The adequate ingestion of dietary protein is the most critical nutritional factor to support the growth and maintenance of lean body mass across the lifespan. Currently, the World Health Organization/Food and Agricultural Organization (WHO/FAO) suggest that daily protein requirements in healthy, non-active adults are 0.8 g/kg/day. However, of primary interest in the present study is the impact that exercise has on the nutritional requirement for dietary protein in habitually active adults (e.g., individuals performing chronic resistance training). Protein requirements for individuals who participate in strength-based exercise training have been suggested to range from 1.2-1.7 g protein/kg/day (1), which equates to a 50-112% increase from the current RDA. The increased requirement in strength training populations may reflect the requirement for protein to repair and/or rebuild muscle tissue by promoting anabolism (2). Nutritional requirements for dietary protein in adults (both active and non-active) have traditionally been determined utilizing the antiquated and often erroneous nitrogen balance (NBAL) technique (3), which is prone to underestimating protein requirements and therefore provides challenges to making accurate nutritional recommendations (4). This observation that NBAL underestimates protein requirements in non-active individuals could suggest that protein requirements are much greater than the current World Health Organization recommendation of 0.8 g/kg/day, which was evaluated using the NBAL technique (3). As a result, there is a need to re-evaluate recommendations utilizing advanced stable isotope methodology in order to characterize how dietary protein needs may be modulated by physical activity. Recent studies using the minimally invasive indicator amino acid oxidation (IAAO) technique have suggested that protein requirements in young men are at least 50% higher than WHO/FAO guidelines based on NBAL data (4). Furthermore, resistance training has been reported to increase (according to NBAL methodology) protein requirements by up to 75% (6). Therefore, in this study, the investigators will use the IAAO technique to determine protein requirements in resistance-trained males. It is hypothesized that protein requirements for resistance-trained males will be i) greater than the current RDA for non-active individual's comparable estimates, and ii) greater than existing NBAL-based estimates for resistance-training individuals.
In this study, the investigators will use the minimally invasive indicator amino acid oxidation (IAAO) technique to determine protein requirements in resistance-trained males. It is hypothesized that the present study will show that protein requirements for resistance-trained males are i) greater than the current recommended dietary allowance (RDA) for non-active individual's comparable estimates, and ii) greater than existing nitrogen balance-based estimates for resistance-training individuals.