Feeding a high-fat diet (HFD) containing palm oil (a saturated fat (SF)) induced anxiodepressive behaviour in mice, found the researchers from the University of Montreal Hospital Research Centre (CRCHUM).
Although an olive oil based HFD also increased obesity and leptin levels in mice (compared with controls), rodents fed the monounsaturated fat (MUF) diet did not exhibit the behavioural anxiety and despair seen in the palm oil fed mice.
"The depressive, anxiety and compulsive behaviours and the metabolic changes observed with the diet rich in saturated fat were not observed with a diet rich in monounsaturated fat, the type of fat found in olive oil," said senior researcher Professor Stephanie Fulton writing in the journal Molecular Metabolism.
Physiologically, the SFHFD mice also showed greater visceral fat deposition, reduced insulin sensitivity, higher glucose levels and increased peripheral inflammation, compared with the olive oil-fed mice or controls.
The changes in the mice occurred in a relatively short timeframe, implying the dangers of even a short-term diet rich in saturated fat.
"It took only 12 weeks for the diet rich in saturated fat to cause obesity, anxiodepressive behaviours and the metabolic changes associated with prediabetes," commented Léa Décarie-Spain, the study's first author.
The SFHFD also induced Inflammation in the nucleus accumbens (NAc), a region of the brain that controls mood and reward.
Inflammation in the NAc was shown to be driven by a complex signalling pathway: inhibitor of kappa-b kinase beta/ nuclear factor kappa-b (IKKBeta/NFKB). (The NFKB pathway is widely recognised as the key contributor in the expression of pro-inflammatory genes).
However, the scientists were able to use a genetically modified virus to inhibit the NFKB activity, protecting the mice from inflammation in the NAc and therefore preventing the anxiodepressive effects of the SFHFD diet.
"This manipulation succeeded in protecting the mice eating the diet rich in saturated fat from brain inflammation; consequently, the signs of depression and anxiety and the compulsive sugar seeking disappeared," explained Décarie-Spain.
These findings may help justify additional research into interventions to protect the NAc against diet-induced inflammation, said the researchers. It is thought that a similar mechanism of inflammation occurs in the human NAc.
Insight into comfort eating
The SFHFD diet also led to heightened food cravings in the mice, which resulted in compulsive sugar-seeking behaviour. The resultant addition to calorie intake may contribute to a vicious circle of increased obesity and mood disorders, suggested the scientists.
"Poor diet quality along with metabolic disturbances can lead to negative emotional states, which can stimulate the quest for comfort through food, and thereby lead to compulsive behaviour," noted Décarie-Spain.
Occasional intakes of high saturated fat content foods would not cause depression, reassured Décarie-Spain. However, "We should simply avoid eating such foods in excess in order to keep a healthy metabolism and inflammation at a minimum. It's a question of moderation."
"We hope that this study will help educate people about the importance of diet, not only because of the link with cardiovascular diseases and certain cancers, but also because of the neurological and psychiatric problems that are increasingly associated with obesity," concluded Fulton. "We also hope that our results will put pressure on the food industry to reduce saturated fat content in foods."
Source: Molecular Metabolism
Available online 31 January 2018. DOI: 10.1016/j.molmet.2018.01.018
“Nucleus accumbens inflammation mediates anxiodepressive behavior and compulsive sucrose seeking elicited by saturated dietary fat”
Authors: LéaDécarie-Spain, Stephanie Fulton et al