The present invention provides a lipid metabolism-improving agent which has excellent effect on lipid metabolism improvement, and being effective to prevent and cure hyperlipidemia and adiposity. This invention also provides lipid metabolism-improving products such as food and drinks, nutrition compositions or feedstuffs blended with the lipid metabolism-improving agent.The lipid metabolism-improving agent is characterized by containing the whey protein hydrolysate as effective ingredient, which is featured in that the distribution of molecular weight is below 10kDa, with main peak from 200Da to 3kDa, APL(Average Peptide Length) from 2 to 8, content of free amino acid below 20%, and antigenecity below 1/10,000 of that of β-lactoglobulin.本發明提供一種脂質代謝改善效果優異、對預防及治療高血脂症、肥胖症等有效之脂質代謝改善劑，以及調配該脂質代謝改善劑的飲食品、營養組成物、飼料等的脂質代謝改善製品。該脂質代謝改善劑之特徵係含有分子量分佈在10kDa以下且主要波峰在200Da至3kDa，APL(平均胜肽鏈長)為2至8，游離胺基酸含量在20%以下，以及抗原性為β-乳球蛋白的抗原性的1/10,000以下之乳清蛋白水解物作為有效成分。
