Fat absorption and metabolism after Roux-en-Y gastric bypass surgery

Background: Triacylglycerol (TAG) plasma excursions after a high-fat meal are blunted after Roux-en-Y gastric bypass (RYGB), but underlying mechanisms are poorly understood. We studied TAG absorption and metabolism in 12 RYGB-operated individuals and 12 unoperated controls (CON) matched on sex, age, and BMI. Methods: Participants followed a 7-day controlled diet and on day 4 underwent ¹H-MR Spectroscopy of liver TAG and a high-fat liquid meal with oral and intravenous labeled stable isotope metabolites, subcutaneous abdominal fat biopsies, and indirect calorimetry. Subsequently, participants collected stool for 96 h. Results: Overall fat absorption from the controlled diet was moderately lower in RYGB than CON (88 % versus 93 %, P < 0.01), without indication of greater specific malabsorption of fat from the high-fat test meal (recovery of TAG and labeled TAG in 96-h stool samples). After an overnight fast, plasma TAG concentrations and incorporation of plasma fatty acids (IV tracer) into TAG did not differ between groups. The postprandial 6-h iAUC of plasma TAG plasma concentrations was markedly lower in RYGB than CON (15 versus 70 mmol/L × min, P = 0.03). The postprandial chylomicron (CM) particle response (plasma ApoB48) was initially higher in RYGB, but with lower CM-TAG plasma concentrations and appearance of labeled palmitate from the oral tripalmitin tracer over the 6 h. Conclusion: Fat absorption is only moderately lower after RYGB compared with unoperated matched controls. Nevertheless, postprandial TAG and CM plasma kinetics after a high-fat meal are markedly altered after RYGB with substantially lower TAG and CM-TAG concentrations despite a faster CM particle release.