Multinational food companies have known for years of research that suggests many of their products trigger chemical reactions in the brain which lead people to overeat, The Telegraph can reveal.
Scientists working for Nestle and Unilever have been quietly investigating how certain foods, such as chocolate biscuits, burgers and snacks, make people binge-eat, thereby fuelling obesity. The companies insist that there is no proof that the foods create bio-chemical reactions that make people eat too much. They are not yet prepared to issue consumer warnings or change the nature of the products.
However, scientists working for the industry have said manufacturers fear they have created foods that undermine the body's abilities to control intake and are battling to find a solution. "We have created a bio-chemical monster," one said.
The revelation will be seized on by those who allege that the food industry has been reckless. More than 300 million people worldwide are now deemed clinically obese, with an estimated 2.5 million dying each year as a result of being overweight. In Britain, more than one in five adults is obese - triple the figure of 20 years ago.
Earlier this year America's leading fast-food chains, including McDonald's and Burger King, were warned of possible legal action from obese people following research on mice and rats suggesting that fast food could trigger overeating. It is now clear that the industry has known for years of similar results from research on humans.
One scientist who acts as a consultant to food manufacturers said: "They are aware that they have been too successful in creating food that some people just can't say no to. It's an enormous problem."
The overeating effect is thought to be triggered by opioids, chemicals which produce a desire to eat more while reducing the "sated" feeling that normally kills appetite.
Research being studied by the industry shows that although the effect is only short-lived, it can have a dramatic effect on food intake. According to a recent review of 20 years of research by scientists at the University of Sussex, when release of opioids was blocked using drugs, intake among human volunteers fell by 21 per cent. The effect was even larger among obese people, whose intake fell by 33 per cent.
Further research also suggests that the opioids effect is strongest with products that involve combinations of foods which are typically high in fat and carbohydrates. These combinations are routinely used to boost the so-called palatability of products, with chocolate being added to cereals and biscuits, cheese added to savoury snacks, and buns with a high sugar content being used for hamburgers and cheeseburgers.
The industry has long sought to drive up the palatability of its products. Now, however, it is becoming clear that palatability reflects the effect food has on the brain.
Dr Martin Yeomans, of the University of Sussex, a leading authority on opioids, said: "I am confident that opioids play a role in food intake."
Dr Yeomans will present the latest evidence linking palatability to over-eating at a scientific meeting this week which is sponsored by leading food companies, including Nestle, the world's largest, and Unilever.
A spokesman for Nestle in Vevey, Switzerland, confirmed that the company has been studying the role of palatability and opioids in food intake for many years. He said: "We have projects currently running to investigate this and other aspects of obesity and the company will make all necessary changes when there is significant scientific evidence to support such action."
However, the company did not consider the evidence strong enough to require action: "We have to be certain that there are no unexpected negative aspects." Unilever, which owns the Knorr, Birds Eye and Ragu brands, is also investigating the links.
At this week's conference in Groningen, Holland, scientists will present strategies for dealing with the issue, including greater consumer education and labelling.
The findings about the effects of opioids were seized on yesterday by Prof John Banzhaf of George Washington University, Washington DC, who played a key role in the billion-dollar lawsuits against tobacco companies during the 1990s.
During the 1990s, evidence emerged that the industry had manipulated cigarettes' content to enhance their addictive nature. In 1998, the industry reached a settlement with 46 American state governments totalling $206 billion.
Prof Banzhaf described the food industry's knowledge of possible links between high-calorie food and over-eating by humans as "astounding". "This would seem to constitute failure to disclose a material fact - information that might sway the decision of consumers, had they known about it," he said.
While there is no suggestion that the food industry knowingly manipulates its products to boost over-consumption, Prof Banzhaf said there were parallels with the case against the tobacco industry. "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."
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