Cancers of the gut are some of the most common, but most preventable forms of the disease, scientists say.
An apple a day really can keep the doctor away
The Institute of Food Research has looked at studies carried out into how changes in diet can help.
Fruit and vegetables are generally beneficial, but it says onions, apples, celery and broccoli are all highlighted as being particularly beneficial.
Scientists are continuing to investigate how agents within the foods help prevent cancer.
Of the 10m cancers newly diagnosed in 2000, about 2.3m were cancers of the digestive organs, the pharynx, oesophagus, stomach or colorectum.
Studies have shown that the risk of gut cancers can be reduced through diet.
The walls of the gut are lined with a layer of cells called the epithelium which is covered with a film of mucus.
The epithelium is the first contact for food, bacteria and anything else ingested into the body.
It is the body's first line of internal defence, but it can be susceptible to the development of abnormalities over time.
The epithelium is renewed by rapidly dividing stem cells, which can also give rise to new growths called polyps.
These usually remain benign, but some may acquire so many genetic abnormalities that they eventually form a cancerous tumour.
Research has suggested that fibre, folic acid, polyunsaturated fatty acids, plant chemicals such as flavonoids (plant pigments) and gut fermentation products such as butyrate can provide protection at various stages of cancer.
Enzymes called COX-2, which enable faulty cells to survive, have been found to be suppressed by quercetin - a flavonoid found in onions and apples, as well as tea.
Other chemicals can also increase the activity of detoxifying enzymes, and some - such as apigenin, found in parsley, artichoke, basil and celery - appear to work more effectively in conjunction with another chemical found in brassica vegetables such as broccoli and cabbage.
These enzymes attack genetically damaged epithelial cells.
Professor Ian Johnson, head of Gastrointestinal Health and Function at the institute, carried out the review of existing research.
He said: "Cancers of the colon and rectum are the most common cancers of the digestive organs worldwide.
"But rates are much higher in developed countries. Colorectal cancer is clearly a disease of affluence and about 80% of cases are attributable in some way to diet.
'Highlighting diet's role'
"Many of the mechanisms have yet to be discovered, but basically what this means is that people can help to protect themselves by controlling their weight and by eating diets rich in fruits and vegetables and other sources of fibre."
He added: "Cancer is a complex multistage process that can take a large proportion of a person's lifespan to develop.
"Nutrition is potentially a powerful tool to interrupt many stages of that process, and could be much more effectively deployed by many people."
Professor Johnson said specific advice about the most beneficial diets could not be offered to patients.
But he added: "The standard advice of five portions of fruit and vegetables a day is sound."
Alison Hesketh, Interim Director of Core, formerly the Digestive Disorders Foundation, told BBC News Online: "We welcome the Institute of Food Research contributing to Gut Week and hope that reviews of the kind will highlight the role that diet plays in maintaining a healthy digestive system."