Purpose of review: Our goal is to explain how 2H(2)O, a stable isotope of water, can be used to quantify metabolic flux in vivo. Although 2H(2)O 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 2H(2)O is a novel tracer for studying metabolism, we do not comment on the interpretation(s) of physiological data.
Recent findings: It is clear that 2H(2)O can now be used to address questions related to carbohydrate, lipid, protein and DNA synthesis. A particular advantage of using 2H(2)O 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 2H(2)O requires few assumptions, the application of this tracer should yield sound information regarding the regulation of biochemical reactions in vivo.