Applications of stable isotopes to pediatric nutrition and gastroenterology: measurement of nutrient absorption and digestion using 13C.

The naturally occurring, nonradioactive, stable isotopes, 2H, 15N, 18O, and in particular, 13C, are valuable tracers in studies of pediatric nutrition and gastroenterology. Techniques using these isotopes have been developed for the measurement of digestion, absorption, utilization, and excretion of nutrients in premature and term infants, as well as in young children. Compounds labeled with 13C enable quantitative measurements of nutrient oxidation rates and percent nutrient malabsorption. Illustrations of these applications are presented in studies of simple and complex carbohydrate metabolism, of medium- and long-chain triglyceride absorption and malabsorption, and of bile salt conservation and loss in the neonate. Modular protocols for the determination of nutrient absorption, oxidation, and loss now can be applied in longitudinal studies which involve comparisons of diet or which monitor recovery following malnutrition or disease. Instrumentation to be available in the future will simplify isotope ratio determinations and create ready access to the methodologies described.