Validity of bioelectrical-impedance analysis in measuring changes in lean body mass during weight reduction

Article Abstract:

Bioelectrical-impedance analysis (BIA) is an inexpensive and convenient method for measuring lean body mass (LBM) in humans. BIA is performed by measuring the amount of electrical resistance (R) that is encountered when an electrical current is passed through the body. R is measured by placing electrodes on the hands and feet and a current of 0.8 milliamps is passed through the electrodes. To estimate LBM, a mathematical calculation is performed that takes into account several different factors, including R, body weight and age. Studies have shown that BIA is an effective method for estimating LBM in subjects with stable body weight. However, it is not clear whether BIA accurately predicts LBM in subjects who are dieting and losing weight. Therefore, a study was performed to evaluate the ability of BIA to accurately predict LBM in 16 obese females following very-low-calorie diets (VLCDs). BIA was performed on all subjects for two days prior to the beginning of the diet period, and for the following 28 days during the VLCD. During the four-week diet period the subjects lost an average of 18 pounds. However, R did not change during the diet period, even though a significant amount of weight was lost. This was an unexpected finding because R is expected to increase as LBM decreases. Eight different mathematical equations were tested and all overestimated the losses in LBM. It is concluded that BIA does not provide an accurate estimate of LBM in obese women on VLCDs. (Consumer Summary produced by Reliance Medical Information, Inc.)

Evaluation, Impedance plethysmography, Weight loss

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Aging and energy expenditure

Article Abstract:

During the aging process, changes occur in the levels of physical activity, the amount of energy expended, and the basal metabolic rate (BMR, the rate at which calories are burned to maintain basic physiological processes). Gains in body weight are common with increasing age, as energy intake exceeds the amount of energy expended. Previous studies have indicated that BMR decreases with increasing age, and that this decrease in BMR is related to a loss of lean body mass (including muscle) that occurs during aging. Other studies have shown that the total daily caloric intake decreases with age, but the reduction in food intake is often not great enough to prevent weight gain. To examine the relationship between the aging process and energy expenditure, the BMR, energy expenditure over a 24-hour period (24EE), and physical activity were measured in 38 elderly (over 60 years of age) and 64 young (age 18 to 30) caucasian males and females were studied. The elderly subjects had a lower average body weight, height, lean body mass, 24EE, and BMR, and a greater percentage of body fat than the young subjects. When age differences in fat and lean body mass were taken into account, only BMR was still lower in the elderly subjects. However, the lower 24EE observed in the elderly subjects was only related to smaller body size and not to a lower BMR, which suggests that lower energy intake in the elderly may be primarily due to reduced levels of physical activity. (Consumer Summary produced by Reliance Medical Information, Inc.)

Aging, Physiological aspects, Demographic aspects, Energy metabolism, Body size, Body weights and measures, Body weight, Basal metabolism

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Body composition in Pima Indians: validation of bioelectrical resistance

Article Abstract:

In metabolic studies, the body composition needs to be measured; this involves estimating the percent body fat and the fat-free mass (FFM). Body composition can be determined using a hydrostatic (underwater) weighing facility or by bioelectrical-resistance (BR) analysis. BR is a safe and quick method for measuring body composition in which an electrical current is passed through the body and the amount of resistance encountered in the body tissues indicates the amount of fat. Previous studies that tested the effectiveness of BR in determining body composition used populations that consisted of different ages and races and were less obese than the Pima Indian population. The Pima Indians reside in Arizona and are a genetically isolated population with a high incidence of non-insulin-dependent diabetes and obesity. The FFM was assessed by hydrostatic weighing and the BR method in 156 Pima Indians with body compositions ranging from 11 to 52 percent body fat. An equation for predicting FFM and percent body fat was developed, and with its use the correlations between hydrostatic weighing and BR were 0.92 for percent body fat and 0.97 for fat-free mass. The subjects' food and fluid intake did not significantly affect body composition as determined by BR. These findings show that bioelectrical resistance, with the use of the new equation, provides a simple and accurate method for determining body composition in Pima Indians. (Consumer Summary produced by Reliance Medical Information, Inc.)

Health aspects, Research, Obesity, Pimas

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