“Just one,” you tell yourself, biting into a freshly baked cookie. The chocolate chips are gooey and sweet in your mouth; the warm dough is still soft and crumbles as soon as it hits your tongue. That first bite is blissful – and gone too soon. Okay, maybe just two, you decide.
A recent study conducted at Université de Montréal (UdeM) and published in Neuropsychopharmacology illustrates the neurological effects of high fat content foods, and provides insight into why we might be tempted to go for seconds. Cecile Hryhorczuk, the first author of the study and a PhD student at the Research Centre of the Centre hospitalier de l’Université de Montréal (CRCHUM), explains this reward system – known as the mesolimbic dopamine system – is the brain’s centre for motivation and pleasure, and it is linked to mood disorders, drug addiction, and overeating. “Several groups before us have studied the impact of fat on the mesolimbic system. However, no one had looked specifically at whether different types of fat have the same effects,” Hryhorczuk told The Daily in an email.
Fundamental changes in our brain’s circuitry could be the cause rather than a consequence of overeating, obesity, and associated mental and metabolic diseases.
And so, Hryhorczuk and a group of her fellow researchers at UdeM set out to determine how diets high in monounsaturated fat and saturated fat influence the dopamine system. Three groups of rats were used in the study. The first group served as a control and was fed a low-fat diet made up of a mixture of the two types of fat. The second group was given a diet rich in monounsaturated fat, and the third group a diet high in saturated fat. “We chose palmitate, a saturated fatty acid, and oleate, a monounsaturated fatty acid, because they are widely present in the food we eat and they are two of the most abundant fatty acids found in the human body,” said Hryhorczuk. By conducting the study on a strain of rats that do not suffer from obesity– a condition linked with many other complications – when fed high fat content foods, the researchers were able to resolve the molecular and behavioural changes induced by the three different diets independent of weight gain, as all groups gained the same amount of weight.
Following eight weeks on their specific diets, each group of rats underwent a series of tests to ascertain the operational effectiveness of their dopamine systems. The results were clear: the rats on the diet high in saturated fat showed significantly dampened dopamine function in both behavioural and biochemical tests. “Our results demonstrate that long-term consumption of saturated fat negatively impacts the reward system in the absence of obesity and peripheral metabolic abnormalities,” said Hryhorczuk.
So back to the cookie. Why is it that one bite of the delicious, fatty, and sugary treat tends to give way to overindulgence? “Both drug and food intake trigger the release of dopamine, a feel-good molecule,” Hryhorczuk explained. “However, on the long term, the system gets used to it and becomes less sensitive. This is what occurs in drug addicts, who develop tolerance and need to increase their dose to reach the same amount of pleasure.” And according to Hryhorczuk’s findings, “the same thing happens with high-fat food: on the long term it reduces the sensitivity of the system to rewards. If we extrapolate to humans, it suggests it could make people look for and consume more of this type of food to get the same pleasure/satisfaction.”
Although clinical studies would be required in order to determine if the effects of diets high in saturated fat translate from rats to humans, this study suggests that what we eat influences not only our gastrointestinal system, but also our neurological one. The most surprising discovery from this study is the fact that fundamental changes in our brain’s circuitry could be the cause rather than a consequence of overeating, obesity, and associated mental and metabolic diseases. Hryhorczuk noted that with the continuing rise in rates of obesity, a healthy diet and exercise may not be enough. “It is thus important to understand the biological mechanisms at play. This is why we conduct research on how food can impact the central nervous system.”