Mind your "girth"!

What body condition index is best? Studied for mice in the new Early View paper by Marta K Labocha and co-workers. Below is a summary by Marta:

In humans, BMI (or the body mass index) is a widely used indicator of a person’s body fat.  In animals other than humans, body fat is also important because animals with more fat typically have greater energy reserves which may allow them to better cope with stressful conditions.   In animals, these indicators of body fat (and sometime other indicators of animal quality) are called condition indices.  These condition indices are typically determined from body measurements, but exactly which measurements to use is both unclear and a topic of keen interest.  Many conditions indices are used without being tested for their accuracy.  To test these indices, we compared how well a broad range of body condition indices predicted body fat content in mice Mus musculus. We also compared the performance of these condition indices with a statistical technique, multiple regression of several morphometric variables (body measurements) on body fat content. Multiple regressions incorporating pelvic circumference (i.e., girth at the iliac crests –around the widest part of the hips) were the best predictors of body fat content and were better than any of the condition indices. So, perhaps not surprisingly, mice with bigger waists are fatter.  What is surprising is that this method has not been used before for mice.  Our results suggest a way to improve condition mass indices for mice, and our methods may be useful for other animals as well.