The research of energy metabolism concentrates on sports medicine, child nutrition, food nutrition, weight lose and diet for astronaut. The  isotope tracing method is one of the methods for studying metabolism, such as using  ²H,¹⁵N,¹³C and ¹⁸O. For example, the doubly labeled water (DLW) technique of using ²H and ¹⁸O is a new method for estimating the consumption of body energy, which is the most accurate method for estimating metabolism and has been preliminarily applied in the laboratory and field research of sports science.