, and undernourishment (hazard ratio [HR] 2.25 [1.11-4.56] and 2.24 [1.19-4.21] for Definitions 1 and 2, respectively) remained in the model. In this cohort, BMI and percentage of body fat did not independently predict 2-year event-free survival.

CONCLUSIONS

Nutritional status is a key prognostic factor in HF above and beyond BMI and percentage of body fat. Patients in normal BMI range and even in overweight and obese groups showed undernourishment. The high mortality observed in undernourishment, infrequent in high BMI patients, may help to partly explain the obesity paradox. Proper undernourishment assessment should become routine in patients with HF.

Energy Metabolism and the Burden of Multimorbidity in Older Adults: Results From the Baltimore Longitudinal Study of Aging

Excessively elevated resting metabolic rate (RMR) for persons of a certain age, sex, and body composition is a mortality risk factor. Whether elevated RMR constitutes an early marker of health deterioration in older adult has not been fully investigated. Using data from the Baltimore Longitudinal Study of Aging, we hypothesized that higher RMR (i) was cross-sectionally associated with higher multimorbidity and (ii) predicted higher multimorbidity in subsequent follow-ups. The analysis included 695 Baltimore Longitudinal Study of Aging participants, aged 60 or older at baseline, of whom 248 had follow-up data available 2 years later and 109 four years later. Multimorbidity was assessed as number of chronic diseases. RMR was measured by indirect calorimetry and was tested in regression analyses adjusted for covariates age, sex, and dual-energy x-ray absorptiometry-measured total body fat mass and lean mass. Baseline RMR and multimorbidity were positively associated, independent of covariates (p = .002). Moreover, in a three-wave bivariate autoregressive cross-lagged model adjusted for covariates, higher prior RMR predicted greater future multimorbidity above and beyond the cross-sectional and autoregressive associations (p = .034). RMR higher than expected, given age, sex, and body composition, predicts future higher multimorbidity in older adults and may be used as early biomarker of impending health deterioration. Replication and the development of normative data are required for clinical translation.

Influence of exercise on the metabolic profile caused by 28 days of bed rest with energy deficit and amino acid supplementation in healthy men

OBJECTIVE

Muscle loss and metabolic changes occur with disuse [i.e. bed rest (BR)]. We hypothesized that BR would lead to a metabolically unhealthy profile defined by: increased circulating tumor necrosis factor (TNF)-α, decreased circulating insulin-like-growth-factor (IGF)-1, decreased HDL-cholesterol, and decreased muscle density (MD; measured by mid-thigh computerized tomography).

METHODS

We investigated the metabolic profile after 28 days of BR with 8 ± 6% energy deficit in male individuals (30-55 years) randomized to resistance exercise with amino acid supplementation (RT, n=24) or amino acid supplementation alone (EAA, n=7). Upper and lower body exercises were performed in the horizontal position. Blood samples were taken at baseline, after 28 days of BR and 14 days of recovery.

RESULTS

We found a shift toward a metabolically unfavourable profile after BR [compared to baseline (BLN)] in both groups as shown by decreased HDL-cholesterol levels (EAA: BLN: 39 ± 4 vs. BR: 32 ± 2 mg/dL, RT: BLN: 39 ± 1 vs. BR: 32 ± 1 mg/dL; p<0.001) and Low MD (EAA: BLN: 27 ± 4 vs. BR: 22 ± 3 cm(2), RT: BLN: 28 ± 2 vs. BR: 23 ± 2 cm(2); p<0.001). A healthier metabolic profile was maintained with exercise, including NormalMD (EAA: BLN: 124 ± 6 vs. BR: 110 ± 5 cm(2), RT: BLN: 132 ± 3 vs. BR: 131 ± 4 cm(2); p<0.001, time-by-group); although, exercise did not completely alleviate the unfavourable metabolic changes seen with BR. Interestingly, both groups had increased plasma IGF-1 levels (EAA: BLN:168 ± 22 vs. BR 213 ± 20 ng/mL, RT: BLN:180 ± 10 vs. BR: 219 ± 13 ng/mL; p<0.001) and neither group showed TNFα changes (p>0.05).

CONCLUSIONS

We conclude that RT can be incorporated to potentially offset the metabolic complications of BR.

The Official Positions of the International Society for Clinical Densitometry: acquisition of dual-energy X-ray absorptiometry body composition and considerations regarding analysis and repeatability of measures

In preparation for the International Society for Clinical Densitometry Position Development Conference of 2013 in Tampa, Florida, Task Force 2 was created as 1 of 3 task forces in the area of body composition assessment by dual-energy X-ray absorptiometry (DXA). The assignment was to review the literature, summarize the relevant findings, and formulate positions covering (1) accuracy and precision assessment, (2) acquisition of DXA body composition measures in patients, and (3) considerations regarding analysis and repeatability of measures. There were 6 primary questions proposed to the task force by the International Society for Clinical Densitometry board and expert panel. Based on a series of systematic reviews, 14 new positions were developed, which are intended to augment and define good clinical practice in quantitative assessment of body composition by DXA.

Validation of longitudinal DXA changes in body composition from pre- to mid-adolescence using MRI as reference

Dual-energy X-ray absorptiometry (DXA) has been used extensively for bone mineral density and body composition assessments. Surprisingly, the role of DXA in monitoring changes in children's body composition, using direct imaging methods such as magnetic resonance imaging (MRI) as reference, is still yet to be validated. We aimed at validating the use of DXA in monitoring change in the thigh lean soft tissue mass (LSTM) and fat mass (FM) when compared with thigh skeletal muscle mass (SM) and FM, measured using MRI as the reference standard, from childhood to midadolescence. At baseline, 22 healthy children (16 boys and 6 girls) aged 8-11yr were included, and then recalled at pubertal stage Tanner2-Tanner4. LSTM-DXA and FM-DXA of the mid-third femur and SM-MRI and FM-MRI of the same region were measured on the same day. The same protocol was repeated 26-48mo later. At baseline, DXA overestimated LSTM-DXA on average by 222g (95% confidence interval [CI]: 33-410g) with a concordance C-LSTM=0.576. FM-MRI and FM-DXA were not significantly different (95% CI=213 to 199g, the C-FM=0.907). At follow-up, change in LSTM-DXA and FM-DXA were not significantly different to change in SM-MRI and FM-MRI, respectively (95% CI of the difference was -278 to 208g for LSTM, and -148 to 236g for FM). The coefficient of concordance between the 2 techniques was 0.88 for both LSTM and FM. This study validates the use of DXA in monitoring changes in LSTM and FM in children, confirming its significant potential in clinical and research roles in pediatric body composition.

Low-fat dietary pattern and change in body-composition traits in the Women's Health Initiative Dietary Modification Trial

BACKGROUND

The Women's Health Initiative Dietary Modification (DM) Trial was a randomized controlled trial that compared the effects of a low-fat (≤20% of total energy) or a usual diet in relation to chronic disease risk in postmenopausal women.

OBJECTIVE

We characterized long-term body-composition changes associated with the DM trial and potential modifiers of these associations.

DESIGN

In the DM trial, 48,835 women aged 50-79 y were randomly assigned to intervention (40%) or comparison (60%) groups. We studied a subset with whole-body dual-energy X-ray absorptiometry scans at baseline and during follow-up. Changes in fat mass (FM), lean mass (LM), and percentage body fat between the intervention (n = 1580) and comparison (n = 2731) groups at years 1, 3, and 6 were compared. By using generalized estimating equations, we calculated overall differences between groups and tested for interactions with age, diabetes, race-ethnicity (white, black, and Hispanic), body mass index (BMI), and hormone therapy (HT).

RESULTS

The intervention women experienced significantly greater reductions in percentage body fat, FM, and LM at years 1 and 3 than did women in the comparison group (all P < 0.05). At year 6, only the FM change was significantly different between groups. Overall, the intervention was associated with reductions in percentage body fat (-0.8%; 95% CI: -1.0%, -0.6%), FM (-1.1 kg; 95% CI: -1.3, -0.8 kg), and LM (-0.17 kg; 95% CI: -0.28, -0.06 kg) during follow-up (all P < 0.003). Intervention associations varied by race-ethnicity, BMI, diabetes, and HT and remained significant after adjustment for physical activity.

CONCLUSION

This intervention was associated with modest long-term body-composition changes; the findings were more robust in years 1 and 3. This trial was registered at clinicaltrials.gov as NCT00000611.

Effect of intra-dialytic, low-intensity strength training on functional capacity in adult haemodialysis patients: a randomized pilot trial

BACKGROUND

Kidney failure is associated with muscle wasting and physical impairment. Moderate- to high-intensity strength training improves physical performance, nutritional status and quality of life in people with chronic kidney disease and in dialysis patients. However, the effect of low-intensity strength training has not been well documented, thus representing the objective of this pilot study.

METHODS

Fifty participants (mean +/- SD, age 69 +/- 13 years) receiving long-term haemodialysis (3.7 +/- 4.2 years) were randomized to intra-dialytic low-intensity strength training or stretching (attention-control) exercises twice weekly for a total of 48 exercise sessions. The primary study outcome was physical performance assessed by the Short Physical Performance Battery score (SPPB) after 36 sessions, if available, or carried forward from 24 sessions. Secondary outcomes included lower body strength, body composition and quality of life. Measurements were obtained at baseline and at completion of 24 (mid), 36 (post) and 48 (final) exercise sessions.

RESULTS

Baseline median (IQR) SPPB score was 6.0 (5.0), with 57% of the participants having SPPB scores below 7. Exercise adherence was 89 +/- 15%. The primary outcome could be computed in 44 participants. SPPB improved in the strength training group compared to the attention-control group [21.1% (43.1%) vs. 0.2% (38.4%), respectively, P = 0.03]. Similarly, strength training participants exhibited significant improvements from baseline compared to the control group in knee extensor strength, leisure-time physical activity and self-reported physical function and activities of daily living (ADL) disability; all P < 0.02. Adverse events were common but not related to study participation.

CONCLUSIONS

Intra-dialytic, low-intensity progressive strength training was safe and effective among maintenance dialysis patients. Further studies are needed to establish the generalizability of this strength training program in dialysis patients.

Soy isoflavone supplementation and bone mineral density in menopausal women: a 2-y multicenter clinical trial

BACKGROUND

Isoflavones are naturally occurring plant estrogens that are abundant in soy. Although purported to protect against bone loss, the efficacy of soy isoflavone supplementation in the prevention of osteoporosis in postmenopausal women remains controversial.

OBJECTIVE

Our aim was to test the effect of soy isoflavone supplementation on bone health.

DESIGN

A multicenter, randomized, double-blind, placebo-controlled 24-mo trial was conducted to assess the effects of daily supplementation with 80 or 120 mg of soy hypocotyl aglycone isoflavones plus calcium and vitamin D on bone changes in 403 postmenopausal women. Study subjects were tested annually and changes in whole-body and regional bone mineral density (BMD), bone mineral content (BMC), and T scores were assessed. Changes in serum biochemical markers of bone metabolism were also assessed.

RESULTS

After study site, soy intake, and pretreatment values were controlled for, subjects receiving a daily supplement with 120 mg soy isoflavones had a statistically significant smaller reduction in whole-body BMD than did the placebo group both at 1 y (P < 0.03) and at 2 y (P < 0.05) of treatment. Smaller decreases in whole-body BMD T score were observed among this group of women at 1 y (P < 0.03) but not at 2 y of treatment. When compared with the placebo, soy isoflavone supplementation had no effect on changes in regional BMD, BMC, T scores, or biochemical markers of bone metabolism.

CONCLUSION

Daily supplementation with 120 mg soy hypocotyl isoflavones reduces whole-body bone loss but does not slow bone loss at common fracture sites in healthy postmenopausal women. This trial was registered at clinicaltrials.gov as NCT00665860.

Resistance training and timed essential amino acids protect against the loss of muscle mass and strength during 28 days of bed rest and energy deficit

Spaceflight and bed rest (BR) result in losses of muscle mass and strength. Resistance training (RT) and amino acid (AA) supplementation are potential countermeasures to minimize these losses. However, it is unknown if timing of supplementation with exercise can optimize benefits, particularly with energy deficit. We examined the effect of these countermeasures on body composition, strength, and insulin levels in 31 men (ages 31-55 yr) during BR (28 days) followed by active recovery (14 days). Subjects were randomly assigned to essential AA supplementation (AA group, n = 7); RT with AA given 3 h after training (RT group, n = 12); or RT with AA given 5 min before training (AART group, n = 12). Energy intake was reduced by 8 +/- 6%. Midthigh muscle area declined with BR for the AA > RT > AART groups: -11%, -3%, -4% (P = 0.05). Similarly, greatest losses in lower body muscle strength were seen in the AA group (-22%). These were attenuated in the exercising groups [RT (-8%) and AART (-6%; P < 0.05)]. Fat mass and midthigh intramuscular fat increased after BR in the AA group (+3% and +14%, respectively), and decreased in the RT (-5% and -4%) and AART groups (-1 and -5%; P = 0.05). Muscle mass and strength returned toward baseline after recovery, but the AA group showed the lowest regains. Combined resistance training with AA supplementation pre- or postexercise attenuated the losses in muscle mass and strength by approximately two-thirds compared with AA supplement alone during BR and energy deficit. These data support the efficacy of combined AA and RT as a countermeasure against muscle wasting due to low gravity.

Strength training improves muscle quality and insulin sensitivity in Hispanic older adults with type 2 diabetes

Hispanics are at increased risk of morbidity and mortality due to their high prevalence of diabetes and poor glycemic control. Strength training is the most effective lifestyle intervention to increase muscle mass but limited data is available in older adults with diabetes. We determined the influence of strength training on muscle quality (strength per unit of muscle mass), skeletal muscle fiber hypertrophy, and metabolic control including insulin resistance (Homeostasis Model Assessment -HOMA-IR), C-Reactive Protein (CRP), adiponectin and Free Fatty Acid (FFA) levels in Hispanic older adults. Sixty-two community-dwelling Hispanics (>55 y) with type 2 diabetes were randomized to 16 weeks of strength training plus standard care (ST group) or standard care alone (CON group). Skeletal muscle biopsies and biochemical measures were taken at baseline and 16 weeks. The ST group show improved muscle quality (mean+/-SE: 28+/-3) vs CON (-4+/-2, p<0.001) and increased type I (860+/-252 microm(2)) and type II fiber cross-sectional area (720+/-285 microm(2)) compared to CON (type I: -164+/-290 microm(2), p=0.04; and type II: -130+/-336 microm(2), p=0.04). This was accompanied by reduced insulin resistance [ST: median (interquartile range) -0.7(3.6) vs CON: 0.8(3.8), p=0.05]; FFA (ST: -84+/-30 micromol/L vs CON: 149+/-48 micromol/L, p=0.02); and CRP [ST: -1.3(2.9) mg/L vs CON: 0.4(2.3) mg/L, p=0.05]. Serum adiponectin increased with ST [1.0(1.8) microg/mL] compared to CON [-1.2(2.2) microg/mL, p<0.001]. Strength training improved muscle quality and whole-body insulin sensitivity. Decreased inflammation and increased adiponectin levels were related with improved metabolic control. Further studies are needed to understand the mechanisms associated with these findings. However, these data show that strength training is an exercise modality to consider as an adjunct of standard of care in high risk populations with type 2 diabetes.

Exercise and vitamin E intake are independently associated with metabolic abnormalities in human immunodeficiency virus-positive subjects: a cross-sectional study

We investigated the relationship among habitual exercise, diet, and the presence of metabolic abnormalities (body fat redistribution, dyslipidemia, and insulin resistance) in a cross-sectional study of 120 human immunodeficiency virus (HIV)-infected subjects with use of bivariate and multivariate regression-analysis models. Total and aerobic exercise were significantly and negatively associated with fasting plasma triglyceride levels in the entire sample and in the fat redistribution group. Inverse associations between total or aerobic exercise and insulin resistance were suggestive but did not achieve statistical significance. Diastolic blood pressure was significantly and inversely associated with supplemental or total but not habitual dietary intake of vitamin E. In conclusion, exercise and vitamin E intake were independently and negatively associated with several phenotypic manifestations of HIV-associated metabolic syndrome, whereas other macro- or micronutrients did not have comparable significance.

Comparison of the effectiveness of 2 dual-energy X-ray absorptiometers with that of total body water and computed tomography in assessing changes in body composition during weight change

BACKGROUND

Little information is available on the assessment of changes in body composition as a function of weight change with the use of the fan beam of dual-energy X-ray absorptiometry (DXA).

OBJECTIVE

The objective was to determine the accuracy of the fan beam of the QDR 4500A densitometer and the pencil beam of the QDR 2000 densitometer in estimating changes in whole-body lean soft tissue mass (LSTM(DXA)) and fat mass (FM) with weight change.

DESIGN

Thirty-seven subjects who lost 5.7 +/- 4.5 kg were measured before and after weight change. Using total body water and computed tomography (CT) of the midthigh, we compared changes in FFM(TBW) and LSTM(CT) with changes in LSTM(DXA).

RESULTS

Overall, compared with TBW, the fan beam gave a larger estimate of change (macro x +/- SD) in LSTM (fan beam - TBW: -0.7 +/- 1.6 kg) than did the pencil beam (pencil beam - TBW: -0.1 +/- 1.6 kg). When the change in LSTM obtained with the fan beam and pencil beam was regressed against the change in FFM(TBW), the slope of the line for the fan beam was 0.97 (r(2) = 0.61) and that for the pencil beam was 0.86 (r(2) = 0.61). Regression analysis showed that the results between the 2 units were not interchangeable. For the midthigh region, the change in LSTM(CT) was moderately correlated with the change in LSTM(DXA) with the fan beam and pencil beam.

CONCLUSIONS

The measurement of change in LSTM with the fan and pencil beams provides the same relation to changes in FFM assessed by TBW, but the 2 systems are not interchangeable.

Precision of single vs bilateral hip bone mineral density scans

This study was performed to determine and compare the precision of single and bilateral hip bone mineral density (BMD) measurements and to determine the precision of spinal and total body measurements by dual-energy X-ray absorptiometry (DXA). Precision (group root-mean-square average coefficient of variation) was determined in 6 subjects scanned six times each at the spine, both hips, and total body, with repositioning after each scan. Mean percentage coefficients of variance (%CVs) in BMD for single and bilateral hip scans were, respectively: 0.65% and 0.67% for the total hip, 1.16% and 1.03% for the trochanter, and 1.66% and 1.31% for the femoral neck, respectively. Mean %CV was 1.04% for spine BMD (L2-L4), 0.67% for total body BMD, 1.12% for total body bone mineral content (BMC), 0.94% for total body fat tissue, and 0.77% for total body nonfat soft tissue. We conclude that precision overall is excellent and that femoral neck precision can be improved with bilateral compared with the traditional single hip scans.

A randomized controlled trial of resistance exercise training to improve glycemic control in older adults with type 2 diabetes

OBJECTIVE

To determine the efficacy of high-intensity progressive resistance training (PRT) on glycemic control in older adults with type 2 diabetes.

RESEARCH DESIGN AND METHODS

We performed a 16-week randomized controlled trial in 62 Latino older adults (40 women and 22 men; mean +/- SE age 66 +/- 8 years) with type 2 diabetes randomly assigned to supervised PRT or a control group. Glycemic control, metabolic syndrome abnormalities, body composition, and muscle glycogen stores were determined before and after the intervention.

RESULTS

Sixteen weeks of PRT (three times per week) resulted in reduced plasma glycosylated hemoglobin levels (from 8.7 +/- 0.3 to 7.6 +/- 0.2%), increased muscle glycogen stores (from 60.3 +/- 3.9 to 79.1 +/- 5.0 mmol glucose/kg muscle), and reduced the dose of prescribed diabetes medication in 72% of exercisers compared with the control group, P = 0.004-0.05. Control subjects showed no change in glycosylated hemoglobin, a reduction in muscle glycogen (from 61.4 +/- 7.7 to 47.2 +/- 6.7 mmol glucose/kg muscle), and a 42% increase in diabetes medications. PRT subjects versus control subjects also increased lean mass (+1.2 +/- 0.2 vs. -0.1 +/- 0.1 kg), reduced systolic blood pressure (-9.7 +/- 1.6 vs. +7.7 +/- 1.9 mmHg), and decreased trunk fat mass (-0.7 +/- 0.1 vs. +0.8 +/- 0.1 kg; P = 0.01-0.05).

CONCLUSIONS

PRT as an adjunct to standard of care is feasible and effective in improving glycemic control and some of the abnormalities associated with the metabolic syndrome among high-risk older adults with type 2 diabetes.

Body-composition assessment via air-displacement plethysmography in adults and children: a review

Laboratory-based body-composition techniques include hydrostatic weighing (HW), dual-energy X-ray absorptiometry (DXA), measurement of total body water (TBW) by isotope dilution, measurement of total body potassium, and multicompartment models. Although these reference methods are used routinely, each has inherent practical limitations. Whole-body air-displacement plethysmography is a new practical alternative to these more traditional body-composition methods. We reviewed the principal findings from studies published between December 1995 and August 2001 that compared the BOD POD method (Life Measurement, Inc, Concord, CA) with reference methods and summarized factors contributing to the different study findings. The average of the study means indicates that the BOD POD and HW agree within 1% body fat (BF) for adults and children, whereas the BOD POD and DXA agree within 1% BF for adults and 2% BF for children. Few studies have compared the BOD POD with multicompartment models; those that have suggest a similar average underestimation of approximate 2-3% BF by both the BOD POD and HW. Individual variations between 2-compartment models compared with DXA and 4 -compartment models are partly attributable to deviations from the assumed chemical composition of the body. Wide variations among study means, -4.0% to 1.9% BF for BOD POD - HW and -3.0% to 1.7% BF for BOD POD - DXA, are likely due in part to differences in laboratory equipment, study design, and subject characteristics and in some cases to failure to follow the manufacturer's recommended protocol. Wide intersubject variations between methods are partly attributed to technical precision and biological error but to a large extent remain unexplained. On the basis of this review, future research goals are suggested.

Fat mass measured by DXA varies with scan velocity

OBJECTIVE

To study the influence of scan velocities of DXA on the measured size of fat mass, lean body mass, bone mineral content and density, and total body weight.

RESEARCH METHODS AND PROCEDURES

The subjects were 71 healthy white adults, 38 women and 33 men. The mean age was 41.7 +/- 13.5 years and body mass index was 28.6 +/- 5.6 kg/m(2). The subjects were scanned consecutively in slow, medium, and fast scan mode by a Lunar DPX-IQ DXA scanner.

RESULTS

Throughout the body mass index and sagittal height ranges, scanned lean body mass significantly decreased with higher scan velocity and lean body mass was 2.7% lower in fast than in medium mode (p < 0.0001). In contrast, fat mass, percentage of body fat, and bone mineral contents were higher with increasing scan velocity. Areas not analyzed by the scanner, so called blue spots, increased with scan velocity and sagittal height, and their presence significantly enhanced the error. Body weight estimated by DXA in slow mode was -0.8% lower than scale weight in the women (p < 0.001) and -0.2% in men (not significant), and the difference was greater with increasing scan velocity.

DISCUSSION

Scan velocity significantly influences the measured fat mass size, lean body mass, bone mineral content, and body weight. To obtain the most accurate results, slow mode is preferable and fast scans should be avoided. Future studies should report and take scan velocity into consideration.

Peak VO2 correction for fat-free mass estimated by anthropometry and DEXA

PURPOSE

Anthropometric (ANTHRO) and dual-energy x-ray absorptiometric (DEXA) estimates of total body and leg fat-free masses (FFM) were obtained in 77 randomly selected sedentary men and women, aged 20-80: intermethod limits of agreement and their clinical significance, as inferred from the differences on peak VO2 corrected for FFMANTHRO and FFMDEXA, were determined.

METHODS

Limits of agreement were calculated as mean bias +/- 95% confidence intervals: peak VO2 at maximum cycle ergometry was related to FFMANTHRO and FFMDEXA by using both standard (y x x(-1)) and power function ratios (allometry).

RESULTS

Data distribution of the ANTHRO-DEXA differences presented significant heteroscedasticity in both sexes, i.e., differences were proportional to the mean (P < 0.05). After logarithmic transformation, the mean bias +/- 95% limits of agreement were expressed as ratios (ANTHRO x DEXA(-1) x// error ratio): these corresponded to 0.95 x// 1.11 or 0.99 x// 1.15 for total body FFM and 0.90 x// 1.10 or 1.02 x// 1.07 for leg FFM in men and women, respectively. In addition, we found different allometric exponents for FFMANTHRO and FFMDEXA: the intermethod differences, therefore, increased after power function expression (P < 0.05).

CONCLUSION

Discrepancies between ANTHRO and DEXA measurements of FFM depend on the magnitude of the estimate: differences are typically within 10 to 15%. Importantly, FFM-corrected peak VO2 values can vary according to the method chosen for body composition assessment, especially when allometry is used for peak VO2 correction. These results demonstrate that ANTHRO-DEXA differences in FFM estimation do have relevant practical consequences for the analysis of maximum aerobic capacity in nontrained humans.

Prediction of body fat by anthropometry in older Chinese people

OBJECTIVE

To derive regression equations for fat percentage by using simple anthropometric measurements applicable in normal and immobile (cannot stand or walk) older people.

RESEARCH METHODS AND PROCEDURES

The study population comprised 352 females and 261 males, apparently well and community-dwelling, aged 69 to 82 years. Fifty-one females and 27 males were recruited for external validation. Body weight, standing height, arm span, triceps and biceps skinfold thicknesses (SFTs), and midarm circumference were measured. The reference method of total body fat percentage was dual-energy X-ray densitometry. Predictive equations for fat percentages were derived by stepwise multiple linear regression on anthropometric indices and gender.

RESULTS

Upper-limb SFTs, body mass index, and gender yielded the more predictive equation. The SEE was 4.1% weight. There was a significant trend of underestimation in overweight subjects, especially in females. The equation using SFTs and midarm circumference was less reliable but more applicable to older immobile people and those with significant kyphoscoliosis.

CONCLUSIONS

The combination of body mass index and upper-limb SFTs gives reliable prediction of fat percentages in older Chinese people, except in the obese.

Measurement of fat mass using DEXA: a validation study in elderly adults

The accuracy of total body fat mass and leg fat mass measurements by fan-beam dual-energy X-ray absorptiometry (DEXA) was assessed in 60 healthy elderly subjects (aged 70-79 yr). Total fat and leg fat mass at four leg regions (total leg, thigh, midthigh, and calf) were measured with the QDR 4500A (Hologic, Waltham, MA). The four-compartment model and multislice computed tomography scans were selected as criterion methods for total fat and leg fat mass, respectively. Total fat mass from DEXA was positively associated with fat mass from the four-compartment model with a standard error of the estimate ranging from 1.4 to 1.6 kg. DEXA fan-beam tended to overestimate fat mass for total leg and total thigh fat mass, whereas only marginal differences in fat mass measurements at the midthigh and calf were demonstrated (</=0.08 kg, P < 0.0005). Although there were significant differences between DEXA fan beam and the criterion methods, these differences were of small magnitude, suggesting that DEXA is an accurate method for measurement of fat mass for the elderly.

Assessing body composition and changes in body composition. Another look at dual-energy X-ray absorptiometry

Dual-energy X-ray absorptiometry (DXA) is selected with increasing frequency as a method for both assessing body composition and measuring the changes in body composition. Issues have been raised about hydration, software version, hardware (fan beam vs. pencil beam), and the subject population in relation to the validity of DXA-derived estimates of body composition. This paper reviews validation studies of DXA to assess the impact of recent developments in its technology. Studies by Prior et al., Kohrt et al., Salamone et al., Going et al., and Pietrobelli et al. demonstrate the effectiveness of DXA estimates of changes in body composition. By contrast, Clasey et al., Nelson et al., and Friedl et al. found limitations in DXA estimates of body composition and its changes. These contradictory conclusions were explored for threats to internal validity in each research study. From this analysis, two validation guidelines are recommended for use when evaluating estimates of body composition. When multicomponent models are used, it is essential that estimates of body water as a fraction of fat-free mass fall in the expected range (71 to 75%) and have a relatively small standard deviation (2 to 3%). For measuring changes in body composition, DXA estimates of total body mass must accurately reflect both baseline and posttreatment scale body weight estimates. Failure to meet these guidelines threatens the internal validity of the study and raises the likelihood of methodological discrepancies. Applying these criteria to DXA studies of body composition under review accounts for much of the contradictory conclusions among investigations.

Impact of bone mineral estimates on percent fat estimates from a four-component model

PURPOSE

The primary purpose of this study was to determine the impact of bone mineral content (BMC) from QDR 1000/W and DPX-L dual-energy x-ray absorptiometers (DXA(QDR) and DXA(DPX-L) on percent fat (%fat) estimates from a four-component model. A secondary purpose was to test the accuracy of %fat estimates from DXA(QDR) and DXA(DPX-L) using %fat estimates from a four-component model as the criterion.

METHODS

Percent fat, fat mass, and fat-free mass (FFM) were determined from DXA(QDR) and DXA(DPX-L) and from a four-component model based on measures of body density from underwater weighing, body water from deuterium dilution, and BMC from DXA(QDR) (4C(QDR)) or DXA(DPX-L) (4C(DPX-L)) in young men (N = 14) and women (N = 10).

RESULTS

BMC was significantly lower using DXA(QDR) compared with DXA(DPX-L) (approximately 11%), resulting in slightly lower estimates of %fat and fat mass and slightly higher estimates of FFM from 4C(QDR) than 4C(DPX-L). Although estimates of %fat, fat mass, and FFM from DXA(QDR) and DXA(DPX-L) were not different than those from a four-component model, there was considerable individual variability between methods. Furthermore, %fat from DXA(QDR) was lower than %fat from 4C(DPX-L).

CONCLUSIONS

We conclude that using BMC from different DXA instruments has a minimal impact on %fat, fat mass, and FFM estimates from a four-component model. The large variability in %fat estimates between the two DXA instruments and those from a four-component model does not support DXA as a criterion method of body composition. Further studies involving larger sample sizes and specific population groups are needed to assess the validity of body composition measurements from DXA.

Validity of fan-beam dual-energy X-ray absorptiometry for measuring fat-free mass and leg muscle mass. Health, Aging, and Body Composition Study--Dual-Energy X-ray Absorptiometry and Body Composition Working Group

The aim of the study was to examine the accuracy of fan-beam dual-energy X-ray absorptiometry (DEXA) for measuring total body fat-free mass (FFM) and leg muscle mass (MM) in elderly persons. Participants were 60 men and women aged 70-79 yr and with a body mass index of 17.5-39.8 kg/m(2). FFM and MM at four leg regions were measured by using DEXA (Hologic 4500A, v8.21). A four-compartment body composition model (4C) and multislice computed tomography (CT) of the legs were used as the criterion methods for FFM and MM, respectively. FFM by DEXA was positively associated with FFM by 4C (R(2) = 0.98, SE of estimate = 1.6 kg). FFM by DEXA was higher [53.5 +/- 12.0 (SD) kg] than FFM by 4C (51.6 +/- 11.9 kg; P < 0.001). No association was observed between the difference and the mean of the two methods. MM by DEXA was positively associated with CT at all four leg regions (R(2) = 0.86-0.96). MM by DEXA was higher than by CT in three regions. The results of this study suggest that fan-beam DEXA offers considerable promise for the measurement of total body FFM and leg MM in elderly persons.

Determination of skeletal muscle and fat-free mass by nuclear and dual-energy x-ray absorptiometry methods in men and women aged 51-84 y (1-3)

BACKGROUND

Skeletal muscle mass (SMM) and fat-free mass (FFM) are important variables in nutritional studies. Accurate techniques for measuring these variables have not been thoroughly validated in elderly subjects.

OBJECTIVES

The objectives of this study were to 1) compare SMM values derived from dual-energy X-ray absorptiometry (DXA) with those calculated by a nuclear method from total body potassium (TBK) and total body nitrogen (TBN) measurement (both: KN) in older subjects, and 2) assess the accuracy of FFM measurement by DXA in these subjects.

DESIGN

TBK, TBN, DXA (model XR36; Norland, Fort Atkinson, WI), bioimpedance, and anthropometric measurements were performed on healthy women (n = 50) and men (n = 25) aged 51-84 y.

RESULTS

Mean SMM by KN was not significantly different from SMM by DXA in either sex. SMM by KN predicted SMM by DXA with an SEE of 2.1 kg (r = 0.95, P < 0.0001 for women and men together). In the men, FFM by DXA agreed well with FFM estimated by TBK, skinfold thicknesses, bioimpedance analysis, and a multicompartment model. In women, FFM by DXA was 4-5 kg less than that by the other methods (P < 0.01). Truncal fat was related to intermethod FFM differences (r = 0.58, P < 0.0001).

CONCLUSIONS

These data indicate that 1) either the nuclear or the DXA method can be applied to estimate SMM in healthy older subjects, and 2) the Norland DXA instrument significantly underestimates FFM in older women, in part, because of the influence of truncal adiposity.

A pilot study of exercise training to reduce trunk fat in adults with HIV-associated fat redistribution

OBJECTIVE

Body fat redistribution ('lipodystrophy'), with gain in abdominal and trunk fat, and decline in facial and limb fat, is a newly recognized problem in patients with HIV infection that has been linked to use of HIV-1 protease inhibitors. Increased abdominal fat may predispose these patients to hypertension, diabetes, and coronary artery disease. At this time no effective treatment is available. We examined whether exercise training could reduce trunk fat in men with fat redistribution.

DESIGN

Open-label pilot study.

METHODS

Ten men with increasing abdominal girth participated in a 16 week pilot study of progressive resistance training with an aerobic component. They trained in a community health club three times per week. Total body lean and fat mass, and trunk fat mass, were assessed by dual-energy x-ray absorptiometry (DXA).

RESULTS

After 16 weeks of exercise, strength increased for three of the four exercises tested (leg press + 13% [p < 0.02], leg extension + 19% [p < 0.03], seated row + 7% [p < 0.13], chest press + 18% [p < 0.0051). There was a significant decline in total body fat by 1.5 kg (= 2.1 percentage points, p < 0.01); most of the decline in body fat occurred in trunk fat, which decreased by 1.1 kg (p < 0.03). Weight, lean mass (+ 1.1 + 2.6 kg, p = 0.23), and bone mineral density measured by DXA did not change. No adverse effects were seen from the training.

CONCLUSIONS

Exercise training may reduce trunk fat mass in HIV-positive men with fat redistribution. Controls trials of this approach are warranted.

Validity of methods of body composition assessment in young and older men and women

We examined the validity of percent body fat (%Fat) estimation by two-compartment (2-Comp) hydrostatic weighing (Siri 2-Comp), 3-Comp dual-energy X-ray absorptiometry (DEXA 3-Comp), 3-Comp hydrostatic weighing corrected for the total body water (Siri 3-Comp), and anthropometric methods in young and older individuals (n = 78). A 4-Comp model of body composition served as the criterion measure of %Fat (Heymsfield 4-Comp; S. B. Heymsfield, S. Lichtman, R. N. Baumgartner, J. Wang, Y. Kamen, A. Aliprantis, and R. N. Pierson Jr., Am. J. Clin. Nutr. 52: 52-58, 1990.). Comparison of the Siri 3-Comp with the Heymsfield 4-Comp model revealed mean differences of </=0.4 %Fat, r values >/= r = 0.997, total error values </= 0.85 %Fat, and 95% confidence intervals (Bland-Altman analysis) of </=1.7 %Fat. Comparison of Siri 2-Comp, DEXA, and anthropometric models with the Heymsfield 4-Comp revealed that total error scores ranged from +/-4. 0 to +/-10.7 %Fat, and 95% confidence intervals associated with the Bland-Altman analysis ranged from +/-5.1 to +/-15.0 %Fat. We conclude that the Siri 3-Comp model provides valid and accurate body composition data when compared with a 4-Comp criterion model. However, the individual variability associated with the Siri 2-Comp, DEXA 3-Comp, and anthropometric models may limit their use in research settings. The use of anthropometric estimation methods resulted in large mean differences and a considerable amount of interindividual variability. These data suggest that the use of these techniques should be viewed with caution.

Body composition assessment by dual-energy x-ray absorptiometry: comparison of prone and supine measurements

The aim of the study was to assess whether changes in the interposition of body compartments affect the results of body composition measurements by dual-energy x-ray absorptiometry (DEXA) in the fan-beam mode. Thirty healthy subjects underwent two sequential measurements: the first was performed in the supine position as described by the manufacturer, and the second in the prone position. Estimates of body composition were compared between the two measurements. Mean body weight did not differ between measurements ([mean+/-SD] supine vprone, 68.561+/-12.461 v 68.589+/-12.469 kg). Mean bone mineral content (BMC) was lower in the prone position versus the supine position. When the head was excluded, this difference reached statistical significance (supine v prone, 1,738+/-361 v 1,688+/-360 g, P=.0001). The mean fat tissue mass (FTM) was lower and lean tissue mass (LTM) higher in the prone measurements. When the head was excluded, the mean FTM difference between the two measurements became greater (FTM supine v prone, 25.129+/-10.445 v 24.030+/-10.388 kg, P=.0001; LTM supine v prone, 37.309+/-9.357 v 38.246+/-9.150 kg, P=.0001). It is concluded that the positioning of the patient on the examination table affects DEXA body composition measurements by the fan-beam mode. This could imply a lack of accuracy of the method, which may be due to subtle changes in regional tissue depth and fat distribution caused by patient repositioning.

Bone mineral and body composition measurements: cross-calibration of pencil-beam and fan-beam dual-energy X-ray absorptiometers

Pencil-beam dual-energy X-ray absorptiometers (DXA) are being replaced with instruments that rely solely on fan-beam technology. However, information has been lacking regarding the translation of bone mineral and body composition data between the two devices. We have compared total body scans using pencil-beam (Hologic QDR-2000W) and fan-beam (Hologic QDR-4500A) instruments for 33 children (ages 3-18 years) and 14 adults. Bone mineral content (BMC), bone mineral density (BMD), fat, lean, and body fatness (%fat) values were highly correlated (r2 = 0.984-0.998) between the two DXA instruments. The mean differences between the paired measurements were: deltaBMC = 7.5 +/- 73.6 g, deltaBMD = 0.0074 +/- 0.0252 g/cm2, delta lean = 1.05 +/- 1.8 kg, delta fat = -0.77 +/- 1.7 kg, and delta%fat = -0.94% +/- 2.5%. The BMC and BMD values were not statistically different, whereas the differences for the body composition values were significant (p < 0.02-0.005). Regression equations are provided for conversion of bone and body composition data between pencil-beam and fan-beam values for the whole body. To test the performance of these equations for a second group (23 subjects), predicted values were compared with the measured data obtained using the fan-beam instrument. The mean differences were -1.0% to 1.4%, except for body fat mass, where the difference was 6.4%. For cross-sectional studies, the two DXA technologies can be considered equivalent after using the translational equations provided. For longitudinal studies in which small changes in body composition for the individual are to be detected, we recommend that the same DXA instrument be used whenever possible. For example, transition from a pencil-beam to a fan-beam instrument could, in extreme cases, result in differences as large as 19% for the estimate of body fat mass.

The Growth Hormone Research Society consensus guidelines for the diagnosis and treatment of adult GH deficiency

The Growth Hormone Research Society (GRS) convened a workshop in Port Stephens, Australia in April 1997 to establish consensus guidelines for the diagnosis and treatment of adults with GH deficiency (GHD). Scientists with expertise in the field, representatives from industry involved in the manufacture of GH and representatives from health authorities from a number of countries participated in the workshop. The workshop considered the following questions: (1) How should adult GHD be defined? (2) Who should be tested for adult GHD? (3) How should the diagnosis of adult GHD be established? (4) How should GH and insulin-like growth factor-I (IGF-I) assays be standardized? (5) Who should be treated for adult GHD? (6) What dose of GH should be used for treatment of adult GHD? (7) How should treatment of adult GHD be monitored? (8) What are the contraindications to treatment of adult GHD? (9) What safety issues need to be considered? (10) How long should treatment of adult GHD be continued? The consensus guidelines developed at this workshop and the rationale for some of these recommendations will be reviewed in this paper.