Dietary Protein Intake, Energy Deficit, And Nitrogen Balance In Normal-Weight Adults: A Randomized Controlled Trial

Consuming protein at levels higher than the recommended dietary allowance (RDA) may be metabolically advantageous for overweight and obese individuals attempting weight loss. However, the dose‐response characteristics that define the optimal level of dietary protein necessary to sustain measures of metabolic homeostasis during short‐term energy deficit (ED) in normal‐weight adults remain unclear. Thirty‐two men and 7 women participated in a 31‐day randomized trial providing diets containing protein at either the RDA (0.8 g·kg −1 ·d −1 ), 2X‐RDA (1.6 g·kg −1 ·d −1 ), or 3X‐RDA (2.4 g·kg −1 ·d −1 ). A weight maintenance (WM, days 1–10) period was followed by 21 days of ED (days 11–31); energy intake was restricted to 60% of daily requirements. Nitrogen balance (NBAL) was assessed during WM (day 9) and throughout ED on days 14, 17, 24, and 30. Independent of protein, NBAL (mgN·kg −1 ·d −1 ) was lower ( P < 0.05) at the start of ED (day 14, −40 ± 5) compared to WM (day 9, −10 ± 5). NBAL remained negative at the conclusion of ED (day 30) for RDA (−39 ± 8). However, NBAL increased ( P < 0.05) rapidly and was maintained at levels comparable to WM beginning on day 17 for 2X‐RDA (0 ± 8), yet failed to achieve WM levels until day 30 (−7 ± 10) for 3X‐RDA. These data confirm that high protein diets conserve NBAL during short‐term ED, but suggest no beneficial effect of protein at levels beyond 2X‐RDA, as 3X‐RDA failed to further enhance nitrogen adaptation. Supported by USAMRMC and USDA ARS