Roux-en-Y gastric bypass in rats progressively decreases the proportion of fat calories selected from a palatable cafeteria diet

Abstract

Roux-en-Y gastric bypass surgery (RYGB) decreases caloric intake in both human patients and rodent models. In long-term intake tests, rats decrease their preference for fat and/or sugar after RYGB, and patients may have similar changes in food selection. Here we evaluated the impact of RYGB on intake during a "cafeteria"-style presentation of foods to assess if rats would lower the percentage of calories taken from fat and/or sugar after RYGB in a more complex dietary context. Male Sprague-Dawley rats that underwent either RYGB or sham surgery (Sham) were presurgically and postsurgically given 8-days free access to four semisolid foods representative of different fat and sugar levels along with standard chow and water. Compared with Sham rats, RYGB rats took proportionally fewer calories from fat and more calories from carbohydrates; the latter was not attributable to an increase in sugar intake. The proportion of calories taken from protein after RYGB also increased slightly. Importantly, these postsurgical macronutrient caloric intake changes in the RYGB rats were progressive, making it unlikely that the surgery had an immediate impact on the hedonic evaluation of the foods and strongly suggesting that learning is influencing the food choices. Indeed, despite these dietary shifts, RYGB, as well as Sham, rats continued to select the majority of their calories from the high-fat/high-sugar option. Apparently after RYGB, rats can progressively regulate their intake and selection of complex foods to achieve a seemingly healthier macronutrient dietary composition.

Keywords: bariatric surgery; conditioned avoidance; diet-induced obesity; supermarket diet.

Fig. 1.

A: percent change in body weight (means ± SE) from the day before surgery (PreSx) for rats that received either Roux-en-Y gastric bypass surgery (RYGB) or a sham operation (Sham) across 18 postsurgical recovery days and across the 8 days during which postsurgical testing was conducted. B: total caloric intake (means ± SE) from presurgical baseline and daily during the 8-day postsurgical choice testing between the surgical groups.

Fig. 2.

Difference between the presurgical baseline (average of days 7 and 8; absolute values displayed in the legend) and the daily postsurgical percentage of calories (means ± SE) selected from fat (A), carbohydrates (B), protein (C), and sugar (D) by rats that received either Roux-en-Y gastric bypass surgery (RYGB) or a sham operation (Sham). *Signifies Bonferroni-corrected and ! signifies uncorrected P ≤ 0.05 of t-tests comparing the surgical groups on individual days following significant 2-way ANOVA interactions.

Fig. 3.

Difference between the presurgical baseline (average of days 7 and 8; absolute values displayed in the legend) and the daily postsurgical percentage of calories (means ± SE) selected from chow (A), refried beans (B), low-fat vanilla yogurt (C), creamy peanut butter (D), and sugar-fat whip (E) by rats that received either Roux-en-Y gastric bypass surgery (RYGB) or a sham operation (Sham). *Signifies Bonferroni-corrected and ! signifies uncorrected P ≤ 0.05 of t-tests comparing the surgical groups on individual days following significant 2-way ANOVA interactions.