Flaxseed slows the growth of prostate cancer in men awaiting surgery, according to a study reported at the recent American Society of Clinical Oncology meeting in Chicago. The finding contradicts previous epidemiologic evidence suggesting that α-linolenic acid (ALA), a fatty acid prevalent in flaxseed and other foods, heightens risk for the disease.
A research team based at the Duke University Medical Center in Durham, N.C., randomly assigned 161 male patients awaiting prostatectomy to four groups: 30 g/day of flaxseed for 30 days; a low-fat diet (≤20% of calories per day); flaxseed as part of a low-fat diet; and no flaxseed or special diet (controls). Analyzing the tumors following surgery, the researchers determined that cancer cell growth was 40%-50% slower among those who consumed flaxseed. Reduced-fat diets showed no effect.
Approximately seven years ago, an NIH scientist documented that in his survey of six epidemiologic studies, five showed an association between ALA and increased prostate cancer risk. But flaxseed was not the source of ALA in the studies—it came instead from animal and dairy products or from salad dressing and mayonnaise.
Flaxseed, however, is rich in lignans, an anti-angiogenic substance in plants that may cut off the blood supply to a tumor, thereby stunting its growth. Flaxseed is also a rich source of vitamin E, which may be protective against prostate cancer.
Writing in Seminars in Preventive and Alternative Medicine (2006;2:205-207), Wendy Demark-Wahnefried, MD, professor of nursing and surgery and the lead author of the Duke study, noted that the research to date suggests that some nutrients in flaxseed may be risky whereas others may be protective. “Indeed, it is highly unlikely that a single nutrient or one specific food is either all bad or all good.” She added, however, that two pilot studies, one animal study, and one cell-culture study, all done at Duke, had previously shown “exceptionally protective effects for flaxseed.”