Sex differences in the composition of weight gain and loss in overweight and obese adults.

Sex differences in the ratio of fat mass (FM):fat-free mass (FFM) during weight change should differentially affect the extent of weight change during energy imbalance in men and women. In the present study, we determined FM and FFM contents by dual-energy X-ray absorptiometry and calculated the P-ratios (protein energy/total energy) of excess weight and weight loss during a randomised controlled trial of four commercial weight loss regimens. Overweight and obese women (n 210) and men (n 77) were studied at baseline and at 2 and 6 months during weight loss on four dietary regimens: Dr Atkins' New Diet Revolution; The Slim-Fast Plan; Weight-Watchers programme; Rosemary Conley's Diet and Fitness Plan.

Errors in dual-energy X-ray scanning of the hip because of nonuniform fat distribution.

The variable proportion of fat in overlying soft tissue is a potential source of error in dual-energy X-ray absorptiometry (DXA) measurements of bone mineral. The effect on spine scanning has previously been assessed from cadaver studies and from computed tomography (CT) scans of soft tissue distribution. We have now applied the latter technique to DXA hip scanning.

Precision and accuracy of measuring changes in bone mineral density by dual-energy X-ray absorptiometry.

Unlabelled: Long-term precision of two Hologic DXA scanners was derived from repeated clinical measurements. With typical subjects, the long-term coefficients of variation were about twice the short-term. The accuracy of the measurement of changes was compromised by anomalies, but this did not seriously affect clinical conclusions.

Dual-energy x-ray absorptiometry measurements of total-body bone mineral during weight change.

Bone mineral measurements were made using dual-energy X-ray absorptiometry during a multicenter diet trial. There were five centers, two using Hologic QDR4500 fan-beam scanners, two using Lunar Prodigy fan-beam scanners,and one using a pencil-beam Lunar DPX. Measurements were made at 0, 2.

Dual-energy X-ray absorptiometry measurements of fat and lean masses in subjects with eating disorders.

Objective: The main objective was to use a dual-energy X-ray absorptiometer (DXA) to examine the total-body and regional fat and lean composition of soft tissue in subjects with and without eating disorders initially and after weight change. It was necessary also to study the effects of differences of calibration of different models of DXA scanner.

Design: A total of 175 women with eating disorders, including anorexia nervosa (AN) and bulimia nervosa, and 43 age-matched controls were measured for soft-tissue composition with a pencil-beam Hologic QDR 1000W scanner and results converted to be equivalent to those from a fan-beam Hologic QDR 4500A, using previously determined crosscalibration factors.

Bone mineral and soft tissue measurements by dual-energy X-ray absorptiometry during growth.

There have been several previous compilations of reference ranges of total body bone mineral measured by dual-energy X-ray absorptiometry (DXA) in children and young adults during growth, but little attempt to compare the results or to consider differences arising from the use of instruments from different manufacturers. We measured bone mineral and soft tissue in 216 girls, aged 11-17 years, using a Hologic scanner. Our results were compared with those from four other studies, all performed on white subjects, but in different countries, and including measurements performed with Hologic, Lunar, and Norland scanners.

Estimation of thigh muscle and adipose tissue volume using magnetic resonance imaging and anthropometry.

Thigh muscle volume is a useful determinant of functional fitness. However, anthropometric prediction of muscle content is influenced by the variability of adipose tissue accumulation. The aims of this study were to predict thigh muscle and adipose tissue volumes from anthropometry and to assess the validity of the method by examining the various components of the measurements and the assumptions involved.

Comparisons between a pencil beam and two fan beam dual energy X-ray absorptiometers used for measuring total body bone and soft tissue.

A pencil beam Hologic QDR 1000W scanner (1000), a fan beam QDR 4500A scanner (4500) and a fan beam Lunar Expert scanner (Expert) were compared for bone mineral and body composition measurement accuracy. Phantoms were scanned with each instrument to assess magnification effects and to compare calibrations for bone mineral and fat proportion. 41 volunteers were scanned with both the 1000 and the 4500, and 21 patients with both the 4500 and the Expert.

Comparisons between Hologic QDR 1000W, QDR 4500A, and Lunar Expert dual-energy X-ray absorptiometry scanners used for measuring total body bone and soft tissue.

Measurements of total-body bone and soft tissue were compared between two fan-beam dual-energy X-ray absorptiometry (DXA) scanners, a Hologic QDR 4500A, a Lunar Expert, and a pencil-beam Hologic QDR 1000W. Phantom studies showed that mass measurements were not compromised by magnification effects, but that the height of a bone within the body affected the measured bone mineral content (BMC) and, to a lesser extent, the bone mineral density (BMD). There were differences in calibration for fat proportion between the three instruments.

Anomalies in dual energy X-ray absorptiometry measurements of total-body bone mineral during weight change using Lunar, Hologic and Norland instruments.

A previous study showed that measurements of total-body bone mineral changes made with a Hologic QDR 1000W were unreliable when the subjects underwent weight change. The study has been extended to dual energy X-ray absorptiometry (DXA) apparatus from other manufacturers. Re-analysis of published results during weight loss using a Lunar DPX showed that they varied with the software used.

Measurement of abdominal fat by magnetic resonance imaging, dual-energy X-ray absorptiometry and anthropometry in non-obese men and women.

Objective: To investigate whether the dual-energy X-ray absorptiometry (DEXA) was a better predictor of abdominal fat, measured by magnetic resonance imaging (MRI) at the level of L2-L3, than anthropometric measurements in non-obese men and non-obese women.

Design: Observational, cross sectional study.

Subjects: 34 healthy subjects (17 men and 17 women) aged 20-53 y with a body mass index (BMI) < 30 kg/m2.

Anomalies in the measurement of changes in bone mineral density of the spine by dual-energy X-ray absorptiometry.

Dual-energy X-ray absorptiometry (DXA) is frequently used for longitudinal studies of bone mineral status because of the high precision obtained, but evidence is emerging that the accuracy of measurements of changes may be a limitation because of artefacts of the analysis procedure, in particular, a dependence of the measured bone area (BA) on the bone mineral content (BMC). Results of spine bone mineral measurements taken at intervals with two DXA scanners, a Hologic QDR 1000 W, and a Norland XR 26 HS, were examined. There was a consistent correlation between changes in BA and in BMC, with a slope of approximately 0.

Anomalies in the measurement of changes in total-body bone mineral by dual-energy X-ray absorptiometry during weight change.

For an eating disorder study over a period of 1 year, we measured total-body bone mineral using a Hologic QDR 1000 W in a total of 157 subjects and observed anomalies that questioned the accuracy of such measurements. Using the recommended Enhanced software, a change in total bone mineral content (delta BMC) correlated positively with a change in weight (delta W; r = 0.66), but a loss of weight was associated with an increase in bone mineral areal density (BMD; r = 0.

Comparisons between fat measurements by dual-energy X-ray absorptiometry, underwater weighing and magnetic resonance imaging in healthy women.

Objective: To compare the results of measurements of total and regional fat by dual-energy X-ray absorptiometry (DXA), underwater weighing (UWW) and magnetic resonance imaging (MRI) in women.

Design: 13 volunteer pre-menopausal women measured with a Norland XR26 HS DXA instrument, hydrodensitometry equipment and a 0.08 Tesla MRI scanner.

Changes in blood volume distribution between legs and trunk during halothane anaesthesia.

To assess the influence of halothane anaesthesia on the distribution of blood volume in supine humans, we used albumin labelled with 99mTc to measure blood volume distribution along the craniocaudal axis. We studied 6 volunteers in the supine position before, during and after anaesthesia with 1% halothane and 66% nitrous oxide. Using collimated detectors above and below the subject, counts were obtained from the legs, pelvis, abdomen, rib cage and head, with the arms excluded.

Comparisons between three dual-energy X-ray absorptiometers used for measuring spine and femur.

Lunar, Hologic and Norland dual-energy X-ray absorptiometry scanners have been compared for measurements of spine and femur bone density. Precision was not greatly different in realistic phantoms and volunteer subjects. Most clinical therapeutic trials are concerned with measuring changes of bone mineral, and interchangeability in this context was examined using phantoms of spine and femur in which changes of bone mineral density (BMD) were simulated.

Precision and accuracy of measurements of whole-body bone mineral: comparisons between Hologic, Lunar and Norland dual-energy X-ray absorptiometers.

Measurements of whole-body bone mineral made by Hologic, Lunar and Norland dual-energy X-ray absorptiometers have been compared. It was found that in each case the results were changed by new software protocols introduced by the manufacturers during the course of the study. With a moderately anthropomorphic model, the later software corrected some anomalies of regional bone mineral content (BMC) observed earlier.

Comparisons between Hologic, Lunar and Norland dual-energy X-ray absorptiometers and other techniques used for whole-body soft tissue measurements.

Objectives: Assessment of the precision and accuracy of dual-energy X-ray absorptiometers (DXA) from three manufacturers, used for measuring soft-tissue composition, and comparability with each other and other techniques.

Design: Measurements of an anthropomorphic model of variable composition and thickness. 11 volunteers measured with each instrument and by underwater weighing (UWW) and three brands of bioelectric impedance analysis (BIA) apparatus.