Abstract: The present invention relates to a method for the non-denaturing preparation of peptide or protein nanoprecipitates, or of peptide or protein and metal ion nanocoprecipitales, in which said protein or said peptide has a molecular weight no higher than 20 kDa, preferably no higher than 15 kDa, advantageously no higher than 10 kDa, and more advantageously no higher than 8 kDa. Said method includes a step of preparing a mixture of an aqueous solution of peptides or proteins, a nonsolvent of the peptide or protein, and optionally a water-soluble metal salt. The present invention also relates to a nanoprecipitate that can be obtained by the method according to the invention, as well as to a pharmaceutical composition comprising same, for use in the treatment or prevention of diabetes.