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. 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.