JUNK foods such as Snickers bars and ketchup really are irresistible. Manufacturers have created combinations of fat, sugar and salt that are so tasty many people cannot stop eating them even when full, according to America’s former food standards watchdog.

David Kessler, former head of the US Food and Drug Administration (FDA), has warned that snacks, cereals and ready meals devised by food scientists can act on the reward centres of the brain in the same way as tobacco.

He argues that manufacturers are seeking to trigger a “bliss point” when people eat certain products, leaving them hungry for more.

“It is time to stop blaming individuals for being overweight or obese,” said Kessler. “The real problem is we have created a world where food is always available and where that food is designed to make you want to eat more of it. For millions of people, modern food is simply impossible to resist.”

While at the FDA, Kessler was best known for his attacks on the tobacco industry, which he accused of manipulating cigarettes to make them even more addictive.

In a new book, The End of Overeating, he suggests food manufacturers have achieved a similar result using precise combinations of fat, sugar, salt and texture to make foods “hyper-palatable”.

Kessler cites Heinz tomato ketchup and Starbucks white chocolate mocha Frappuccino as examples of the thousands of modern foods that have been engineered to stimulate feelings of pleasure.

A study carried out by Kessler with researchers at Yale University using functional magnetic resonance imaging techniques, showed that about 50% of obese people and 30% of those who are overweight were prone to so-called “excessive activation”.

“The right combination of tastes triggers a greater number of neurons, getting them to fire more,” said Kessler. “The message to eat becomes stronger, motivating the eater to look for even more food.”

In other research, scientists have used rats to study how different combinations of fat, sugar and salt trigger the release of neurotransmitters in the brain’s pleasure centres.

The most powerful combination involved sucrose (table sugar) mixed with chocolate and alcohol – the same mixture found in desserts such as tiramisu.

Kessler said: “Many of us have what’s called a ‘bliss point’ – the point at which we get the greatest pleasure from sugar, fat or salt.

“As more sugar is added, food becomes more pleasurable until we reach the bliss point, after which it becomes too sweet and the pleasure drops off.” The same thing happens with fat and salt.

At the optimum point, food stimulates many people’s appetites instead of suppressing it, according to Kessler, who ran the FDA from 1990 to 1997 and is now professor of paediatrics, epidemiology and biostatistics at the University of California.

There have been a series of warnings about obesity in Britain. A landmark report by the National Audit Office in 2001 found that 20% of adults were obese – a figure that has since risen to 25% – while a further 38% were overweight.

The findings alarmed Sir Liam Donaldson, the chief medical officer, so much that he warned of a “health time bomb” – particularly among children.

In 2007 the government’s science-led Foresight report said: “The wide variety and appeal of modern foods, with their increased palatability and ability to heighten sensory stimulation, drive us to reward ourselves with more food.”

Experts claimed that such evidence showed the need for state intervention. However, when Gordon Brown announced the Healthy Weight, Healthy Lives strategy early last year, he said: “There should be no doubt that maintaining a healthy weight must be the responsibility of individuals first – it is not the role of government to tell people how to live their lives.”

Tim Lang, professor of food policy at City University and a government adviser, said politicians’ obsession with promoting “choice” was damaging public health.

“If I walk to my local park for some exercise,” he said, “I pass more than 30 food outlets before I get there. It’s that combination of availability, advertising and seductive taste that makes modern food so addictive. ”

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