Debate over the health benefits and risks of flaxseed and omega-3 fatty acids, in particular alpha-linolenic acid (ALA- a form of omega-3 fatty acids), is ongoing and often contentious. People tend to become very defensive about their food choices, especially when they are making those choices because they are trying to prevent and/or treat a serious health problem, such as prostate cancer.
One controversy related to omega-3 fatty acids is whether ALA and flaxseed, which is a rich source of ALA, are beneficial or harmful to prostate health. According to medical oncologist and prostate cancer researcher Snuffy Myers, M.D., flaxseed and ALA, contrary to popular marketing, are not helpful for overall health nor for prostate health. Myers also states there is little to no evidence in the medical literature to support the use of flaxseed or flaxseed oil, that these products are hyped by marketers, and that people should turn to fish and fish oil as the best sources of omega-3 essential fatty acids. (1)
Omega-3 Essential Fatty Acids
Omega-3 essential fatty acids are so-named because the body needs them for overall health. However, because the body cannot manufacture them they must be acquired through diet and/or supplementation. This fact is also true for omega-6 essential fatty acids. One significant difference between these two types of essential fatty acids -- and there are several differences -- is that omega-6s are plentiful and even excessive in the Standard American Diet (yes, our "SAD" diet) while omega-3s tend to be deficient.
The three dietary omega-3s are alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). In addition to flaxseed and flaxseed oil, ALA is found in soybeans and soybean oil, pumpkin seeds and pumpkin seed oil, walnuts and walnut oil, and purslane. EPA and DHA are found in cold-water fish such as halibut, herring, mackerel, salmon, sardines, and tuna. These fish do not themselves produce EPA and DHA, but instead acquire it from the krill and algae they eat.
EPA and DHA are the omega-3s necessary for health. This does not mean ALA has no role in your well-being. However, ALA is much less active than EPA and DHA and is mostly limited to cardiovascular benefits, and even in this capacity it is less effective than the other two omega-3s. In fact, before ALA can be utilized by the body, it must be converted into EPA, which is then transformed into DHA. Because the conversion rate of ALA to EPA and DHA in men is very low -- less than 4 percent of ALA is changed to EPA and less than 0.1 percent becomes DHA -- it is clearly better to get omega-3s from sources that provide EPA and DHA rather than ALA. Young women experience a significantly higher conversion rate -- 21 percent of ALA becomes EPA, and 5 to 9 percent of EPA is converted into DHA -- because the conversion is supported by estrogen activity. (1)
Flaxseed and Flaxseed Oil
Flaxseed is often touted as providing protection and relief from a number of ailments, although the validity of these claims has been questioned by some researchers. One group that examined the claims was from Memorial Sloan-Kettering Cancer Center.
Experts at Sloan-Kettering reviewed the available literature on flaxseed in human studies from nine databases, 20 additional journals, and various bibliographies. The reviewers found 13 categories in which flaxseed had been studied, including prostate cancer, constipation, attention-deficit hyperactivity disorder, high cholesterol, atherosclerosis, breast cancer, cyclic breast pain, menopausal symptoms, diabetes, high blood pressure, lupus nephritis and HIV/AIDS. The reviewers concluded that nearly all the studies were of poor quality, and that "although flaxseed and flaxseed oil have several promising future uses, the available literature does not support recommendation for any condition at this time." (Basch 2007)
When it comes to health impact, which one is worse, flaxseed or flaxseed oil? Although advocates of flaxseed and flaxseed oil might say the oil is the better deal because it delivers much greater amounts of ALA than does flaxseed, high levels of ALA also appear to increase the risk of advanced prostate cancer (see "Alpha-Linolenic Acid and Prostate Cancer" below).
In defense of flaxseed (but not the oil), Dr. Myers notes there is "good evidence" that flaxseed can quickly reduce the severity of high blood pressure, and that it is also beneficial in reducing elevated blood sugar levels in people with diabetes. This quality is attributed to flaxseed's high soluble fiber content. (1)
Alpha-Linolenic Acid and Prostate Cancer
Research has uncovered evidence that ALA from foods such as flaxseed, egg yolks, and canola oil may increase the growth and spread of prostate cancer. In a Harvard School of Public Health study that included more than 40,000 men followed for 10 years, the investigators found that ALA consumption increased the risk of advanced prostate cancer while omega-3s from fish reduced the risk. (1)
In a study published in the American Journal of Clinical Nutrition, researchers explored the association between the risk of prostate cancer and intake of the omega-3 fatty acids alpha-linolenic acid, EPA, and DHA; and the omega-6 fatty acids linoleic acid and arachidonic acid. A total of 47,866 men aged 40 to 75 who had no history of cancer in 1986 were followed for 14 years.
During the follow-up period, 2,965 new cases of total prostate cancer were identified, and 448 of these were advanced. An analysis of the men's intake of omega-3 and omega-6 fatty acids showed that intake of ALA was not related to a risk of total prostate cancer. ALA, however, was associated with an increased risk of advanced prostate cancer, with ALA from non-animal sources (e.g., flaxseed, flaxseed oil, canola oil) presenting a greater risk than from meat and dairy sources.
Intake of EPA and DHA, however, was associated with a lower risk of prostate cancer, both total and advanced, while consumption of the omega-6 fatty acids were unrelated to prostate cancer risk. The authors concluded that men who had increased intake of alpha-linolenic acid may have an increased risk of advanced prostate cancer. (Leitzmann 2004)
On the other hand, not all the available research has found ALA-rich flaxseed to be detrimental to prostate health. A team of scientists from The University of Texas M.D. Anderson Cancer Center conducted a randomized controlled trial to examine the effects of a low-fat and/or flaxseed-supplemented diets on the prostate and other biomarkers for prostate cancer. A total of 161 men with prostate cancer who were scheduled for prostatectomy were assigned to one of four diet groups: usual diet, flaxseed-supplemented diet, low-fat diet, or flaxseed and low-fat diet. The men followed the diets for an average of 30 days.
At the start of the study and before surgery, all the men had their blood drawn and tested for prostate-specific antigen (PSA), testosterone, C-reactive protein, cholesterol levels, and other biomarkers. After the surgeries, the men's tumors were examined, and men who had consumed either of the flaxseed-supplemented diets had significantly lower cancer proliferation rates than men who had followed a normal or low-fat diet. No differences were seen in any of the biomarkers except for cholesterol, which was significantly lower in the low-fat diet groups.
The study's authors concluded that flaxseed is safe and may provide some protection against prostate cancer. (Demark-Wahnefried 2008)
Fish and Prostate Cancer
For prevention and lowering your risk of prostate cancer, a large study from Harvard School of Public Health provides some answers. For 12 years, researchers followed 47,882 men who had participated in the Health Professionals Follow-up Study. The men's dietary intake was assessed every four years. During the follow-up period, 2,482 cases of prostate cancer were identified, of which 617 were determined to be advanced prostate cancer, including 278 metastatic cancers.
The investigators determined that men who ate fish more than three times per week had a reduced risk of prostate cancer, and the strongest association was for metastatic cancer. Each 500 mg of omega-3 fatty acids the men got from eating fish was associated with a 24 percent decreased risk of metastatic cancer. (Augustsson 2003) (View the amounts of omega-3s found in fish and seafood.)
Numerous other studies have also shown a significant reduction in prostate cancer risk associated with omega-3 fatty acids.
What About Krill Oil?
Krill oil is an oil extracted from shrimp-like crustaceans called krill. Like fish oil, krill oil is a rich source of EPA and DHA. At a molecular level, krill oil has a phosphate molecule attached, which makes the EPA and DHA in krill oil phospholipids. This is important because phospholipids significantly increase the absorption (bioavailability) of the EPA and DHA, allowing the omega-3s to be more readily available throughout the body. Fish oil is in a triglyceride form, which is less bioavailable.
Krill oil may be of higher quality than fish oil, and one reason is that krill are at the lower end of the food chain and so are much more unlikely to accumulate dioxin, PCBs, mercury, and other toxins than are fish. Krill oil is also generally produced from krill harvested from cold Antarctic waters, which tend to be less contaminated than waters from which fish are harvested for fish oil. However, there are fish oil supplements made from fish caught in unpolluted waters as well.
Unlike fish oil, krill oil contains higher levels of a potent antioxidant called astaxanthin, which in addition to its ability to fight free radicals and oxidative stress, also helps make krill oil less perishable than fish oil. One major problem with fish oil is that it oxidizes, which means every time you open the bottle to take a dose, the fish oil loses a bit more of its potency. Oxidation also leads to the formation of harmful free radicals. Fish oil capsules mostly eliminate this problem.
One major concern about krill oil is that krill, along with plankton, make up the largest biomass on the planet. As such they are a critical and basic source of food for marine animals. While krill oil makers and others who harvest krill for food insist krill are an easily renewable food source, not everyone agrees, especially given the declining state of ocean health -- even the Antarctic from which much of the krill is harvested.
How Much Omega-3 Do You Need?
How much omega-3 do you need? A number of studies have indicated that EPA and DHA may be helpful in a number of health conditions, including arthritis, asthma, cancer, cardiovascular disease, dementia, depression, diabetes, high blood pressure, and schizophrenia. Therefore, in 2008, the Technical Committee on Dietary Lipids of the International Life Sciences Institute North America announced recommended daily intakes of both EPA and DHA. (1)
The Committee recommended that adults consume 250 to 500 mg of EPA and DHA daily, and it noted that people could not achieve this goal by taking ALA. Since flaxseed is a rich source of ALA, it is not recommended as a way for individuals to reach their daily omega-3 intake. Instead, people need to eat cold-water fish, take fish oil supplements, or supplements of DHA extracted from algae.
Dr. Myers recommends a much higher intake of fish oil supplements for men who want to prevent prostate cancer. Although there are no formal recommendations for fish oil doses regarding prostate cancer prevention and fish oil/omega-3s have not been proven to prevent prostate cancer, Myers suggests, for maximum benefit, 4,000 to 6,000 mg daily, or eating five servings of cold-water fish per week.
These recommendations concerning intake of EPA and DHA are especially critical for men, because those who depend on ALA and flaxseed for their omega-3s risk an omega-3 deficiency since their conversion rate of ALA to EPA and DHA is so poor. In addition, there are other risks for men who depend on ALA for their omega-3s, and so at this point there seems to be no reason to get ALA from flaxseed, flaxseed oil, or other similar products.