The present invention provides a novel NMR metabolomics method for observing an animal by labeling the animal itself. A labeled animal labeled with a stable isotope is produced by feeding an animal a labeled food labeled with the stable isotope. Metabolism of a biological substance in the animal is analyzed based on nuclear magnetic resonance data of the biological substance containing the stable isotope. The nuclear magnetic resonance data is acquired by performing NMR measurement on a body of the labeled animal, a portion of the body, or an extract.