Does daily limited access to a highly palatable sweet food induce binge eating in laboratory rats?

1
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 29303
Results Food Intake in grams by meal
Day of Experiment
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.
18 hr Food deprivation ending at 800 am
No Daily Access to FL
Limited Daily Access to FL

800 Pre-weighed Meal 1 placed in cage900
Weigh and return Meal 1930 Remove and weigh
Meal 1, Place Meal 2 in cage1000 Weigh and
return Meal 21030 Remove and weigh Meal 2 Food
Intake measured in grams for each meal.
1st Meal 2nd Meal Total 1st Meal 2nd Meal Total
4.5 0.5Chowa 0.3 0.1Chowa 4.8 0.5ChowChowa,? 3.6 0.5 Chowa 0.4 0.2Chowa 4.0 0.5ChowChowa,?
4.3 0.5 Chowa 3.3 0.5 FLb 7.7 1.0 ChowFLb,? 3.3 0.4Chowa, 5.6 0.6 FLb, 8.8 0.8 ChowFLb,?
6.5 0.6 FLb 0.7 0.2Chowa 7.2 0.7FLChowb,? 7.5 0.7 FLb 0.3 0.1 Chowa 7.8 0.8 FLChowb,?
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).
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 2nd
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.
Wk2 Wk4 Wk6 Wk8 Wk10 Wk12

No Daily FL Access (n11) No Daily FL Access (n11) No Daily FL Access (n11) Daily FL Access Daily FL Access Daily FL Access
C-C FL-C C-FL C-C FL-C C-FL
C-FL C-C FL-C C-FL C-C FL-C
FL-C C-FL C-C FL-C C-FL C-C

Daily FL Access (n12) Daily FL Access (n12) Daily FL Access (n12) No Daily FL Access No Daily FL Access No Daily FL Access
C-C FL-C C-FL C-C FL-C C-FL
C-FL C-C FL-C C-FL C-C FL-C
FL-C C-FL C-C FL-C C-FL C-C

Limited daily access to Froot Loops triggers
binge eating.
Methods
Results Satiation in Meal 1
Subjects Data were obtained from 23 male
Sprague-Dawley rats weighing 346 12 g (range
325-375 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 (plt 0.05).
Status of Hypothesis
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 1st meal. Limited access to FL
did not affect intake in the 1st meal. Histograms
with different letters are significantly
different (plt0.05).
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.
Implications
B
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.
B
A
A
A

A
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 davisgr_at_wofford.edu
No Daily Access to FL
Limited Daily Access to FL
1st meal of Chow Chow FL Chow Chow
FL
2nd meal to be Chow FL Chow Chow FL
Chow