Gastric bypass reduces fat intake and preference

Abstract

Roux-en-Y gastric bypass is the most effective therapy for morbid obesity. This study investigated how gastric bypass affects intake of and preference for high-fat food in an experimental (rat) study and within a trial setting (human). Proportion of dietary fat in gastric bypass patients was significantly lower 6 yr after surgery compared with patients after vertical-banded gastroplasty (P = 0.046). Gastric bypass reduced total fat and caloric intake (P < 0.001) and increased standard low-fat chow consumption compared with sham controls (P < 0.001) in rats. Compared with sham-operated rats, gastric bypass rats displayed much lower preferences for Intralipid concentrations > 0.5% in an ascending concentration series (0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%) of two-bottle preference tests (P = 0.005). This effect was demonstrated 10 and 200 days after surgery. However, there was no difference in appetitive or consummatory behavior in the brief access test between the two groups (P = 0.71) using similar Intralipid concentrations (0.005% through 5%). Levels of glucagon-like peptide-1 (GLP-1) were increased after gastric bypass as expected. An oral gavage of 1 ml corn oil after saccharin ingestion in gastric bypass rats induced a conditioned taste aversion. These findings suggest that changes in fat preference may contribute to long-term maintained weight loss after gastric bypass. Postingestive effects of high-fat nutrients resulting in conditioned taste aversion may partially explain this observation; the role of GLP-1 in mediating postprandial responses after gastric bypass requires further investigation.

Fig. 1.

The proportion of total energy intake from protein, fat, and carbohydrates (A) and from various food groups (B) 6 years after laparoscopic gastric bypass (black columns) and laparoscopic vertical-banded gastroplasty (white columns). Data are shown as means ± SE (*P < 0.05, **P < 0.01).

Fig. 2.

Energy (kJ) from 60% high-fat (HF) diet, of 60% HF diet + Bisto (gravy-type flavor) and normal chow (LF-Bistro) in gastric bypass rats (n = 13) and sham-operated rats (n = 13) before and 10 days after surgery. LF, low fat. Data are means ± SE (***P < 0.001: total energy intake preoperative vs. postoperative after gastric bypass).

Fig. 3.

Body weight (BW) changes for the gastric bypass (n = 18, ○) and sham-operated rats ad libitum fed (n = 12, ■) used for the 2-bottle preference test in the early phase (left) and body weight changes for the gastric bypass (n = 10, ○) and sham-operated rats ad libitum fed (n = 10, ■) used for the 2-bottle preference test in the late phase (middle) after surgery. Right: PYY and GLP-1 level for the gastric bypass (n = 9, white columns) and sham-operated rats ad libitum fed (n = 10, black columns) 200 days after surgery. Data are means ± SE (***P < 0.001).

Fig. 4.

Two-bottle preference test in sham-operated rats (n = 12, ■) and in gastric bypass rats (n = 18, ○) during the early phase experiment (postoperative day 10, A–C) and in gastric bypass (n = 10, ○) and sham-operated rats (n = 10, ■) during the late phase experiment (postoperative day 200, D–F). Seven Intralipid concentrations were used in ascending order: 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 5%. A and D, preference; B and E, Intralipid intake; C and F, total calorie intake. Data are means ± SE. When 2-way ANOVA revealed a significant group × concentration interaction, post hoc Bonferroni test was used for concentration-to-concentration analysis between the 2 groups (**P < 0.01, ***P < 0.001).

Fig. 5.

A: body weight changes for the gastric bypass (n = 8, ○) and sham-operated rats fed ad libitum (n = 8, ■) and used for the brief access test performed around postoperative day 150. B and C: postoperative Intralipid concentration-response functions relative to a water baseline are shown without (B) and with 23-h water restriction (C). D and E: absolute number of initiated trials for each Intralipid concentration are shown without (D) and with (E) water restriction. Data are means ± SE (***P < 0.001).

Fig. 6.

Conditioned taste aversion. A: saccharin (S) and water (W) intake in sham-operated rats after oral gavage with 1 ml sterile isotonic saline (n = 8), 1 ml of corn oil (n = 8), intraperitoneal injection of 76.2 mg/kg body wt LiCl (n = 6), and in gastric bypass rats after oral gavage with sterile isotonic saline (n = 8) and corn oil (n = 8). B: saccharin intake expressed as % total fluid intake in sham-operated rats after oral gavage with sterile isotonic saline (n = 8), corn oil (n = 8), intraperitoneal injection of 76.2 mg/kg body wt LiCl (n = 6), and in gastric bypass rats after oral gavage with sterile isotonic saline (n = 8) and corn oil (n = 8). Experiments were performed on postoperative day 100. Data are means ± SE (**P < 0.01, ***P < 0.001; saccharin vs. water).