PHILADELPHIA -– Two veterinary researchers from the University of Pennsylvania have been awarded the 2008 Ziskind-Somerfeld Research Award given for the top science paper of the year.
The paper, “Decreases in Dietary Preference Produce Increased Emotionality and Risk for Dietary Relapse,” demonstrated that stress contributes to increased consumption of food high in fat and carbohydrates and could possibly increase the risk of obesity. The study, appearing originally in the Journal of Biological Psychiatry, compared the physiologic, behavioral, biochemical and molecular changes that occur after chronic exposure — and then withdrawal — from diets high in either fat or carbohydrates and examined how these alterations may contribute to continued patterns of unhealthy eating.
The research team used mice genetically engineered to be more sensitive to stress and provided them with high fat and high carbohydrate meals for an hour per day, allowing them to eat as much as they wanted. After four days, researchers began exposing the mice to chronic and variable stressors, mild and unpredictable in nature, like the stresses encountered by humans in everyday life.
Researchers Sarah L. Teegarden and Tracy L. Bale of Penn’s School of Veterinary Medicine then observed the behavioral, physiological and biochemical changes that occurred, revealing significant changes in arousal, anxiety-like behaviors and chemical and molecular responses to stress, including the expression of reward-related signaling molecules in response to withdrawal from the highly preferred high-fat diet. It is these biochemical changes that are believed to contribute to the drive for dietary relapse.
“Because stress appears to contribute to the desire and consumption of high-calorie foods, then an important step toward improved public health is finding and treating those people who are most susceptible to stress-induced eating,” said Tracy Bale, assistant professor of neuroscience in Penn Vet, said.
The team checked the mice for signs of stress by observing their behavior — often how anxious or vigilant they appeared — as well as the presence of stress hormones and molecular markers. The findings supported existing evidence that linked stress with overeating and weight gain and showed that individual differences in the response to stress may be an important factor in stress-induced overeating.
“Our study now adds to a growing body of literature, suggesting not only that there are differences in dietary preferences during stress but that stress produced from dietary withdrawal does indeed drive behaviors to seek out and to consume more calories in the form of palatable foods,” said Teegarden, a Penn Vet doctoral candidate, said.
According to the American Obesity Association, more than 127 million American adults are overweight or obese, and the success rate for treating this behavior without drugs is only 5 percent. Despite the known consequences of obesity, behavioral noncompliance remains high, supporting the powerful rewarding properties of such foods.
“Evolutionary forces, it seems, are not very concerned with our weight, only our survival,” Bale said. “Evolution is not concerned with being overweight but with famine. Our bodies are wired to respond to highly caloric foods. Even at the molecular level, there are parts of the brain that respond to high-fat foods.”
On the basis of these studies, the team surmised that obesity may be a disease with some addiction-like properties. As such, consumption of preferred diets would lead to activation of brain reward pathways and a reduction in stress state. Therefore, dietary restriction, modeled here as a reduction in dietary preference, may produce increases in emotionality and stress state.
The study was supported by the University of Pennsylvania Diabetes Center, University of Pennsylvania Center for Molecular Studies in Digestive and Liver Disease and University Research Foundation.