A nutritional composition that includes from about 75% to about 95% of a first protein source that includes from about 85% to about 99% of protein by weight of the first protein source to provide an endogenous source of tryptophan in an amount between about 1% to about 6% of tryptophan by weight of the first protein source; and from about 0.5% to about 2% of a second protein source by weight of the nutritional composition, the second protein source consisting of an exogenous source of tryptophan such that the nutritional composition provides a ratio of tryptophan to large neutral amino acids in the range from about 0.080:1 to about 0.167:1.