Li et al. describe analyses of GLOW data that re-consider the relationship between obesity and fracture risk. The report addresses an interesting aspect of the ongoing debate - the potential role of physical disability or frailty. Although others have considered this issue, the data included here add somewhat and serve to highlight the problem. The limitations of the study, including the self reported nature of the data, the lack of incident fall data, and the lack of BMD, are significant and are mostly acknowledged by the authors. In general, the results are clearly described and the conclusions are reasonable. Most of the concerns are relatively minor and concern clarity.

1. The major analyses consider obesity as a dichotomous variable. The cohort is overweight (mean BMI 27) and thus a large proportion were obese (29%). There is one supplemental table in which BMI is treated as a continuous variable. It would be useful to further examine the BMI distribution to determine if the relationships between BMI, FI and fracture are non-linear.
2. The Discussion paragraph on limitations is overly long and a bit redundant with other sections. It could be considerably reduced.
3. The third paragraph in the Discussion is somewhat confusing. It starts out with this sentence "Obesity was not significantly related to decreased MOF risk when frailty was not considered, even though obese women tended to have a lower fracture risk..." and goes on to include a number of other logical disparities. The authors might review this text and make their points more clearly.
4. The term "frailty" is used throughout, but it has a variety of meanings and definitions, and its appropriate use is debated. The FI used here is more like a comorbidity index, and it's not clear what components of it are most influential in the analysis results. Since the FI has been previously used in GLOW, it probably can't be re-named, but at least it should be acknowledged that it represents a non-traditional use of "frailty".
5. It would be useful to describe the power available for the planned analyses.