Addicted Rats Teach Us Obesity Lessons

The connection between obesity, junk food, and addiction is becoming more and obvious. Remember last year, when the news came out about the rat studies at the Scripps Research Institute? Remember when we learned that junk food could be as addictive as cigarettes or Peruvian marching powder? For rats in cages, anyway.

JoAnne Allen is one of those cautious writers who passes along the caveat that any good scientist who is being interviewed will remind a journalist about. Namely, animal studies are far from being directly applicable to humans. She says,

The study, involving rats, found that overconsumption of high-calorie food can trigger addiction-like responses in the brain and that high-calorie food can turn rats into compulsive eaters in a laboratory setting…

Nevertheless, the findings in animal experiments do act as signposts. Dopamine is a consistent chemical, and the brains of those overweight rats were undersupplied with receptors for dopamine, just like the brains of human drug addicts. So the conclusion that they were addicted to junk food was hard to avoid. Same changes in behavior and brain function, and same addiction-like response. Despite the difference in their circumstances, obese rats and obese humans have a lot in common. When it comes to therapeutic treatment, what works for one might work for the other.

The Scripps Institute research also attracted the attention of UCLA addiction researcher Adi Jaffe, who has studied addiction to drugs, sex, and gambling for years. Hearing about this brought out his interest in the possibility of food addiction, too. Writing for Psychology Today, he has referred back to the original article, “Dopamine D2 receptors in addiction-like reward dysfunction and compulsive eating in obese rats,” by Johnson and Kenny, in Nature Neuroscience, 13, 635-641. Jaffe’s piece is subtitled,

Junk food may just be the most socially acceptable form of drug dealing…

That’s a rather shocking statement, but the proof is in the ever-increasing girth of American adults and the always-growing number of children and teenagers who are obese. Jaffe points out the similarities between fast-food junkies and hard-core drug addicts. People hooked on heroin or cocaine, or liquor or cigarettes, often come to a point in their lives of wanting to quit. But not quite enough to actually do it. Being marginally smarter than rats, human addicts are often quite aware that their jobs and their social relationships are being destroyed. Jaffe says,

Obese individuals are quite the same, eating more and more food regardless of their desire to adopt a healthier diet and in-spite of ridicule, low self-esteem, and decreased functioning that often accompanies extreme weight gain.

Scripps researchers Johnson and Kenny did not conclusively prove that the compulsive eating that leads to obesity is exactly the same as drug addiction, Jaffe says, but the similarities are awfully suspicious. The rats, like human drug addicts, experienced a “reduction in the density of a specific kind of dopamine receptor.” Previous studies have indicated that receptor is important to our ability to restrain impulses. So it is not surprising that the scarcity of such receptors could cause unregulated eating and uncontrolled drug-taking. The research shows something else, Jaffe says:

More importantly, it reveals a common process that unfolds when over-exposure to the reward, in this case food, occurs. This tells us that there can likely be common pathways to these different addictive disorders, though whether any specific person ended up a food- or drug-addict because of this kind of process is still an open question.

Jaffe is of course still interested in these topics, and still reporting on rat studies. His latest Psychology Today article is about dopamine, reversal learning, substance abuse, and similar impulse disorders, and the reduced ability of addicts to exert behavioral control over themselves.

Your responses and feedback are welcome!

Source: “Junk food addiction may be clue to obesity: study,” Reuters, 03/28/10
Source: “Obesity, drug addiction, and dopamine,” Psychology Today, 06/05/10
Source: “Loss, but not absence, of control — How choice and addiction are related,” Psychology Today, 01/02/11
Image by rotokirby (Kirby Kerr), used under its Creative Commons license.