Phytoestrogen content of foods consumed in Canada, including isoflavones, lignans, and coumestan.

Recent investigations are focusing on the association between phytoestrogen intake and reduced risk of many diseases and conditions.  The three major classes of phytoestrogens are isoflavones, lignans, and coumestans.  A number of epidemiological studies investigating phytoestrogen intake and risk of various diseases have yielded conflicting results.  It is believed that these conflicting results may in part be due to inaccuracies in estimating phytoestrogen intake resulting from inaccurate phytoestrogen values in current food databases.  The objective of the present study was to develop a database of the phytoestrogen content of 121 foods commonly consumed in the typical Western diet.  These values were used to estimate phytoestrogen intake in future epidemiological studies.

One hundred and twenty one foods were identified as important phytestrogen sources in the Typical Western diet and subsequently analyzed for their isoflavone (genistein, daidzein, glycitein, formononetin), lignan (secoisolariciresinol, matairesinol, pinoresinol, lariciresinol), or coumestan (coumestrol) content.  A variety of samples of each food/beverage were pooled to represent a homogenous representative sample of each food.  Phytestrogen content of all foods was determined via gas chromatography-mass spectrometry methods and expressed on an as is (wet) basis per 100g and also per serving.  All samples were analysed in duplicate. 

The highest amount of total phytoestrogens (per 100g) were found in oilseeds and nuts, followed by soy products, cereals and breads, legumes, meat products and other processed food, vegetables, fruits, and alcoholic and non-alcoholic beverages.  As expected, the highest amount of isoflavones was found in soy products (soybeans and soy nuts), primarily as daidzein and genistein.  High levels of isoflavones were also found in legumes, meat products and other processed foods, breads and cereals, nuts and oilseeds, vegetables, alcoholic beverages, and fruits.  All foods analyzed contained lignans, and except for the soy and soy containing products, most possessed higher levels of lignan than isoflavones.  The highest amount of lignans were found in nuts and oilseeds, followed by breads and cereals, legumes, fruits, vegetables, soy products, processed foods, and both alcoholic and non-alcoholic beverages.  The highest amount of coumestans was found in mung bean sprouts, flaxseed, and soy nuts.