Junk food companies may face massive multimillion-dollar class action lawsuits, following several new research findings, which indicate their products could be as addictive as tobacco or heroin.

Research suggests that junk food high in fat or sugar can cause changes in the brain similar to those in people addicted to cigarettes or drugs -- and may have triggered a global splurge in binge-eating.

Already, global franchises McDonald's, Burger King, Kentucky Fried Chicken, Pizza Hut and others have been warned of the likelihood of litigation.

The warning came from Professor John Banzhaf of the George Washington University's law school, who said companies selling food high in fat and sugar were "deeply vulnerable" to being sued.

Banzhaf played a key role in the campaign against tobacco companies in the 1990s, filing hundreds of lawsuits against them.

When evidence emerged that the industry had manipulated the content of cigarettes to increase their addictive qualities, Banzhaf and the anti-tobacco lobby managed to force out-of-court settlements totaling $206-billion in 1998 between the industry and 46 American state governments.

According to the Telegraph, Banzhaf has now seized on the junk food research findings, and while there has been no suggestion the food industry knowingly manipulated its products to boost overconsumption, or binge-eating, he nevertheless maintained there were distinct parallels with the case against the tobacco industry.

As he put it: "They said smokers smoke for the taste, and it had nothing to do with the brain. It sounds to me that we have something very similar here."

Banzhaf has written to six multinationals selling junk food, the Daily Mail reported. "A heavy fast-food diet over time blocks the normal mechanism in the brain that produces hormones that tell us to stop eating when we are full," he said.

"Most of these companies sell this food without any nutritional information, labeling or warnings. A product that is both dangerous and addictive is very difficult to defend."

Scientists with companies like Nestlé and Unilever have, for some time now, been investigating how certain foods - chocolate biscuits, hamburgers and various snacks - compel people to binge-eat, fuelling obesity.

The companies have insisted that there was no proof that the foods created biochemical reactions that make people eat too much - and hence were not prepared to issue consumer warnings or change the nature of their products. But scientists working for these companies have revealed that manufacturers fear they may have produced foods that undermined the body's ability to control intake and are battling to find a solution.

"We have created a biochemical monster," the Telegraph quoted one scientist as saying.

And, it would appear, the results are plain to see for all: more than 300-million people worldwide are clinically obese, with an estimated 2.5-million of these dying each year as a result of being overweight.

Research at institutes around the world has produced startling findings on the effects of junk food.

· Psychologists at Princeton University, New Jersey, have shown that rats fed a diet containing 25% sugar were thrown into a state of confusion and anxiety when the sugar was removed.

The rodents' symptoms included chattering teeth and the shakes, similar to those seen in humans suffering from nicotine or morphine withdrawal.

As people put on more weight, they increased resistance to the hormone leptin, which is linked to weight and appetite.

Leptin is secreted by fat cells and sends a signal to the brain when the body has consumed enough food.

In overweight people, this signal does not work properly.

Similarly, research has revealed that fatty meals may also cause the overproduction of a substance in the brain called gelanin that stimulates overeating. Rockefeller University's Dr Sarah Leibowitz found that a single high-fat meal was enough to stimulate gelatine production.

· According to another study, by Professor Ann Kelley, a neuroscientist, and Matthew Will, of the University of the Wisconsin, rats that were fat and overweight underwent significant changes in brain development.

Will was quoted by the Daily Mail as saying: "The research suggests that a high-fat diet alters brain biochemistry with effects similar to those of powerful opiates, such as morphine."

· Researchers at the University of Sussex have suggested that high-fat foods stimulate "pleasure chemicals" in the brain called opiods.

Although their effect was short-lived, they did have a dramatic effect on food intake.

Their research found that, when the release of opiods was blocked with drugs, intake among human volunteers fell 21%.

The effect was even greater among obese people, whose intake fell by 33%.

· A spokesman for Nestlé confirmed the company had been studying the role of palatability and opiods in food intake for many years.

"No pessimist ever discovered the secrets of the stars, or sailed to an enchanted land, or opened a new heaven to the human spirit."   Helen Keller