Fatty foods are addictive and trigger responses in the brain similar to cocaine and heroin, at least in rats, according to a Nature Neuroscience study.
Behavioural and molecular neuroscientists from the Scripps Research Institute in Jupiter, Florida, fed rats a high-fat diet and then measured their responsiveness to reward. “We basically bought all of the stuff that people really like—Ding-Dongs, cheesecake, bacon, sausage, the stuff that you enjoy, but you really shouldn’t eat too often,” said co-author Paul Kenny (Reuters).
The reward circuits in the brains of addicts often have dulled responses, leading them to seek more addictive substances to get their fix. Rats given greater access to the tasty foods developed binge- and compulsive-like eating behaviour and gained more weight. They also needed more stimulation to reach a certain reward threshold over time.
“It presents the most thorough and compelling evidence that drug addiction and obesity are based on the same underlying neurobiological mechanisms,” says Kenny (news release). “The animals completely lost control over their eating behaviour, the primary hallmark of addiction.”
Even when the rats were conditioned to associate a light signal with a shock to the foot, the obese rats would continue to eat despite seeing the light. Skinny rats fed standard lab chow pellets stopped eating when they saw the light.
When researchers removed junk food and tried to put the junk-food rats on a nutritious diet—the “salad bar option”—they refused to eat. “The change in their diet preference was so great that they basically starved themselves for two weeks after they were cut off from junk food,” Kenny says (news release). “It was the animals that showed the ‘crash‘ in brain reward circuitries that had the most profound shift in food preference to the palatable, unhealthy diet.”
When the researchers knocked down the gene for a dopamine receptor—which is downregulated in human drug addicts—in rats consuming the rich diet, the animals became compulsive eaters sooner. As you become obese over a period of time, the D2 receptors go down. “This energy-dense stuff is very new to us as a species,” Kenny says (SciAm). “It’s probably corrupting brain circuitry.”
Although this finding can’t be directly applied to humans, it helps us to understand why individuals who often express a desire to limit activities with well-known negative health impacts still struggle to control those behaviours. There’s more to it than sheer willpower. “What we’re seeing in our animals is very similar to what you’d see in humans who overindulge,” Kenny says (Reuters). “It seemed that it was okay, from what we could tell, to enjoy snack foods, but if you repeatedly overindulge, that’s where the problem comes in.”
Image: punchstock