A diet rich in saturated fat and sugar not only leads to obesity, it creates inflammation in the nucleus accumbens, a part of the brain that controls mood and the feeling of reward. And this inflammation can lead to depressive, anxious and compulsive behavior and disrupt metabolism,according to a new study.
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Many studies conducted on humans have shown that a Mediterranean diet low in saturated fat has a protective effect against depression. In this study, the researchers were able to identify the neuronal mechanisms that link obesity to depression.
The study showed that anxiodepressive behaviours result from inflammation observed in the nucleus accumbens. A genetic manipulation made it possible to inhibit the molecule that plays a key role in spreading the inflammation to that part of the brain.
"This manipulation succeeded in protecting the mice with a diet rich in saturated fat from inflammation; consequently, the signs of depression and anxiety and the compulsive behaviours associated with sugar disappeared," explained Décarie-Spain. These advances pave the way for further research into an anti-inflammatory genetic intervention in the nucleus accumbens that could inhibit depression caused by inflammation.
This discovery is also a good illustration of the vicious circle experienced by people with obesity caused by a diet rich in sugar and saturated fat. "Their diet leads to negative emotions, which stimulates the quest for comfort through food, which increases the risk of developing compulsive behaviour," noted Décarie-Spain.
Saturated fat is found mainly in palm oil, widely used in the processed food industry, as well as in products of animal origin.
This study was conducted with animals, but it is believed that the mechanism that occurs in the nucleus accumbens of humans is similar.
"We hope that this study will help educate people about the importance of diet, not only because of the cardiovascular diseases and cancers associated with obesity, but also because of the neurological and psychiatric problems that are increasingly linked to obesity," said Fulton. "We also hope that our results will put pressure on the food industry to replace these types of fat with monounsaturated fats."
A few cookies or a hamburger from time to time won't bring on a case of depression, the researchers cautioned. "We should simply avoid eating such foods on a regular basis in order to keep our metabolism healthy and free of inflammation," said Décarie-Spain. "It's a question of moderation."
This study follows on an earlier study published by Fulton in 2013 which showed that obesity leads to anxiodepressive behaviours and hormonal changes, which have an impact on the reward signal and vulnerability to stress.