In 1990 Willett et al published the results from the US nurses health study involving follow up of 88 751 women aged 34-59 years who were without cancer or inflammatory bowel disease at recruitment. After adjustment for total energy intake, consumption of animal fat was found to be associated with increased risk of colon cancer. The trend in risk was highly significant (P = 0.01), with the relative risk in the highest compared with the lowest quintile being 1.89 (95% confidence interval 1.13 to 3.15). No association was found with vegetable fat. The relative risk in women who ate beef, pork, or lamb as a main dish every day was 2.49 (1.24 to 5.03) compared with women reporting consumption less than once a month. The authors suggested that their data supported the hypothesis that high intake of animal fat increases the risk of colon cancer, and they supported existing recommendations to substitute fish Figure 1.5 Intake of dietary fat and meat may increase risk of colorectal cancer and chicken for meats high in fat. 

Intake of vegetables, fruit, and fibre 

 Dietary fibre has been proposed as accounting for the differences in the rates of colorectal cancer between Africa and westernised countries-on the basis that increased intake of dietary fibre may increase faecal bulk and reduce transit time. Various other factors, related to risk of colorectal cancer, are now thought to contribute to explaining these differences. 
 Fibre has many components, each of which has specific physiological functions. The components are most commonly grouped into insoluble, non-degradable constituents (mainly found in cereal fibre) and soluble, degradable constituents, such as pectin and plant gums (mainly found in fruits and vegetables). Epidemiological studies have reported differences in the effect of these components. Many studies, however, found no protective effect of fibre in cereals but have consistently found a protective effect of fibre in vegetables and perhaps . Fruits are a good source of fibre and may protect against cancer of fruits and vegetables, with fibre intake acting merely as an indicator of consumption.