Lignans are a "phytoestrogen," which means they are a chemical hormone that effectively acts like estrogen and are found in a plant. Technically, phytotestrogens are not estrogen hormones, but bind themselves to estrogen to compound and increase the activity of an estrogen hormone. In animals, estrogen is a chemical involved in the production of female sex hormones. Within the plant itself, lignans are dormant and do not exert an important influence on the growth of the plant. Lignans are part of other chemical compounds in the plant that serve other purposes, such as secoisolariciresinol and matairesinol.
Lignans are produced in the human body as a byproduct of other chemicals in the plant being broken down by proteins and bacteria found in the digestive tract. Once broken down, lignans are a source of estrogen for human beings, though they are a relatively weak source of estrogen in comparison to sources from animal products. Individuals with diets rich in lignans have been found to have lower incidents of heart disease, as well as having a decrease in the side effects associated with menopause.
According to the Linus Pauling Institute at Oregon State University, there is evidence that high consumption of lignans may be involved in reducing the risk of cancer. Studies have shown a possible positive correlation between lignans and a reduction in ovarian cancer and prostate cancer. Although lignans act as an antioxidant in experimental settings, it is difficult to pinpoint their exact role in preventing cancer in human beings because it is metabolized quickly by proteins and bacteria in the digestive tract.
Lignans are found in several different food sources, including vegetables and whole grains, but seeds are by far and away the best source of lignan. The food with the highest serving of lignans is flaxseed, which contains 85.5 milligrams of lignans per ounce. Lignans are only found in the actual seed component of flaxseed and flaxseed oil has no lignans. Other seeds that contain a high amount of lignan include sesame seeds and pumpkin seeds.