Define Carcinogenic - Dietary Factors?

Dietary constituents can also be carcinogenic. But to what extent diet is one of the contributing factors to cancer development is not known. The incidence of cancers, especially stomach cancers is high in parts of the world where people eat a lot of heavily smoked, pickled or salt-cured foods that produce carcinogenic nitrosamines. Alcohol has also been associated with a high incidence of some cancers, especially cancers of the mouth and throat. Beverages such as beer and scotch may contain damaging nitrosamines, as well as, alcohol. Other beverages such as wine and brandy may contain the carcinogen urethane, which is produced during fermentation.

Nitrosamines have been implicated in the etiology of cancer. Nitrosamines are a broad class of compounds formed from the nitrosation of substituted amides, ureas and guanidines. Nitrosamides are direct acting carcinogens meaning that the activation is non-enzymatic occurring by spontaneous hydrolysis.

A number of laboratory and epidemiological studies have shown the correlation between dietary factor and etiology of specific cancers. Severe calorie restriction in animals has shown to inhibit the growth of most types of tumors. But calorie restriction is not a means to prevent tumor formation. There is a lot of epidemiological evidence to show that there is an association between the high intake of calories by humans and increased risk for endometrial and gall bladder cancer.

Some epidemiological studies suggest that risk for cancer increased with high protein intakes. For instance, cancers of breast and colon occur with greater frequency in the industrialized nations. Some researchers have suggested a possible association between high intakes of total protein or animal protein and the risk of these specific cancers.

Both the type and amount of fat are believed to influence tumor formation in animals. A high fat intake in humans has been linked to increased risk for breast and colon cancers. The possible mechanism that has been given is a high fat intake increased intestinal anaerobic bacteria and biliary steroid secretion. These anaerobic bacteria are capable of synthesizing estrogens. The estrogens are believed to be potential carcinogens in mammary tissues. In addition, bile acids are degraded by intestinal bacteria to the secondary bile acids such as deoxycholate and lithocholate. These may act as carcinogens in the colon. Another theory is that trans-fatty acids are more carcinogenic than cis fatty acids.