Protein Supplementation Principle for Training: Quality is More Important than Quantity

Abstract

One of the best benefits of exercise training is to increase physical fitness by preserving muscle health against aging. After exercise, regeneration of new cells after muscle damage helps adaptation of the body against new challenge for survival. This recovery process demands carbon and nitrogen sources for reconstructing new cells in the tissue. It is noteworthy that the cell regenerative process during recovery is part of inflammation program (Tidball, 2005), which generates subjective fatigue feeling and pain. Therefore, providing sufficient protein to challenged muscle in time around workout is crucial in preventing fatigue feeling and ensuring fast recovery. To evaluate the quality of dietary protein source should base on its adsorption efficiency, which is more important than the amount of protein provided. There are many dietary sources, which can be used for protein supplementation. Whey protein isolate is generally considered the best source for training individuals. The main reason is that whey protein can be quickly digested and absorbed in human body. Any delay in protein delivery to challenged muscle will prevent fast recovery for regenerating cells. Therefore, supplementation timing is important for optimal training effect in muscle growth. This is particularly important for both the individuals aged above 70 yrs, when muscle loss is the main concern (Esmarck et al., 2001), and the young individuals under sport training (Cribb & Hayes,2006;Levenhagen et al., 2001). Protein is not only important for individuals under exercise training. It is essential for any individual who has high cell proliferation rate, such as during acute illness and fast growing age. However, how much protein should be taken is an important question in human health. Too little protein intake inhibits growth; yet too much protein intake accelerates aging, in particular, increases cancer mortality (Levine et al., 2014). Recommended dietary allowance of 0.75 gram per kilogram body weight according to WHO and 0.8 gram per kilogram body weight according to USDA for those aged older than 19 yrs are considered maximal (National Research Council [US] Subcommittee on the Tenth Edition of the Recommended Dietary Allowances, 1989). These values are not provided based on human longevity data (all-cause mortality), but nitrogen balance outcomes as indirect evidence. Furthermore, high protein supplementation for elderly in the weight falling phase (> 69 years old) shows increased longevity, but the same supplemented quantity for middle-aged individuals in the weight rising phase (50 ~ 65 years old) is associated with shorter longevity (Levine et al., 2014). A lifespan animal study (Solon-Biet et al., 2014) confirms the causal relationship between protein and longevity. In a human training study, ingestion of only 20 g protein for men weighted -- 86 kg is sufficient to maximally stimulate protein synthesis and albumin protein synthesis after resistance exercise (Moore et al., 2009). Similar result has also been reported with approximately the same protein quantity (0.2 g per kg), which can sustain higher protein synthesis rate for at least 5 hrs above fasted condition (Moore et al., 2009). These results clearly indicate that even for someone who challenges the muscle regularly, protein supplementation does not need to supplement to a level suggested by WHO or USDA. Yet, we must stress again that elderly should be considered as different case. For men aged -- 71 yrs, ingestion of 0.4 g per kg is required to maximally stimulate protein synthesis (Moore et al., 2014).