Health and Vegetarians Part 3

Cancer

Cancer is the second leading cause of death in Britain, accounting for 25% of all deaths. It has been estimated that diet may be linked to 30-70% of cancers (Doll, 1990). Certain cancers, such as colon, breast and prostate are clearly diet related (Cummings & Bingham, 1998).

Sir Kenneth Calman, Chief Medical Officer, has stated (1997) that "there is a relationship between eating red meat and cancer".

The Oxford Vegetarian Study found cancer mortality to be 39% lower among vegetarians compared with meat-eaters (Thorogood, 1994).

A study of 23,000 largely vegetarian Seventh Day Adventists found cancer mortality rates to be 50-70% of those of the general population for several cancer sites unrelated to smoking or alcohol (Phillips, 1975).

Professor Nick Day of the University of Cambridge and the European Prospective Study into Cancer has stated that vegetarians may suffer 40% fewer cancers than the general population.

The World Cancer Research Fund's dietary advice to minimise cancer risk involve reducing the intake of dietary fat and increasing the consumption of fruits, vegetables and wholegrains.

Colon Cancer

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.

Chen (2002) found that the risk of distal stomach adenocarcinoma was positively associated with red meat intake.

Breast Cancer

Evidence also suggests a vegetarian diet is protective against breast cancer (Phillips, 1975). This may be due to the increased fibre and reduced fat intake of vegetarian diets. Vegetarian diets can alter the levels of circulating sex hormones which may have a beneficial effect. Fibre is thought to be protective by modifying circulating oestrogen levels.

Studies of adolescent girls have shown age of menarche to be delayed in vegetarians (Sabate, 1992). Later age of menarche is believed to lower the risk of breast cancer in adult life.

Other Cancers

Studies have shown vegetarians to suffer less from various other cancers.

Mills (1989) studied the incidence of prostate cancer amongst 14,000 Seventh Day Adventists and found a relationship between increased risk and increasing animal product consumption.

Mills (1988) also found pancreatic cancer to be associated with consumption of animal products. Increasing consumption of fruit, vegetables and pulses was shown to have a protective effect.

Rao (1989) found a vegetarian diet to be protective against oesophageal cancer.

Studies have also shown vegetarians to have lower incidence of lung cancer. This can be largely attributed to vegetarians tending to be non-smokers. High consumption of fruit has also shown to be protective against lung cancer (Fraser, 1991).