Vegetarians have lower rates of colon cancer than non-vegetarians (Phillips, 1980). Incidence of colon cancer has been strongly linked to the consumption of meat (Armstrong, 1975, Singh & fraser, 1998). Willett (1990) carried out a study of over 88 000 women aged 34 to 59 years. Women eating red meat daily ran over twice the risk of developing colon cancer than women eating red meat less than once a month.
Reduced incidence of colon cancer in vegetarians may be attributed to dietary differences which include increased fibre intake, increased consumption of fruit and vegetables, and decreased intake of total fat and saturated fat. The mechanism by which a vegetarian diet is protective against colon cancer is unclear and a great deal of research is being carried out in this area.
It has been suggested that secondary bile acids are carcinogens which may play an important role in colon cancer. These are derived by bacterial metabolism from primary bile acids made in the liver and secreted into the intestine. Vegetarians have lower levels of secondary bile acids than non-vegetarians (Turjiman, 1984). The differences in bacterial populations between the intestines of vegetarians and non-vegetarians may also be important. Bacterial flora in vegetarians has been shown to possess reduced ability to transform bile acids into potential carcinogens (Johansson, 1990).
The role of dietary fibre in prevention of colon cancer may also be important. This was first noted in 1971 when it was suggested the high incidence of colon cancer in Western countries was linked to low fibre diets. Other dietary components associated with high fibre foods, such as folate, have also been implicated as having protective effects.