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

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).

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.

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.

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.