Researchers from the Dunn Clinical Nutrition Centre in Cambridge say that diet also contributes to varying extents to the risk of many other cancers, including cancers of the lung, prostate, stomach, oesophagus and pancreas.

Generally fruit, vegetables and fibre have a protective effect against cancer, whereas red and processed meat increase the risk of developing the disease.

The researchers also found that there is no evidence that vitamin supplements help to prevent cancer.

Writing in the British Medical Journal, the researchers say cancer is responsible for more deaths annually in the UK that ischaemic heart disease.

Around half of cancer deaths are due to tumours at four principal sites: lung, bowel, breast and prostate.

These cancers are virtually absent in many countries in the developing world, but increase in incidence within one or two generations when migrants move from low to high risk areas.

Therefore, the researchers conclude, cancers common in Western populations are due to environmental factors, and should be largely preventable.

They rate diet as one of the most important of all environment factors.

"What is remarkable about the diet-cancer story is the consistency with which certain foods emerge as important in reducing risk across the range of cancers," the researchers write.

"Vegetables and fruit are almost invariably protective for the major cancers. Consumption of these foods in Britain is less than half that in Mediterranean populations where cancer rates are low."

The researchers advise that in the UK:

• Average consumption of fruits and vegetables should at least double to five portions a day;
• Fibre consumption should increase from 12 grams a day to 18 grams a day;

In addition, The World Cancer Research Fund has recommended that daily intake of red meat should be limited to less than 80 grams a day.

Breast cancer

Red meat intake 'should be limited'

It is believed that dietary fat could be linked to a greater risk of breast cancer, although the link has still to be proved conclusively.

Postmenopausal women who are overweight have up to a two-fold greater risk of breast cancer.

This increased risk is associated with higher serum concentrations of the female sex hormone oestrogen.

Oestrogen is synthesised from the hormone androstendione in fat tissue. Therefore, in women who lose weight, serum concentrations of oestrogen fall, and the risk of cancer should fall too.

Both meat and alcohol are associated with increased risk of breast cancer, as are low intakes of vegetable and fibre.

Colorectal cancer

It is well established that fibre and vegetables reduce the risk of colorectal cancer, largely because they help to regulate bowel function.

Fibre is fermented in the large bowel and produces short chain fatty acids that may protect against cancer by arresting cell growth, and stimulating damaged cells to self-destruct.

People who eat greater amounts of red and processed meat are at higher risk of colorectal cancer.

Meat is likely to increase risk of bowel cancer because of chemicals that form on its surface during grilling, roasting, frying, and barbecuing.

An abundance of the enzymes used by the body to break down these compounds can lead to the development of cancer.