Studies of energy metabolism in human subjects using carbon 14-labeled compounds: I. Effect of sex, state of nutrition and body weight

Abstract

Employing isotope equipment which produces a continuous record of C 14O 2 specific activity in expired air, the patterns of oxidation of a variety of intravenously administered C 14-labeled compounds were studied in obese, malnourished and normal weight subjects of both sexes. C 14O 2 specific activity curves derived from palmitate-1, acetate-1 and glucose-6-C 14 oxidation were similar in male and female control subjects; the rate and magnitude of glucose-1-C 14 oxidation, however, was considerably augmented in women with active ovarian function, when compared to the male or postmenopausal female patterns. Oxidation of all substrates to C 14O 2 was markedly increased in malnourished patients while a significant suppression of glucose-6 and acetate-1-C 14 oxidation was noted in the majority of obese individuals. Attempts to correlate the respiratory data with various metabolic parameters were largely unsuccessful, except for a significant correlation between surface area and the magnitude of C 14-acetate oxidation. The potential advantages and pitfalls of this method of studying intermediary energy metabolism in human subjects is discussed.