By Dale Kiefer
Strong Evidence of Anti-Cancer Effects
Over the past 18 years, numerous medical and nutritional scientists have published research that validates and expands on the Wisconsin team’s groundbreaking work. Thanks to their efforts, we now know that CLA isomers, when added to the diets of laboratory animals, protect the animals against experimentally induced breast cancer, colon tumors, and skin cancer. These effects occurred regardless of whether the CLA was given during or after tumor initiation.3,5,24,25
Mounting evidence suggests that CLA’s anti-tumor activity comes primarily from the c9t11 isomer. The evidence for CLA’s ability to decrease the incidence, progression, tumor burden, and number of metastases in models of breast, prostate, skin, and colon cancer had grown so convincing by the mid-1990s that the National Academy of Sciences published a statement in 1996 declaring, “[CLA] is the only fatty acid shown unequivocally to inhibit carcinogenesis in experimental animals.”26
One of the animal models used in CLA research routinely serves as a model of a type of human breast cancer called ductal carcinoma in situ.5,24 The finding that CLA inhibits the formation of new tumors in rodents suggests that it may also reduce breast cancer metastasis in women. Confirming this expectation is an important new goal for oncology researchers, as the growth of secondary tumors (metastasis) is the leading cause of death among cancer patients.5
CLA also inhibits the growth of transplanted breast and prostate cancer cell lines in laboratory rodents.27,28 This effect was so dramatic that one research team was inspired to write, “Mice fed the CLA-supplemented diet displayed not only smaller local tumors than the regular diet-fed group, but also a drastic reduction in lung metastases.”28 Considerable evidence indicates that CLA inhibits the initiation stages of cancer, and research also shows that CLA inhibits the post-initiation and promotion phases of cancer growth.5 At least one study found that CLA inhibits the formation of secondary tumors in mice, even after cancerous mammary cells are seeded into the mice.29
In fact, recent evidence suggests that CLA fights cancer at every step in its progression, beginning with its initial development. By blocking cell cycle proteins that regulate the creation of new cells, CLA has been shown to stop runaway cell proliferation before aberrant (but benign) tissue transforms into far-from-benign cancer.5,30,31
In one experiment, researchers fed mice fed CLA for two weeks before inoculating them with aggressive human breast adenocarcinoma cells. Although the mice used in the study were bred for their inability to resist immune challenges, the CLA-treated mice developed 73% fewer local tumors by nine weeks after inoculation than did the control mice, which had not been pre-treated with dietary CLA. Furthermore, CLA dramatically inhibited the spread of breast cancer cells to lungs, peripheral blood, and bone marrow. The researchers concluded, “These results indicate the ability of dietary CLA to block both the local growth and systemic spread of human breast cancer via mechanisms independent of the host immune system.”27
Other research has shown that in a rodent model of human breast cancer, dietary exposure to CLA while mammary glands are maturing confers protection against the cancer. Even when CLA was withdrawn from the diet after mammary glands had matured, rats previously nourished with CLA continued to enjoy significant protection against mammary tumors. The mechanism by which CLA protects in this instance appears to be distinct from its anti-initiation activity.24,32
More recently, scientists in western New York gathered data from more than 1,100 women with confirmed breast cancer, as well as from about 2,000 cancer-free control patients. By assessing the subjects’ self-reported dietary intake of CLA, the researchers were able to look for statistical relationships between CLA intake and health status. Although no clear correlation appeared to exist between dietary intake of CLA and overall breast cancer risk, “a marginally significant reduction in risk of having an [estrogen receptor-negative] tumor” was reported among women with the highest intake of CLA. Regarding CLA, the researchers noted, “There may be associations with tumor biology at least among premenopausal women.”33
Recent reports indicate that CLA may also protect against breast and other types of cancer by inhibiting angiogenesis, the process by which tumors create a new blood supply network to obtain nutrients needed for growth. Halting or reversing angiogenesis is an anti-cancer strategy that has received intense attention by researchers from a variety of disciplines in recent years.34,35
CLA also promotes apoptosis (programmed cell death, or cellular suicide) of cancer cells.36-38 Cancer cells are adept at evading apoptosis, which accounts for much of their insidious nature. Apoptosis allows the body to remove damaged or potentially harmful cells in a way that minimizes waste and ameliorates damage to surrounding tissues. CLA evidently affects the functioning of immune system components involved in apoptosis.38
Recently, a research team in Argentina published a report on diet and the incidence of colon cancer among the local population. Argentineans consume a great deal of beef that is rich in saturated fat and cholesterol, while eating relatively little fish or dietary fiber. Fiber is generally recognized as protective against colon cancer, while heart-healthy omega-3 fatty acids, which are present primarily in seafood, may also help prevent cancer. Despite the Argentineans’ seemingly unhealthy eating habits, they do not succumb to colon cancer as commonly as might be expected.39
An analysis of epidemiological data revealed that high consumption of lean meats (less that 15% fat content) is actually associated with a significant reduction in the incidence of colon cancer among the populace. By contrast, high consumption of fatty meats, such as cold cuts and sausages, was associated with an increased risk of developing colon cancer. Because lean beef is a primary source of CLA, the researchers reasoned that CLA’s protective effects outweigh any presumed negative effects associated with the saturated fats and cholesterol in lean beef.39
Intentionally consuming more beef in order to obtain CLA is not a practical method of protecting one’s health. Most beef comes from cattle that are commercially fed and therefore have relatively little CLA. Numerous scientific studies indicate that those who over-consume beef have higher risks of common diseases.46-49 Those seeking to obtain CLA should consider supplements that provide standardized CLA concentrations.
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