title: The influence of diet on isotope ratio mass spectrometry values.
abstract: OBJECTIVE
  Athletes have increasingly used testosterone (T) and other endogenous anabolic steroids that cannot be detected by conventional gas chromatography-mass spectrometry. This led to gas chromatography-combustion-isotope ratio mass spectrometry(GC/C/IRMS), which measures the relative amount of 13C in urinary steroids. Because exogenous testosterone is relatively low in 13C content, this study will determine if consuming a diet low in 13C plants, such as soy, can be confused with a GC/C/IRMS-positive test for exogenous testosterone.
  
  
  METHODS
  Cross-sectional study in which 22 vegetarians known to consume a diet depleted of 13C isotope were compared with a geographic control group of 14 subjects consuming a normal diet.
  
  
  METHODS
  Two distinct subject populations with respect to diet.
  
  
  METHODS
  Subjects were recruited from a soy-based cooperative and control volunteers. Twenty-two of 24 research subjects completed the protocol compared with 14 of 22 control subjects.
  
  
  METHODS
  Independent variables were delta13C IRMS values,urinary steroid profile, and isoflavone analysis.
  
  
  METHODS
  Comparisons were made with respect to dietary analysis, isoflavones, and urinary steroid measurements using GC-C-IRMS.
  
  
  RESULTS
  The delta13C values for 2 major metabolites of T (androsterone and etiocholanolone) were lower for the vegetarians than the controls (P = 0.005). The vegetarians excreted a median of 23 micromol/d of total isoflavones compared with 2.7 micromol/d for the control group (P =0.0002).
  
  
  CONCLUSIONS
  The carbon isotope ratios of urinary testosterone metabolites of vegetarians consuming a diet that is markedly depleted of 13C content were lower than that of control subjects, but not low enough to result in World Anti-Doping Agency criteria for a positive IRMS analysis.
authors.affiliation: Department of Pathology, UCLA Olympic Analytical Laboratory, 2122 Granville Avenue, Los Angeles, CA 90025, USA. ggreen@mednet.ucla.edu
authors.forename: Gary
authors.initials: G
authors.lastname: Green
authors.forename: Rodrigo
authors.initials: R
authors.lastname: Aguilera
authors.forename: Brian
authors.initials: B
authors.lastname: Ahrens
authors.forename: Boro
authors.initials: B
authors.lastname: Starcevic
authors.forename: Felice
authors.initials: F
authors.lastname: Kurtzman
authors.forename: Jinbo
authors.initials: J
authors.lastname: Su
authors.forename: Don
authors.initials: D
authors.lastname: Catlin
mesh_terms: D000293:Adolescent; D000328:Adult; D045930:Anabolic Agents / Q000652:urine; D002247:Carbon Isotopes / Q000032:analysis*; D003430:Cross-Sectional Studies; D004032:Diet; D004300:Doping in Sports; D005260:Female; D008401:Gas Chromatography-Mass Spectrometry / Q000592:standards*; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D045730:Soy Foods; D015813:Substance Abuse Detection; D055815:Young Adult
chemical_list: D045930:Anabolic Agents; D002247:Carbon Isotopes