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A lignan is a type of polyphenolic compound that occurs naturally in some plants. Sources that are particularly rich in lignan phytochemcials (in order of highest to lowest concentration) are flax, sesame, sunflower, and pumpkin seeds. However, lignan compounds are also found in many vegetables, fruits, and botanical-derived beverages, such as tea and wine. Since there is more than one type of lignan compound, they are collectively referred to as lignans.
One specific lignan compound, secoisolariciresinol diglycoside (SDG), is a precursor to a variety of phytoestrogens with antioxidant properties. Several studies have shown that supplementation with SDG may help to reduce serum levels of low-density lipoproteins (the “bad” kind of cholesterol) and lower blood pressure. This substance has also shown promise in preventing the development of diabetes and atheriosclerosis.
There is also clinical evidence to suggest that lignan compounds may deter the development of certain cancers. For example, some study results have led researchers to speculate that there is a correlation between high dietary lignan intake and a lower risk of ovarian and prostate cancer. Similar studies exploring the effects of lignans and breast cancer are inconclusive, though. However, it is clear that lignans are high in antioxidants.
Some lignan compounds are readily assimilated by the body since they are metabolized by intestinal flora during digestion. These lignans are known as enterolignans and specifically include enterolactone and enterodiol. They are also referred to as the mammalian lignans. Matairesinol, obtained from dietary fiber, is one type of lignan that undergoes this conversion. However, matairesinol is also absorbed directly to a degree before being metabolized.
Pinoresinol is a lignan that has been studied for its potential ability to help prevent colon cancer. In fact, pinoresinol is the primary phenol found in extra virgin olive oil, which may explain why the Mediterranean diet has been associated with a lower risk of developing this type of cancer. The anti-cancer value of this compound has been observed in studies when introduced to cancer cells in vitro. In addition to apoptosis (cellular death) of the cancer cells occurring, it was noted that the best results were achieved with low concentrations of pinoresinol, as they may be found in extra virgin olive oil naturally. This suggests that all of the polyphenolic compounds in olive oil may work together synergistically and more effectively than high doses of pinoresinol alone.
Sesame oil, a staple fat used in Asian cooking, contains several lignans, most notably sesamin. Studies using animal models have shown that sesamin inhibits delta 5 desaturation of n-6 fatty acids by blocking the synthesis of arachidonic acid, a proinflammatory agent found exclusively in animal products. This activity translates to a significant reduction in inflammation when sesamin and related sesame lignans are included in the diet.
Lignan supplements are available in liquid and capsule form. If electing to consume flaxseed oil, keep in mind that some of the lignans may be lost during processing. For this reason, it’s best to choose unrefined and unfiltered flaxseed oil. In addition, in order for the raw seeds to yield their health-giving benefits, they should be ground prior to being added to baked goods or other foods.
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