The small intestine plays a vital role in nutrient absorption, hormone regulation, and glucose metabolism. Anatomical variability in total small bowel length (TSBL) may contribute to differences in metabolic outcomes. Although TSBL varies significantly between individuals, its relationship with glycaemic control and metabolic syndrome remains under-investigated. This study aimed to assess the relationship between TSBL, glycated haemoglobin (HbA1c), and metabolic syndrome in patients undergoing primary bariatric bypass surgery.

This cross-sectional study included 478 patients who underwent standardized intraoperative TSBL measurement at a high-volume bariatric center in Taiwan. Individuals on antidiabetic medications or with significant renal dysfunction were excluded. Associations between TSBL and clinical parameters were analyzed using univariate and multivariate regression models, adjusting for sex, height, body mass index (BMI), and other relevant covariates.

Longer TSBL was independently associated with higher HbA1c levels and a greater likelihood of metabolic syndrome, even after adjustment for BMI and other confounders. The final multivariate model explained 13.1% of the variance in TSBL (R² = 0.131).

These findings suggest that intestinal morphology may influence metabolic regulation beyond the effects of obesity alone. Anatomical variation in small bowel length could represent a previously underappreciated determinant of glycaemic control and metabolic risk. Further multi-center prospective studies are warranted to elucidate the physiological mechanisms linking bowel length to metabolic function and to inform personalized surgical strategies.