Background: The aim of this study was to determine if presurgery (T1), post-surgery (T2), or the change in body mass index (BMI) between these time points are useful predictors for predicting longer-term (T3) outcome in gastric bypass surgery.
Methods: The sample consisted of 72 gastric bypass surgery patients with an average age of 40.5. The mean presurgery BMI was 54.7 (SD = 8.6). T2 assessments (BMI, depressed mood, binge eating status) occurred on average 21 weeks (SD = 19) after surgery and T3 assessments occurred on average 63 weeks (SD = 34) after surgery.
Results: Three separate hierarchical linear regressions were performed to assess the predictive value of (1) BMI at T1, (2) BMI at T2, and (3) change in BMI from T1 to T2 on the dependent variable, BMI at T3, when age, sex, ethnicity, education status, age of overweight, binge eating status, depressed mood, and number of weeks after surgery were controlled for. When these demographic and psychological variables were controlled for, lower BMI at T1 and lower BMI at T2 predicted lower BMI at T3. However, change in BMI from T1 to T2, did not significantly predict BMI at T3 (p < .001).
Conclusions: Higher presurgery BMI and post-surgery BMI predict poorer 1-year follow-up BMI in gastric bypass surgery, and these measures can be used as easy "rules of thumb" for predicting longer term outcome.