One way our diet may increase the risk of cancer is by dietary carcinogens. There are four groups of carcinogens:

• Naturally present carcinogens.
• Carcinogens forming during food preparation.
• Preservatives and coloring agents added to food.
• Some substances are changed in to carcinogens in the body.

Naturally present carcinogens:

An example of this is 'Aflatoxin', a mycotoxin produced by fungi. Grains and nuts can be contaminated by fungus, which then produce chemicals called aflatoxins. They are known to cause liver cancer in Africa and the Far East, especially in people who are carriers of hepatitis antigens.

Carcinogens forming during food preparation:

Polycyclic hydrocarbons, such as benzopyrenes, are formed during barbecuing meat on an open fire (e.g. preparing jerked chicken). These polycyclic hydrocarbons are also one of the main constituents in cigarette smoke that cause lung cancer.

The traditionally high intake of fried and broiled food, such as meats, can increase the risk of breast, distal colon, prostate and pancreas cancers. Several studies showed that populations that eat fried or broiled meats have a relative risk greater than 2 (deviation from median) for colon and breast cancer.

More than 20 such chemicals have been identified. They are present in fairly small amounts, but their action is promoted, an effect associated with n-6 polyunsaturated oils such as corn or safflower oil at 30-40% of energy in animal and human studies. A lower fat intake, 15-22% of energy, dramatically decreases those effects.

Preservatives and coloring agents added to food: (Need some more tests to establish this relationship).

Food colorings are added to increase the appeal of the food but not all are good for us. An example is "butter yellow". Artificial sweeteners (like saccharine & cyclamates) and preservatives which produce nitrosamines are known to cause bladder and stomach cancers respectively.

Some substances are converted in to carcinogens:

Nitrosamines are formed from sodium nitrite. Sodium nitrite is present in drinking water and vegetables.