March 30, 2010
The Palm Beach Post
By Jeff Ostrowski
In a study that compares cupcakes and cookies to cocaine, scientists at Scripps Florida say rats fed a diet of junk food grew addicted to high-calorie, high-fat fare.
The fat rats became so hooked on junk food that when researchers took away the bad stuff and replaced it with healthy food, the rodents chose to starve themselves.
Scripps Florida scientists Paul Kenny and Paul Johnson say junk food changed the rats’ brain chemistry in the same way that chronic cocaine use alters an addict’s brain function. Their study, published Sunday in the journal Nature Neuroscience, bolsters the increasingly popular theory that Americans’ bulging waistlines can be blamed in part on the addictive attributes of unhealthy food.
As part of three years of experiments, Kenny, an associate professor, and Johnson, a graduate student, served one group of rats healthy, nutritionally balanced fare. Another group got unlimited access to the worst stuff Johnson could find at Publix, including bacon, sausage, cheesecake, pound cake, Ding Dongs and frosting.
Not surprisingly, the rats fed junk food put on weight and became less active.
More surprisingly, the fat rats exhibited the sort of self-destructive behavior associated with human junkies. The rats would eat junk food even if they knew doing so would result in a mild but distinctly uncomfortable electrical shock to their feet.
When Kenny and Johnson replaced the unhealthy food with the healthy diet the rats had been raised on, the animals refused to eat at all.
“They actually voluntarily starved themselves,” Kenny said.
Kenny blames the same culprit that afflicts cocaine addicts: the brain’s dopamine D2 receptor. The brain releases dopamine in response to enjoyable experiences such as eating cheesecake, having sex or snorting cocaine.
But, scientists believe, too much pleasure skews the brain’s reward pathways by overstimulating the D2 receptor and causing it to shut down. For the rats addicted to junk food, Kenny said, the only way to stimulate their pleasure centers was to eat more high-fat, high-calorie food.
“They’re not experiencing rewards the way they should,” Kenny said. “When you experience that, one way of feeling better is to go back to the junk food.”
As part of his research, Kenny used a virus to essentially block healthy rats’ D2 receptors. Those rats quickly developed compulsive eating habits.
Kenny hopes his research might lead to a drug or vaccine to treat overeating. The experiments were supported by a $250,000-a-year grant from the National Institutes of Health and smaller grants from Bank of America and The Margaret Q. Landenberger Research Foundation.
Intriguingly, nearly all the rats given junk food became obese. But despite the fact that Americans are faced with a smorgasbord of easily available junk food, most of us can handle the temptation.
Kenny says that’s because overeating is driven by not just the genetic factors that make us crave junk food but also by social pressures. Humans know junk food is bad for us, and we try to avoid it. But rats don’t find their impulses tempered by clothes that no longer fit or by books by Dr. Oz, TV shows like The Biggest Loser and movies such as Super Size Me.
“The rats don’t suffer from the same social pressures that we do,” Kenny said.
Nutrition experts aren’t surprised by the Scripps researchers’ conclusion that junk food is addictive. In last year’s best-selling book The End of Overeating, former FDA Commissioner David Kessler argued that salty, sugary, fatty food triggers dopamine production.
“Certainly, we see this addictive pattern in humans,” said Sandy Livingston, a licensed nutritionist in Palm Beach Gardens. “They know they shouldn’t overeat, but they do it anyway.”
Livingston hopes research like this helps overeaters better deal with their gluttony by realizing that the behavior is driven not by personal failings but by powerful chemical reactions in the brain.
“A lot of people blame themselves — ‘Why don’t I have any willpower?’” Livingston said. “It’s very hard to rely on willpower, because willpower will lose. If your body wants something enough, you’re always going to lose.”
Jordan Rubin, author of The Maker’s Diet and founder of nutritional supplements firm Garden of Life in West Palm Beach, said he’d like to see more research into exactly which types of food and food additives are addictive. For instance, foods such as beef and avocados are high in fat, but Rubin believes addiction is caused not by fat alone but by fat in combination with other foods, such as white flour or the additive MSG.
“Food can be highly addictive,” Rubin said. “When people describe overeating and weight loss as a battle, this is why.”