A.S.P.E.N. 2003 Research Workshop on using tracers to measure carbohydrate, fat, and amino acid metabolism in humans.
The 2003 A.S.P.E.N. Research Workshop was held during Nutrition Week on January 18 in San Antonio, Texas. The workshop brought scientists and clinicians from around the world together to discuss the latest developments in methodology to measure substrate use and flux in vivo. Methods presented were designed to track the fate of nutrients that are given orally, enterally, or parentally to humans. Talks presented a variety of approaches to tackle particularly difficult problems of assessing intracellular processes in vivo in living animals and humans. The present paper reviews those various approaches that have been developed using (i) differential administration of tracers across organ beds to define organ-specific intracellular metabolism without tissue biopsies; (ii) animal models that will tolerate complicated multicatheter placement situations; (iii) methods that take advantage of complicated pathways of metabolism that allow movement of specific portions of a molecule for determining gluconeogenesis; (iv) nuclear magnetic resonance and in vivo magnetic resonance spectroscopy to measure intramolecular distribution of tracers; and (v) the multiple stable isotope approach to follow biosynthetic pathways associated with fatty acid flux in the fed-state in humans. Improved accessibility of these methods provides much hope for their expanded use in understanding the basic mechanisms of metabolic regulation and the physiologic changes in nutrient use that occur in disease states.