Schwarcz - Let them eat flax 70 all-new commentaries on the science of everyday food & life

Joe Schwarcz is a professor of Chemistry and the Director of the Office for Science and Society at McGill University in Montreal, Canada. He hosts a popular weekly phone-in radio show, makes numerous television appearances, frequently gives entertaining and educational public lectures, and writes a column for the Montreal Gazette. He has received many honors, including the American Chemical Societys prestigious Grady-Stack Award for Interpreting Chemistry for the Public. In 2005 he received the Royal Canadian Institutes Sanford Fleming medal in recognition of his outstanding achievements in the promotion of knowledge and the understanding of science.

Hippocrates prescription for his patients who suffered abdominal pains was simple: Let them eat flax! And its probably not bad adviceas long as the pain stems from constipation. It turns out that flaxseeds, which come from the plant used to make linen, are an excellent source of dietary fiber. This indigestible plant component provides a laxative effect by allowing wastes to absorb water as they journey through the digestive tract. But modern science suggests that eating flax may do more than increase the frequency of bathroom visits. How about decreasing the risk of heart disease and cancer? Could Charlemagne really have been on to something when, in the eighth century, he decreed that his subjects should consume flax regularly? It seems so.

Lets begin our story in an unusual place. The barnyard! Not any old barnyard, mind you, but one where the chickens dine on flaxseeds instead of the usual chicken feed. Why? Because some egg producers are trying to improve the nutritional value and the public image of eggs. Lets face it, when eggs are mentioned, the first word that often comes to mind is cholesterol, which in turn conjures up thoughts of clogged arteries and premature demise. In truth, blood cholesterol responds much more to the saturated fats found in meat and full-fat dairy products than it does to cholesterol in egg yolk. Still, eggs suffer from an image problem. Omega-3 fats, on the other hand, positively bask in the limelight these days. Found mostly in fish, these fats have been linked with a reduced risk of heart disease, breast cancer, inflammatory bowel disease, Alzheimers disease, and arthritis. Slipping these fats into eggs would certainly be a healthy boost to their image! Especially considering that many people worry about pollutants like mercury and PCBs, both of which crop up in fish.

Flaxseed is one of the few plant sources high in omega-3 fats. The term omega-3 refers to the molecular structure of these fats, indicating the presence of a carbon-carbon double bond on the third carbon from the end of the molecule. Alpha-linolenic acid (ALA), the specific omega-3 found in flaxseed, differs slightly from eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), which are the major fats in fish, but some ALA is converted to EPA and DHA in the human body, as well as in the chicken body.

Most research has focused on the health benefits of EPA and DHA, but ALA itself has also been linked with a reduced risk of heart disease. The Nurses Health Study, monitored by Harvard University researchers, has followed the health status of over 75,000 nurses who, starting in 1984, filled out food questionnaires every four years. Women who consumed the most alpha-linolenic acid from foods had a 46 percent lower risk of sudden cardiac death than women who consumed the least. The major sources of ALA were green leafy vegetables, walnuts, canola oil, and flax.

Canadian guidelines recommend 1.1 grams of omega-3s for women and 1.5 grams for men on a daily basis. These are really no more than educated guesses based on studies carried out mostly with fish oils. A British trial, for example, showed that heart patients advised to eat two servings of oily fish a week, or to take daily fish oil capsules for two years, had a significantly lower death rate than patients who were told to increase their fiber intake and reduce fat consumption. An Italian study of over 2,800 heart-attack survivors also showed that fish oil capsules providing 850 milligrams each of EPA and DHA dramatically reduced the incidence of death in the first nine months following a heart attack. The protection, however, seems to fade with time, even if fish oil consumption is maintained.

Where do omega-3 eggs fit into this picture? Feeding flax-seeds to chickens makes great use of the you are what you eat phenomenon, and results in eggs that have roughly twelve times more omega-3 fats than regular eggs. Of course, the important question is whether eating such eggs makes a significant contribution of omega-3s to the diet. Perhaps surprisingly, it does. Each egg has roughly 0.35 grams of ALA and 0.13 grams of EPA and DHA, so a couple of eggs provide a significant portion of the recommended intake, about the same as a couple of ounces of a high-oil fish, like salmon. No nutritional authorities suggest that we should be eating two eggs every day, but five to seven a week is reasonable. And even at that rate, switching to omega-3 eggs makes sense. This is roughly equivalent to a weekly serving of fish.

By now youre thinking that this must be too good to be true. There must be a but coming up, right? Right! Back in 1994, the scientific community was stunned by a study that linked high blood levels of alpha-linolenic acid with an increased risk of prostate cancer. Total fat consumption had been associated with this cancer before. That was no great surprise, since dietary fat is known to increase the production of male sex hormones, which are linked to prostate cancer. Furthermore, many pesticides are fat soluble, and a high-fat diet increases the bodys pesticide load, which is certainly undesirable. But all previous indications had been that a diet high in fish oils decreases the risk of prostate cancer. Could ALA be different from other omega-3s? Was it protecting the heart while increasing the risk for prostate cancer? Several studies since have also suggested that ALA may be linked to prostate cancer, but there is considerable controversy surrounding the issue. Plasma levels of ala, for example, show no association with ALA levels in tissue taken from prostate cancer patients. The prudent analysis of the data suggests that it is probably not a good idea for men to consume flax oil on a regular basis.

Ready for another but? Consuming flaxseeds themselves has consistently been linked to a reduced risk of both prostate cancer and breast cancer. Perhaps this is because other components of the seed, such as lignans, have proven anti-cancer properties, and may overcome any detrimental effect that may be attributed to ala. A study at Duke University clearly showed that men awaiting surgery for prostate cancer benefited from a daily consumption of three tablespoons of ground flax. Testosterone levels were lowered, and there was a decrease in cancer cell proliferation.

So we now have the following scenario. The omega-3 fat in flax protects against heart disease, probably by reducing inflammation in the arteries and by smoothing out irregular heartbeats. Flax is also an excellent source of soluble fiber, which binds bile acids in the intestinal tract. This forces the liver to make more bile acids to aid in digestion. Since the raw material for bile acid synthesis is cholesterol, flax consumption ends up lowering cholesterol levels. Soluble fiber also slows the transit time of food through the stomach and small intestine, which in turn reduces the rate at which glucose is absorbed into the bloodstream. Diabetics have seen blood glucose levels drop with increased flax intake; in one study, blood glucose levels were lowered by almost 30 percent with a daily consumption of 50 grams of flax-seed. The lignans in the seed might also have a protective effect against cancer. Certainly, the work of Drs. Lillian Thompson and Paul Goss at the University of Toronto is encouraging. These researchers showed that women awaiting surgery for breast cancer had slower-growing tumors if they ate muffins containing 25 grams of milled flaxseed on a daily basis.