Results of the present study add to a growing body of literature on the characteristics associated with weight loss following bariatric surgery. Participants lost approximately 25% of their preoperative body weight within the first 20 weeks of gastric bypass surgery. They lost another 10% over the next 20 weeks and almost 40% of their initial body weight by the second postoperative year. Of the potential predictor variables of interest investigated, gender, baseline cognitive restraint, and self-reported dietary adherence at postoperative Week 20, when participants had returned to regular food, were significant predictors of percent weight loss over time.
Men who underwent bariatric surgery lost significantly more weight over time than did women. This result is not particularly surprising, as men have been found to lose more weight than women in other studies of bariatric surgery as well as studies of behavioral and pharmacological treatments for obesity.28
This difference is typically attributed to metabolic differences between the genders, although obese men, and their response to weight loss, surgical or otherwise, are studied far less frequently.
The contributions of baseline cognitive restraint and adherence to the postoperative diet represent novel and interesting findings. Those individuals who reported higher levels of cognitive restraint at baseline experienced greater weight losses postoperatively. Cognitive restraint is typically characterized as an individual’s ability to intentionally limit food intake, typically to prevent weight gain.25
Given the positive association between baseline cognitive restraint and dietary adherence found in this study, it may be that the ability to restrict food intake prior to surgery predicts adherence to the rigorous postoperative diet. As a whole, individuals in the present study reported relatively low levels of cognitive restraint preoperatively and could be described as “unrestrained eaters.” However, we found an association between baseline cognitive restraint and the % kcal/d from sweets (r = −0.30, p = 0.0003), % kcal/d from fat (r = −0.21, p = 0.01) and % kcal/d from protein (r = 0.20, p = 0.01), suggesting that those with higher levels of dietary restraint consumed comparatively healthier diets prior to surgery.
Self-reported adherence to the postoperative diet at postoperative week 20, when participants had returned to eating regular foods, also was associated with larger postoperative weight losses. Those individuals above the median in dietary adherence, as compared to those below the median, experienced a weight loss 2.4% percentage points greater at postoperative Week 40 and 3.8% percentage points greater at Week 66. By Week 92, both groups had regained some weight. However, those high in self-reported dietary adherence achieved a weight loss that was 4.5% percentage points greater than those who reported less adherence to the postoperative diet, representing a 28% greater weight loss. Interestingly, those individuals initially categorized as high in dietary adherence reported a significant deterioration in their adherence to the postoperative diet over the course of the study, although their adherence remained significantly greater at Week 92 than those initially categorized as low in dietary adherence.
Presently, there are no accepted standards for the postoperative diet following bariatric surgery. Adherence to the dramatically reduced portion sizes is believed to be a significant challenge for many patients. This study, like others,8,14–19
suggests that while patients often are able to decrease their caloric intake within the first postoperative year, caloric intake increases over time. The present study is the first, however, to provide evidence that adherence to the postoperative diet is predictive of postoperative changes in weight.
Baseline self-esteem and depressive symptoms, as well as positive and negative affect, were not associated with postoperative weight loss. These characteristics were, however, associated with changes dietary adherence during the postoperative period. In general, studies that have investigated the relationship between baseline psychosocial characteristics and/or psychopathology following bariatric surgery have been contradictory.4–7
This lack of conclusive association has led some to question the value of the assessment of preoperative psychosocial status. These evaluations typically assess the presence of formal psychopathology that may contraindicate bariatric surgery but also evaluate the environmental influences and psychosocial factors that may have contributed to the development of extreme obesity, and, perhaps most importantly, their potential relationship with postoperative outcome.20
Results of the present study underscore the importance of a preoperative assessment of eating behaviors, whether conducted by a mental health professional or dietitian.
Consistent with other investigations,4–6
participants experienced improvements in psychosocial status postoperatively. Self-esteem improved, positive affect increased, and negative affect and depressive symptoms decreased. Participants also experienced changes in their eating behavior. Dietary restraint increased, while hunger and disinhibition decreased 20 weeks after surgery and remained at these levels through the second postoperative year. Participants also reported a postoperative reduction in total caloric intake, as well as the percentage of kcals/d from sweets and desserts. These findings are likely related to the restrictive aspects of gastric bypass surgery, as well as concerns about the “dumping syndrome” following consumption of sugar. There was a significant increase in percentage of kcal/d from protein 20 weeks after surgery, but by 92 weeks protein intake returned to baseline levels. However, the overall change from baseline was modest and its clinical significance unclear. The lack of lasting change in protein is somewhat concerning, given that patients were explicitly instructed during their preoperative nutrition counseling session to increase the amount of protein they consume postoperatively.
While providing important new information, the present study has a number of limitations. Perhaps most critically, we experienced significant attrition. Only 56% of participants completed the final assessment, despite repeated mailings and phone calls and/or emails encouraging them to complete the study. High rates of attrition are a relatively common experience in obesity studies and represent a significant threat to the integrity of treatment outcomes studies. However, in a post-hoc analysis, we found no significant differences in the baseline variables of interest between those individuals who did and did not remain in the study. While the mixed model used in the present study is a recommended analytic method to handle missing data, it is not a perfect substitute for lower attrition rates.
Our reliance on self-report measures is another limitation. The self-reported weights used in the present study are likely to have overstated participants’ weight losses by 2 to 3 kg.29
Postoperative weight losses, however, remained substantial even with this likely overestimation. While self-report measures of psychological symptoms and eating behaviors are widely-used, they are not the ideal measures of psychopathology or dietary intake. Future studies should strive to augment these assessments with validated clinical interviews. While results of the present study suggest that cognitive restraint and adherence to the postoperative diet are related to change in weight in the first two postoperative years, their relationship to longer term weight losses is unknown. Regardless, these findings suggest the possible utility of pre- or postoperative dietary counseling interventions to improve dietary adherence and optimize postoperative outcomes.