Dieting makes people feel depressed because cutting out fatty foods alters their brain, a new study has claimed.
Scientists have found that ditching a high-fat diet triggers actual chemical changes in the brain that could make people enter a vicious cycle of poor eating.
Since fatty and sugary foods cause chemical changes before obesity even occurs, the University of Montreal researchers likened going on a diet to drug withdrawal.
"By working with mice, whose brains are in many ways comparable to our own, we discovered that the neurochemistry of the animals who had been fed a high fat, sugary diet were different from those who had been fed a healthy diet," Dr Stephanie Fulton said.
"The chemicals changed by the diet are associated with depression. A change of diet then causes withdrawal symptoms and a greater sensitivity to stressful situations, launching a vicious cycle of poor eating," Fulton said.
The researchers fed one group of mice a low-fat diet and a high-fat diet to a second group over six weeks, monitoring how the different food affected the way the animals behaved.
Fat represented 11 per cent of the calories in the low-fat diet and 58 per cent in the high-fat diet, causing the waist size in the second group to increase by 11 per cent, which is not yet obese.
The relationship between rewarding mice with food and their resulting behaviour and emotions was then measured, and the brains of the mice were studied to see if there had been any changes.
Results showed mice that had been fed the higher-fat diet exhibited signs of being anxious - such as avoiding open areas - and their brains had been altered.
A molecule the researchers looked at was dopamine, which enables the brain to reward people with good feelings and encourages them to learn certain kinds of behaviour.
They found another molecule, CREB, involved in memory, which causes the production of dopamine, is more activated in the brains of the higher-fat mice.
"CREB is much more activated in the brains of higher-fat diet mice and these mice also have higher levels of corticosterone, a hormone that is associated with stress. This explains both the depression and the negative behaviour cycle," Fulton said.