A high protein diet upregulates whole‐body protein turnover during energy deficit

Abstract

The effects of dietary protein level on whole‐body protein turnover (WBPTO) during energy deficit (ED) are not well described. Using a randomized‐block design, 24 males and five females (21 ± 3 yr) participated in a controlled trial. Volunteers consumed either standard (SP; 0.8 g·kg−1·d−1), moderate (MP; 1.6 g·kg−1·d−1), or high (HP; 2.4 g·kg−1·d−1) protein diets for 31 days. A weight maintenance (WM, days 1–10) period was followed by 21 days of ED (days 11–31), during which energy intake was restricted to 60% of total daily energy expenditure. Whole‐body protein breakdown, synthesis, and oxidation were determined at rest during WM (day 10) and ED (day 31) using primed, continuous [13C]‐leucine infusions. Volunteers lost (P < 0.05) 3.3 ± 0.9 kg body mass in response to ED regardless of dietary protein level. Protein breakdown decreased (P < 0.05) in response to ED for SP and MP diets, but did not change for HP. Synthesis decreased (P < 0.05) following ED regardless of dietary protein level. Protein oxidation (μmol·kg−1·h−1) increased linearly between SP (9.7 ± 0.5), MP (11.8 ± 0.5), and HP (13.9 ± 0.5) diets during WM, with increased oxidation observed only for HP (16 ± 0.7) during ED (diet‐by‐energy interaction, P < 0.05). These data demonstrate that the level of dietary protein intake modulates WBPTO during sustained ED, as consumption of a high protein diet upregulates WBPTO during ED.