To provide agent for promoting the synthesis of proteins that has effect on promoting the synthesis of proteins.This invention provides agent for promoting the synthesis of proteins that uses a whey protein hydrolysate which has a molecular weight distribution under 10kDa, with a main peak between 200Da～3kDa and APL(average peptide length) in the range of 2～8, and includes free amino acids under 20% of the total amount of all constituents, and branched chain amino acids over 20% of the total amount of all constituents, and shows antigenicity that is under 1/100,000 of that of β-lactoglobulin.本發明的課題在於提供具有蛋白質合成促進效果的蛋白質合成促進劑。本發明提供一種蛋白質合成促進劑，其係使用乳清蛋白質水解物，該乳清蛋白質水解物的分子量分布為10kDa以下且主要峰部在200Da~3kDa、APL(平均胜肽鏈長)為2~8、游離胺基酸含量相對於全部構成成分為20%以下、分支鏈胺基酸含量為20%以上、抗原性為β-乳球蛋白的抗原性的1/100,000以下。
