Food companies have doubled the amount of sugar they add to some of their most popular products — including soups and cereals — in an attempt to attract sweet-toothed customers.

Some of the biggest increases in sugar have been in breakfast cereals, and even wholemeal bread has become far sweeter. It now routinely contains nearly a teaspoonful of sugar in every three slices.

Experts warn that the trend, which can be traced back over three decades, is likely to get worse as sugar prices fall and salt levels are reduced by health watchdogs.

In 1978 Kellogg’s Special K had 9.6g of sugar per 100g, but this has now nearly doubled to 17g — a similar level to vanilla ice-cream.

Soaring consumption of sugar has been blamed for high levels of tooth decay and increases in diabetes. Many scientists have implicated it in rising rates of obesity.

Ian Tokelove, a spokesman for the Food Commission, which campaigns for healthier foods, said: “Most of us are eating too much sugar, but we are being swamped with it in our food.

“We naturally have a sweet tooth and manufacturers have been quick to use that to try to increase sales in a crowded marketplace. It’s cheap to use and it’s been one of the first things to be added when companies want to make a product a bit different.”

Food companies maintain that sugar forms a useful part of a balanced diet, but an article in the British Medical Journal in 2005 warned: “Sugar is as dangerous as tobacco and, in terms of world health, far more important.”

The Food Standards Agency (FSA), which launched a crack-down on salt two years ago, wants companies to reduce the amount of added sugar in food products and is even considering imposing legal limits.

The Sunday Times discovered the increases in sugar levels by analysing data in an industry handbook on the nutritional value of foods — McCance and Widdowson’s The Composition of Foods, which has editions covering 1978 to 2002.

The 1978 edition shows that cans of tomato soup contained on average 2.6g of sugar per 100g in 1978. By contrast, many soups today have double that amount. A can of Waitrose tomato soup on sale last week had 6.4g of sugar per 100g, with almost three spoonfuls of sugar in every bowl.

The amount of sugar in a typical loaf of wholemeal bread rose from 2.1g per 100g in 1978 to 2.8g per 100g in 2002. A loaf of Hovis wholemeal bread now has 3.7g of sugar per 100g while Sainsbury’s wholemeal bread has 3.5g per 100g.

Kellogg’s has increased the sugar content in some of its best-selling cereals. Cornflakes now have 8g of sugar per 100g compared with 7.4g in 1978; All-Bran has 17g compared with 15.4g in 1978, and Rice Krispies have 10g of sugar, up 1g since 1978.

Much of the extra sugar in the modern diet is blamed on processed foods. A study by Which? released earlier this month found Asda sticky chilli chicken contained 19.2g of sugar per 100g and Tesco crispy beef with sweet chilli sauce had 23.1g per 100g.

Jack Winkler, professor of nutrition policy at London Metropolitan University, said that despite government efforts to reduce sugar in the modern diet, it was likely to increase because European Union trade reforms were reducing its price.

“It’s hard to think of a more irresponsible policy than cutting the price of sugar in the middle of an obesity epidemic. It means manufacturers will be putting more of it in their products, not less,” he said.

It is not just manufactured foods that have seen their sugar content rise. Supermarkets have also been selecting sweeter varieties of fruit and vegetables to appeal to customers.

According to McCance and Widdowson, between 1978 and 2002 the amount of sugar in a banana rose from 16.2g per 100g to 20.9g; the quantity in a pear rose from 7.6g per 100g to 10g; the content for carrots rose from 5.4g per 100g to 7.4g.

Waitrose said its tomato soup was one of a number of products being reformulated with lower amounts of added sugar.

Jenny Walton, a nutritionist for Kellogg’s, said some of its cereals had been made with extra sugar because other ingredients, such as salt, had been reduced.

Hovis said: “Hovis Wholemeal does contain a small amount of brown sugar. The quantities of sugar do not affect the nutritional benefits of the bread.”

Sainsbury’s said that it was reviewing a number of products to see if the sugar and salt levels could be reduced.

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