Since non-EAAs do not stimulate MPS (Tipton et al., 1999), a complete mixture of EAAs in the protein source is required for this (Churchward-Venne et al., 2014). Of these EAAs, the branched-chain amino acid (BCAA) leucine is a key determinant, as it can independently enhance MPS rates (Anthony et al., 2000). Leucine is known to be an activator of the mTOR and thus, as mentioned before, plays an important role in MPS and skeletal muscle Thypertrophy (Bodine et al., 2001; Drummond et al., 2009; Nader et al., 2005). Therefore, the addition of BCAAs, of which mainly leucine, to a non-optimal or lower quality protein dose or protein source could be a promising strategy to increase MPS. For example, a clinical study by Churchward-Venne et al. (2014) showed that addition of 5.0 g leucine to a non-optimal dose of whey protein (6.25 g) in a mixed macronutrient drink can increase MPS to the same extent and duration as the optimal dose of whey protein (25 g) in healthy recreationally active young men (18-35 years). When 3.0 g of leucine was added to the suboptimal dose, MPS was effectively stimulated only during the early stage (0-1.5h) (Figure 5). However, when higher amounts of leucine were added (5 g/portion) to the non-optimal dose, this activated MPS not only in the early stage but also the late (1.5-4.5h) equivalent to an optimal amount of whey protein. This indicates that, when adding leucine to a suboptimal protein dose, a higher amount of leucine than present in the optimal whey dose (3 g/portion) is necessary in order to keep prolonged MPS stimulation. EAA, and especially leucine, composition in the protein therefore show to be of high relevance in relation to MPS and are of high importance when evaluating different protein sources.