While known mostly for their fiber contribution to the diet, whole grains also contain lignans, estrogen-like compounds that also act as antioxidants.
Lignans may sound like something you’d rather keep out of your food, but names can be deceptive. Lignans are a unique group of phytochemicals (plant chemicals) known as phytoestrogens, estrogen-like compounds that also act as antioxidants.
Phytoestrogens, in addition to their antioxidant activity, may reduce the risk of estrogen-sensitive cancers, like breast cancer, by binding to estrogen receptors and thus preventing estrogen attachment.
The most noted of the phytoestrogens are the isoflavones of soybeans. Isoflavones have helped give soy its reputation as a health-promoting food. Lignans may do the same for foods like flax, already becoming popular for its content of omega-3 fatty acids.
Animal lignans are formed in the proximal colon from plant lignan precursors, which occur naturally in a variety of foods, whole grains, beans, fruits and berries, vegetables, wines, teas and coffee. However, one the richest sources of plant lignan precursors comes from one of oldest domesticated crops, flaxseeds, which date back more than 7000 years. Flaxseeds as a source of lignans have been the focus of research as potential protective agents against breast cancer.
In a 2005 study conducted at Princess Margaret Hospital, University of Toronto, and reported in the May 2005 issue of Clinical Cancer Research, patients taking flaxseed in muffins showed reduced tumor markers compared to controls.
More recently, researchers from the Dept. of Nutritional Sciences at the University of Toronto fed flaxseed to mice with breast tumors to see if flax alone or in combination with tamoxifen could inhibit tumor growth.
Results of the study published in the journal Experimental Biology and Medicine (April 2007) showed that flaxseed reduced tumor growth in these mice in a dose-dependant manner, and that it enhanced the anti-estrogen effect of tamoxifen.
Many studies have suggested that phytoestrogens may lower plasma cholesterol. Flaxseeds contain an abundance of a lignan precursor that goes by the acronym SDG, which is fortunate since few people can pronounce secoicilariciresinol diglucoside. Concentrations of SDG vary with the species.
A recent study published in the British Journal of Nutrition (January 2008) reported the results of a double-blind placebo-controlled clinical trial designed to look at the cholesterol-lowering effects of an SDG-rich flaxseed extract consisting of 33 percent SDG. The purpose of the study was to separate the potential cholesterol-lowering effect of the lignans from that of the associated fiber and omega-3 fatty acids contained in flaxseeds.
The study, which also looked at the potential of lignans to affect blood glucose concentrations, was conducted in Beijing at the Tumor Hospital Institute. Researchers found significant evidence that SDG lowered both total and LDL cholesterol in subjects with high blood cholesterol. And those who took 600mg of SDG showed a significant lowering of blood glucose after six weeks.
We’ve been putting flax on our cereal as a plant source of highly valuable omega-3 fatty acids, but look for the word lignan to begin popping up on labels of foods with added flax, much as isoflavones became the reason for our expanded appetite for soy products.
Until recently, it has been difficult to accurately assess the value of lignan precursors in many foods. With the rising interest in this potentially protective food component, lignans are certain to become part of the modern health vocabulary.