Measuring in vivo metabolism using heavy water

Purpose of review Our goal is to explain how (H2O)-H-2, a stable isotope of water, can be used to quantify metabolic flux in vivo. Although (H2O)-H-2 was originally used more than 65 years ago, recent reports have described new applications. Investigators have also refined the original work. We discuss those points, emphasizing factors that should be considered when interpreting data. As our goal is to discuss why (H2O)-H-2 is a novel tracer for studying metabolism, we do not comment on the interpretation (s) of physiological data. Recent findings It is clear that (H2O)-H-2 can now be used to address questions related to carbohydrate, lipid, protein and DNA synthesis. A particular advantage of using (H2O)-H-2 is that investigators can study metabolism in free-living individuals. Using this novel tracer method, it is thus possible to elucidate new, highly relevant, knowledge regarding health and disease. Summary As the use of (H2O)-H-2 requires few assumptions, the application of this tracer should yield sound information regarding the regulation of biochemical reactions in vivo.