An apple a day may help to keep bowel cancer at bay, say researchers.

The key could be chemicals in the fruit called procyanidins, a team from the French National Institute for Health and Medical Research believe.

These chemicals were shown to significantly reduce the number of precancerous lesions in lab animals.

The research, which could lead to new cancer treatments, was presented at a meeting of the American Association for Cancer Research.

Parallel research suggests the chemicals - one of a class of compounds called polyphenols - work by altering signalling pathways that control the process by which cells commit suicide at the end of their natural life.

This process goes awry in cancer cells, leading to uncontrolling division, and the formation of tumours.

Lead researcher Dr Francis Raul said: "These studies not only offer insights into the mechanisms of the chemopreventive properties of these polyphenols, they also offer proof of their potential to prevent colon cancer."

Polyphenols of various types are concentrated in the skin of apples. They are antioxidants, preventing molecules called free radicals from inflicting damage on the body's tissue.

Different diets

The French researchers split the polyphenols found in apples into two general categories, and exposed cancer cells to each.

The first class of monomer polyphenols, which included the flavonoids, failed to have any significant effect at concentrations ranging from 10 to 100 micrograms per millilitre.

But the second class, featuring the procyanidins, triggered signals that lead to cell suicide, thus thwarting the growth and spread of cancer.

Next, the researchers fed rats who had been injected with a substance known to trigger colon cancer a liquid containing apple-derived procyanidins.

After about six weeks on this diet, these rats were found to have about half the number of precancerous lesions in their colons as counterparts on a regular diet.

Dr Raul said the results might eventually lead to new treatments to combat tumour growth.

He said: "For now, our work suggests that eating the whole apple, including the skin, might offer some anti-cancer benefits.

"That is certainly something we can comfortably do without further study."

Another study by American researchers presented at the meeting investigated the effect of eating vegetables on non-Hodgkin lymphoma (NHL), a type of lymph cancer.

They found that people who consume three or more servings of vegetables per day - not including potatoes - are 40% less at risk of developing the disease than people who eat less than one serving a day.

Healthy diet

Sara Hiom, of Cancer Research UK, said apple skins were are also high in fibre, and independent research has shown that increased fibre intake can independently reduce the incidence of bowel cancers.

She said: "As yet there is no solid evidence to confirm any single fruit or vegetable type as having 'cancer preventive' properties for humans.

"We continue to promote increasing intake of a wide variety of fruits and vegetables as part of a healthy diet."

Jola Gore-Booth, chief executive of the charity Colon Cancer Concern, said: "People whose diets are low in fibre, fruit and vegetables and who do not exercise regularly, appear to be at an increased risk of developing bowel cancer."