Provided that energy needs are met, the adequate ingestion of dietary amino acids is the most critical nutritional factor to support the optimal remodeling and deposition of lean body mass in individuals of all ages. Current recommendations according to the World Health Organization/Food and Agricultural Organization 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 amino acids in highly active adults - e.g., individuals performing weight training. Protein requirements for individuals who participate in strength-based exercise training have been suggested to range from 1.2-1.7g protein/kg/day (Rodriguez et al., 2009; Tarnopolsky, 1992; Phillips et al., 2007), which equates to a 50-112% increase from the current RDA. The increased requirement in this population may reflect the requirement for protein to repair/rebuild lean tissues by promoting anabolism (Phillips, 2004). Nutritional requirements for dietary amino acids in adults (both active and non-active) have traditionally been determined utilizing the antiquated and often erroneous nitrogen balance technique (Costaneda et al., 1995; Campbell et al., 1984), which is prone to underestimating protein requirements and therefore provides challenges to making accurate nutritional recommendations (Humayun, Elango, Ball, and Pencharz, 2007). This observation that nitrogen balance underestimates protein requirements in non-active individuals could suggest that protein requirements are much greater than the current WHO/FAO recommendation of 0.8 g/kg/day which was evaluated using the nitrogen balance technique (Rand, Pellett and Young, 2003). As a result, there is a need to re-evaluate recommendations utilizing advanced stable isotope methodology in order to characterize how dietary amino acid 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 nitrogen balance data (Humayun, Elango, Ball, and Pencharz, 2007). Furthermore, resistance training has been reported to increase (according to nitrogen balance methodology) protein requirements by up to 75% Tarnopolsky et al., 1992). Therefore, in this study, the investigators will use the IAAO technique to determine protein requirements in weight-trained males. It is hypothesized that the present study will show that protein requirements for weight-trained females are i) greater than the current RDA for non-active individual's comparable estimates, and ii) greater than existing nitrogen balance-based estimates for weight-training individuals.
In this study, the investigators will use the minimally invasive indicator amino acid oxidation (IAAO) technique to determine protein requirements in weight-trained males. It is hypothesized that the present study will show that protein requirements for weight-trained females are i) greater than the current RDA for non-active individual's comparable estimates, and ii) greater than existing nitrogen balance-based estimates for weight-training individuals