Betaine stable isotopes are a group of naturally occurring compounds that contain carbon, hydrogen, and nitrogen atoms with different isotopes. These isotopes can be used as tracers to study the metabolism of betaine in biological systems. By measuring the ratio of stable isotopes in betaine, researchers can gain insights into the sources of the molecule, its transformations, and its role in various physiological processes. Betaine stable isotopes have applications in fields such as nutrition, medicine, and environmental science.