Abstract
Background: The physiological changes underlying the beneficial effects of bariatric surgery (BS) are unclear, particularly whether postoperative weight loss results from the reduction of food intake after surgery or from the surgery itself. Few studies have assessed the association between energy intake and weight loss after Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). Also, the differences in energy and macronutrient intake in individuals with obesity versus individuals with healthy weight have received relatively little attention. The primary aim of this cross-sectional study was to investigate the association between dietary intake (energy and macronutrient) and weight loss after RYGB and SG. In addition, the effects of BS on quality of life, eating disorders, and anthropometry, were measured.Methods: Firstly, a systematic review was undertaken to investigate the change in nutrient intake in the short- and long-term period following BS, specifically RYGB and SG, and compare intakes to the recommended Acceptable Macronutrient Distribution Ranges. This review also explored whether daily energy intake was associated with weight loss in the included studies. Secondly, three study groups were recruited for a cross-sectional study that included individuals with severe (class III) obesity (n = 45), individuals post-BS (n = 50) at steady state for body weight (≥ 24 months after surgery), and individuals with healthy weight (n = 50). Outcome measures included anthropometry, weight history, a 3-day quantitative dietary diary, the eating-disorder-examination-questionnaire, and the 36-Item-Short-Form-Health-Survey that assesses the quality of life. Lastly, the accuracy of estimating portion sizes was assessed during a single meal buffet feeding experiment within a subset of participants (n = 25).
Results: Systematic review: Both SG and RYGB bariatric surgeries were associated with a decrease in overall energy intake, showing weighted mean difference of -886 kcal/day from baseline at 12 months post-surgery (95% CI -1039 to -732; p < 0.001). No detectable differences were observed in overall energy intake between the different types of surgeries. After BS, carbohydrate and protein intake were within recommended intakes, however, fat intake was slightly higher than recommended.
Further analysis of the literature revealed that, in general, daily energy intake is not associated with weight loss at 12 months after BS. Cross-sectional study: There was no significant correlation between energy intake and weight loss among individuals who had undergone BS at ≥ 24 months after surgery. Energy intakes; adjusted for covariates including age and, gender; were not significantly different between groups including operated group (1516 ± 656 kcal/day), unoperated obesity group (1865 ± 648 kcal/day) and the healthy weight group (1988 ± 486 kcal/day) (P= 0.059). Individuals with obesity had significantly higher disordered eating behaviours compared to individuals with healthy weight, while the operated group had significantly lower weight concerns compared to the obesity group (P < 0.001). Regarding quality of life, individuals with obesity had a lower quality of life compared to those with a healthy weight (P < 0.001). Individuals who had BS had a better quality of life compared to those with obesity (P < 0.001). Estimation of portion size was significantly more accurate in the operated group (7% overestimation) than in the obesity group (78% overestimation). However, there was no significant difference in the estimation of portion size between obesity and healthy weight groups (27% overestimation).
Conclusions: The findings suggest that the degree of weight loss maintenance after BS is not associated with energy intake. Hence, the mechanism behind weight loss maintenance after BS may involve other biological mechanisms. In addition, our results show that BS is associated with improved eating behaviours and quality of life. Further prospective studies validating the influence of BS on energy intake and meal size are warranted.
| Date of Award | 1 May 2024 |
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| Original language | English |
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| Supervisor | Francesco Rubino (Supervisor) & Majella O'Keeffe (Supervisor) |