Reporting weight change: standardized reporting accounting for baseline weight

Background: Although it is recognized that a standardized approach to reporting weight change is essential to meaningful comparisons among cohorts and across studies, consensus is lacking. This study aimed to propose a method of reporting weight change that would allow meaningful comparisons among studies of patients who underwent bariatric surgery and to demonstrate its utility using an example from the Longitudinal Assessment of Bariatric Surgery (LABS).

Methods: Relationships among several measures of weight change are described. Results from an observational, longitudinal cohort study of adults undergoing bariatric surgery and from simulation studies are used to illustrate the proposed method.

Results: Baseline weight is a critical parameter when assessing weight change. Men undergoing a bariatric procedure other than gastric bypass or adjustable band tended to have greater weight loss 12 months after surgery than men undergoing gastric bypass when not accounting for baseline weight, but the opposite was found when results were adjusted for baseline weight. Simulation results show that with relatively modest sample sizes, the adjusted weight loss was significantly different between the 2 groups of men.

Conclusion: A consistent metric for reporting weight loss after bariatric surgery is essential to interpret outcomes across studies and among subgroups. The baseline weight adjusted percent of weight loss (A%WL) uses a standard population (e.g., the LABS cohort) to account for differences between cohorts with respect to baseline weight, and its use can change the interpretation of results compared with an unadjusted measure.