Dietary factors and the risk of cancer

At present, much is known about the role of food intake in the etiology of cardiovascular diseases. The relationship between the intake of saturated fatty acids and the occurrence of ischemic heart diseases, for example, is now generally recognized. However, the role of food components in the induction of various types of cancer is less clear, although it is beyond doubt that dietary factors do play an important role. The types of cancer frequently occurring differ from one country to another. In Japan, cancer of the stomach occurs more often than in the US or Europe, while the incidence of breast and colon cancer is higher in the US and Europe than in Japan. The fact that in Japanese people who migrated to the US, the incidence of stomach cancer decreased whereas the incidence of breast and colon cancer increased, suggests that lifestyle and environmental factors are important.

As far as the role of dietary factors in the etiology of cancer is concerned, laypersons mostly think that contaminants and additives are the main risk factors. A well-known publication in which the contribution of dietary factors to the occurrence of cancer has been estimated is The causes of cancer written by Doll and Peto (1981). According to their estimates, the effects of contaminants and additives on the occurrence of cancer range from a decrease of 5% (due to a protective effect of antioxidants) to an increase of 1 to 2%.

Table 15.3 Summarizing of the conclusions about associations between food components and cancer, based on literature data

Food component

Association1

Type of cancer

Alcohol

Vitamin A and ß-carotene

Nitrate, nitrite Vitamins C and E Products of pyrolysis

Colon, breast Prostate, pancreas Mouth, throat, esophagus Lung, bladder Prostate Stomach

- Stomach

Recently, a number of these products have been found to be highly mutagenic and/or carcinogenic higher incidence of tumors is associated with higher intake of dietary factor. (+): higher incidence of tumors is probably associated with higher intake of dietary factor. -: lower incidence of tumors is associated with higher intake of dietary factor. (-): lower incidence of tumors is probably associated with higher intake of dietary factor.

Epidemiological studies on the role of contaminants and additives in the induction of cancer are very cumbersome. Usually, exposure is very low and identification of exposed subjects is very difficult. Sometimes, there are large differences in effect between studies in experimental animals to which relatively high, single doses are given for a relatively short period of time, and human studies in which very low doses are ingested during long periods. An example is the long dispute about the safety of saccharin, a non-caloric sweetener. Saccharin has been used since its discovery in 1879. Studies carried out in the 1960s and 70s in rodents showed that high doses of saccharin caused bladder cancer. As a result of this finding a ban on the use of saccharin was proposed in some countries. To investigate potential effects on humans, different types of epidemiological studies were carried out. In descriptive studies, trends in the use of saccharin were compared with the occurrence of bladder cancer. In other studies, the incidence of bladder cancer in diabetics (from whom a rather large consumption of artificial sweeteners could be expected), was compared with that in non-diabetics. In case-control studies, bladder cancer patients and controls were compared for the use of saccharin. In a cohort study, the incidence of bladder cancer in saccharin users was compared with that in unexposed groups. The results of the various studies led to the conclusion that there is no increased risk of bladder cancer for humans from the use of saccharin. The composition of the diet with regard to macro- and micronutrients is of more importance for the occurrence of cancer than the intake of additives. Based on a large number of studies on micro- and macronutrients, Doll and Peto estimated that probably about 35% of all cancers are caused by an unbalanced nutrient content of the diet (with a confidence interval of 10 to 70%).

In 1986 the Dutch Nutrition Council reported that despite all the research that had been carried out, no definite conclusions could be drawn on the role of the different food components in the induction of cancer. Based on literature data, only general conclusions were presented about associations between dietary factors and several types of cancer. A few of these are listed in Table 15.3.

Weight Loss Resolutions

Weight Loss Resolutions

Are You Tired Of Failed New Year's Weight Loss Resolutions That Leave You Even More Overweight Than Ever Before? Not Anymore Finally Succeed With Your New Years Weight Loss Resolution Once And For All And Get The Body Of Your Dreams.

Get My Free Ebook


Post a comment