Our objective is to provide a novel lipid metabolism-improving reagent effective in preventing and treating hyperlipidemia and obesity and to provide this reagent in food, beverages, nutritional supplements, and fodders with the ability to improve lipid metabolism. The whey protein hydrolysate as the active ingredient in the lipid metabolism-improving reagent has a molecular weight distribution of 10 kDa or less, with the main peak between 200 Da to 3 kDa, average peptide chain length (APL) of 2-8, free amino acid content of 20% or less, antigenicity of 1/10,000 or less compared with that of ²-lactoglobulin.
