Intestinal Energy Absorption is Associated with Post-Bariatric Surgery Weight Loss

Metabolic and bariatric surgery (MBS) is the most effective treatment for severe obesity; however, a significant subset of patients do not achieve the expected weight loss or experience substantial weight recurrence over time. While intestinal energy absorption potentially influences weight loss outcomes, this phenomenon has not been investigated in post-MBS patients. Therefore, we assessed the relationship between diet, intestinal energy absorption, and weight outcomes in individuals post-MBS.

Caloric intake, determined via dietary questionnaires, and fecal energy density, determined via bomb calorimetry, were used as a proxy to assess calorie absorption before and after gastric bypass or sleeve gastrectomy. Within a total of 67 patients, fecal energy density was measured at 0, 1, 6, 12, 18, and 24 months. A dynamic linear mixed-effects model was used to examine the longitudinal association between intestinal energy harvest and subsequent weight loss following MBS. Multivariate regression was developed to identify potential weight loss predictors, and random forest algorithms were employed to forecast weight results based on intestinal energy absorption.

Intestinal energy absorption changed over the pre- and post-MBS periods. Random forest models indicated that intestinal energy absorption enhanced the predictability of patient weight loss outcomes.Fecal energy density was modestly but significantly associated with weight loss at later postoperative time points (p = 0.04), suggesting that reduced intestinal energy absorption contributes to more sustained weight reduction post-MBS. Associations between diet and energy absorption were not significant.

MBS changes energy absorption capacity post-surgery. A higher relative fecal energy content (lower energy absorption) at early timepoints are associated with better weight loss outcomes at later timepoints post-MBS. Findings may guide the development of diagnostic tools and treatment guidelines for patients at risk of suboptimal weight loss outcomes.