Methods for producing stable isotope-labeled recombinant protein are provided. The methods include isolating a stable isotope-labeled recombinant protein from a Trichoplusia ni larva expressing a recombinant protein, which Trichoplusia ni larva has ingested a food source comprising stable isotope-labeled algae, thereby resulting in incorporation of a stable isotope into the recombinant protein to produce the stable isotope-labeled recombinant protein.