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Some food processing methods may impede one of the body's natural methods of protection against intestinal diseases, such as ulcerative colitis or Crohn's disease.

Researchers are discovering that starch, which was previously thought to be broken down totally in the first half of the gut, can in fact get as far as the large intestine in the same way as plant fibre does. The small amount of starch that makes it this far is likely to be fermented by bacteria in the large intestine and release chemicals such as butyrate, thought to protect against certain diseases.

But scientists at the Institute of Food Research in Norwich have found that only certain starchs make it to the large intestine.

"Raw starch, (such as that found in muesli) is resistant to being broken down before it reaches the large intestine," said Louise Botham, research scientist at the Institute. "And some cooking methods give resistance, for example, pasta cooking."

The researchers are investigating whether processing methods could be changed to create more beneficial starch, said Dr Botham.