Calculating Diet-Induced Thermogenesis in Mice.

Diet-induced thermogenesis (DIT) is the increase in energy expenditure (EE) associated with food intake. Increasing DIT may lead to weight loss, so it is expected that increasing DIT will decrease body mass index and body fat mass. DIT in humans has been measured in various ways, but there is no way to calculate absolute DIT values in mice. Therefore, we developed a method to measure DIT in mice by applying a method more commonly used in humans. First, we measure the energy metabolism of mice under fasting conditions. EE is then plotted against the square root of activity, and a linear regression equation is fitted to the data. Next, we measure the energy metabolism of mice fed ad libitum and plotted EE in the same way. DIT is calculated by subtracting the predicted EE value from the EE value of mice fed at the same activity count. This method not only allows observation of the time course of the absolute value of DIT but also allows calculation of the ratio of DIT to caloric intake and the ratio of DIT to EE.