Fatty foods may cause cocaine-like addiction

[Guest guest]

By Klein, Health.com

March 28, 2010 2:42 p.m. EDT

(Health.com) -- Scientists have finally confirmed what the rest of us have

suspected for years: Bacon, cheesecake, and other delicious yet fattening

foods may be addictive.

A new study in rats suggests that high-fat, high-calorie foods affect the

brain in much the same way as cocaine and heroin. When rats consume these

foods in great enough quantities, it leads to compulsive eating habits that

resemble drug addiction, the study found.

Doing drugs such as cocaine and eating too much junk food both gradually

overload the so-called pleasure centers in the brain, according to J.

Kenny, Ph.D., an associate professor of molecular therapeutics at the

Scripps Research Institute, in Jupiter, Florida. Eventually the pleasure

centers " crash, " and achieving the same pleasure--or even just feeling

normal--requires increasing amounts of the drug or food, says Kenny, the

lead author of the study.

" People know intuitively that there's more to [overeating] than just

willpower, " he says. " There's a system in the brain that's been turned on or

over-activated, and that's driving [overeating] at some subconscious level. "

In the study, published in the journal Nature Neuroscience, Kenny and his

co-author studied three groups of lab rats for 40 days. One of the groups

was fed regular rat food. A second was fed bacon, sausage, cheesecake,

frosting, and other fattening, high-calorie foods--but only for one hour

each day. The third group was allowed to pig out on the unhealthy foods for

up to 23 hours a day.

Not surprisingly, the rats that gorged themselves on the human food quickly

became obese. But their brains also changed. By monitoring implanted brain

electrodes, the researchers found that the rats in the third group gradually

developed a tolerance to the pleasure the food gave them and had to eat more

to experience a high.

They began to eat compulsively, to the point where they continued to do so

in the face of pain. When the researchers applied an electric shock to the

rats' feet in the presence of the food, the rats in the first two groups

were frightened away from eating. But the obese rats were not. " Their

attention was solely focused on consuming food, " says Kenny.

In previous studies, rats have exhibited similar brain changes when given

unlimited access to cocaine or heroin. And rats have similarly ignored

punishment to continue consuming cocaine, the researchers note.

The fact that junk food could provoke this response isn't entirely

surprising, says Dr.Gene-Jack Wang, M.D., the chair of the medical

department at the U.S. Department of Energy's Brookhaven National

Laboratory, in Upton, New York.

" We make our food very similar to cocaine now, " he says.

Coca leaves have been used since ancient times, he points out, but people

learned to purify or alter cocaine to deliver it more efficiently to their

brains (by injecting or smoking it, for instance). This made the drug more

addictive.

According to Wang, food has evolved in a similar way. " We purify our food, "

he says. " Our ancestors ate whole grains, but we're eating white bread.

American Indians ate corn; we eat corn syrup. "

The ingredients in purified modern food cause people to " eat unconsciously

and unnecessarily, " and will also prompt an animal to " eat like a drug

abuser [uses drugs], " says Wang.

The neurotransmitter dopamine appears to be responsible for the behavior of

the overeating rats, according to the study. Dopamine is involved in the

brain's pleasure (or reward) centers, and it also plays a role in

reinforcing behavior. " It tells the brain something has happened and you

should learn from what just happened, " says Kenny.

Overeating caused the levels of a certain dopamine receptor in the brains of

the obese rats to drop, the study found. In humans, low levels of the same

receptors have been associated with drug addiction and obesity, and may be

genetic, Kenny says.

However, that doesn't mean that everyone born with lower dopamine receptor

levels is destined to become an addict or to overeat. As Wang points out,

environmental factors, and not just genes, are involved in both behaviors.

Wang also cautions that applying the results of animal studies to humans can

be tricky. For instance, he says, in studies of weight-loss drugs, rats have

lost as much as 30 percent of their weight, but humans on the same drug have

lost less than 5 percent of their weight. " You can't mimic completely human

behavior, but [animal studies] can give you a clue about what can happen in

humans, " Wang says.

Although he acknowledges that his research may not directly translate to

humans, Kenny says the findings shed light on the brain mechanisms that

drive overeating and could even lead to new treatments for obesity.

" If we could develop therapeutics for drug addiction, those same drugs may

be good for obesity as well, " he says.