Developing an Animal Model
of Binge Eating

Research Team: Kishan Govind, Robynn Mackechnie & Dr.G.R. Davis (faculty sponsor)

Community of Scholars Summer 2007
Funding by the Fullerton Foundation

Results will be presented at the annual meetings of
The Association of Southestern Biologists (April 2008)
and
The Society for the Study of Ingestive Behavior (July 2008)

Robynn's Abstract
Kishan's Abstract
Two Page Overview

last updated 24 August 2008

Background Information:

In humans, dieting is a form of limiting one's access to food, especially to highly palatable foods which tend to be high in carbohydrates and fats. Often dieters develop cravings for the very foods that they avoid, and when they "break their diet" they overeat (binge eat) on the highly palatable food. Likewise, stress may alter the eating patterns of humans, and dieters may be more likely to break their diet in response to stress. Because these factors are difficult to study under tightly controlled conditions in humans, there is a great need for an animal model in which feeding behaviors can be studied while carefully manipulating the availability and palatability of foods and controlling the degree to which animals are stressed. We have conducted experiments on 80 laboratory rats, 40 under non-stressed conditions (Robynn's rats) and 40 which were subjected to a variety of stressors (Kishan's rats.) Robynn and Kishan investigated how food intake was affected by restricting access to a highly palatable high carbohydrate food (Froot Loops®) and whether stress altered their intake of this food.

Questions of Interest:

What condition(s) trigger episodes of binge eating in laboratory rats?

How does stress affect food intake in laboratory rats?

More specifically:

How is the intake of a highly palatable sweet food (Froot Loops ®; FL) affected by
........ a) limiting the access to that food, and
........ b) combining that limited access with stress?

Based on our research, we now have answers to these and other questions!

A summary of our Major Findings!

Robynn's 250 word Abstract	Robynn's Research Poster	Robynn's Experience
Kishan's 250 Word Abstract	Kishan's Research Poster	Kishan's Experience
Major Findings	Overview (2 pages)	Photos

Spreadsheets	Statistics	Word documents
Calendar of Experiments (ppt)	Powerpoints	Most Recent Results
Midpoint Progress Report	How to give Froot Loops to Rats	Photos
Questions we addressed	Pilot Studies	Ideas for Future Experiments
How Much Can Hungry Rats Eat?		Links

The first challenge we faced was how to provide the test food Froot Loops in such a way that would allow us to quickly and accurately measure how much eat rat consumed. Placing Froot Loops in the food hopper along with rat chow in the cage lids would result in mixing of the Froot Loops with the bedding in each cage thereby greatly increasing the difficulty of measuring FL intake. After a number of pilot studies in which we tested various means by which to provide FLs, we arrived at a technique that works very well: FLs are threaded onto a 3/16 inch diameter plexiglass rods which can be laid on cage lids and the rats can removed FL from these rods about as easily as they can eat chow from the hopper. Thus, we controlled for the ease of access and simultaneously made possible accurate weighings of FL intake. However, threading FLs onto the rods was a tedious task that consume many hours of effort by all members of the research team. Because many Froot Loops had a lumen to small to fit the rods, eventually we discovered that enlarging the lumen with a Dremel tool allowed us to use most of the FLs. Nevertheless, the time spent drilling FLs and threading them onto rods provided a chance for the reseach team to discuss a wide range of topics (from our emerging results to the fate of Harry Potter in the series finale!) The photographs below show us at work.


Kishan making a Froot Loop rod. (The smile is fake.)	On some days, 180 Froot Loop rods were required for 60 rats.

Robynn running a statistical test.	Robynn showing signs of fatigue while threading Froot Loops onto rods.

Kishan drilling to enlarge the hole in a Froot Loop to make it fit on a 3/16 diameter rod.	A lucky rat eating a fragment of a Froot Loop from a rod.

We noted that fragments of FLs that fell to the bedding were eaten first and then rats return to the rods on the cage lids to extract more FLs.	Robynn weighing meals in the animal room for her non-stressed rats. Robynn and Kishan measured daily caloric intake for 80 rats over 28 consecutive days.

Dr. Davis demonstrating that scientific research can be interesting and humorous.	At one of the weekly Community of Scholars Coffees, Dr. Davis describes some of the work underway in the lab.

Questions we addressed

Q: Do rats regulate food intake as kcal or grams or some combination?
A: Our results agree with previous reports which indicate that unlike humans, rats are very good at regulating their daily food intake such that they consistently consume about 100 kcal per day. Our rats, when provided Froot Loops (FL) generally reduced their consumption of rat chow in proportion to their intake of FLs. In this sense, rats differ rather dramatically from humans when typically demonstrate a poor ability to regulate caloric intake, especially when tempted by highly palatable foods rich in sugar and fat.

Q: How were our laboratory rats stressed?
A: Some laboratories use foot shock as a stressor. Others have shown that restraining rats in tightly fitting plastic tubes is stressful. We were not equipped to deliver foot shocks and thus sought some other means by which to stress our rats. We modified a procedure that has appeared in the literature for over 20 years that has come to be called Chronic Mild Stress. CMS is produced by a series of stressors repeated on a weekly chedule. Stressors include paired housing, tilted cages, water and food deprivation, irregular photoperiods, exposure to noise, novel items and stroboscopic lights, etc. Because it was essential that we measure daily food intake for each animal, we excluded paired caging from our protocol. Futhermore, our aim was to investigate intake of a palatable food in rats that were never food deprived. Therefore, we excluded food deprivation as a stressor. We adopted a schedule of stressors that was repeated weekly: tilting the animals cage for three hours on Tuesdays and Fridays, housing the animals in wet bedding for 24 hours beginning on Wednesday, 36 hours of continuous light beginning each Saturday, 18 hours of water deprivation (beginning on Monday and Friday) followed by hone our with an empty water bottle before restoring access to water. It has even been shown that replacing the bedding is a mild stressor.

Q: Does the percentage energy intake as FL change over the 4 weeks of the experiment?
A: The first day rats were given FL, FL accounted for about 10% of their 24 hour calorie intake. By the second week of the experiment, FL intake accounted for approximately 25% of daily caloric intake and this ratio persisted through the remainder of the 4 week experiment.

Q: Is total energy intake the same for all groups over the 4 weeks of the experiment?
A: No. In the non-stressed animals, those given access to FL on 3 days per week or less regularly consumed significantly less that rats that had daily access to FL or no Froot Loops at all (control animals.) Among the stressed animals, cumulative caloric intake was reduced to the same extent among all groups (no FL access, daily FL access, 3 days per week or irregular access.)

Q: Is there an upper limit for caloric intake per day?
A: Maybe. All groups of rats except for one regulated their daily caloric intake at about 100kcal per day. The exception was the group of stressed rats given MWF FL access. These animals consumed significantly more calories (120-125 kcal) on those days when FL were available.

Q: Do stressed rats eat more, less, or the same as unstressed animals?
A: Stressed rats eat less than non-stressed rats.

Do stressed rats consume a highly palatable food (Froot Loops®) to reduce stress?
A: There is no clear answer. Stressed rats are similar to non-stress rats in that 25% of their caloric intake is FL. Those stressed rats with MWF access to FL consumed more than any other group. Since FL are high in sugar and thus might act upon brain systems associated with pleasure and reward, it is conceivable that FL consumption could be a means of relieving stress via these neural pathways.

Are the stressors incorporated into our protocol appropriate to induce chronic mild stress (CMS)?
A: Yes. Literature indicates that rats subjected to stressors commonly used induce symptoms of depression in laboratory rats result in a reduction in weight gain within two to four weeks. Our stressed rats weighed significantly less than non-stressed rats by Day 10 of the experiment.

How long must rats be exposed to our particular set of stressors before evidence of CMS are obvious?
A: The evidence of Chronic Mild Stress is apparent by Day 10.

Are some stressors more potent than others?
A: Dramatically curtailed food intake consistently observed following water deprivation combined with tilted cages suggested that this set of stressors produced acute stress.

Q: What effect does the commercial chow diet have upon baseline energy intake and binge eating?
A: Our rats consume approximately 100 kcal of Teklad 8604 rodent diet per 24 hours whereas rats maintained on LabDiet 5001 regulate daily intake to about 70-75 kcal. We're not sure why there is a difference although it is unlikely that differences in palatability of various types of chow is responsible since rats seems to regulate intake based on kilocalories per day.

Q: Is it more appropriate to define binge eating in terms of caloric intake or intake as grams?
A: There are serious issues here. For example, consuming only a small amount of very energy dense food (such as Crisco, 9.2 kcal/g) could lead to dramatic increases in daily caloric intake whereas consuming the same mass of a highly palatable food but less energy dense food such as Froot Loops (3.8 kcal/g) would produce only small changes in daily caloric intake, especially if rats reduce their chow (3.3 kcal/g) intake commensurately with their FL intake.

Q: Does the time at which the highly palatable food is offered affect consumption?
A: Rats given FL two hours prior to lights off may eat to satiety so that they then skip the normal large meal of RC that occurs shortly after lights off. Thus total caloric intake would be fairly constant athough the proprortion of calories from FL would be greater than in control animals. However, it would be interesting to repeat these experiments but change the food access schedule such that experiments are conducted during the first two hours of the dark phase when it is well documented that rats normally consume a large meal.

Q: When creating the 8 groups of experimental animals matched for body weight and FL intake over a pre-test 24 hour period, it appeared that some animals might be characterized as binge-eating prone (BEP) and binge-eating resistant (BER) according to the criteria of Boggiano who classified rats into these groups based on four trials. In our experiments, do those rats that consumed the largest quantities of FL in the pre-test consistently consume the greatest amount of FL during the 4 weeks of the experiment? Likewise, do those rats who ate very little during the pre-test continue to eat the least during the 4 wk experiment? If so, should our data be analyzed after classifying animals as BEPs or BERs?
A: We have not yet analyzed our results to address this questions but should be able to do so if there are sufficient numbers of BEPs and BERs in each of our 8 groups of rats.

Major Findings

Non-stressed rats

1) Rats exhibit excellent daily caloric intake regulation (unlike humans.)

2) We found no evidence of binge eating.

3) Rats given FL every day did not weigh more than control rats maintained exclusively on rodent chow.

4) Surprisingly, rats given intermittent access to FL on an irregular schedule or 3 days per week cumulatively consumed fewer calories and gained less weight than other groups of rats.

5) Corwin (2003) reported that intermittent access to 100% fat triggered episodes of binge eating. Using an identical protocol, we find that rats do not binge eat on Froot Loops. This suggests that the tendency to binge eat depends at least in part on the nature of the palatable food provided.

Stressed rats

6) Stressed rats consumed fewer calories and gained weight less rapidly than non-stressed rats.

7) Stressed rats over-eat only if access to Froot Loops is intermittent (MWF). This may be binge eating.

8) Stressed rats with daily access to FL do not over-eat.

Implications:

Our results sharply contrast with the findings of Corwin (2003) who described binge eating on Crisco in non-stressed rats. Taken together, it appears that the propensity toward binge eating depends at least in part on the nature of the palatable food provided. Futhermore, in most of the conditions we studied, our rats effectively regulated their caloric intake at about 100 kcal/day. This is rather different from human who often succumb to the temptation of highly palatable foods. Human tend not to compensate for the consumption of highly palatable foods by commensurately reducing intake of other food items. Thus, there are limitations for using laboratory rats as an animal model to investigate human behaviors.

Unresolved Issues

Researchers need a more precise definition of binge eating.

Consumption of relatively small amounts of test foods rich in fats (and thus high in energy density) can produce dramatic changes if food intake is expressed as caloric intake. In constrast, rats would have to consume very large quantities of a highly palatable foods such as Froot Loops which are similar in energy density to rat chow. In this case, intake may be limited by the physical dimensions of the stomach.

Much remains to be done in an effort to develop a useful animal model of human eating behaviors.

Prospective experiments

At the conclusion of our scheduled 28 days of experimentation, these same rats could be used to

a) test with Crisco to see how stressed rats' consumption of 100% fat compares with non-stressed rats

b) measure food intake in the 1st two hours of the dark period, when rats normally consume the largest meal. Our current protocol makes food intake measurements at a time when rats normally eat small amounts. Shifting the experiment to the early portion of the dark period may reveal more pronounced binges.

c) see how long any effects of stress persist by measuring food intake for several additional days or weeks

d) see the effects of mild food deprivation (reduce daily intake to 80% or 66% of controls) on the consumption of FL. This mild food restriction, similar to dieting, might be expected to result in large binges. Rats could be maintained on a lower fixed amount of chow for a week or two before testing with Froot Loops. We conducted this follow-up experiment and report the results here: How much can hungry rats eat?

Harlan Teklad Rodent Diets (8604 used by Wofford labs)

Purina Mills Rodent Diets (5001 used by Corwin lab)

% Calories from Protein, Fat, & Carbohydrate

Biological values for laboratory rodents (mass, ages, physiologic parameters, etc.)

Guidelines for Posters (48" x 48") for Association of Southeastern Biologists Annual Meeting hosted by Wofford College and Furman University at Spartanburg Renaissance Marriot. We will make posters 42 inches tall by 46 inches wide so that both can be displayed together on a single bulletin board in Milliken Science Building.

Guideline for abstracts (maximum 250 words exclusive of authors and title) and posters (48" x 96") for Society of the Study of Ingestive Behavior Annual Meeting in Paris, France July 2008

Poster template with Wofford logos (42 x 46)


A Wofford Frat Rat eating Froot Loops Shish-ke-bob intended for Lab Rat.	Dr. Anderson listens reverently as Robynn explains the experiment or Dr. Anderson auditioning for role as Guard at Tomb of the Unknown Soldier.

Kishan relaxing after
a hard day in the lab.

Developing an Animal Model of Binge Eating