The role of fats in cancer promotion has received much attention of late, as there is a strong correlation between various forms of cancer and total fat intake. Carcinogenic processes have two distinct stages: Initiation and Promotion. Initiation involves an irreversible interaction between a carcinogen and the genetic material of its target tissue. Not much is known about initiators, but asbestos (lung cancer), viruses (lymphatic cancers and cervical cancer) as well as tobacco smoke (lung cancer) are known to initiate cancer. Initiation does not generally lead to observable tumours unless promoters are present. These promoters can cause the transformed cells to form tumours. As the consumption of excess fats and certain types of fat can promote cancer, it is important to plan dietary strategies accordingly. In table 3.3 the association between fat and certain other parameters is presented. Clearly, fat is strong promoter of colon and prostate cancer, and fruits and vegetables act as anti-promoters.
Table 3.3. The association between selected dietary components and cancer.(From Ref. 8)
Cancer of the breast, colon and prostate is common in countries with Western lifestyles such as Switzerland, the US and South Africa, but is rare in Japan. Japanese migrating to the US soon develop the same incidence of US prevalent cancers in view of a change in diet. In developing countries as much as 80% of total calories come from cereals and grains, but in industrialized countries there is a calorie intake shift towards animal fat, vegetable oil and refined sugar. This latter diet reduces the incidence of gastric cancer but increases the incidence of colon, ovarian, prostate and breast cancer. The drop in gastric cancer has been attributed to refrigeration, which has replaced salting, pickling and smoking as a means of food preservation. Countries such as Austria where smoked foods are used extensively, also have high incidences of gastric cancer.9
International correlation studies have shown that a high-fat intake increases the incidence of prostatic, breast and colon cancer. Prostate cancer has been correlated with diets high in animal fats such as fatty meats, cheeses, cream and eggs. The US, Britain, the Netherlands, Denmark and South Africa have some of the world’s richest diets, and also have the highest incidence of breast cancer.9 Diabetes and pancreas cancer are also positively correlated with a high-fat diet.10 Saturated fatty acids in particular are associated with breast cancer, particularly in postmenopausal women,11 colorectal adenomas,12 and ovarian cancer, where a 20% increase in risk was observed for every 10g of saturated fatty acids consumed.13 The association between polyunsaturated fats and cancer is even more profound. Animal studies have shown that high linoleic acid consumption in particular promotes mammary tumours to a greater extent than saturated fatty acids. Safflower oil and corn oil, both rich sources of linoleic acid, where more likely to induce tumours than were olive oil or even coconut oil because these oils are poor in linoleic acid.6
Fibre, vitamin A, C and E, the trace element selenium, and some phytochemicals in certain vegetables, beans, seeds and herbs have been identified as anti-promoters which offer protection against cancer. The food types that offer this protection, as well as the distribution of phytochemicals, are discussed in chapter 7 and summarized in figure 7.3 and figure 7.4. These foods contain sulfides, phytates, flavonoids, glucerates, carotenoids, coumarins, mono- and tri-terpenes, lignans, phenolic acids, indoles, isothiocyanates, phthalides, and polyacetylenes which interfere with the processes of cancer initiation or promotion, and in this way block the formation of tumours (fig. 3.6).14
Figure 3.6. The effect of dietary phytochemicals on the processes of cancer initiation and promotion. (From reference 14).
Vitamin A probably acts as an anti-promoter for lung, colon, stomach, bladder, oesophagus and oral cavity cancers. Vitamin C and E are associated with reduced incidence of gastric cancer and selenium with a reduced incidence of breast and colon cancer.9 Fibre on the other hand protects against cancer by decreasing the length of time that faecal matter stays in the digestive tract, thus limiting the build up of potential carcinogens.15 Finns for example have a high consumption of whole grains and the associated high faecal mass has been cited as a contributing factor to the low incidence of colon cancer in this nation. The vegetarian lifestyle thus offers considerable protection against cancer, and a vegan diet seems to be more effective than other vegetarian diets. In studies conducted on vegetarians it was found that ovo-lacto vegetarians (vegetarians that include dairy products and eggs in their di