title: Phytoestrogen content of purified, open- and closed-formula laboratory animal diets.
abstract: OBJECTIVE
  Phytoestrogens exert estrogenic effects on the central nervous system, induce estrus, and stimulate growth of the genital tract of female animals. Over 300 plants and plant products, including some used in laboratory animal diets, contain phytoestrogens. Therefore, the source and concentration of phytoestrogens in rodent diets were determined.
  
  
  METHODS
  Twelve rodent diets and six major dietary ingredients were assayed for phytoestrogens (daidzein, genistein, formononetin, biochanin A, and coumestrol), using high-performance liquid chromatography. Three rodent diets recently formulated to reduce phytoestrogen content also were assayed.
  
  
  RESULTS
  Formononetin, biochanin A, and coumestrol were not detected. Soybean meal was the major source of daidzein and genistein; their concentrations were directly correlated to the percentage of soybean meal in each diet.
  
  
  CONCLUSIONS
  High, variable concentrations of daidzein and genistein are present in some rodent diets, and dietary phytoestrogens have the potential to alter results of studies of estrogenicity. Careful attention should be given to diet phytoestrogen content, and their concentration should be reported. A standardized, open-formula diet in which estrogenic substances have been reduced to levels that do not alter results of studies that are influenced by exogenous estrogens is recommended.
authors.affiliation: Comparative Medicine Branch, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina, USA.
authors.forename: J E
authors.initials: JE
authors.lastname: Thigpen
authors.forename: K D
authors.initials: KD
authors.lastname: Setchell
authors.forename: K B
authors.initials: KB
authors.lastname: Ahlmark
authors.forename: J
authors.initials: J
authors.lastname: Locklear
authors.forename: T
authors.initials: T
authors.lastname: Spahr
authors.forename: G F
authors.initials: GF
authors.lastname: Caviness
authors.forename: M F
authors.initials: MF
authors.lastname: Goelz
authors.forename: J K
authors.initials: JK
authors.lastname: Haseman
authors.forename: R R
authors.initials: RR
authors.lastname: Newbold
authors.forename: D B
authors.initials: DB
authors.lastname: Forsythe
mesh_terms: D000821:Animal Feed / Q000032:analysis*; D000818:Animals; D000830:Animals, Laboratory; D003375:Coumestrol / Q000032:analysis; D004968:Estrogens, Non-Steroidal / Q000032:analysis*; D005260:Female; D005526:Food, Formulated; D019833:Genistein / Q000032:analysis; D007529:Isoflavones / Q000032:analysis; D048789:Phytoestrogens; D028321:Plant Preparations; D012377:Rodentia; D013025:Glycine max
chemical_list: D004968:Estrogens, Non-Steroidal; D007529:Isoflavones; D048789:Phytoestrogens; D028321:Plant Preparations; C007768:formononetin; C004742:daidzein; D019833:Genistein; C004541:biochanin A; D003375:Coumestrol