Eating unlimited amounts of high-fat food for just six weeks before resuming a more reasonable diet is enough to cause anxiety, intense cravings and other withdrawal-like symptoms in mice.
The rodents also experienced chemical changes in their brains that suggested parallels between the ways they respond to fatty and sugary foods and the ways they respond to harder drugs, like cocaine.
Together, the new findings add to a growing body of research into the addictive qualities of junk food.
"What this means from my interpretation is that it's important to prepare oneself for the low that can be experienced from changing the diet and removing palatable high-fat, high-sugar rewards," said Stephanie Fulton, a neuroscientist at the University of Montreal. "We can try to plan for the low and replace food with other things that give us pleasure, whatever that might be."
Over the last decade or so, a growing number of studies have begun to suggest that certain kinds of food can truly be addictive, said Nicole Avena, a neuroscientist at the University of Florida, Gainesville.
Rats that are cyclically deprived of sugar or fat and then given free access to sweet or rich foods, for example, binge on those foods when they're available, and they show intense signs of craving. Once they're addicted, rats will go to great lengths to get fat-and-sugar filled foods like Oreos, including crossing a grid that zaps them with electric shocks.
Some of the first studies in the field showed simply that, when sugar is taken away from rats, the animals go through withdrawal symptoms, including anxiety, depression and tremors. Follow-up work found that those symptoms accompany changes in dopamine and opioid systems — two types of neurotransmitters that are involved in cravings and withdrawal.
In more recent, detailed and nuanced research, Avena's group and others have documented specific changes in the behavior and brain chemistry of rodents after a period of overeating junk food that mimic what happens when the animals abuse drugs.
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For the new study, Fulton and colleagues wanted to see what would happen to mice that ate a tasty but less-than-healthful diet for a relatively short period of time.
After six weeks on chow that was rich in saturated fats, the rodents in her study had gained just 11 percent of their body weight, making them far from obese.
But when half of the mice were put back on a low-fat diet, the researchers reported in the International Journal of Obesity, the animals acted increasingly anxious. In a maze test, for example they chose to spend more time sitting still in the darkness than exploring exposed areas.
After being taken off the high-fat diet, mice also showed increased signs of craving — with more motivation to get a high-sugar solution.
At the same time, the researchers measured changes in brain chemicals, including dopamine and a molecule called CREB, which have been linked in previous work to both food cravings and drug addictions.
"Even periods of high-fat feeding that don't leave to obesity can produce several important biochemical and behavioral changes that make it hard to give up," Fulton said.
The new study is one of many that are adding up to demonstrate how high-fat, high-sugar foods affect not just our waistlines, Avena said, but also our brains.
"It's important that people know these types of studies are going on and that the findings that are being discovered are relatively consistent," she said. "It might make people think twice about the kinds of foods they eat and why they are eating them and whether there might be some kind of addition-like compulsion to eat certain kinds of foods."
"It's a new way to think about food," she added. "It's about us having to eat foods as opposed to us wanting those foods."