RYGB progressively increases avidity for a low-energy, artificially sweetened diet in female rats

Abstract

Weight re-gain within 2 y after Roux-en-Y gastric bypass (RYGB) is significantly associated with increased intake of and cravings for sweet foods. Here we describe a novel model of this late increase in sweet appetite. Ovariectomized RYGB and Sham-operated rats, with or without estradiol treatment, were maintained on Ensure liquid diet and offered an artificially sweetened low-energy diet (ASD) 2 h/d. First, we tested rats more than six months after RYGB. ASD meals were larger in RYGB than Sham rats, whereas Ensure meals were smaller. General physical activity increased during ASD meals in RYGB rats, but not during Ensure meals. Second, new rats were adapted to ASD before surgery, and were then offered ASD again during 4–10 wk following surgery. Estradiol-treated RYGB rats lost the most weight and progressively increased ASD intake to >20 g/2 h in wk 9–10 vs. ~3 g/2 h in Sham rats. Finally, the same rats were then treated with leptin or saline for 8 d. Leptin did not affect body weight, Ensure intake, or activity during meals, but slightly reduced ASD intake in estradiol-treated RYGB rats. Food-anticipatory activity was increased in estradiol-treated RYGB rats during the saline-injection tests. Because increased meal-related physical activity together with larger meals is evidence of hunger in rats, these data suggest that (1) RYGB can increase hunger for a low-energy sweet food in rats and (2) low leptin levels contribute to this hunger, but are not its only cause. This provides a unique rat model for the increased avidity for sweets that is significantly associated with weight recidivism late after RYGB.

Gastric bypass in female rats lowers concentrated sugar solution intake and preference without affecting brief-access licking after long-term sugar exposure

“…Thus, in these experiments, RYGB exerted its principal effect on body weight in terms of stabilization, as opposed to loss, in an environment with highly palatable caloric food options. Although we did not see a long-term decrease in body weight following RYGB relative to the presurgical value, our data regarding patterns of weight regain or weight stabilization following RYGB surgery are congruent with data from RYGB female rats collected in other laboratories (3,4,19). Additionally, these results agree with reports of changes in food choice and preference along with significant body weight loss (37)(38)(39)52) in male rodents.…”

“…Whether the failure to see such an increase in sucrose trials initiated by RYGB rats in the present study is due to the lack of presurgical BA test experience with sucrose or to a sexual dimorphism remains to be determined. With respect to the latter, manipulation of sex hormones (in ovariectomized females) has been shown to interact with the effects of RYGB surgery, specifically by increasing weight loss, influencing food intake or preference, and/or influencing some gut hormone effects on intake (3,4,19). It is possible, therefore, that, in this context, sex hormones may have impacted some of the behavioral consequences of surgery (i.e., BA trial initiation).…”

Oromotor and somatic taste reactivity during sucrose meals reveals internal state and stimulus palatability after gastric bypass in rats

“…The failure for surgery to affect taste reactivity to sucrose during the initial stage of the infusion is similar to the results in some other studies that focus on the orosensory hedonic characteristics of sugar and/or fat solutions. In brief-access tests, in which rats are allowed to freely lick varying concentrations of a stimulus in short periods (5-10 s) of access, RYGB rats will sometimes respond in the same concentration-dependent manner as SHAM rats (38,75; but see 50). Consistent with these findings, RYGB rats tested in a progressive ratio task, which requires the animal to perform progressively higher numbers of responses to obtain a reinforcer, were just as motivated to work for sucrose as SHAM rats (42).…”

“…As with intact rats, in some contexts, RYGB rats will increase intake of low-energy foods and fluids, demonstrating that stimulus concentration can be a factor in post-RYGB outcomes (75,80). Alternatively, or in addition to its colligative and energy properties, the molecular identity of the stimulus may be relevant.…”