Comparability of Weight Loss Reporting After Gastric Bypass and Sleeve Gastrectomy Using BOLD Data 2008–2011

Weight loss after bariatric surgery is commonly reported as either a percentage of initial body weight (%IBW) or 100 % minus %IBW which is a percentage of total weight loss (%TWL). These are basically equivalent expressions. Weight loss is also reported as %EWL or as a percentage of excess body mass index loss (%EBMIL). These last two expressions incorporate the concepts of ideal body weight and BMI = 25 as reference points. More straightforward but less commonly used is absolute weight loss. This study compares these various measures using the Bariatric Outcomes Longitudinal Database (BOLD).

BOLD data, 2008–2011, was accessed for outcomes on 239,659 gastric bypass (GB) and sleeve gastrectomy (SG) patients with approval of the Surgical Review Corporation. The outcome data was converted into %TWL, %EWL, and %EBMIL. %EBMIL was varied by changing the reference BMI from 1 to 25 kg/m². The post operation data was analyzed for both procedures. Variation coefficients (VC) were compared using different measurements on the same data pool. We assumed that the lesser the variation, the more reliable the measure is, and therefore, we made use of the VC to compare the different reporting methods.

There were 164,247 patients who remained after removal of errors and missing data. Demographics are as follows: 78.1 % female, 73.1 % white, 12.5 % black, 8.71 % Hispanic, 81.6 % GB, 18.4 % SG, mean age of 44.8 years, height of 167.0 cm, weight of 132.0 kg, and BMI of 47.1 kg/m². GB patients had 26.8 %TWL at 6 months (VC = 21.5) and 34.2 %TWL at 12 months (VC = 27.0). %EWL was 54.7 at 6 months (VC = 27.3) and 69.4 at 12 months (VC = 30.9). Varying the reference BMI for %EBMIL showed the lowest VC to be 0–2 kg/m² for GB up to 12 months post operation. SG patients had 24.0 %TWL at 6 months (VC = 25.4) and 29.5 at 12 months (VC = 30.5). %EWL was 50.0 % at 6 months (VC = 31.4) and 60.2 % at 12 months (VC = 34.5). Varying the reference BMI for %EBMIL showed that the lowest VC occurred when the reference weight was chosen as 0 kg/m² for both GB and SG. %TWL or, equivalently, %IBW had the lowest variation coefficient and therefore is the more accurate measure of weight loss following bariatric surgery.

For ease and accuracy of comparison, the percentage of initial body weight or percentage of total weight loss should be used for the expression of weight loss after surgery.