I’m not sure what the legality of posting studies from scientific journals is, but here’s the publicly posted abstract of a study from the Journal of Applied Physiology:
Inverse relationship between protein intake and plasma free amino acids in healthy men at physical exercise
Am J Physiol Endocrinol Metab 278: E857-E867, 2000;
Anders H. Forslund1, Leif Hambr?us1, Hugo van Beurden1, Ulf Holmb?ck1, Antoine E. El-Khoury2, Gunilla Hjorth1, Roger Olsson1, Mats Stridsberg1, Leif Wide1, Torbj?rn ?kerfeldt1, Meredith Regan2, and Vernon R. Young2
1?Department of Medical Sciences, Nutrition and Clinical Chemistry, Uppsala University, SE-75237 Uppsala, Sweden; and 2?Laboratory of Human Nutrition, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
The effect of a “normal” (n?=?8) and “high” (n?=?6) protein intake (1?and 2.5?g ??kg1 ??day1, respectively) and of exercise on plasma amino acid (AA) concentrations, insulin, and glucagon concentrations was followed throughout a continuous 24-h period in adult male subjects at energy balance after six days on a standardized diet and exercise program. Subjects were fasting from 2100?on day 6?to 1200?on day 7?and then fed 10?identical meals hourly until 2100.?Physical exercise was performed (46% maximal oxygen uptake) between 0830?and 1000?(fasting) and in a fed state (1600-1730) on each day. The normal-protein group showed fasting plasma AA concentrations that were higher (P?<?0.05) than those for the high-protein group, except for leucine, methionine, and tyrosine. Glutamine, glycine, alanine, taurine, and threonine concentrations were distinctly higher (~30% or greater) throughout the 24-h period in subjects consuming the normal- vs. the high-protein diets. Exercise appeared to increase, although not profoundly, the plasma concentrations of amino acids except for glutamate, histidine, ornithine, and tryptophan. The profound diet-related differences in plasma AA concentrations are only partially explained by differences in the renal clearance of the amino acids. We speculate on the possible metabolic basis for these findings.
I, having the advantage of being able to read the authors discussion in the full article, take this to mean that higher protein intake spares body proteins. (Muscle tissue) Seems reasonable given my limited knowledge of the mechanics of nitrogen balance…
Somebody let me know if it’s legal to post the full text, and if anyone is interested I will.