Some food products naturally contain phytoestrogens, but there are few in Western diets that are significant sources. The foods that are the most significant sources are soy beans, containing isoflavones, and flaxseed, which contains lignans. These foods have, however, until recently been relatively little used in Canada and the United States in the human diet. While the Japanese diet contains from 20 to 80 mg of isoflavones per day, Canadian and U.S. diets tend to be below 1 mg/day in the absence of soy protein. The number of foods sold in the West that have ingredients derived from soybeans has been increasing. Many of these have soybean oil, soy protein, or other ingredients serving functional roles in the food. However, with increasing interest among consumers in dietary choices that help to improve health and reduce risk of disease, products in which soy is featured are quite readily available, and it is common, at least in Canada, to find bread and other bakery products with flaxseed added. Soy foods sales in the United States increased at a 15% compounded annually growth rate between 1992 and 2003, with a major increase occurring between 2000 and 2001 (1). Growth rates are reported to have declined somewhat in 2004 (2). The U.S. Food and Drug Administration approval of a health claim associating soy protein intake with reduced risk of heart disease in 1999 is attributed with fueling the very sizable growth since 2000. The claim identifies 25 g/day as the amount needed to derive the claimed health benefit. Because the isoflavone content of soy products is highly variable, depending on the method of processing (3), it is difficult to estimate quantitatively the impact of the increased rate of soy product consumption on soy isoflavone intake, although an overall increase can be expected. In contrast,