Accelerated protein digestion and amino acid absorption after Roux-en-Y gastric bypass1,2

Abstract

Background: Roux-en-Y gastric bypass (RYGB) involves exclusion of major parts of the stomach and changes in admixture of gastro-pancreatic enzymes, which could have a major impact on protein digestion and amino acid absorption. Objective: We investigated the effect of RYGB on amino acid appearance in the systemic circulation from orally ingested protein and from endogenous release. Design: Nine obese glucose-tolerant subjects, with a mean body mass index (in kg/m2) of 39.2 (95% CI: 35.2, 43.3) and mean glycated hemoglobin of 5.3% (95% CI: 4.9%, 5.6%), were studied before and 3 mo after RYGB. Leucine and phenylalanine kinetics were determined under basal conditions and during 4 postprandial hours by intravenous infusions of [3,3,3-2H3]-leucine and [ring-2D5]-phenylalanine combined with ingestion of [1-13C]-leucine intrinsically labeled caseinate as the sole protein source of the meal. Changes in body composition were assessed by dual-energy X-ray absorptiometry. Results: After RYGB, basal plasma leucine concentration did not change, but marked changes were seen postprandially with 1.7-fold increased peak concentrations (before-mean: 217 mmol/L; 95% CI: 191, 243 mmol/L; 3 mo-mean: 377 mmol/L; 95% CI: 252, 502 mmol/L; P = 0.012) and 2-fold increased incremental AUC (before-mean: 4.1 mmol min/L; 95% CI: 2.7, 5.5 mmol min/L; 3 mo-mean: 9.5 mmol min/L; 95% CI: 4.9, 14.2 mmol min/L; P = 0.032). However, the postprandial hyperleucinemia was transient, and concentrations were below basal concentrations in the fourth postprandial hour. These concentration differences were mainly caused by changes in leucine appearance rate from orally ingested caseinate: peak rate increased nearly 3-fold [before-mean: 0.5 mmol/(kg fat-free mass min); 95% CI: 0.4, 0.5 mmol/(kg fat-free mass min); 3 mo-mean 1.4 mmol/(kg fat-free mass min); 95% CI: 0.8, 1.9 mmol/(kg fat-free mass min); P = 0.002], and time to peak was much shorter (before-mean: 173 min; 95% CI: 137, 209 min; 3 mo-mean: 65 min; 95% CI: 46, 84 min; P , 0.001). Only minor changes were seen in endogenous leucine release after RYGB. Conclusions: RYGB accelerates caseinate digestion and amino acid absorption, resulting in faster and higher but more transient postprandial elevation of plasma amino acids. Changes are likely mediated by accelerated intestinal nutrient entry and clearly demonstrate that protein digestion is not impaired after RYGB.