The present invention is directed to a heat sterilized spoonable nutritional composition comprising: a protein source in an amount of 12 to 20% by weight of the composition, the protein source consisting of whey protein containing whey protein micelles and a source of casein, wherein the nutritional composition is a liquid or semi-liquid composition having a viscosity of between 400 and 4000 mPa·s at 20° C. measured at a shear rate of 100 s−1. The inventive heat sterilized spoonable nutritional composition preferably has a cysteine content of 1.2 to 2.4% by weight of the composition. The present invention is furthermore directed to a process for preparing a heat sterilized spoonable nutritional composition comprising protein in an amount of 12 to 20% by weight based on the weight of the composition, said protein consisting of whey protein containing whey protein micelles and casein, which comprises the steps of: (i) Providing an aqueous solution of a protein source consisting of whey protein containing whey protein micelles and (ii) Adding a protein source containing casein; (iii) Optionally performing a homogenization treatment step; (iv) Performing an indirect UHT heat treatment step; (v) Optionally performing a homogenization treatment step, wherein following steps (i) to (v) a heat sterilized spoonable nutritional composition is obtained having a viscosity of between 400 and 4000 mPa·s at 20° C. measured at a shear rate of 100 s−1. Finally, the invention concerns the use of a protein source consisting of whey protein containing whey protein micelles and a source of casein, for preparing a spoonable nutritional composition and/or for controlling the viscosity of a liquid or semi-liquid spoonable nutritional composition, wherein the spoonable nutritional composition comprises 12 to 20 weight % total protein. The invention also concerns medical uses and treatments applying or using the inventive heat sterilized spoonable nutritional composition.