The invention generally relates to metabolic labeling of a target organism with a stable isotope. In a first aspect, the present invention relates to a method for metabolic labeling of a target organism with a stable isotope. The present invention also relates to a method of producing a diet for metabolic labeling of a target organism and to a diet composition for metabolic labeling of a target organism. In a further aspect the invention describes the use of the diet composition according to the present invention for producing a metabolically labeled target organism as a reference for a quantitative proteomic approach. The present invention also relates, in a further aspect, to the use of a diet composition for pulse SILAC labeling. The present invention also relates to the use of a target organism labeled by the method according to the first aspect of the present invention as a spike-in standard in quantitative proteomics approaches.
