Olive Oil May Help Prevent Colon Cancer

Including olive oil in your diet may help reduce your risk of developing colon cancer, Spanish researchers suggest.

Their study results showed that rats fed an olive oil-supplemented diet had a lower risk of colon cancer than those fed diets supplemented with safflower oil. In fact, the rats that received olive oil had colon cancer rates almost as low as those fed fish oil, which several studies have already linked to a reduction in colon cancer risk.

Adding olive oil to the diet has other advantages as well. According to Dr. Michael Thun, head of epidemiological research for the American Cancer Society, "There has been interest in the health benefits of olive oil for some time, but not usually with a focus on colon cancer. The cardiovascular benefits of diets higher in olive oil are well established in improving the ratio of good-to-bad cholesterol. In addition, olive oil does not promote the secretion of bile acids as many other fats do."

Animal studies have shown that a diet high in some kinds of fat (such as corn or safflower oil) increases the risk of colon cancer, which depends on both the amount of fat consumed and the type of fatty acid it contains. Additional studies have indicated that dietary fish oil inhibits or prevents colon cancer.

In a study at University Hospital Germans Trias Pujol in Barcelona, Spain, researchers assessed the effect of an experimental diet containing 5% olive oil on the development of colon cancer in rats. In the study, 108 rats were divided into three groups of equal size. Half of the rats in each group received a cancer-causing agent and the remaining half did not. For 19 weeks, each group of rats was fed one of three diets containing: fish oil (n3 fatty acids); safflower oil (n6 fatty acids); or olive oil (n9 fatty acids). At study week 12 or 19, rat colons were removed and examined for the presence of fatty acids in bowel tissue, premalignant conditions, and tumor formation.

In their report, published in the journal Gut, the investigators explain that rats given the cancer-causing agent and a diet high in safflower oil had more premalignant changes in the linings of their colons and a higher incidence of colon cancer than those fed a diet high in fish oil or olive oil. Nineteen weeks after the first injection of the cancer-causing agent, 58% of the treated rats that were fed a diet high in olive oil, 45% of those fed a diet high in fish oil, and 83% of those fed a diet high in safflower oil had colon cancer. Examination of colon tissue revealed that a diet high in fish oil or olive oil reduced the bowel tissue concentrations of arachidonate, a substance that enables the formation of cancer, to a greater extent than did a diet high in safflower oil.

The authors note that previous studies showed that fish oil can slow the division of rectal cells in humans, but the effect of olive oil on colon cells "has been scarcely assessed," leading them to conclude that their findings on olive oil "may be of relevance."

Oleic acid is the predominant fatty acid in olive oil (about 75%), but oleic acid is also found in fats that are in foods linked to cancer in animal studies, such as beef; poultry; and corn, soybean, and sunflower seed oil. The researchers therefore believe that other components of olive oil such as squalene and flavonoid and polyphenolic compounds may have a chemoprotective effect against colon cancer.

However, additional studies are necessary, according to Thun. In an interview, Thun said, "this is a good model for human colon cancer, but it is still an animal model. People should base the quantity of olive oil they consume on factors other than its possible protective effects against colon cancer."

SOURCES: Reuters Health, Jan. 26, 2000 AND the journal Gut, Feb. 2000; 46:191-199.