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Adding flaxseed to the diets of men with prostate cancer appears to slow tumor growth, according to data from a study of 161 men with prostate cancer. Those who consumed 30 g of ground flaxseed daily had significantly lower levels of the tumor proliferation marker MIB-1 than did men on their usual diet.
"Prostate cancer proliferation rates were significantly lower in men assigned to flaxseed supplementation," said Wendy Demark-Wahnefried, Ph.D., a researcher in the school of nursing at Duke University, Durham, N.C.
Flaxseed is a rich source of lignans, which have been shown to affect androgen metabolism and have antimitotic, antiangiogenic, antioxidant, and estrogenic effects. Flaxseed also is a rich source of omega-3 fatty acids, which play a role in cell membrane function, inhibit protein kinase activity, and increase natural killer cell activity. Previous studies have suggested, too, that a low-fat diet might help prevent prostate cancer.
The study included men with pathologically confirmed prostate cancer who were electing prostatectomy as their primary treatment. Their mean age was 59 years, and 70% were white. They had to be at least 21 days from scheduled surgery and not on neoadjuvant therapy. The men could not have started any new supplements (excluding multivitamins) during or within 3 months of the study period. Also, they could not use antibiotics during or 7 days prior to the study, because normal gut flora is necessary to process lignans.
The men were randomized to supplementation with flaxseed (40 patients), a low-fat diet (40), flaxseed plus a low-fat diet (40), or their usual diet (41). Men on their usual diet served as controls. Men receiving flaxseed supplementation (donated by Enreco Inc.) consumed 30 g of ground flaxseed daily. Men on a low-fat diet were limited less than 20% of daily calories from fat.
At baseline and immediately prior to surgery, blood, urine, and seminal fluid were collected, and the men completed questionnaires. Following surgery, prostatic tissue was analyzed. Men were stratified by race and combined Gleason score (classified as either above or below 7). Overall, 68% of men had a Gleason score of less than 7.
Men in all four groups followed their protocols for roughly 30 days. Adherence (confirmed by biomarkers) was high in the three intervention groups: almost 7 days per week. The attrition rate of 9% was due mainly to men deciding against surgery or to advancement of their surgery date.
Men in the flaxseed-only group and those in the combination flaxseed/low-fat diet group had significantly lower levels of MIB-1, indicating lower rates of tumor proliferation, expressed as the ratio of cancer cells that are actively dividing to those that are not dividing: 1.66 in the flaxseed group and 1.5 in the combination group, compared with 2.56 in the low-fat diet group and 3.23 in the control group. Other biomarkers associated with prostate cancer, including apoptosis and androgen metabolism, did differ significantly.
"Unfortunately, we did not see what we'd been able to find in our pilot studies, which was a reduction in testosterone levels and PSA [prostate-specific antigen] in our flaxseed groups," Dr. Demark-Wahnefried said. "In our control group, the PSA and androgen levels really bottomed out. So there were no differences detected."
The researchers had speculated that flaxseed might reduce cancer proliferation by altering androgen metabolism, she said. They hope to identify the mechanism in future studies.
There were no differences between the groups in terms of side effects.
George S.L. et al. Impact of flaxseed supplementation and dietary fat restriction on prostate cancer proliferation and other biomarkers: Results of a Phase II randomized controlled trial (RCT) using a presurgical model. Abstract 1510.
Commentary |
Men with newly diagnosed prostate cancer often ask about diet and dietary supplements. To date, we have had little solid data to offer them. New research suggests, however, that consuming 30 g of ground flaxseed per day may slow tumor growth. Dr. Demark-Wahnefried, a researcher at Duke University's school of nursing and division of urologic surgery, studied 160 men undergoing radical prostatectomy. Men were randomly assigned to their regular diet, their regular diet plus flaxseed, a low-fat diet, or a low-fat diet plus flaxseed for 21 and 30 days prior to surgery. Men on the low-fat diet were to consume less than 20% of calories from fat. At the end of the study, all men underwent radical prostatectomy and tumor tissue was examined for proliferation. The researchers found that men who consumed flaxseed had slower tumor growth—nearly half the rate of men in the control arms. The combination of low-fat diet plus flaxseed did not give an advantage over flaxseed alone. While the study is early, it does provide evidence that dietary supplements may have a role in the management of prostate cancer. Future studies will be needed to examine whether this lower proliferation rate translates into improved outcomes. — Stephen J. Freedland, M.D., and Judd W. Moul, M.D.
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