Karen R. Segal

Thermic effects of food and exercise in lean and obese women

The thermogenic responses of ten lean and ten moderately obese women to food, exercise, and food plus exercise were measured using open circuit respirometry for five minutes every half hour for four hours under six conditions: during five minutes of bicycle exercise at a workload of 300 kpm/min with and without eating a 910 kcal mixed meal; cycling at a workload just below the anaerobic threshold with and without food; and at rest with and without food. Over the four-hour period, the thermic effect of food at rest was similar for the lean and obese groups: 50 kcal and 47 kcal, respectively. Eating before exercise increased the exercise metabolic rate by 11% for the lean women and by 4% for the obese women (P less than 0.005). Exercise potentiated the thermic effect of food for the lean women but nor for the obese women: the thermic effect of food was 2.54 times greater during exercise than at rest for the lean group, but only 1.01 times greater for the obese women (P less than 0.005). This reduced response to the combined stimulus of food plus exercise may constitute a subtle metabolic factor associated with obesity.

Comparison in man of total body electrical conductivity and lean body mass derived from body density: Validation of a new body composition method

This article reports a study in which total body electrical conductivity (TOBEC) measurements and lean body mass (LBM) estimated from hydrostatic weighing in human subjects were compared. The TOBEC method provides a new approach to assessment of human body composition that is based on the principle that the electrical conductivity of lean tissue is far greater than that of fat. In a sample of 32 men and women varying widely in age (20 to 53 years), body weight (45 to 155 kg), and adiposity (9.5 to 53.0% body fat), the TOBEC measurement was found to be extremely reliable (r = 0.999) and to correlate highly with hydrostatically estimated LBM (r = 0.903, P less than 0.0001). When the TOBEC scores were transformed to provide a single variable; namely, the subjects height times the square root of the TOBEC score, a higher correlation with LBM was obtained (r = 0.943). Taking gender into account further enhanced the prediction of LBM from TOBEC (r = 0.951). These observations strongly reinforce the results of a previous investigation in which high correlations were found between TOBEC and both total body potassium and total body water. Accordingly, this new method promises to provide a useful technique for the evaluation of body composition that is at once simple, rapid, objective, and noninvasive.

A new method for estimation of body composition in the live rat.

Abstract Measurement of total body electrical conductivity (TOBEC) has been used to estimate lean and fat content of meat based on the principle that electrical conductivity of lean tissue is far greater than that of fat. This approach was used to estimate body composition of live rats. An instrument designed for commercial analysis of ground meat (DjMe 100) was used to measure TOBEC in 30 male Sprague-Dawley rats (197-433 g). Individual TOBEC values were obtained in 20 seconds and repeated twice for each rat. The animals were then killed with ether, hair was shaved, lungs collapsed and body density measured hydrostatically. Carcasses were homogenized and analyzed for fat, nitrogen, and water. A high correlation was found between TOBEC and lean body mass by densitometry (r = .97) and between TOBEC and fat-free mass derived from direct carcass analysis (r = .97). Rats weighing up to 450 g could be accommodated in this particular instrument. Measurement of TOBEC should prove useful in estimating body composition and monitoring its changes in live rats and other small laboratory animals.

Levels of serum sex hormones and risk factors for coronary heart disease in exercise-trained men.

On the basis of previous findings, it has been hypothesized that hyperestrogenemia may be the major predisposing factor for coronary heart disease and that an elevation in the estradiol-to-testosterone ratio, or a closely related hormonal alteration, may cause the expression of risk factors for coronary heart disease. The present study was carried out to investigate whether exercise training, which has been reported to reduce risk factors for coronary heart disease, affects the serum sex hormone levels. The serum sex hormone levels, established risk factors for coronary heart disease, and physical fitness were measured in 10 men who had undergone at least six months of intensive exercise training and in 10 sedentary men of similar age. Despite evidence for a strikingly higher level of physical fitness and a lower level of risk factors in the trained group, no significant difference in mean serum estradiol level was found. Nor did three subjects from the sedentary group show a decrease in estradiol level after three to four months of exercise training. The mean estradiol-to-testosterone ratio, however, was significantly lower in the trained group and might account for the lower level of risk factors in that group. If the hypothesis is correct, exercise training may decrease established risk factors for coronary heart disease without decreasing the risk of coronary heart disease.

Nutritional assessment of hospital patients: New methods and new opportunities

Recently, two new methods (total body electrical conductivity [TOBEC] and bioelectrical impedance analysis [BIA]) have become available for the rapid, safe, and convenient estimation of total body water in hospital patients. Despite these clear advantages, the clinical usefulness of the TOBEC and BIA methods in patient diagnosis and care is likely to be restricted by illness‐related changes in the hydration of the lean body and in the distribution of water between the intracellular and extracellular water compartments. If these methods can be refined so as to permit their measurement of extracellular water as rapidly as they now measure total body water, the ability of clinicians to assess and monitor the nutritional and metabolic status of their hospital patients will be greatly enhanced.