Manufacturers have doubled the amount of sugar in some foods in the past 30 years.

The increases were seen across dozens of food types. Even fruit was not immune, with companies selecting sweeter varieties to cater for the public’s changing palate.

The research comes amid increasing concern over the ill-effects of sugar. Rocketing sugar levels have contributed to tooth decay and an increase in the incidence of diabetes.

A recent article in the British Medical Journal said that sugar was as dangerous as tobacco and posed a greater threat to world health. “Sugar should be classified as a hard drug, for it is addictive and harmful,” it said.

The latest study, of food composition since 1978, found some of the biggest increases were in breakfast cereals and wholemeal bread. Kellogg’s Special K has nearly twice the amount of sugar it did in 1978. At 17g per 100g, it contains a similar amount to vanilla ice-cream.

A typical loaf of wholemeal bread had a third more sugar in 2002 than it had 1978. Hovis wholemeal bread has even more sugar, with 3.7g per 100g. Sainsbury’s wholemeal bread has 3.5g sugar per 100g. This means there is a teaspoon of sugar in every three slices.

In data from a 1978 industry handbook, cans of tomato soup had 2.6g of sugar per 100g. Many soups today contain double that. Waitrose tomato soup had almost three teaspoons of sugar (6.4g) per serving.

Between 1978 and 2002, the average banana’s sugar level rose from 16.2g per 100g to 20.9g. Sugar in pears increased from 7.6g per 100g to 10g. Sugar in carrots rose from 5.4g per 100g to 7.4g.

The consumer group Which? revealed last month that ready-meals contained up to 23.1g of sugar per 100g.

After a campaign to reduce salt intakes, the Food Standard Agency now wants to reduce added sugar.

A spokesman, Ian Tokelove, said: “We naturally have a sweet tooth and manufacturers have been quick to use that to increase sales in a crowded marketplace. It’s been one of the first things to be added when companies want to make a product a bit different.” Experts say that sugar levels could rise further as a byproduct of the campaign against salt.

Jack Winkler, professor of nutrition policy at London Metropolitan University, said that European trade reforms were making sugar cheaper. “It’s hard to think of a more irresponsible policy than cutting the price of sugar in the middle of an obesity epidemic,” he told The Sunday Times.

Waitrose said that it was reducing the sugar in its tomato soup. Jenny Walton, of Kellogg’s, said that extra sugar was added to some cereals because other ingredients, such as salt, had been reduced. Hovis said: “Hovis Wholemeal does contain a small amount of brown sugar. The quantities do not affect the nutritional benefits of the bread.” Sainsbury’s said that it was reviewing products to decide whether sugar and salt levels could be reduced.

Sweeteners

Kellogg’s Special K

17g of sugar per 100g – almost twice the level of 1978. A spokesman said that extra sugar had been added to some cereals when salt was reduced

Bread

Sugar in a typical loaf of wholemeal bread rose by a third between 1978 and 2002. Hovis has 3.7g sugar per 100g. A spokesman said that it did not affect nutritional benefits

Carrots

Sugar levels rose from 5.4g per 100g to 7.4g. Sugar in bananas rose from 16.2g to 20.9g, and levels in pears rose from 7.6g to10g. In 1978, cans of tomato soup had 2.6g per 100g. Today, most cans have twice that

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