My husband has prostate cancer. I want to make your shakes for him to get some soy into his diet but lately I have been reading that he should avoid flax. Can you comment on if this is true?
In addition to being the best plant source of omega-3 fatty acids, flaxseed is also the richest source of dietary lignans. Lignans are a mixture of soluble fiber and insoluble fiber (2). There are 75 to 800 times more lignan in flax than in any other food (3). Lignans are converted by bacteria in the intestinal tract to potent hormone-like compounds called phytoestrogens that are able to prevent the formation of a tumor (2). Studies have suggested that phytoestrogens have a protective effect against hormone-related cancers such as breast and prostate cancer. Specifically rat and mice studies have revealed a protective effect of lignans on breast, colon, and skin cancers (3). Lignans also function as antioxidants, which aid in the fight against cancer. It is important to note that flaxseed oil generally does not contain the lignans. Although a few brands do add some lignans back after the oil is processed, the seeds are still a much higher dietary source of the lignan component.
The controversy regarding the consumption of flaxseed for the prevention of prostate cancer started with a study that showed increased rates of prostate cancer in men who had higher intakes of ALA, the main fatty acid in flaxseed and flaxseed oil. (6) However, the source of ALA in this study was not from flaxseed, but beef, which does contain a small amount of ALA. No studies have yet been done examining the risk of prostate cancer in men with various levels of flaxseed oil consumption.
However, research concerning the effects of flaxseed on hormone sensitive cancers like prostate cancer is ongoing. A pilot study of 25 men with prostate cancer was published in 2001 (1). The men consumed 30g/day of ground flaxseed (about 2 tablespoons) plus a low-fat diet (less than 20% of total calories from fat) for an average of 34 days. The results showed significantly reduced serum testosterone, slower growth rate of cancer cells, and increased death rate of cancer cells in early-stage prostate cancer. However, more studies are needed to determine if flax is beneficial as a complementary or preventive therapy when used in conjunction with conventional medical advice. This study is currently being expanded through a large NCI grant (personal communication with Dr. Demark-Wahnefried).
In summary, until research becomes available, I recommend men with prostate cancer consume ground flaxseed (1-2 tablespoons per day) but avoid flax oil. Hopefully more and larger studies will help define the optimal diet for prostate cancer patients. Please read some of the other questions and answers on my web site also regarding diet for men with prostate cancer, particularly concerning calcium and vitamin D intake. The links are listed below.
Flaxseed is available in flour, meal, and seed form. It can be found in some multi-grain breads, cereals, breakfast bars, and muffins. Toasted seeds could be mixed into bread dough or sprinkled over salads, yogurt, or cereal. However, grinding them in a coffee grinder is essential to optimize their health benefits. Additional uses of flax and information regarding its health benefits can be obtained from the Flax Council of Canada (2), www.flaxcouncil.ca and from Jane Rinehardt-Martin, RD (4) at www.flaxrd.com.
response was researched and prepared by Rebecca McKee, RD as part of
a graduate class at Eastern Michigan University (DTC 592 Medical Nutrition
Therapy). Final editing was done and approved by Diana Dyer, MS, RD.
These questions and answers are intended to be of a general informative nature. Please consult with the Registered Dietitian in your cancer center or your health care provider for nutritional advice that can be individualized to your specific medical condition.
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