Fat content affects heat capacity: a study in mice.

The specific heat capacity of the human body is a widely used number in calculations related to studies in energy metabolism and temperature regulation. A value of 3.47 kJ kg-1 K-1 has been used during the last century, but there have been no direct studies on the dependence of this value on the body fat content. We present here results of measurements of the specific heat capacity of lean and obese mice. The mice were killed and heated to 40.6 degrees C, transferred to a calorimeter and the specific heat capacity was determined from body mass of the mice and temperature rise of water in the calorimeter. We measured the fat fraction of body mass (mf), fat free body mass and water content of the mice and found a marked dependency of the specific heat capacity (Cp) on body fat. In obese mice (fat content 52.76% body wt) the heat capacity was 2.65 kJ kg-1 K-1 and in lean mice (fat content 7.55% body wt) the heat capacity was 3.66 kJ kg-1 K-1.