OC26 - 24-hour dynamic metabolic phenotyping in individuals after bariatric surgery

Background/Introduction Obesity is a growing global health issue. Sleeve gastrectomy (SG), the most common bariatric surgery, induces significant weight loss by altering neurohormonal pathways regulating metabolism, energy intake, and expenditure. However, some individuals experience suboptimal weight loss. This may be due to disruptions in diurnal rhythms of glucose tolerance, metabolism, and appetite, particularly through increased food intake later in the day—a known risk factor for weight gain. Purpose This pilot study aimed to investigate 24-hour variations in key metabolic parameters following SG, including fasting and postprandial glucose, insulin, resting energy expenditure, and self-reported hunger and appetite. Methods Eight participants (mean [SD]; age, 44.8 [10.8] years; five females; BMI on the day of surgery, 41.6 [8.0] kg/m2; BMI 12 months after SG. 29.7 [6.4] kg/m2; 12- month weight loss: 29.0 [3.8] %; paired T-test, p<0.0001) completed a 2-day in- laboratory protocol under highly controlled conditions. Participants adhered to fixed sleep/wake cycles and consumed four isocaloric, isocompositional meals at 1, 5, 9, and 13 hours after awakening. Comprehensive 24-hour metabolic assessments were conducted, including serial measurements of glucose, insulin, cortisol, indirect calorimetry, and appetite ratings via visual analog scales (VAS). Results No significant variation in early-phase postprandial (EPP) glucose (0-30min) area under the curve (AUC) (p=0.745), or insulin (p=0.139) was recorded. Late-phase (30–120min) postprandial (LPP) glucose AUC showed an increase across the day (p<0.001), with significantly higher values for the last compared to the first meal (p<0.001). LPP insulin AUC also varied significantly across the day (p = 0.004), with reduced secretion following the last compared to the first meal (p < 0.001). Analysis of the 24-h temporal patterns of cortisol, energy expenditure, respiratory exchange ratio, and appetite ratings are ongoing and will be presented as well. Conclusion(s) This study is the first to characterize diurnal metabolic profiles post- SG under rigorously controlled conditions. Our findings suggest a progressive decline in glucose tolerance and insulin secretion across the day, mirroring patterns in healthy individuals. Though limited by small sample size, these preliminary results highlight the potential importance of meal timing in post-SG metabolic outcomes and warrant further research to support personalized postoperative care.