Changes in food preferences, dietary intake, and eating behaviours following gastric bypass surgery

Gastric bypass surgery is an effective treatment for obesity. Postoperative weight loss is facilitated through reductions in energy intake (EI); however, it remains unclear whether this is through reduced portion sizes of the same foods consumed pre-surgery and/or through specific changes in macronutrient intakes. The aim of this thesis was to investigate the effect of gastric bypass surgery on EI, eating behaviours and food preferences in relation to body composition. A systematic review of the literature on changes in dietary intake and appetite following gastric bypass found that only a decrease in EI and an increase in postprandial satiety were sustained beyond 6-months post-surgery. However, the findings of this review were limited by the quality of data available, and particularly by an overreliance on subjective measures of EI without acknowledgment of the phenomenon of misreporting. The present work employed objective and covert measures to evaluate changes in 24-hour EI and eating behaviours under residential conditions in patients after gastric bypass surgery, compared to weight-stable controls, from 1-month pre-surgery to 3- and 12-months post-surgery. Participants had ad-libitum access to a range of foods tailored to their preferences. All patients lost weight, and EI was significantly reduced from preoperative values at both 3- and 12-months post-surgery. This reduction was facilitated through smaller portion sizes of the same foods consumed pre-surgery, rather than through changes in food selection. Decreases in subjective food preferences were not associated with meaningful changes in macronutrient intakes. Reduced EI and food preferences were more pronounced in patients who reduced their dietary energy density, indicating that there may be additional motivations or drivers that mediate postoperative reductions in EI. Understanding how individual differences contribute to postoperative weight loss would allow for interventions to be individually tailored to optimise outcomes and may aid the development of non-surgical treatments for obesity.