Isoflavones (Phytoestrogens) at soy affect studies

Plant substances with oestrogenic-like characteristics are called "Phytoestrogens". The isoflavones contained in the soy plant are among the most important because they are often found at high, and variable, levels in most "traditional laboratory diet formulas".

Phytoestrogens will influence any body functions that involve estradiol, through both their agonistic and antagonistic effects. They will influences many research projects, and already their importance in this regard has been recognised by many worldwide organizations and institutions.

At the Laboratory Animals (2007, 41, 1-18) the former president of the FELASA Prof. Merel Ritskes-Hoitinga published an article about the potential impact of isoflavones (phytoestrogens, e.g. Genistein u. Daidzein aus Soja). The focus was on animal models at reproduction, skeleton, central nervous system and oncology.

In summary there are the main conclusions:

- Many traditional soy based lab animal diets are containing in part very high levels of isoflavones (>500 mg/kg IF).

- The concentration of Isoflavones is varying strongly from batch to batch.

- Isoflavones may have a strong impact on studies; safe limits can’t be defined.

- At significant soy levels the isoflavone level should be monitored to evaluated data retro perspective.

- Beside „purified diets“ based on casein (like AIN93M) there are soy free standard diets available that contain extremely low levels of isoflavones.

Isoflavone content at lab diets

DTraditional laboratory diet formulas are containing high, and variable, levels of Isoflavone induced by high levels of soya:

TGE: Total Genistein Equivalent, based on the content of Genistein, Daidzein and Coumestrol
OECD Validation, 2003, EHP Vol 111, No 12
Jensen M.N., Ritskes-Hoitinga M., How isoflavone levels in common rodent diets can interfere with the value of animal models and with experimental results; Laboratory Animals, 2007, 41, 1-18,

Corresponding literature is numerous - enclose a short list of overviews:

COT Report 2003 - Phytoestrogens and Health (ca. 430 Seiten)
http://cot.food.gov.uk/sites/default/files/cot/phytoreport0503.pdf 

ILAR Journal Vol 45(4), 2004 (ca. 100 Seiten) - Animal Models and Experimental Design Considerations For Endocrine Disruptor Research and Testing
http://ilarjournal.oxfordjournals.org/content/45/4.toc

Jensen M.N. and Ritskes-Hoitinga, M, 2007, How isoflavone levels in common rodent diets can interfere with the value of animal models and with experimental results, Laboratory Animals (2007) 41, 1–18;
http://www.ncbi.nlm.nih.gov/pubmed/17234046