Flax seeds

In a study of men with prostate cancer, a low-fat diet supplemented with ground flaxseed reduced serum testosterone, slowed the growth rate of cancer cells, and increased the death rate of cancer cells, according to a recent report in the journal Urology (Vol. 58, Iss. 1: 47-52).

Flaxseed is high in lignans, fiber-related compounds that can bind to male hormones and increase their elimination through the digestive system. Lignans also act as plant-derived estrogens, and this combination of hormonal effects might inhibit prostate cancer formation and growth. In addition, flaxseed is a rich source of omega-3 fatty acids, which have been linked in some studies to a lower incidence of prostate cancer.

Wendy Demark-Wahnefried, PhD, RD, LDN, and colleagues from Duke University Medical Center and Durham Veterans Affairs Medical Center, tested this dietary intervention in 25 men who were recently diagnosed with prostate cancer and were awaiting radical prostatectomy. Men in the study followed a low-fat (≤ 20% of total calories) diet supplemented daily with 30 grams of ground flaxseed for an average period of 34 days.

During this time, the participants’ serum testosterone levels decreased by 15%. Compared with past records of men with prostate cancer (matched by age, race, PSA level at diagnosis, and biopsy Gleason score) prostatectomy specimens of participants showed fewer cells in the process of dividing and more cells that had undergone apoptosis, a process of natural cell death and degeneration.

The authors conclude, “These findings suggest that a flaxseed-supplemented, low-fat diet may have an effect of prostate cancer biology that may be mediated through a hormonal mechanism.”

Tim Byers, MD, MPH, co-chair of the ACS workgroup on nutrition and physical activity for cancer survivors, and professor of preventive medicine, University of Colorado School of Medicine, agrees with the authors’ conclusion, but notes that it would be premature to make any firm recommendations for men with prostate cancer based on this small study.

“This was a study in which two dietary changes were tested at the same time — a diet very much lower in total fat than most men consume (20% of calories from fat) and flaxseed oil supplements,” Byers says. “The reductions in cholesterol and testosterone levels observed may be due as much to the low fat diet as to the flaxseed. If this dietary intervention does have effects on testosterone metabolism, it would likely not be a more effective alternative to conventional anti-androgen therapy and would probably have little impact as a complementary therapy for men already taking conventional hormonal therapy.”

Byers continues, “On the other hand, as a complementary dietary intervention, this combination of substantial reduction in dietary fats along with flaxseed supplements might eventually turn out to be useful for men [with early stage prostate cancer] who have surgery, radiation, or management without undergoing conventional hormonal therapy.

“Low fat diets of this type might also be effective in reducing the risk of getting prostate cancer,” he says. “The side effects of this type of intervention are minimal, and this is a very heart-healthy, low-fat diet. I look forward to continued research in this important area in which the interventions might be evaluated in the context of randomized, controlled trials,” concludes Byers.