Effects of gastric bypass surgery on postprandial gut and systemic lipid handling

Obesity is often associated with increased postprandial triglyceride (TG) concentrations, mainly from chylomicrons- and VLDL-TG. These alterations are usually reverted to normal after gastric bypass surgery (GB), through mechanisms which remain unknown. The objective of this study was therefore to assess the contribution of exogenous labelled fatty acids ingested with a meal to postprandial blood chylomicrons and VLDL-TG concentrations after GB.

7 GB patients 3-5 years after surgery (GB: 2M/5F, mean BMI 30 ± 2 kg/m², mean age 40 ± 3 years), 6 overweight non operated subjects (OW: 1M/5F, mean BMI 31 ± 3 kg/m², mean age 38 ± 2 years) and 8 normal weight healthy subjects (NW: 4M/4F, mean BMI 22 ± 1 kg/m², mean age 26 ± 4 years) were studied over 7 h following ingestion of a liquid meal containing 18 g fat labelled with 250 mg ¹³C₁₆ palmitate, 22 g protein, 36 g fructose and 36 g glucose. TG, ¹³C palmitate (¹³C-palm) and apoB48 concentrations were measured hourly in whole plasma and/or in chylomicrons and VLDL lipoprotein sub-fractions.

OW subjects had higher chylomicron-than NW (chylo-TG 96.5 (23.1) vs 28.8 (11.8) mmol/l*420min (p = 0.02)), but similar total, chylo-¹³C-palm and apoB48 iAUCs. In GB, chylo- ¹³C-palm and apoB48 increased earlier after meal ingestion, but then remained lower than in NW and OW throughout the postprandial period. GB also had lower chylo-TG iAUCs than OW (8.9 (11.5) vs 96.5 (23.2) mmol/l*420min, p = 0.003). Their apoB48 iAUCs were not different from NW and OW (509.2 (90.5) vs 710.2 (80.5) and 870.1 (297.6) pg/ml*420min, all p > 0.05).

An accelerated postprandial apoB48 rise, together with unchanged postprandial apoB48 iUAC, suggests that intestinal fat absorption and chylomicron secretion was quantitatively unaltered, but accelerated after gastric bypass. In contrast, the decreased postprandial chylo-TG and ¹³C-palm iAUCs suggest that plasma chylomicron clearance was enhanced after gastric bypass.