I stumbled onto this article what do you guys think? Proc. Natl. Acad. Sci. USA Vol. 94, pp. 14930-14935, December 1997 Physiology Slow and fast dietary proteins differently modulate postprandial protein accretion (amino acid turnover / postprandial protein anabolism / milk protein / stable isotopes) Yves Boirie*, Martial Dangin*,, Pierre Gachon*, Marie-Paule Vasson, Jean-Louis Maubois§, and Bernard Beaufrère*,¶ * Laboratoire de Nutrition Humaine, Université Clermont Auvergne, Centre de Recherche en Nutrition Humaine, BP 321, 63009 Clermont-Ferrand Cedex 1, France; Nestec, Ltd., Nestlé Research Center, P.O. Box 44, CH 1000 Lausanne 26, Switzerland; Laboratoire de Biochimie, Biologie Moléculaire et Nutrition, Université Clermont Auvergne, BP 38, 63001 Clermont-Ferrand Cedex 1, France; and § Laboratoire de Technologie Laitière, Institut National de la Recherche Agronomique, 35042 Rennes Cedex, France Communicated by John Waterlow, University of London, London, United Kingdom, October 7, 1997 (received for review April 20, 1997) The speed of absorption of dietary amino acids by the gut varies according to the type of ingested dietary protein. This could affect postprandial protein synthesis, breakdown, and deposition. To test this hypothesis, two intrinsically 13C-leucine-labeled milk proteins, casein (CAS) and whey protein (WP), of different physicochemical properties were ingested as one single meal by healthy adults. Postprandial whole body leucine kinetics were assessed by using a dual tracer methodology. WP induced a dramatic but short increase of plasma amino acids. CAS induced a prolonged plateau of moderate hyperaminoacidemia, probably because of a slow gastric emptying. Whole body protein breakdown was inhibited by 34% after CAS ingestion but not after WP ingestion. Postprandial protein synthesis was stimulated by 68% with the WP meal and to a lesser extent (+31%) with the CAS meal. Postprandial whole body leucine oxidation over 7 h was lower with CAS (272 ± 91 µmol·kg1) than with WP (373 ± 56 µmol·kg1). Leucine intake was identical in both meals (380 µmol·kg1). Therefore, net leucine balance over the 7 h after the meal was more positive with CAS than with WP (P < 0.05, WP vs. CAS). In conclusion, the speed of protein digestion and amino acid absorption from the gut has a major effect on whole body protein anabolism after one single meal. By analogy with carbohydrate metabolism, slow and fast proteins modulate the postprandial metabolic response, a concept to be applied to wasting situations. In conclusion, we demonstrate that the speed of amino acid absorption after protein ingestion has a major impact on the postprandial metabolic response to a single protein meal. The slowly absorbed CAS promotes postprandial protein deposition by an inhibition of protein breakdown without excessive increase in amino acid concentration; by contrast, a fast dietary protein stimulates protein synthesis but also oxidation. This impact of amino acid absorption speed on protein metabolism is true when proteins are given alone, but as for carbohydrate, this might be blunted in more complex meals that could affect gastric emptying (lipids) and/or insulin response (carbohydrate); thus, further studies are needed to confirm the specific roles of nonprotein substrates on whole body protein metabolism. This concept of slow and fast proteins could be applied to circumstances in which protein deposition has to be improved (i.e., protein-energy malnutrition) and in which excessive protein intakes have to be avoided (elderlies, renal diseases). so its not as good taking wpi alone pwo....??