Tailoring diet for cancer prevention - Medical Profession Acknowledges Diseases May Be Diet Related

Nutrition Health Review, Spring, 1993

NEW YORK: The key to the diet/cancer puzzle may lie in nutrient interactions and in individual response to dietary factors, determined in turn by genetic, physiologic and life-style factors, according to a report published in the Archives of Internal Medicine (1:93).

The AMA's Council on Scientific Affairs (CSA), issued the report, titled "Diet and Cancer: Where Do Matters Stand?" to review recommendations made by the National Research Council in its 1982 report, "Diet, Nutrition, and Cancer."

At the time of its publication, recommendation #1 of "Diet, Nutrition, and Cancer" (to reduce fat intake as a means of reducing cancer risk) was judged to be the strongest. The report states: "It is now clear from numerous ... experiments that the cancer-enhancing property of dietary fat is the result of two effects: a general effect due to excessive calories, and a specific effect due to the essential fatty acid, linoleic acid."

The report says that linoleic acid, an essential fatty acid required for growth, "enhances carcinogen-induced mammary, pancreatic, and probably colon cancer in rodents."

A new development that further complicates the dietary fat/cancer relationship is the discovery of the anticarcinogenic (anti-cancer) properties of CLA (a class of dietary fatty acids). As little as 0.5 percent of CLA in the diet significantly reduced carcinogen-induced mammary neoplasia in rats.

The discovery of CLA is of interest for a number of reasons. It represents the first clear example of a fatty acid that inhibits cancer. Additionally, CLA, which inhibits cancer, is closely related to linoleic acid, which enhances cancer. Finally, the principal dietary sources of CLA appear to be animal products, specifically dairy products, meat from ruminant (cud-chewing) animals, and turkey. Several laboratories are conducting research into the potential of CLA to reduce cancer risk in humans, particularly those at high risk of developing malignancies.

Recommendation #2 was intended to encourage increased consumption of fruits and vegetables. It singled out specific food items known to contain substances that inhibit cancer.

The CSA report states: "(S)imply identifying substances that inhibit cancer is not enough. For each prospective anticarcinogen it is necessary to determine the precise mechanism of action." The CSA report cites examples in which a substance can be both an anticarcinogen and carcinogen, depending upon the amount of the dose administered.

"An important challenge is learning how to use these compounds in a rational way to substantively reduce the incidence of human cancer without inadvertently exposing the public to increased health risks," the CSA report says.