Overeating is the largest determinant of obesity, which is one of the biggest health crises affecting Canadians. A new animal study out of the Hotchkiss Brain Institute (HBI) at the University of Calgary’s Cumming School of Medicine provides new insight into how high fat diets rapidly rewire the reward circuits in the brain, which can lead to an increase in food-seeking and risk-taking behaviours in the pursuit of food. The study will be published in Proceedings of the National Academy of Sciences of the United States on February 15th.
The study could contribute to the understanding of what underlies the development, and implications, of overeating.
“Our research shows that one full day of consumption of sweet, fatty foods increases the number of synapses onto dopamine neurons – the neurons that are responsible for motivational behaviour,” says Stephanie Borgland, PhD, associate professor in the Department of Physiology and Pharmacology, member of the HBI and senior study author. “This change in the brain can last at least a week, thereby promoting food-seeking and overeating, even days after the initial exposure to the food.”
The animals in the study were exposed to an unlimited amount of sweetened high fat food, similar to shortbread cookies, for a 24-hour period before then returning them to their regular chow. Researchers observed synaptic changes occurred in the ventral tegmental area (VTA), a region of the mid-brain that plays a central role in reward-seeking. The increase in synapses to the VTA dopamine neurons suggests the brain is being primed to want to eat more, despite hunger levels.
In addition to the synaptic changes observed in the brain, behavioural changes were also observed following the ‘pig out’. Researchers noted the animals showed an increase in risk-taking behaviour (such as entering a well-lit area, despite their innate fear of light) to once again reach the same sugary, high fat food following the 24-hour period, than those who were not fed the fatty diet.
“This research could help guide strategies to decrease overeating due to food priming induced by palatable food consumption or food-related cues,” says Shuai Liu, PhD, HBI postdoctoral research scholar and first author on the study.
While this study was conducted in animal models, the human brain has similar circuits that drive food intake. Currently, researchers do not know if consuming junk food can change synapses in the human brain. However, they do know, through fMRI, that food advertising primes people to eat more and this activates brain regions involved in reward processing.
The study was funded by the Canadian Institutes of Health Research.
Source of text: University of Calgary
Original research article: Liu S, Globa AK, Mills F, Naef L, Qiao M, Bamji SX, Borgland SL. Consumption of palatable food primes food approach behavior by rapidly increasing synaptic density in the VTA. Proc Natl Acad Sci U S A. 2016 Feb 16. pii: 201515724.