1. The use of a whey fraction containing serum proteins of α-lactalbumin (α-LA) and casein macropeptide (CMP), in which the mass ratio between α-LA and glycomacropeptide (GMP) is ≥2, for the production of a nutritional, dietary or pharmaceutical composition, contributing to maintaining a healthy body mass. 2. The use according to claim 1, where the mass ratio of α-LA to CMP is ≥3, preferably ≥4.3. The use according to claim 1, wherein said whey fraction has an α-LA content of from 20% to 36%, and a CMP content of 3% to 15% of the total protein. The use according to claim 1 or 3, wherein said whey fraction is also characterized by (a) a lactose content of 10% or less； (b) a total protein content of 12.5% to 95%； (c) a fat content of 15% or less and / or (d) a mineral content of 4.5% or less. 5. The use according to claim 4, wherein said whey fraction has a total protein content of from 35% to 80%, preferably from 70% to 77%. The use of claim 1, wherein said whey fraction comprises hydrolyzed whey proteins. The use according to claim 1, wherein the pH of said nutritional, dietary or pharmaceutical composition is below 5.5, preferably below 5 and most preferably below 4.6.8. A dairy product comprising a whey fraction containing α-lactalbumin (α-LA) and casein macropeptide (CMP), in which the mass ratio between α-LA and GMP is ≥2.9. The dairy product of claim 8, in which the mass ratio of α-LA to CMP is ≥3, preferably ≥4.10. The dairy product of claim 8, wherein the whey fraction provides at least 30% of the total calorie content of the dairy product. The dairy product of claim 8, which is a dairy product1. Применение сывороточной фракции, содержащей сывороточные белки α-лактальбумин (α-LA) и макропептид казеина (СМР), в которой массовое соотношение между α-LA и гликомакропептидом (GMP) составляет ≥2, для производства питательной, диетической или фармацевтической композиции, способствующей поддержанию здоровой массы тела.2. Применение по п.1, где массовое отношение α-LA
