Currently, the DRI makes no recommendation with regard to the quality of protein consumed, or the distribution of that protein throughout the day. The data from this study demonstrates that both quality and distribution of dietary protein throughout the day is important. The quality and distribution of protein are of particular interest to those who are energy restricted, who might benefit from the consumption of a higher quality protein source (e.g. milk, egg, beef), resulting in a higher EAA content per gram of protein. Neither carbohydrate nor dietary fat intake was associated with percent CAF, which confirms previous data, highlighting the importance of protein intake [6
Previous research has demonstrated a plateauing of muscle contractile protein synthesis following approximately 9-10 g of EAA; meaning dietary intake of EAAs above this threshold does not significantly contribute to the accretion of skeletal muscle [1
]. Researchers have postulated [11
] and recently shown that a small difference in the quantity of lean mass has a significant effect on resting energy expenditure [12
]. Also, the majority of energy used to provide ATP for muscle protein turnover comes from the oxidation of fat, as this is the preferred energy substrate of muscle at rest [13
]. Therefore, a focus on maximizing the muscle synthetic response with ~10 g of EAA may decrease CAF through increased resting energy expenditure from increased lean mass.
In conclusion, moderate to strong correlations between variables indicate that quality and distribution of protein may play an important role in regulating CAF, which is a strong independent marker for disease and mortality. These results warrant further investigation into quality and protein distribution, both of which are currently not covered under the DRI.