Does daily limited access to a highly palatable sweet food induce binge eating in laboratory rats? Katie Isbell, Robynn Mackechnie, Pres Garrett, and G.R. Davis*. Department of Biology, Wofford College, Spartanburg, SC Acknowledgements The authors thank students in the Bio 250 Spring 2007 class at Wofford College for their involvement in this research: Jennifer Almond, Andy Barnes, KC Correll, Krupa Desai, Shana Glenn, Melissa Hayes, Hollis Inabinet, Kelsi Koenig, Jamie Newton, & Emily Scales. * Corresponding author: When rats or humans eat to satiety on one food, they consume very little of that same food offered as a second meal, but will consume a more palatable food offered as a second meal. This form of overeating is called sensory specific satiety (SSS). Another form of overeating is binge eating, defined as the consumption of a larger than normal amount of food within a given time. Episodes of binge eating in humans often follow periods of self-imposed restricted access to a palatable foods (i.e. dieting) and are frequently associated with mood and eating disorders. To understand the mechanisms responsible for binge eating, it would be useful to develop an animal model for which the triggers of binge eating can be investigated under controlled laboratory conditions. Laboratories pursuing an animal model of binge eating (Corwin, 2004; Boggiano et al., 2007) report that ad libitum daily access to a highly palatable food for 2 hours does not result in episodes of binge eating. Perhaps severely restricting daily access to a highly palatable food will trigger binge eating. In this study, we provided laboratory rats with a small quantity (1.1 g) of a highly palatable food (Froot Loops®, FL) every day for at least two weeks. We then measured FL intake when FL were available ad libitum to see if limited daily access resulted in binge eating. Food intake was compared to a group of rats which were not provided daily access to FL. Limited daily access to Froot Loops® triggers binge eating. Subjects: Data were obtained from 23 male Sprague- Dawley rats weighing 346 ± 12 g (range g, age = 102 days) on 1st experimental day. Animals were housed individually in plastic cages with lights on at 7 am and lights off at 7 pm. Diet: Daily ad libitum Teklad 8604 rodent chow and water except on experimental days. Prior to experiments, all rats were given 5 FL in a plastic cup to overcome neophobicity. Groups: Daily Access to 5 FL (~1.1 g provided irregularly during the light period) or No Daily Access to FL. Experimental days: Biweekly for 12 weeks following 18 hour food deprivation (to assure rats eat to satiety during first meal), rats were given a 1st meal of Chow (C) or FL at 8 am Cumulative Food Intake in grams was measured at 60 and 90 minutes. A 2nd meal of C or FL was provided when the 1st meal was removed. Cumulative Food Intake of the second meal was measured at 30 and 60 minutes. Statistics: Repeated Measures ANOVA followed by Student-Newman-Keuls (SNK) post hoc pair-wise testing for significant differences (p< 0.05). Counterbalanced Crossover Experimental Design Hypothesis Introduction Wk2Wk4Wk6Wk8Wk10Wk12 No Daily FL Access (n=11)Daily FL Access C-CFL-CC-FLC-CFL-CC-FL C-CFL-CC-FLC-CFL-C C-FLC-CFL-CC-FLC-C Daily FL Access (n=12)No Daily FL Access C-CFL-CC-FLC-CFL-CC-FL C-CFL-CC-FLC-CFL-C C-FLC-CFL-CC-FLC-C Methods Day of Experiment Results: Satiation in Meal 1 Results: Food Intake in grams by meal Status of Hypothesis Implications Each rat received each meal sequence (C-C, C-FL, and FL-C; counterbalanced) following at least two weeks of Daily Access or No Daily Access to FL. At the end of week 6, FL access was reversed for each group (arrows indicate crossover). 18 hr Food deprivation ending at 8:00 am 8:00 Pre-weighed Meal 1 placed in cage 9:00 Weigh and return Meal 1 9:30 Remove and weigh Meal 1, Place Meal 2 in cage 10:00 Weigh and return Meal 2 10:30 Remove and weigh Meal 2 Food Intake measured in grams for each meal. Rats eat to satiety in the 1st meal: Cumulative Food Intake at 90 minutes (gray bars) is not significantly different from intake at 60 Minutes (black bars.) Rats consume significantly more FL than chow as a 1 st meal. Limited access to FL did not affect intake in the 1 st meal. Histograms with different letters are significantly different (p<0.05). No Daily Access to FLLimited Daily Access to FL A A A A B B 1 st Meal2 nd MealTotal1 st Meal2 nd MealTotal 4.5 ± 0.5 Chow a 0.3 ± 0.1 Chow a 4.8 ± 0.5 Chow+Chow a,￮ 3.6 ± 0.5 Chow a 0.4 ± 0.2 Chow a 4.0 ± 0.5 Chow+Chow a,￮ 4.3 ± 0.5 Chow a 3.3 ± 0.5 FL b 7.7 ± 1.0 Chow+FL b,￭ 3.3 ± 0.4 Chow a, 5.6 ± 0.6 FL b,* 8.8 ± 0.8 Chow+FL b,￭ 6.5 ± 0.6 FL b 0.7 ± 0.2 Chow a 7.2 ± 0.7 FL+Chow b,￭ 7.5 ± 0.7 FL b 0.3 ± 0.1 Chow a 7.8 ± 0.8 FL+Chow b,￭ No Daily Access to FLLimited Daily Access to FL Different letters (a, b) in columns indicate significant differences in values. Different symbols (￭, ￮) in rows indicate significant differences in total intake in grams. * = significantly different from FL intake in 2 nd Meal in “No Daily Access to FL” group. Row 1: Rats consume very little additional chow as a second meal when satiated on chow in the first meal. This is expected based on sensory specific satiety. Furthermore, limited access to FL does not affect chow intake. Row 2: As expected based on sensory specific satiety, rats satiated on rat chow in the first meal consume a more palatable food (Froot Loops) offered as a second meal. Rats with limited daily access to FL did eat significantly more FL in a second meal (5.6 ± 0.6 g) than did rats without daily access to FL (3.3 ± 0.5 g). However, the total intake in grams for chow and FL was not affected by limiting the daily access to FL. Row 3: Rats consume large quantities of FL in a first meal and very little chow as a second meal (as predicted by sensory specific satiety.) However, limited daily access to FL did not affect the intake of FL in the first meal nor did it affect total intake for both meals. Columns 3 and 6: Total food intake for both meals was greater if FL were offered as either the first or second meal. However, rats that were given limited daily access to a highly palatable food ate no more than animals that were not given FL access daily. Because the energy density of RC (3.3 cal/g) and FL (3.8 cal/g) is similar, when intake is expressed as calories (data not shown) the results follow the same pattern. The only effect of limited daily access to a highly palatable food was a significant increase in the intake of that food offered as a second meal. Although total food intake was greater if FL were offered as either the first or second meal, overall food intake for a two meal sequence was not affected by limited daily access to FL. Thus, these data do not support the hypothesis that limited daily access to a highly palatable food triggers binge eating. Others have reported episodes of binge eating in laboratory rats for which access to a highly palatable food (100% fat) is limited to three days per week (Corwin, 2004) or limited access to high fat/high sugar foods is combined with stress (Boggiano et al., 2007.) In those studies, daily ad libitum access for 2-4 hours to a highly palatable food did not result in binge eating. Our rats receiving daily access to FL were provided only ~1.1 g of FL. It appears that this very limited access to a highly palatable food does not induce craving for that food that would be manifest as an elevated intake of that food when available ad libitum on experimental days. Thus, the conditions of limited daily access to FL in our protocol did not trigger binge eating. It would be interesting to determine in future experiments whether further limiting FL access to only three days per week would trigger episodes of binge eating. 1 st meal of Chow Chow FL Chow Chow FL 2 nd meal to be Chow FL Chow Chow FL Chow