Isoflavones food sources

The three main classes of phytoestrogens (and common food sources) are isoflavones (soybeans), lignans (cereals and oilseeds such as flaxseed), and coumestans (alfalfa sprouts). The biologic potency of phytoestrogens varies and is less than that of synthetic estrogen. 

The value of antioxidant protection by way of natural food sources has been pointed out in the literature with considerable frequency. Among the components of soy flour known to have some antioxidant properties are isoflavones and phospholipids. Amino acids and peptides in soybean flour also possess some antioxidant activity. There also may be some antioxidant impact from aromatic amines and sulfhydryl compounds. 

Table 1. Food sources and content in major isoflavones. Where concentrations are...

Many isoflavone foods could provide an essential dietary source as the bioactive nonnutrients because isoflavones (2) are widely foimd in then-leguminous plants such as soybeans (Photo 1) and kowhai (Photos 2 and 3). 

Flavonoids are also important antioxidants in many food sources. Flavonoids are divided into anthocyanins, flavanols/flavans, flavanones, flavones, flavonols, and isoflavones/isoflavonoids [15]. The sum of individual flavonoids (SIF) can be a simple indicator of flavonoid levels in dietary food sources which provides useful information for their potential benefits in human health. 

Soybeans (Glycine max) are protein-rich legumes widely grown around the world as a food crop. They are the major dietary source of isoflavones, which are broken down in the intestine into the phytoestrogens genis-... 

Hendrich S, Murphy SP. Isoflavones Sources and Metabolism. In Wildman REC, editor. Handbook of neutraceuticals and functional foods. Boca Raton CRC Press, 2001. p. 55-72. 

Genovese MI, Barbosa AC, Pinto Mda S, Lajolo FM. 2007. Commercial soy protein ingredients as isoflavone sources for functional foods. Plant Foods Hum Nutr 62 53-58. 

Isoflavones, a special kind of polyphenols, show similar behaviour regarding absorption and metabolism to this family of compounds. Thus, Scalbert et al [12] put forward two primary sources of evidence concerning the absorption of polyphenols first, indirect evidence for their absorption through the gut barrier as can be seen from the increase in the antioxidant capacity of the plasma following the consumption of polyphenol-rich foods, and second, their recovery in urine after the ingestion of given amounts of a particular polyphenol. 

Isoflavones are mainly found in legumes and particularly in soy. Soy is the major source of genistein and daizdein, although their presence has also been reported in black beans, green split peas, and clover sprouts. The widespread use of soy products in infant foods, vegetarian formulations and as an ingredient in the composition of several foods leads to its ubiquitous presence in foodstuffs. Other isoflavones with nutritional relevance are brochamin and formononetin, which occur in... 

Flax seed has a warm, earthy and subtly nutty, butter flavour. The seed can be eaten entirely, and has traditionally been used as an add-on to cereal or bread. Today flaxseed is experiencing a renaissance among nutritionists, the health conscious public, food and feed processors (see Chapter 6) and chefs alike. It is one of the richest sources of lignan and a-linolenic acid (> 50%), one type of fatty acid in the polyunsaturated co-3 fatty acid (PUFA) family, considered essential fatty acids. Lignans, like isoflavones, are one of the major classes of phytoestrogens, which are estrogen-like chemicals and act as antioxidants. 

Component biomarkers are found more easily than food biomarkers, because food markers are included within component biomarkers. For example, plasma isofla-vones are measured as a marker of the exposure to isoflavones, although as they have an almost unique dietary source, soybean products and their derivatives. 

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