Could fast food really be addictive?

The short answer: perhaps. Some research suggests that foods high in fat and calories may be addictive, at least in rats.

In 2002 Caesar Barber, a 56-year-old diabetic and two-time heart-attack victim, filed suit against McDonald's, Burger King, Wendy's and KFC, claiming that his illnesses were partly their fault. He'd eaten in their establishments for years, he maintained, without ever being warned that their food could harm his health. On the face of it, the case sounded bogus. Surely it's no secret that a Whopper is not health food. Barber seemed to be using the legal system to compensate for his own lack of control and common sense.

Still, there may be a kernel of truth to Barber's argument ‑- or at least to the notion that he wasn't entirely responsible for his plight. Maybe Barber couldn't control his fat cravings because he was actually addicted to fast food. Research suggests the idea isn't entirely preposterous.

For instance, studies on rats suggest the brain can become hard-wired to crave a hit of extra-crispy chicken, just as it might any addictive substance. In a trial conducted at Albert Einstein College of Medicine in New York City, rats fed a diet similar in composition to the typical fast-food meal ‑- that is, high in calories and fat ‑- were less able to respond to leptin, a hormone that signals the hypothalamus gland to regulate eating behavior and signal fullness. Chowing down on fatty foods sent the rats' leptin levels soaring, but their hypothalamuses didn't register the increase, so the rats continued to eat. When the rats were put on a diet and forced to lose weight, subsequent dips in leptin sent their brains the mixed-up signal that they were in danger of starvation, causing them to overeat.

The inappropriate leptin response kicked in after the rats ate just a few high-fat meals, researchers found. Within 72 hours, the rats lost almost all their ability to respond to leptin. The fatter the rats become, scientists speculate, the more resistant they become to leptin's effects, and the harder it is to reverse the trend.

Of course, a rat is not a person any more than a laboratory is a fast-food joint. The biological processes of eating and hunger are complex. They're governed by more than a single hormone and, at least for us humans, convoluted by a host of psychological and social factors. Although most of the leptin studies have been conducted on rats, some research does suggest a similar response in humans.

Not surprisingly, Barber's case was dismissed for lack of merit. His legal strategy was modeled after suits brought against the tobacco industry, but whereas the addictive properties of tobacco are clear, burger-and-fries dependency is still in question.