Diet and experimental colorectal cancer

National and international geographic variations in the incidence and mortality rates of colorectal cancer along with changes in prevalence among migrant populations would suggest that environmental factors have a role in the aetiology of this disease. Animal models of chemically induced colonic carcinogenesis have been widely used to assess the effect of dietary components such as fat and fibre. These studies have shown that the type of fat is important. Polyunsaturated vegetable oils rich in omega-6 fatty acids have a promotional role whereas fish oil rich in omega-3 fatty acids has no promotional effect and may even inhibit tumour formation. Studies of the effect of fibres have shown that insoluble dietary fibres such as wheat bran and cellulose may have a protective role. However, soluble fibres such as pectin and psyllium offer little protection and in fact carrageenan may have a promotional effect. It has been suggested that phytic acid (inosital hexaphosphate), a component of many fibre-rich diets, rather than fibre per se, has a role in the suppression of colonic carcinogenesis. Despite conflicting evidence, it may be plausible to advocate a high fibre, low fat diet as a measure of secondary prevention of colorectal cancer.