Phytoestrogens types

Thus, it is apparent that soya, some soya products and linseed oil influence blood lipid levels, particularly cholesterol and LDL cholesterol. While the extent of the reduction appears to largely depend on an individual s initial serum cholesterol level, the maximum reductions observed are of the order of 10-15%. For hyperlipidemic individuals this may not be a marked reduction, but such an effect on the general population may well have a beneficial effect on the overall incidence of cardiovascular disease and atherosclerosis. The possibility that non-phytoestrogenic dietary components may contribute to the hypocholes-terolemic properties cannot, however, be discounted. Indeed, certain types of dietary fibre have been shown to have a hypolipidemic effect via their ability to increase faecal excretion rates. 

Recently, attention has focused on the potential hazardous effects of certain chemicals on the endocrine system because of the abihty of these chemicals to mimic or block endogenous hormones, or otherwise interfere with the normal function of the endocrine system. Chemicals with this type of activity are most commonly referred to as endocrine disruptors. Some scientists believe that chemicals with the ability to disrupt the endocrine system are a potential threat to the health of humans, aquatic animals, and wildlife. Others believe that endocrine disrupting chemicals do not pose a significant health risk, particularly in light of the fact that hormone mimics exist in the natural environment. Examples of natural hormone mimics are the isoflavinoid phytoestrogens (Adlercreutz 1995 Livingston 1978 Mayr et al. 1992). 

The 17P-hydroxysteroid oxidoreductase enzymes (HSOR) occur as two distinct isoforms (I and II). They are involved in the conversion of estrone to estradiol. The type I enzyme converts estrone to estradiol (also androstenedione to testosterone) and the type II catalyses the reverse reaction. Phytoestrogens have been shown to inhibit both HSOR enzymes in vitro. 

Phytoestrogens can modulate expression of both sub-types of estrogen receptor (Patisaul et al, 1999,2001 Wang et al, 1996). However, the data is limited to measurements of mRNA content and it is unclear whether this differential expression results in any functional change. 

Assessment of whether a chemical has the potential to cause adverse effects in humans arises usually from direct observation of an effect in animals or humans, such as the acute poisoning episodes that have occurred when potatoes contain high levels of glycoalkaloids. Epidemiological studies have also been used to infer a possible relationship between intake of a particular type of food, or constituent of that food, and the potential to cause an adverse effect. Such observations led to the characterisation of the aflatoxins as human carcinogens. However, natural toxic substances that occur in plant foods have often been identified through observations in animals, particularly farm animals. It was observations of adverse effects in farm animals that led to the further characterisation of the phytoestrogens and the mycotoxins. In other instances, the concern arises from the chemical similarity to other known toxins. 

Figure 4.1 Different types of phytoestrogen and food where they can typically be found.

Trial reference Phytoestrogen source n Trial type and duration Hot flushes... 

In 1987, Ken Setchell first described the method for the isolation of phytoestrogen in soy (Setchell et al., 1987). The phytoestrogens daidzein, genistein, coumestrol, formononetin, and biochanin-A were separated on a Cl8 reversed-phase column (Hypersil ODS) with methanol-0.1 M ammonium acetate buffer, pH 4.6 (60 40 v/v), as eluent. The retention and resolution were affected by buffer concentrations, pH type, and proportion of organic solvent in the mobile phase. Detection in the low picograms range was achieved with an electrochemical detector, and the compounds were positively identified by HPLC-thermospray mass spectrometry. 

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. 

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