Background

Several studies have demonstrated that following metabolic and bariatric surgery (MBS), patients' mood improves. Indeed, improvement in depression symptoms appear to peak approximately 1-2 years post-MBS but unfortunately those improvements deteriorate, with average depressive mood returning to pre-surgical levels (or worse) by 7-10 years post-MBS. Additionally, once reaching their lowest weight (on average 1-2 years after surgery), most patients regain some amount of weight, with some regaining a significant amount of weight. The fact that weight nadir and increases in depression score appear to begin at the same time has led many in the field to conclude that depression increases because patients are no longer losing weight and have begun regaining weight. However, one major limitation of this past literature is that weight loss and depression have been averaged across all participants at each timepoint, rather than looking at within participant patterns, studying how mood changes in relation to each individual's weight nadir. In the current study, we examined 157 participants across 9 timepoints (pre-surgical baseline to 3 years post-surgery), which provided 1,113 total data points. We found that depression score increases and weight-nadirs occurred at similar times after surgery (approximately 12 months). However, there was no difference in BDI before and after individual weight nadir (β= 0.067, p=.638). This finding demonstrates that mood and weight loss changes following MBS are largely unrelated, and further suggests that previous research on the link between patients' mood and weight outcomes may be misleading.