"Fatness" And Early Retirement

The Michigan Retirement Research Center has published a study on the relationship between "fatness" as they call it and early retirement. I do not understand why they chose to call it "fatness" rather than "obesity", but their findings are interesting nevertheless. Here is their abstract of the study:

Theoretical models argue that poor health will contribute to early exit from the labor market and the decision to take early Social Security retirement benefits (Old-Age or OA benefits). However, most empirical estimates of the causal importance of health on the decision to take early OA benefits have been forced to rely on global measures such as self-rated work limitations or self-rated health. We contribute to the empirical literature by using a more objective measure of health, fatness, to predict early receipt of OA benefits. We do so by estimating the causal impact of fatness within an empirical model using the method of instrumental variables, and testing the robustness of our findings using the most common measure of fatness in the social science literature – body mass index – with what is a more theoretically appropriate measure of fatness – total body fat and percent body fat. Overall, our conclusion is that fatness and obesity are strong predictors of early receipt of OA benefits.