The invention relates to the use of specific protein and/or peptide fractions having a high aspartate content for regulating plasma glucose concentrations and increasing insulin sensitivity in a mammal. It has been found that high amounts of aspartate equivalents, especially in relative absence of glutamate equivalents, increase the glucose uptake of peripheral cells and improve the reaction of the liver on dietetic glucose consumption. As a result it has a favourable effect on the blood glucose levels of a person suffering from hyperglycaemia, in particular postprandial and post-surgery hyperglycaemia and/or insulin resistance. The invention relates to a complete food fortified with aspartate equivalents as well as a supplement rich in aspartate equivalents that is given simultaneously with or even minutes up to an hour prior to the consumption of a meal comprising glucose. The nutritional or pharmaceutical composition contains at least one protein having a high aspartate content, preferably of soy or dairy origin, which is further enriched with aspartate equivalents from another protein and/or free aspartate equivalents. The protein fraction comprises glutamate equivalents in a weight ratio of aspartate equivalents to glutamate equivalents (asp:glu) between 0.41:1 and 5:1.