A study published in the September 2004 issue of the "International Journal of Cancer" as well as other studies have established a correlation between diets that produce a high amount of lignans and reduced risk of cancer. In fact, lignans are believed to be one of the main protective factors that cause vegetarian diets and other diets high in plant foods to be protective against cancer.
Lignans are phytochemicals produced in your body -- specifically in your colon -- from precursors found in food. Different foods contain varying levels of lignan precursors and diets that consist of foods with high levels of lignan precursors will result in higher levels of lignan production.
The highest lignan-yielding food to be tested so far is flaxseed. A comparison of various foods in a 1991 issue of "Nutrition and Cancer" demonstrated that flaxseed flour and defatted flaxseed meal produced about 60,000 mcg of lignans per 100 g sample. Seed oils placed a distant second, with about 20,000 mcg, followed by dried seaweed at 900, whole legumes at 562, cereal brans at 486, legume hulls at 371, whole grain cereals at 359, vegetables at 144 and fruits at 84.
Although flaxseed products already are high in lignan precursors, labels sometimes declare a product to be "high-lignan." This is especially common with flaxseed oil. The filtration of flaxseed oil actually removes some of the lignan precursors from the oil. To counteract the reduction in lignan-yielding potential, producers add them back into the final product. There is no regulation regarding labeling something as "high-lignan," so there is no level that producers must meet in order to use it; in fact, there's no guarantee that they even added anything back in: It's possible that some producers might just be referencing the fact that flaxseed is a naturally rich source of lignan precursors.
Avoid relying solely on one source of food for any specific nutritional benefit. For peak health and disease prevention, eat a variety of wholesome foods. Try grinding a teaspoon of flaxseed to put in your oatmeal, muffins or buckwheat pancakes a few times a week, but also eat lots of different fresh vegetables, fruits, whole grains and legumes. Diets rich in all of these foods are correlated with a longer, healthier life and reduced risk of almost every disease known to man.