Effects of caloric restriction on body composition and total body nitrogen as measured by neutron activation

Elemental analysis in living human subjects using biomedical devices

Today, patients undergoing dialysis are at low risk for aluminum-induced dementia. Workers are unlikely to experience cadmium-induced emphysema and the public's exposure to lead is an order of magnitude lower than in 1970. The research field of in vivo elemental analysis has played a role in these occupational and environmental health improvements by allowing the effects of people's chronic exposure to elements to be studied using non-invasive, painless, and relatively low-cost technology. From the early 1960s to the present day, researchers have developed radiation-based systems to measure the elemental content of organs at risk or storage organs. This reduces the need for (sometimes painful) biopsy and the risk of infection. Research and development has been undertaken on forty-nine in vivo measurement system designs. Twenty-nine different in vivo elemental analysis systems, measuring 22 different elements, have been successfully taken from design and testing through to human measurement. The majority of these systems employ either neutron activation analysis or x-ray fluorescence analysis as the basis of the measurement. In this review, we discuss eight of the successful systems, explaining the rationale behind their development, the methodology, the health data that has resulted from application of these tools, and provide our opinion on potential future technical developments of these systems. We close by discussing four technologies that may lead to new directions and advances in the whole field.

Multi-component molecular-level body composition reference methods: evolving concepts and future directions

Excess adiposity is the main phenotypic feature that defines human obesity and that plays a pathophysiological role in most chronic diseases. Measuring the amount of fat mass present is thus a central aspect of studying obesity at the individual and population levels. Nevertheless, a consensus is lacking among investigators on a single accepted 'reference' approach for quantifying fat mass in vivo. While the research community generally relies on the multi-component body volume class of 'reference' models for quantifying fat mass, no definable guide discerns among different applied equations for partitioning the four (fat, water, protein and mineral mass) or more quantified components, standardizes 'adjustment' or measurement system approaches for model-required labelled water dilution volumes and bone mineral mass estimates, or firmly establishes the body temperature at which model physical properties are assumed. The resulting differing reference strategies for quantifying body composition in vivo leads to small, but under some circumstances, important differences in the amount of measured body fat. Recent technological advances highlight opportunities to expand model applications to new subject groups and measured components such as total body protein. The current report reviews the historical evolution of multi-component body volume-based methods in the context of prevailing uncertainties and future potential.

Effect of a moderately energy- and salt-reduced diet on body compartments and blood pressure control in obese men with mild hypertension

Ten middle-aged moderately obese men with untreated mild hypertension were studied during a 6-week weight maintenance period and a 9-week period on a diet containing 5 MJ when body mass decreased by 8.4 kg (SE 1.4). According to urinary sodium excretion there was a mean reduction of 89 mmol/day (SE 16) in sodium intake. Mean arterial pressure fell by 2.5 to 14.1 mmHg (95% confidence interval) which was correlated to the reduction of body mass. The sympathetic nervous activity diminished with decreasing noradrenaline excretion and heart rate. There were no changes in the renin-aldosterone system. Estimation of the body composition with a four-compartment model utilizing determinations of body mass, total body potassium and total body water (TBW) showed reductions of body fat (8.4 kg (SE 1.4] and body cell mass (BCM) (2.4 kg (SE 0.6], but not of TBW. Extracellular water (ECW) increased significantly as judged from ECW/BCM calculations. Plasma volume was determined by Evan's blue and did not change significantly. We suggest that the observed changes in body composition represent one aspect of the adjustment to a weight reducing diet, while blood pressure is lowered by another mechanism in the adaptive response to dieting, i.e. reduction in sympathetic nervous activity.

Body composition and energy expenditure: relationship and changes in obese subjects before and after biliopancreatic diversion

Changes in total and segmental body composition were studied in 101 obese women before and 2, 6, 12, and 24 months after biliopancreatic diversion (BPD) and data 24 months after surgery were matched to 53 control subjects. The patients were studied by anthropometry, indirect calorimetry, and double-emission x-ray absorptiometry (DXA). The combination of calorimetry and body composition analysis allowed estimation of visceral and muscle lean mass. We observed a significant (analysis of variance [ANOVA]: P <.05) progressive reduction of fat and lean body mass (LBM) following BPD, with stabilization of both parameters between 12 and 24 months at levels not different from controls. Fat loss was significant in the arms, legs, and trunk segments. After 24 months, there was no significant difference in segmental fat mass between post-BPD patients and controls. Calorimetric data seem to confirm lean body mass (LBM) reduction. Visceral lean mass (kg) was significantly reduced from 8.1 +/- 2.2 in obese subjects to 6.5 +/- 1.8 in post-BPD patients at 24 months (P <.05); the control value was 7.2 +/- 1.8. Muscular lean mass (kg) was also significantly reduced, from 50.2 +/- 5.8 to 39.8 +/- 5.7 in the same subjects (P <.05), with a control value of 42.5 +/- 5.9. The decrease in muscle and visceral LBM reached control values without significant differences. Viscera/muscle ratio in pre-BPD patients was preserved in post-BPD patients at 24 months, but it was reduced during weight loss. Body composition studies showed a logarithmic relationship between fat and lean mass and a physiological contribution of lean mass to weight loss in the BPD patients. In conclusion, weight loss after BPD was achieved with an appropriate decline of LBM and with all parameters reaching, at stable weight, values similar to weight-matched controls.

Human body composition: in vivo methods

In vivo methods used to study human body composition continue to be developed, along with more advanced reference models that utilize the information obtained with these technologies. Some methods are well established, with a strong physiological basis for their measurement, whereas others are much more indirect. This review has been structured from the methodological point of view to help the reader understand what can be examined with each technique. The associations between the various in vivo methods (densitometry, dilution, bioelectrical impedance and conductance, whole body counting, neutron activation, X-ray absorptiometry, computer tomography, and magnetic resonance imaging) and the five-level multicompartment model of body composition are described, along with the limitations and advantages of each method. This review also provides an overview of the present status of this field of research in human biology, including examples of reference body composition data for infants, children, adolescents, and adults.

Assessment of fat-mass loss during weight reduction in obese women

Methods for assessing body fat mass (FM) loss were compared in 32 obese (body mass index [BMI], 29 to 41 kg/m2) premenopausal women before and after a weight loss of 13.0 +/- 3.4 kg (mean +/- SD). A four-component (4C) model was used as the criterion. The other methods were as follows: three-component models (body density with total body water [3W] or bone minerals [3M]), underwater weighing, dual-energy x-ray absorptiometry ([DXA] XR-26, software 2.5.2; Norland, Ft Atkinson, WI), bioelectric impedance analysis (BIA) with an obese-specific equation [Segal et al), skinfolds (Durnin and Womersley), and an equation with BMI (Deurenberg et al). The 3W model (bias +/- SD, 0.5 +/- 0.4 kg), XR-26 (0.6 +/- 2.1 kg), and BMI equation (-0.3 +/- 2.1 kg) gave practically unbiased mean estimations of fat loss. All other methods underestimated fat loss by at least 1.6 kg (range of bias, -2.7 to -1.6 kg). The small bias (0.7 +/- 1.0 kg) between underwater weighing and model 4C before weight reduction indicates that the two-component assumptions were valid in premenopausal, weight-stable obese women. However, particularly the water fraction of the fat-free body component (4C model) was increased after weight reduction (before, 72.9% +/- 1.4%; after, 75.7% +/- 2.2%), making both underwater weighing and the 3M model uncertain for assessment of body composition changes. A general tendency for overestimating FM was seen before and more clearly after weight reduction. However, most methods underestimated fat loss, apparently because of unexpected changes in hydration of the fat-free body component.

Composition of weight loss in severely obese women: a new look at old methods

Seven severely obese, outpatient dieters lost weight (mean +/- SEM, 14 +/- 1 kg), and the composition of weight lost was determined by six different models. Total body water (TBW), total body potassium (TBK), and body density, bone mineral content, and fat as determined by dual photon absorptiometry (DPA) were measured while subjects were weight-stable, before and after weight loss. Fat loss was calculated by three two-compartment models (2C-TBW, 2C-TBK, and hydrodensitometry [2C-HD]), one three-compartment model (HD with correction for water content of fat-free mass [FFM], 3C), and one four-compartment model (HD with correction for water and mineral content of FFM, 4C), and was measured directly by DPA. Mean composition of weight loss was similar for all models (mean weight lost as fat: 89% for DPA, 91.5% for 4C, 89% for 3C, 88.6% for 2C-HD, and 87% for 2C-TBW) except 2C-TBK (weight lost as fat, 66%). There was a much wider range of individual values for the 2C-TBW and 2C-TBK models (17% to 138% and 18% to 93%, respectively) than for the multicompartment models (63% to 112%) and DPA (76% to 107%). Almost opposite results were obtained for the same individual when using the 2C-TBK and 2C-TBW models. The discrepancy between these models was due to the inverse relationship between changes in TBW and TBK in the group as a whole (r = -.34, NS). In addition, TBK loss was found to be dependent on the initial level of hyperinsulinemia, calculated as the area under the 2-hour oral glucose tolerance curve.(ABSTRACT TRUNCATED AT 250 WORDS)

The use of stable isotopes in metabolic investigation

The use of tracers to define substrate dynamics has been the sine qua non of metabolic investigation in vivo, because static measurements of substrate content alone are inadequate. The judicious use of radioactively labelled compounds remains the principal tracer approach in some adult subjects. However, in certain young adults, in pregnant women and in children, stable isotope tracers offer a practical alternative for answering important metabolic questions. In the last decade, the developmental problems previously associated with employing stable isotope tracers for this purpose have largely disappeared. Furthermore, the use of stable isotopically labelled materials offers certain additional advantages which are either difficult or impossible to achieve using radiotracers. These include the ability to measure simultaneously substrate content and isotopic enrichment with very high specificity and precision, the ability to determine the intramolecular location of the label, the ability to use the mass of the stable isotope substrate as a probe of the metabolite system response to perturbation, and the ability to study simultaneously and repeatedly the same subject with multiple substrate tracers. The practical application of these principles has been amply demonstrated by the expanding use of non-radioactive tracers to study body composition, energy balance, and the inter-organ transport and oxidation of the three major metabolic fuels--glucose, fat and amino acids. Continued development in the organic synthesis of new, stable isotopically labelled biochemicals will allow investigation of additional areas of biomedical importance which have been hitherto inaccessible to this approach, particularly in the pathophysiology of metabolic events in the growing child.

Noninvasive techniques for measuring body elemental composition : State of the art and future prospects

In the past 20 yr, in vivo analysis of body elements by neutron activation has become an important tool in medical research. In particular, it provides a much needed means to make quantitative assessments of body composition of human beings in vivo. The data are useful both for basic physiological understanding and for diagnosis and management of a variety of diseases and disorders. This paper traces the development of the in vivo neutron activation technique from basic systems to the present state of the art facilities. A scan of some of the numerous clinical applications that have been made with this technique reveals the broad potentialities of in vivo neutron activation. The paper also considers alternative routes of future development and raises some of the questions now faced in making the technique more widely available to both medical practitioners and medical investigtors.In vivo neutron activation has opened a new era of both clinical diagnosis and therapy evaluation, and investigation into the modeling of body composition. The techniques are new, but it is already clear that considerable strides can be made in increasing accuracy and precision, increasing the number of elements susceptible to measurement, and reducing the dose required for the measurement.

Measurement of body fat and hydration of the fat-free body in health and disease

Body fat mass, fat-free body mass and body water are basic components of body composition which are used in nutritional and metabolic studies and in patient care. A method of measuring total body fat (TBF), fat-free mass (FFM) and its hydration (TBW/FFM) involving prompt gamma in vivo neutron activation analysis (IVNAA) and tritium dilution has been compared with the more traditional methods of densitometry and skinfold anthropometry in 36 normal volunteers, and with skinfold anthropometry in 56 patients presenting for nutritional support. While the mean values of TBF were in reasonable agreement for the three methods in normals it was founds that skinfold anthropometry underestimated TBF relative to the IVNAA/tritium method by, on average, 3.0 kg (19%) in patients. Furthermore, the ranges of values in normals of the ratio TBW/FFM for the anthropometric (0.62 to 0.80) and densitometric (0.65 to 0.80) methods were much wider than the range for the IVNAA/tritium method (0.69 to 0.76), in which TBW was measured by tritium dilution in all cases. In the patients, the ranges of this ratio were 0.52 to 0.90 for the anthropometric method and 0.67 to 0.82 for the IVNAA/tritium method; clearly anthropometry yields values of TBW/FFM which are outside accepted biological limits. On the basis of these findings, ranges of TBW/FFM are suggested for both normal adults (0.69 to 0.75) and patients requiring nutritional support (0.67 to 0.83). Finally it is concluded that the IVNAA/tritium method is a suitable method for measuring TBF and FFM and particularly so when body composition is abnormal.

Effect of weight reduction on the renin-aldosterone axis

Eight normotensive obese subjects participated in an inpatient study designed to determine the effect of a constant sodium intake (150 mEq) on the renin-aldosterone axis during 12 weeks of weight reduction. Two 800-calorie (3,200 kj) ketogenic diets, differing in carbohydrate content (10 g vs 70 g) were used for the study. Supine and upright plasma renin activity (PRA) and serum aldosterone (SA) were determined at the baseline and every 4 weeks. Total body water (TBW) was determined by the tritiated water technique at the baseline and 12 weeks after dieting. Extracellular water (ECW) was determined by 77Br space. Routine serum chemistries were obtained at 2-week intervals. Analysis of variance indicated no significant differences in the PRA and SA between the two diets. At the baseline, while on a self-selected 150 mEq sodium diet, there was a 3- to 4-fold increase in PRA after 2 h of ambulation (supine PRA 0.83 +/- 0.22 increased to 3.41 +/- 0.96 ng/ml/h). After the hypocaloric diets were instituted, the absolute values for PRA in the supine and upright positions declined. However, the magnitude of the postural response (3- to 4-fold increase) remained unchanged during the 12 weeks of weight reduction. There was no decline in the absolute values for supine or upright SA, during the entire study. Weight loss was significant (from 102.56 +/- 6.0 to 81.7 +/- 3.7 kg; P less than .001) and was accompanied by a mean +/- SE reduction in the TBW of 3.01 +/- 0.88 liters (P less than .011).(ABSTRACT TRUNCATED AT 250 WORDS)

An improved calibration for the in vivo determination of body nitrogen, hydrogen, and fat

Additional investigation of the authors' original technique for measuring total body nitrogen by prompt gamma neutron activation has demonstrated the need for certain changes in the calibration procedures in order to apply the method to studies of patients with abnormal metabolism. In the present technique, total body nitrogen, hydrogen, and fat were derived, simultaneously, from data obtained by neutron capture gamma-ray analysis combined with the measurements of body weight, total body water, and total body calcium. In this improved calibration technique total body nitrogen is more accurately measured, not only in normal subjects, but also in obese subjects and in patients with marked changes in hydration, such as cancer patients. The fat values calculated do not rely on a fixed relationship of total body water or total body potassium with lean body mass as in the previous studies, but are calculated as the difference between body weight and the sum of body water, protein and bone mineral ash. This improved technique has been applied to the study of three groups of subjects, the general population with a normal weight distribution and two extremes represented by obese and cancer patients.