Cancer Update: Two Studies Worth Heeding
Last reviewed by Faculty of Harvard Medical School on February 24, 2010
By Stacy Kennedy, M.P.H., R.D., L.D.N.
The amount of conflicting nutrition information targeted to cancer patients and survivors can be overwhelming. Many of the supplements, vitamins and foods such as concentrated juices and powders are promoted based on results from test tube or animal studies. Companies often rely on testimonials from users as "evidence."
When it comes to making decisions about what to eat, drink or take in pill form, nothing can replace large randomized, controlled, human trials. Findings from test tube and animal studies may be interesting but they are preliminary and certainly not conclusive. Research to determine how certain nutrients affect cancer development and progression must follow a scientific process that advances from test tube to animal then human studies.
Here are two studies published in the past year concerning nutrition and cancer that are examples of the type of evidence experts need to make specific recommendations about what people can do.
Can Soy and Flaxseed Reduce the Risk of Colon Cancer?
Scientific journals and the media have reported extensively over the past 10 years on the link between soy-based foods and breast and prostate cancers. But the relationship between soy and other similar foods and colon cancer has not been described in detail.
Soy contains compounds called phytoestrogens, which are naturally occurring compounds in foods that have weak, estrogen-like effects in the body. (The type of phytoestrogens in soy foods receiving the most press is called isoflavones.) Some research suggests that they may help prevent the development of estrogen-dependant cancers, such as breast cancer by blocking estrogen's effects. Phytoestrogens may also influence the body's ability to create its own estrogen.
Now a Canadian study published in The Journal of Nutrition in December 2006 has found that a greater intake of phytoestrogens is significantly associated with a reduced risk of colon cancer. But it wasn't just isoflavones that were beneficial. Another group of phytoestrogens called lignans, which are much more prevalent in the American diet than soy, were also protective. Lignans are found in flax seeds, whole grains foods, nuts, seeds, fruits and vegetables.
The study included information on 1,095 people diagnosed with colon cancer and 1,890 people who were cancer-free. Study participants completed questionnaires about their diet and a subset of participants also provided blood samples. The study participants who had the greatest amount of lignan-rich foods in their diet, had a 27% lower risk of colon cancer compared with the group who ate the least amount of lignans. Those with the highest intake of isoflavones had a 29% lower risk of developing colon cancer compared with those consuming the least amount of isoflavones.
One interesting finding: You don't have to eat large portions of lignan or isoflavone-rich foods to get the benefits. For example, authors stated that one eight-ounce glass of soy milk or a small bowl of miso soup daily contain sufficient amounts of isoflavones while two peaches, ½ slice of multigrain bread or a "pinch" of ground flaxseed provide adequate amounts of lignans.
While these findings are exciting, they aren't conclusive and don't show cause-and-effect. Only randomized, controlled clinical trials intervention studies can do that. But the results are encouraging enough that people should try to include lignan-rich foods in your diets They may help to prevent colon cancer. If nothing else, you may benefit from the other vitamins, minerals and fiber that these foods offer. The table below lists food sources of isoflavones and lignans.
How You Cook May Be as Important as What You Cook
An international group of scientists met in Lyon, France in October 2006 to review data on the cancer-promoting potential of cooking methods involving frying. Their findings were published in the December 2006 issue of the peer-reviewed journal, The Lancet Oncology.
They analyzed animal and human studies conducted in China and found that heating cooking oil to high temperatures may lead to the development of cancer-causing compounds in the fumes. Cooking techniques included stir-frying, deep-frying and pan-frying. Specifically, the researchers found a significant increase in the risk of lung cancer in non-smoking women who regularly prepare their meals using these methods. The risk of cancer increased proportionately with the amount of exposure to the fumes produced from frying. The type of cooking oil used in frying did not make a difference in cancer risk.
These unhealthy byproducts of frying are thought to occur through oxidation, or the creation of free radicals, which results in cell damage. Another way frying can be detrimental to health is through the creation of polycylic aromatic hydrocarbons (PAH). PAHs have been detected in cooking oil fumes when oil is heated to high temperatures. They are known cancer-causing chemicals.
The best advice? Choose cooking methods such as baking, broiling and steaming. Limit frying of any kind.
Stacy Kennedy, M.P.H., R.D., L.D.N., C.N.S.D. is senior clinical dietician at Dana-Farber Cancer Care/Brigham and Women's Hospital. She completed her dietetic internship at Massachusetts General Hospital and received her Master of Public Health in Nutrition from the University of North Carolina.