Factors Associated With Long-Term Weight Loss Following Bariatric Surgery Using 2 Methods for Repeated Measures Analysis

Abstract

We used electronic health record data from 162 patients enrolled in the NUgene Project (2002-2013) to determine demographic factors associated with long-term (from 1 to up to 9.5 (mean = 5.6) years) weight loss following Roux-en-Y gastric bypass surgery. Ninety-nine (61.1%) patients self-reported white, and 63 (38.9%) self-reported black, mixed, or missing race. The average percent weight loss was -33.4% (standard deviation, 9.3) at 1 year after surgery and -30.7% (standard deviation, 12.5) at the last follow-up point. We used linear mixed and semiparametric trajectory models to test the association of surgical and demographic factors (height, surgery age, surgery weight, surgery body mass index, marital status, sex, educational level, site, International Classification of Diseases code, Current Procedural Terminology code, Hispanic ethnicity, and self-reported race) with long-term percent weight loss and pattern of weight loss. We found that black, mixed, and missing races (combined) in comparison with white race were associated with a decreased percent weight loss of -4.31% (95% confidence interval: -7.30, -1.32) and were less likely to have higher and sustained percent weight loss (P = 0.04). We also found that less obese patients were less likely to have higher and sustained percent weight loss (P = 0.01). These findings may be helpful to patients in setting expectations after weight loss surgery.

Keywords: Roux-en-Y gastric bypass; bariatric surgery; long-term weight loss; predictors; race; repeated measures.

Figure 1.

The analytical sample used in this analysis was drawn from patients enrolled in the NUgene Project (2002–2013) at either Northwestern Medicine Hospital or NorthShore University HealthSystem. Of all the patients who underwent bariatric surgery, patients were initially excluded if they had 2 or more surgeries, if they had a nonapplicable surgery, if their health records were missing critical information (surgery age and relevant weights), or if the surgery date was incorrect. Patients were further excluded if a large proportion of observations were taken while pregnant or if the surgery was not a bypass. Specific observations were excluded if they occurred within 1 year after surgery, and any patients were excluded if all of their observations were within 1 year after surgery.

Figure 2.

Trajectory-based model and average observed percent weight loss by group among 162 bypass patients enrolled in the NUgene Project (2002–2013) from 1 to over 9.5 years of follow-up after Roux-en-Y gastric bypass surgery at Northwestern Medicine Hospital and NorthShore University HealthSystem. The dash-dot-dot-dash line represents the trajectory plot of group 4, the large dashed line represents the trajectory plot of group 3, the dot-dashed-dot line represents the trajectory plot of group 2, and the small dashed line represents the trajectory plot of group 1. For each group, confidence intervals are depicted for the trajectory plots, and the average observed percent weight loss among each group is shown as a solid line.