Strengths and validity of three methods for assessing rat body fat across the life course

There are several different methods available for the determination of body fat composition. Two current methods requiring special instrumentation are magnetic resonance imaging (MRI) and dual energy x-ray absorptiometry (DXA). The use of these techniques is very limited despite desirable properties, due to their high costs. Dissection of all fat depots (DF) requires no special instrumentation and allows examination and evaluation of each fat depot in more detail. MRI, DXA, and DF each have their unique advantages and disadvantages when they are applied to animal models. Most studies have determined body fat in young animals, and few studies have been performed in aging models. The aim of this study was to compare MRI, DXA, and DF data in offspring (F1) of mothers fed with control and high-fat diet. We studied rats that varied by age, sex, and maternal diet. The relationships between the three methods were determined via linear regression methods (using log-transformed values to accommodate relativity in the relationships), incorporating when useful age, sex, or diet of the animal. We conclude that the three methods are comparable for measuring body fat, but that direct equivalence gets masked by age, sex, and sometimes dietary group. Depending on the equipment available, the budget of the laboratory, and the nature of the research questions, different approaches may often suggest themselves as the best one.