Quantifying Malabsorption After Roux-en-Y Gastric Bypass and Sleeve Gastrectomy Using Near Infrared Spectroscopy.

Background: Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) are common bariatric procedures that lead to substantial and sustained weight loss. Although both procedures induce hormonal and physiological effects, RYGB includes both a restrictive and malabsorptive component due to anatomical rerouting, whereas SG is considered primarily restrictive. This study aimed to quantify differences in energy and fat absorption between both procedures using near-infrared spectroscopy (NIRS).

Methods: Female patients, 12-24 months post-RYGB or SG, followed a strictly controlled, tailor-made diet for 6 days. Faecal samples collected over the final 3 days were analysed using NIRS to assess energy and fat malabsorption. Physical activity and stool consistency were also evaluated.

Results: Twenty-nine patients were initially included; one RYGB patient was excluded due to implausibly high reported energy intake leaving 14 RYGB and 14 SG patients. We found higher (p = 0.03) malabsorption in patients after RYGB (194.8 malabsorbed kcal, 13.2%) as compared to patients after SG (111.7 malabsorbed kcal, 7.6%). Furthermore, in the RYGB group, malabsorbed fat was higher (p = 0.01) with 9.7 g (15.4%) malabsorbed as compared to 3.9 g (6.1%) malabsorbed in SG. Even when adjusting for percentage weight loss, both differences remained statistically significant.

Conclusion: Fat and energy malabsorption are significantly higher following RYGB compared to SG, and NIRS proves to be a feasible method for assessing these differences. However, the differences are relatively modest and do not appear to be directly proportional to the reduction in functional intestinal length exposed to nutrients.