Accuracy and reliability of total body electrical conductivity (TOBEC) for determining body composition of rats in experimental studies

Prediction of body composition by total body electrical conductivity technique is affected by fat reserves of Japanese quail

The effect of fat accumulation on the prediction of in vivo body composition by a total body electrical conductivity (TOBEC) technique was evaluated using Japanese quail at 2 life periods (0 to 21 d and 28 to 70 d of age) that differ significantly in the fatness of birds. In total, 119 quail of 14 age categories were weighed and scanned by the TOBEC analyzer, and their carcasses were subjected to chemical analysis. The prediction equations for chemical composition (percentage of water, lipids, and lean tissue) and body masses (weight of body, water, lipids, and lean tissue) were obtained by linear regression analysis. The equations involved the E-value as the independent variable. In both growth phases, a high accuracy of estimation was found for the total body, lean, and water masses (0.85 ≤ R(2) ≤ 0.98), whereas a low accuracy of estimation was observed for percentages of lipids, lean tissue, and water (0.27 ≤ R(2) ≤ 0.64). Most of the variables showed a worse estimation in the late than in the early growth phase; the maximum difference was observed for the lipid mass (R(2) = 0.35 vs. 0.90, respectively). The correlations between analyzed variables and the residual error distributions of regression models demonstrated that the lower power of the models in the late versus early growth phase may be attributed to an enhanced fat accumulation in sexually mature birds. Their high fat reserves considerably decrease body hydration, which negatively influences the estimation of body composition based upon the TOBEC procedure.

The recognition and treatment of growth disorders - a 50-year retrospective

The past 50 years have seen great progress in the understanding and treatment of classic growth disorders. Advances such as the recognition of hormone receptor defects, the development of recombinant growth hormone, and the expanding awareness of epigenetic phenomena affecting growth are among these great achievements. Yet growth failure remains a pervasive problem among children with complex health conditions, such as survivors of childhood cancers, premature infants, organ transplant recipients, and children with cystic fibrosis. The significant increases in life expectancy among these groups underscores the potential consequences of poor growth, whether due to the underlying conditions or medical treatments, as they may have long-lasting effects into adulthood. The ongoing contributions of human biologists to the study of human growth remain essential in the recognition and treatment of growth disorders, by defining normal patterns of growth and body composition, the interplay of growth and maturation, the role of environmental, behavioral and genetic factors, and the long-term consequences of growth patterns. Examples will be given based on two common genetic disorders, cystic fibrosis and sickle-cell anemia, to highlight the relationships between growth failure, survival, and malnutrition. Also, a study of bone mineral accretion in children with cystic fibrosis will illustrate the importance of understanding patterns of growth in healthy children, and their application in the diagnosis and management of children with chronic disease. These examples accentuate the need for continued participation of human biologists in the study of growth and development and the care of children.

Physical limitations of the TOBEC method: accuracy and long-term stability

While measurement of electrical conductivity provides one way of estimating body composition in live animals, the accuracy of methods based on this principle requires further study. In this work, we evaluate the effect of the ambient conditions and sample geometry on the response given by an SA-2 model (EM-SCAN) apparatus as well as the reproducibility of the measurements over time. A 2 degrees C variation of the sample temperature (a normal range for living animals) can result in a 6-10% variation in the response. When the conductive mass of a sample is increased in length, the response of the apparatus does not increase once the sample length reaches half the length of the measurement chamber. Samples having the same conductive mass but different shapes can show up to a 17-fold variation in signal. The geometry of the sample itself appears to be of prime importance for determining the strength of the response. We find that the reference phantom provided by the manufacturer is inadequate for calibration and is unable to detect the 10% variation over time of the signal of the apparatus. Until these problems are resolved, the usefulness of the EM-SCAN SA-2 to investigate body composition accurately is questionable.

Determination of body composition in conscious adult female Wistar utilising total body electrical conductivity

Total body electrical conductivity (TOBEC) is a noninvasive method for estimating fat free mass (FFM) in live animals. In this study, we have evaluated the use of the Em-Scan SA-3000, which is claimed by the manufacturers to perform better than earlier analysers. Previous studies in rats using these earlier versions of the TOBEC analyser have always used anaesthesia to minimise movement artefacts. As repeated anaesthesia also has the potential to induce artefacts by disrupting food intake, for example, we have also attempted to determine if this TOBEC analyser can be used to predict body composition in conscious adult weight-stable female Wistar rats. A simplified cafeteria diet was used to produce large variations in body composition (40-350 g fat/carcass) and a full chemical body composition analysis was performed to generate a TOBEC calibration equation. The TOBEC parameter was more strongly correlated to FFM (r(2)=.785) than it was to body weight (r(2)=.669) or other body composition parameters. Using the TOBEC calibration equation to predict fat mass on these data, there was an excellent correlation with the value obtained by chemical analyses (r(2)=.952, slope=0.958). To determine if the TOBEC calibration equation derived from this calibration study would then be useful for the routine estimation of body composition an additional, validation study was performed. This validation study was performed 6 months later, used an independent group of obese female Wistar rats and was undertaken by different TOBEC operators. This validation study, again, showed a good correlation between the TOBEC- and chemical-derived fat mass (r(2)=.918, slope=1.003) indicating stability of the calibration equation with time and independence from operator. We therefore conclude that it is possible to meaningfully estimate body fat changes in conscious rats using this TOBEC analysis system.

Validation of measures of food insecurity and hunger

The most recent survey effort to determine the extent of food insecurity and hunger in the United States, the Food Security Supplement, included a series of questions to assess this complex phenomenon. The primary measure developed from this Food Security Supplement was based on measurement concepts, methods and items from two previously developed measures. This paper presents the evidence available that questionnaire-based measures, in particular the national food security measure, provide valid measurement of food insecurity and hunger for population and individual uses. The paper discusses basic ideas about measurement and criteria for establishing validity of measures and then uses these criteria to structure an examination of the research results available to establish the validity of food security measures. The results show that the construction of the national food security measure is well grounded in our understanding of food insecurity and hunger, its performance is consistent with that understanding, it is precise within usual performance standards, dependable, accurate at both group and individual levels within reasonable performance standards, and its accuracy is attributable to the well-grounded understanding. These results provide strong evidence that the Food Security Supplement provides valid measurement of food insecurity and hunger for population and individual uses. Further validation research is required for subgroups of the population, not yet studied for validation purposes, to establish validity for monitoring population changes in prevalence and to develop and validate robust and contextually sensitive measures in a variety of countries that reflect how people experience and think about food insecurity and hunger.

Effect of age on protein conservation during very-low-energy diet in obese Sprague-Dawley rats

OBJECTIVE

To examine the effect of age on body protein losses occurring during severe energy restriction in obesity.

RESEARCH METHODS AND PROCEDURES

Weanling (young) Sprague-Dawley rats (YR) were fed a high fat (35% energy) diet (HFD) until mean body weight approached that of a group of chow-fed retired breeder (aged) rats (AR). Both groups were then fed HFD for an additional 2 weeks, after which selected controls from YR and AR groups were killed for baseline carcass analysis. Remaining rats were fed a very-low-energy diet (VLED, 33% kcal of HFD) for 3 weeks and then killed for carcass analysis.

RESULTS

YR had greater fat stores before VLED, and lost proportionately more fat and less protein during VLED than did AR. Weight loss composition during VLED was 66.7% fat, 11.1% protein, and 22.2% water in YR, and 39.4% fat, 26.2% protein, and 34.3% water in AR. Greater YR fat loss during VLED (70.6+/-30.4 vs. 32.6+/-29.1 g in AR; mean+/-SD) was paralleled by significantly larger decreases in epididymal and retroperitoneal fat pad weights, mean adipocyte size, and lipoprotein lipase activity. Greater protein loss in AR (21.6+/-13.9 g vs. 11.8+/-10.7 g in YR) coincided with larger decreases in visceral organ weights and serum thyroxine and triiodothyronine. Energy expenditure changes during VLED were similar between groups.

DISCUSSION

Dietary obese young rats appear better able than aged rats to conserve body protein while losing body fat during severe energy restriction.

Evaluation of the non invasive TOBEC (total body electrical conductivity) procedure for prediction of chemical components of male broilers with special consideration of dietary protein level

TOBEC (total body electrical conductivity) measurement as a non invasive procedure for the estimation of body chemical composition was used to calculate calibration curves for the prediction of crude protein mass (CPM), crude water mass (CWM), crude ash mass (CAM) and fat-free mass (FFM) of male broiler chickens. A growth experiment with 3 protein levels (130, 230 and 330 g CP/kg diet, isoenergetic with 13.3 MJ AMEN/kg) was combined with TOBEC measurements and body chemical analysis in order to obtain the values necessary for calibration. A total of 196 TOBEC measurements and body chemical analysis were undertaken in time intervals of two days beginning with batch until day 17 of age. Different dietary protein levels resulted in marked differences in body weights and body chemical compositions but in similar TOBEC-responses for a given mass of FFM, CPM, CAM or CWM. Values for birds fed a diet with 130 g CP/kg diet tended to be more variable. Linear broken relationships were found between FFM, CPM, CAM and CWM, respectively and TOBEC values (E#). A set of different regression equations is given and yielded high proportions of variance accounted for the piece wise regression model (R2 ranged from 0.83 to 0.99). In spite of these high determinations the prediction of crude fat mass (CFM) by subtracting the FFM from the body weight resulted in most cases in weak determinations between observed and predicted CFM (R2 ranged from 0.38 to 0.86). The highest R2 was observed when the E# was expressed per unit metabolic body weight to the power of 0.67 and regressed on FFM expressed to the same power. In conclusion, FFM, CPM and CWM may be predicted reasonably well by TOBEC. However, these high determinations are not high enough to predict CFM accurately. In addition, the application of such regressions to an individual bird seems to be impossible. Assessment for groups of animals should be possible if errors of estimation, standard deviations and differences to be detected are taken into account in the calculation of the number of birds necessary for the TOBEC measurements.

Ever higher: constant rise of body weight set-point in growing zucker rats

The mass of food hoarded by rats given access to food only 2 h per day is proportional to the rats' body weight deficit. The intersect of the regression line of hoarded food plotted against body weight gives an indication of the body weight set-point. In the present work, the hoarding behavior of six obese and six control rats was measured every day at various body weights from 8 to 24 weeks of age. Every other week the animals were anesthetized and their percentage of fat was measured in vivo with a total body electrical conductivity method (TOBEC). Lean mass and body length of the obese, and their controls, increased similarly in both groups over the period of the measurements. On the other hand, the body weights increased more in obese, from 174 +/- 5 to 729 +/- 18 g (n = 6), than in controls, from 157 +/- 5 g to 452 +/- 14 g (n = 6). The body weight set-point, calculated every other week for both groups of rats, increased progressively with age. At the age of 24 weeks, the mean set-point for body weight regulation was 758 +/- 13 g in obese and 467 +/- 12 g in controls. This result suggests that the obese fa/fa rat defends its fat content, or a variable correlated to the fat content.

A further assessment of an electromagnetic method to measure body composition

Two experimental investigations of the electromagnetic method to measure body composition are presented. In the first experiment, the impedance of a single-loop transmitting antenna, located at the centre of a 150 m helical receiving coil, was observed to have a sharp minimum at 2.40 MHz. The impedance of the antenna at this frequency with respect to a series resistor was observed to go through a maximum when a small volume of 1% saline, of cross-section 0.5 cm2, was introduced coaxially into the coil. The frequency shift for larger volumes of saline (> 0.8 l) was highly correlated with the surface area of the liquid (r = 0.998, 0.997) and less well correlated with volume (r = 0.966, 0.967). In the second experiment, a five-turn solenoid, 2 m long and 1.5 m in diameter, was used to induce voltages in two coaxial receiving antennae placed 1 m apart inside the solenoid. The differential induced voltage was observed to vary as coaxial saline phantoms were traversed through the solenoid, with the variation being well correlated with the surface area of the liquid (r = 0.993, 0.996) and less well correlated with the volume of liquid in the phantom (r = 0.987, 0.958) for volumes above 100 ml. These observations suggest that the (resonant or non-resonant) electromagnetic field only responds to surface eddy currents in a coaxial saline phantom and therefore the TOBEC method may not be valid.