Frequently Asked Questions

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?

Summary
Flaxseed is considered by the health community a “functional food”, a food with special qualities that promotes health (1). Flaxseeds contain high amounts of an omega-3 fatty acid (alpha linolenic acid - ALA), which is an essential fatty acid that the body needs and can not produce on its own. In addition, flaxseed also contains lignans, a type of fiber that is thought to prevent the formation of tumors (2). However, the role of flaxseed in the prevention and treatment of cancer is still the subject of much research.

Details
The flaxseed is 41% oil by weight and 70% of that oil is polyunsaturated with a high ratio of alpha-linolenic acid (an omega-3 fatty acid) to linoleic (an omega-6 fatty acid) (2). This makes flaxseed the richest plant-based source of omega-3 fatty acids (1). A diet containing high amounts of saturated (animal) fat and omega-6 polyunsaturated fatty acids is thought to promote prostate cancer. The omega-3 fatty acids and monounsaturated fatty acids are thought to be neutral or protective (5). Studies on animals with implanted cancer cells have shown that omega-6 fatty acids promoted tumor cell growth (5). Omega-3 fatty acids have been known to interrupt the role of the omega-6 fatty acid in tumor growth. However, the role of the fatty acid ALA in cancer development remains controversial (5).

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.

References:

1. Wahnefried W, Price DT, Polascik TJ, Robertson CN, Anderson EE, Paulson DF, Walther PJ, Gannon M, Vollmer RT. Pilot study of dietary fat restriction and flaxseed supplementation in men with prostate cancer before surgery: exploring the effects on hormonal levels, prostate-specific antigen, and histopathologic features. Urology 2001: 58; 47 – 52.
2. Flax council of Canada. 2002. Available at: www.flaxcouncil.ca. Accessed: February 28, 2003.
3. Thompson LU. Experimental studies on lignans and cancer. Baillieres Clin Endocrinol Metab. 1998;12:691-705.
4. Dietitian Jane. 2002. Available at: www.flaxrd.com. Accessed February 28, 2003.
5. Cohen LA. Nutrition and prostate cancer a review. Ann N Y Acad Sci. 2002;963:148-55.
6. Giovannucci E, Rimm EB, Colditz GA, et al. A prospective study of dietary fat and risk of prostate cancer. J Natl Cancer Inst 1993;85:1571-79.

This 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.

FAQ posted 4/03

Top

Back to Main QandA Page Prostate Cancer My husband has prostate cancer. Are your nutrition guidelines appropriate for him, too? posted 4/01, updated 5/02 My husband has prostate cancer. I recently read that a high calcium intake may cause prostate cancer. How high is too high? Should I be restricting his calcium intake? posted 5/02 My husband had prostate cancer. Should he be avoiding flax? posted 4/03 A few words of wisdom and encouragement from a man with prostate cancer. posted 2/04 Are there some good web sites for prostate cancer information? posted 4/04   Back to Main QandA Page Flaxseeds Is it safe to use flaxseeds whole? I have not found anything that will grind whole flaxseed. Is the omega-3 fatty acid content of brown flaxseeds and golden flaxseeds really different? updated 4/02 Do you have more recipes using flaxseeds? posted 1/02, updated 4/02 Should women with ER+ breast cancer avoid flaxseeds and flax oil that contain the phytoestrogens called lignans? Will taking my medications mixed with flaxseed powder and applesauce cause them to not be absorbed? posted 2/02 How quickly does one need to eat ground flaxseed to prevent spoilage? posted 5/02 What is the best way to clean out my coffee grinder when switching from grinding my coffee to flaxseeds? posted 12/02 My husband had prostate cancer. Should he be avoiding flax? posted 4/03 Does consuming flaxseeds potentially interfere with the anti-estrogen effect of Tamoxifen? posted 9/03, updated 2/04, updated 3/05 Are flaxseeds safe to eat after heating? posted 1/04 The May 2004 issue of Prevention Magazine says that women with ER+ breast cancer should not be eating flaxseeds. Do you agree? posted 4/04

Top

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.