Gastric bypass in rats does not decrease appetitive behavior towards sweet or fatty fluids despite blunting preferential intake of sugar and fat

Abstract

After Roux-en-Y gastric bypass surgery (RYGB), patients report consuming fewer fatty and dessert-like foods, and rats display blunted sugar and fat preferences. Here we used a progressive ratio task (PR) in our rat model to explicitly test whether RYGB decreases the willingness of rats to work for very small amounts of preferred sugar- and/or fat-containing fluids. In each of two studies, two groups of rats - one maintained on a high-fat diet (HFD) and standard chow (CHOW) and one given CHOW alone - were trained while water-deprived to work for water or either Ensure or 1.0 M sucrose on increasingly difficult operant schedules. When tested before surgery while nondeprived, HFD rats had lower PR breakpoints (number of operant responses in the last reinforced ratio) for sucrose, but not for Ensure, than CHOW rats. After surgery, at no time did rats given RYGB show lower breakpoints than SHAM rats for Ensure, sucrose, or when 5% Intralipid served postoperatively as the reinforcer. Nevertheless, RYGB rats showed blunted preferences for these caloric fluids versus water in 2-bottle preference tests. Importantly, although the Intralipid and sucrose preferences of RYGB rats decreased further over time, subsequent breakpoints for them were not significantly impacted. Collectively, these data suggest that the observed lower preferences for normally palatable fluids after RYGB in rats may reflect a learned adjustment to altered postingestive feedback rather than a dampening of the reinforcing taste characteristics of such stimuli as measured by the PR task in which postingestive stimulation is negligible.

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

“…B: total caloric intake (means Ϯ SE) from presurgical baseline and daily during the 8-day postsurgical choice testing between the surgical groups. taining 60% fat such as Research Diets D12492; 14, 22, 26, 27, 37), a pure fat solid or fluid (such as corn oil or Intralipid; 14,16,17,26,36), or a full-nutrition sweet and fatty beverage (Ensure; 5, 16, 17, 26, 37) after surgery. These animals also choose to consume proportionally greater amounts of normal chow or other low-fat/low-sugar choices (e.g., water, V8 vegetable drink) than sham-operated rats.…”

“…Surgical groups were assigned such that total caloric intake and body weight did not differ between the groups across replicates. All of the rats underwent either RYGB (average presurgical body weight ϭ 572 Ϯ 6 g) or a sham operation (Sham; average presurgical body weight ϭ 562 Ϯ 9 g) as previously described (e.g., 3,16,17). Before surgical manipulations, the rats were acclimated for at least 24 h to stainless-steel mesh flooring; wood chip bedding was removed and replaced with cage board placed underneath the mesh flooring insert.…”

“…These diets consisted of wet mash, which is a ϳ1:4 mixture of powdered chow and water, and a custom-made gel diet, which consisted of corn starch, whey powder, corn oil, gelatin, baby vitamins, and water (as per Ref. 16). Food was removed from the rats on the evening before surgery; a 10-g chow pellet ration was left to minimize postsurgical hunger, and water was available ad libitum.…”

“…While self-report measures in humans are vulnerable to inaccuracies (e.g., 9, 15, 23, 24, 33; also see 19), these results are mirrored in rat models of RYGB. After RYGB, rats lose body weight, consume fewer overall calories, and show blunted preferences for high-fat laboratory diets, as well as for sucrose solutions, the soybean oil emulsion Intralipid, and dietary supplements like Ensure that are high in fat and sugar (e.g., 3,5,14,16,22,26,27,36,37).Although these data from rodent models of RYGB are compelling, the nutritive stimuli studied are not always representative of "real-world" choices from which patients will select their new diet. We addressed this in the current report by presenting rats before and after either RYGB or a sham operation with a "cafeteria" or "supermarket" diet, which consists of ad libitum access to many different palatable items (For reviews see 25, 34).…”

“…While self-report measures in humans are vulnerable to inaccuracies (e.g., 9, 15, 23, 24, 33; also see 19), these results are mirrored in rat models of RYGB. After RYGB, rats lose body weight, consume fewer overall calories, and show blunted preferences for high-fat laboratory diets, as well as for sucrose solutions, the soybean oil emulsion Intralipid, and dietary supplements like Ensure that are high in fat and sugar (e.g., 3,5,14,16,22,26,27,36,37).…”