Cancers of the gut are one of the major causes of death from cancer, but a review published this week shows that they are also amongst the most preventable through changes in diet.
Of the 10 million new cases of cancer diagnosed in 2000, around 2.3 million were cancers of the digestive organs – pharynx, oesophagus, stomach or colorectum. Studies have shown that they are not purely genetic and can be modified by diet.
Professor Ian Johnson, author of the review and head of Gastrointestinal Health and Function at the Institute of Food Research, said: “The adverse effects of diet are caused by over-consumption of energy coupled with inadequate intakes of protective substances, such as micronutrients, dietary fibre and a variety of plant chemicals”.
The walls of the gut are lined with a layer of cells, the epithelium, covered with a film of mucus. The epithelium is the first contact for food, bacteria and anything else ingested. It is the body’s first line of internal defence, but can also be susceptible to the development of abnormalities over time. The epithelium is normally 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.
There is evidence that some food components including fibre, folate, polyunsaturated fatty acids, plant chemicals such as glucosinolates or flavonoids and gut fermentation products such as butyrate can provide protection at various stages of cancer formation. For example, in research published in the same journal, enzymes called COX-2 that enable genetically abnormal cells to survive were suppressed by the flavonoid quercetin Compounds can also increase the activity of detoxifying enzymes, and components in the diet have been shown to act synergistically in this way – so that they are even more effective when combined. These enzymes delete genetically damaged epithelial cells.
“Cancers of the colon and rectum are the most common cancers of the digestive organs worldwide”, said Professor Johnson. “But rates are much higher in developed countries. Colorectal cancer is clearly a disease of affluence and about 80 per cent of cases are attributable in some way to diet. 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“.
“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”, he said.