Industry insiders have disclosed to The Sunday Times that food manufacturers are using fat to bulk up and extend the shelf life of common foods.

Until traditional local bakeries closed in the 1960s and 1970s, bread rarely contained fat. But it is used in new processed versions to ensure bread stays moist and fresh longer.

Research by The Sunday Times last week identified Marks & Spencer Organic Wholemeal Bloomer and Warburtons Seeded Batch as having some of the highest fat levels. Three slices of each contained 12 grams and 12.3g respectively. A standard-sized Mars bar, weighing 62.5g contains 10.9g of fat.

By contrast, some brands of sliced white bread, which has generally been regarded as the least healthy option, contained as little as 1.3% fat. The fat content of brown breads varied from 2.1% to 8.9%.

Although a small proportion of fat in brown bread might be accounted for by oil from the wheatgerm used to produce the bread, most of it is in the form of added vegetable fat and oil.

Modern production methods allow fat to be chemically manipulated so that the texture — described by industry insiders as the “mouth feel” of a processed food — does not give away the inflated fat content.

Malcolm Kane, former chief food technologist for Sainsbury’s, said: “The disproportionate amount of fat in the average daily diet, which is masked by the judicious use of other ingredients, is why people find it so difficult to control their fat intake.

“It is entirely possible for the industry to warn people about the high fat content of processed foods because they already do it with low fat products. Manufacturers don’t do it because they don’t have to.”

Jens Kristott, a food technologist for Britannia Food Ingredients which supplies the cocoa butter fat for Mars bars, said: “People think there is no fat in bread and there shouldn’t be. It is used in industrial bread-making because it makes the whole process much cheaper. Instead of wasting time and energy leaving the bread to rise naturally in a warm place, you can force in bubbles of air using fat to hold the structure.”

Tom Sanders, professor of nutrition at King’s College London, believed food manufacturers were adding fat because it was cheap and readily absorbed flavourings: “I am very surprised they are putting so much into bread. I have noticed that the average ready-made sandwich used to contain about 300 calories and now seems to contain about 450. That might be part of the reason why.”

A spokesman for Marks & Spencer said ingredients were clearly identified on its product labels in line with the company’s image as a responsible retailer.

Warburtons attributed its bread’s high fat content to the seeds in it. It said fat was added to bread to make it keep longer and was done in response to consumer demand.

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