I composed the first seven years of the "Fitness Master" on a word processor, essentially an electric typewriter with I kid you not! a seven-line screen, no spell check, and no internal hard drive. Insert a single floppy disk, however, and you could store about six pages of single-spaced text.

Whether this is better proof of how quickly computer technology has advanced or how old I have become is questionable, but one thing is sure: all those articles were forever lost when the repair estimate to fix the thing exceeded the original cost.

In one of those long-lost articles, I agreed with a reader's assertion that I was addicted to exercise. Back then it was called the runner's high, and the theory was that endurance exercise released the beta endorphins, the body's own feel-good drug, a group of proteins produced by the pituitary gland that improve mood, memory retention, and learning, and reduce the perception of pain.

I argued, however, that this addiction unlike an addiction to alcohol or cigarettes or recreational drugs was a positive one.

Today, at least 14 years after the fact, I'd like to amend that. But I'm not about to change my beliefs about the benefits of exercise or report that science has debunked the runner's-high theory.

I'm going to amend my definition of addiction.

Although there are hundreds of ways to define the word and many that are quite complex, the one used by Narconon, a drug-free social education program, is straightforward and suggests that you really can't be addicted to exercise.

But Narconon's three characteristics of addiction loss of control, compulsive preoccupation, and continued use despite negative consequence do suggest that you can be addicted to junk food, a question that's been bandied about once again ever since the Society for Neuroscience's annual meeting on October 20.

At that time Paul Kenny, an associate professor of molecular therapeutics at Scripps Research Institute in Jupiter, Florida, released the results of a study in which one group of rats was allowed unlimited access to the sorts of junk foods humans eat. Sausage, pound cake, bacon, and cheesecake were just some of the items used.

Compared to two other groups of rats, one that was fed only healthy foods and one that was fed junk food but in limited amounts, the unlimited-access group ate twice the amount of calories and quickly became obese.

But the real surprise came when the researchers electronically stimulated the rats' brains. After only five days on the unlimited-junk-food diet, the pleasure center in the rats' brains had become desensitized, meaning they'd now require more junk food to receive the same amount of pleasure from it.

Kenny's coauthor, Paul Johnson, said, "This is the hallmark of addiction," a fact that became shockingly evident, when appropriately enough an electronic shock was used.

The researchers allowed the rats from all three groups to eat junk food and then shocked their feet. The rats used to eating healthy food and those who ate junk food in restricted amounts quickly stopped eating because of the pain.

But the rats from the unlimited-junk-food group did not even once they realized the shocks would continue if they continued to eat the junk food.

Next, the researchers took away the junk food from the unlimited-junk-food group and only offered them good things to eat. For two weeks, the rats refused to eat.

In summarizing their results, Johnson said, "This is the most complete evidence to date that suggests obesity and drug addiction have common neurological underpinnings."

But this isn't the first time this link has been made.

Breakthrough research done by neuroscientist Bart G. Hoebel from Princeton University and published in the journal Obesity Research in June of 2002 showed sugar affected rats much in the same way as the unlimited-junk-food diet. In Hoebel's experiment, rats were given increasing amounts and then were suddenly denied it.

Like heroin-addicted humans in withdrawal, the rats first grew anxious, then suffered the shakes to the point their teeth chattered.

This reaction is no surprise to Kathleen DesMaisons, author of The Sugar Addict's Total Recovery Programme. She says sugar works like morphine and heroin to create "a wonderful feeling of euphoria and well-being, but when it wears off, you feel edgy, irritable, and cranky [which is the] actual withdrawal.

"If you use the drug [sugar] again, it relieves the symptoms, so you get caught in the cycle of needing it."

Sounds a lot like addiction to me.

If subsequent studies with human subjects replicate Johnson and Kenny's recent results, expect those somewhat left-of-center groups like the Center for Science in the Public Interest to demand that junk food be regulated in a manner similar to alcohol and cigarettes. Considering that a number of cities have already passed ordinances banning trans fats and requiring restaurants to post the nutritional information for menu items, placing a tax and an age requirement on the purchase of junk food would seem to be the next step.

Whether a measure like that would infringe upon civil liberties is an interesting question. But a more pressing one is, Do you control your eating, or does your eating control you?