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

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 [ 13 C]‐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.