The effect of vertical sleeve gastrectomy on food choice in rats

Abstract

Objective: Diets high in fat are implicated in the development and maintenance of obesity, and obese individuals display greater preferences for high-fat foods than do their lean counterparts. Weight-reduction bariatric surgery is associated with changes in food choice. In particular, after Roux-en-Y gastric bypass (RYGB), humans and rodents select or prefer foods that are lower in fat content. We asked whether a bariatric surgical procedure limited to the stomach, vertical sleeve gastrectomy (VSG), causes a similar reduction of fat intake/preference.

Research design and methods: Rats received VSG or Sham surgery or remained surgically naïve, and were assessed for food preference using three diet-choice paradigms. Using progressive-ratio (PR) and conditioned taste aversion paradigms, we further asked whether surgically induced changes in food choice are secondary to changes in the reward value of food and/or to the formation of a food aversion. Finally, food choice was compared between VSG- and RYGB-operated rats.

Results: VSG rats decreased their intake of dietary fat, and shifted their preference toward lower caloric-density foods. This change in food choice was not associated with changes in motivated responding on a PR schedule for either a fat or a carbohydrate food reinforcer. When VSG and RYGB were compared directly, both procedures caused comparable changes in food choice. The conditioned taste aversion paradigm revealed that VSG rats form an aversion to an intra-gastric oil administration whereas RYGB rats do not.

Conclusions: VSG and RYGB, two anatomically distinct bariatric procedures, produce similar changes in food choice.

Figure 1

Rats which received Sham or VSG surgery, or remained surgically naïve, were monitored for body weight (A) and food intake (B), and body composition was assessed 6 wk post-operatively (C, D). * p<0.05 for Sham vs. VSG, † p<0.05 for Naïve vs. VSG, and # p<0.05 for Naïve vs. Sham.

Figure 2

Rats which received Sham or VSG surgery, or remained surgically naïve (Cohort A), were tested for food choice using a macronutrient-selection paradigm (A–C). Intake of each macronutrient (A), total combined food intake (B), and food intake of each macronutrient normalized to total food intake (C) are presented. Rats which received Sham or VSG surgery (Cohort B) were tested for food choice using a high-fat diet (HFD) versus low-fat diet (LFD) paradigm (D–F). Intake of each diet (D), total combined food intake (E), and HFD preference normalized to total food intake (F) are presented. * p<0.05 for Sham vs. VSG, † p<0.05 for Naïve vs. VSG, # p<0.05 for Naïve vs. Sham.

Figure 3

Rats which received Sham surgery or VSG surgery, or remained surgically naïve, were tested for preference for caloric density using 2 liquid diets: undiluted Ensure (100%), or Ensure which had been diluted by 50% with water for 2 d. Data depicted are: intake of each diet for each day (A, C), preference (kcal of 100% Ensure/ total kcal) for each day (B, D), and total caloric intake over both days (E). * p<0.05 for Sham vs. VSG, † p<0.05 for Naïve vs. VSG, and # p<0.05 for Naïve vs. Sham.

Figure 4

Rats which received Sham surgery or VSG surgery, or remained surgically naïve, were tested for motivated responding for food cues using a lever-pressing paradigm. No differences were found among groups for motivated responding (progressive-ratio) for sucrose (A) or oil (C) reinforcers under food-restricted (FR) or ad libitum-fed (Ad-lib) conditions. However, on a fixed-ratio schedule, VSG rats earned fewer food reinforcers compared to sham rats when pressing for either sucrose (B) or oil (D).

Figure 5

Rats which received Sham surgery, VSG surgery, or RYGB surgery were tested for food choice using a macronutrient-selection paradigm. Intake of each macronutrient (A), total combined food intake (B), and food intake of each macronutrient normalized to total food intake (C) are presented. Symbols indicate significant differences when compared to Sham (* p<0.05, ** p<0.01, and *** p<0.001).

Figure 6

Rats which received Sham surgery, VSG surgery, or RYGB surgery were tested for conditioned taste aversion to an intra-gastric infusion of water, oil, or LiCl. * p<0.05 versus water, and ** p<0.01 versus water.