Calorimetric results in man: energy output in normal and overweight subjects.

In order to test the practicability of 24-hr investigations with the gradient-free Vienna Whole-Body Calorimeter, energy output was measured over 24-hr periods in 18 human subjects. Heat loss was partitioned into dry and evaporative components. Sixteen female subjects were divided into normal-weight (less than 100% according to the Broca index), overweight (100%--120%), and obese (over 120%) groups. A male with severe hypothyroidism, and a female with no signs of impairment of thyroid function who had weight problems that were suspected to be due to low energy expenditure, were studied separately. Subjects reported that the calorimeter chamber was sufficiently comfortable for at least a 24-hour investigation. Overweight and obese subjects showed both greater total heat output and greater inter-individual variability than the normal weight group. Normal and overweight subjects were on steady levels of food intake that were representative of usual intake. For normal subjects there was a relatively close correspondence between energy intake and output, but not for overweight subjects. Thyroid hormone therapy produced a large increase in energy output in the hypothyroid patient. Energy expenditure was found to be unusually low in the patient with weight problems and was increased by about 50% after thyroid hormone administration.