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Whole-body protein turnover response to short-term high-protein diets during weight loss: a randomized controlled trial

S. M. Pasiokos, L. M. Margolis, J. P. McClung, J. J. Cao, L. D. Whigham, G. F. Combs, A. J. Young
International Journal of Obesity 2014 v.38 no.7 pp. 1015-1018
adults, body mass index, dietary protein, energy, high protein diet, isotope labeling, leucine, oxidation, protein synthesis, randomized clinical trials, weight control, weight loss
Objective: Determine whole-body protein turnover responses to high protein diets during weight loss. Design: Thirty-nine adults (age, 21 ± 1 yr; VO2peak, 48 ± 1 ml'kg-1'min-1; body mass index, 25 ± 1 kg•m2) were randomized to diets providing protein at the recommend dietary allowance (RDA), 2X-RDA, or 3X-RDA. A 10-day weight maintenance period preceded a 21-day, 40% energy deficit. Postabsorptive (FASTED) and postprandial (FED) whole-body protein turnover was determined during weight maintenance (day 10) and energy deficit (day 31) using [1-13C]-leucine. Results: FASTED flux, synthesis, and breakdown were lower (P < 0.05) for energy deficit than weight maintenance. Protein flux and synthesis were higher (P < 0.05) for FED than FASTED, whereas feeding attenuated (P < 0.05) breakdown during weight maintenance but not energy deficit. Oxidation increased (P < 0.05) linearly between dietary protein levels, and feeding stimulated oxidation, although oxidative responses to feeding were higher (P < 0.05) for energy deficit than weight maintenance. FASTED net balance decreased linearly between dietary protein levels, but in the FED state, net balance was lower for 3X-RDA as compared to RDA and 2X-RDA (diet-by-state, P < 0.05). Conclusion: Consuming dietary protein at levels exceeding the RDA during short-term weight loss upregulates protein oxidation but does not enhance whole-body protein balance.