In humans, dieting is a form of limiting one's access to ...



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.

Like several other labs around the country, we are interested in identifying conditions that trigger episodes of binge eating in laboratory rats and examining how

stress affects food intake in laboratory rats. Specifically, in our 2007 Community of Scholars research, we asked: How is the intake of a highly palatable sweet food (Froot Loops ®; FL) affected by limiting the access to that food, and combining that limited access with stress?

We 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.

We patterned our experiments very closely upon the research described by R.L. Corwin of Penn State University for the non-stressed rats. Like Dr. Corwin and her colleagues, we divided our non-stressed rats in to four groups of 10 rats each. The control group was provided free access to an unlimited amount of rat chow every day. For 28 consecutive days, Robynn measured the daily intake of chow for these rats. A second group, in addition to all the chow they could eat, was offered Froot Loops for 2 hours every day. This group was designated R7 because they had regular access to Froot Loops for two hours each day 7 days a week. For R7, Robynn measured the daily chow intake and also the amount of Froot Loops consumed daily. A third group called R3, received Froot Loops 3 days each week for two hours on Mondays, Wednesdays, and Fridays. Corwin has shown that this schedule causes binge eating in rats given 100 % fat (Crisco.) We want to know if this schedule triggers binge eating on Froot Loops. The fourth group of rats received Froot Loops on an irregular schedule and were designated as the I group.

The major findings from Robynn’s non-stressed rats are: 1) Rats exhibit excellent daily caloric intake regulation (unlike humans.) 2) We found no evidence of binge eating. 3) Rats given Froot Loops every day did not weigh more than control rats maintained exclusively on rodent chow. 4) Surprisingly, rats given intermittent access to Froot Loops on an irregular schedule or three days per week cumulatively consumed fewer calories and gained less weight than other groups of rats. Essentially, Robynn found that unstressed rats do not binge eat on Froot Loops. Her results sharply contrast with the findings of Corwin (2003) who described binge eating on Crisco in non-stressed rats. This suggests that the tendency to binge eat depends at least in part on the nature of the palatable food provided. Robynn’s results also reveal the limitations of using an animal model to make predictions about human eating behaviors. For example, it is well documented that easy access to highly palatable foods leads to overconsumption and weight gain in humans. Thus, rather than attempt to use rats to predict human behaviors, maybe we should ask how it is that rats are able to minimize overeating and weight gain when tempted with highly palatable foods. With this knowledge, it may be possible to develop means by which humans might emulate the eating patterns of rats!

The major findings from Kishan’s stressed rats are: 1) Stressed rats consumed fewer calories and gained weight less rapidly than non-stressed rats. (This observation confirmed that the stressors we used were effective.) 2) Stressed rats over-eat only if access to Froot Loops is intermittent, that is on MWF. This may be binge eating and seems to coincide with the tendency of humans to overeat on highly palatable foods that are not always available. 3) Stressed rats with daily access to FL do not over-eat. When projected to humans, many of whom live in some degree of stress, Kishan’s results suggest that regularly eating small amounts of highly appealing foods is preferable to avoiding them most of the time and then succumbing to the temptation periodically which could results in bouts of extreme overconsumption.

Kishan’s and Robynn’s experiments have been summarized in research posters that will be presented in April 2008 at the annual meeting of the Association of Southeastern Biologists, and in July 2008 in Paris, France at the international meeting of the Society for the Study of Ingestive Behaviors. Of course, over the summer additional questions emerged. For example, it may be that how quickly an animal or person eats may influence how much they can eat before “getting full.” We’ve designed an experiment to be conducted during the fall of 2007 to get an answer to this question. Thus the research conducted with the support of the Fullerton Foundation for the Community of Scholars will extend into the next semester with the involvement of another student who has demonstrated a strong interest in this area of research.

The health consequences of excessive weight are well known and provide strong justification for basis research such as we report here. Much remains to be learned about the mechanisms that contribute to overeating in humans. Although there are obvious limitations to using rats as model organisms, these animals may provide insights that may lead to treatment strategies for humans who tend to overeat and thus become overweight or obese.

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