title: Measuring the glycemic index of foods: interlaboratory study.
abstract: BACKGROUND
  Many laboratories offer glycemic index (GI) services.
  
  
  OBJECTIVE
  We assessed the performance of the method used to measure GI.
  
  
  METHODS
  The GI of cheese-puffs and fruit-leather (centrally provided) was measured in 28 laboratories (n=311 subjects) by using the FAO/WHO method. The laboratories reported the results of their calculations and sent the raw data for recalculation centrally.
  
  
  RESULTS
  Values for the incremental area under the curve (AUC) reported by 54% of the laboratories differed from central calculations. Because of this and other differences in data analysis, 19% of reported food GI values differed by >5 units from those calculated centrally. GI values in individual subjects were unrelated to age, sex, ethnicity, body mass index, or AUC but were negatively related to within-individual variation (P=0.033) expressed as the CV of the AUC for repeated reference food tests (refCV). The between-laboratory GI values (mean+/-SD) for cheese-puffs and fruit-leather were 74.3+/-10.5 and 33.2+/-7.2, respectively. The mean laboratory GI was related to refCV (P=0.003) and the type of restrictions on alcohol consumption before the test (P=0.006, r2=0.509 for model). The within-laboratory SD of GI was related to refCV (P<0.001), the glucose analysis method (P=0.010), whether glucose measures were duplicated (P=0.008), and restrictions on dinner the night before (P=0.013, r2=0.810 for model).
  
  
  CONCLUSIONS
  The between-laboratory SD of the GI values is approximately 9. Standardized data analysis and low within-subject variation (refCV<30%) are required for accuracy. The results suggest that common misconceptions exist about which factors do and do not need to be controlled to improve precision. Controlled studies and cost-benefit analyses are needed to optimize GI methodology. The trial was registered at clinicaltrials.gov as NCT00260858.
authors.affiliation: Department of Nutritional Sciences, University of Toronto and Glycemic Index Laboratories, Inc, Toronto, Ontario, Canada. thomas.wolever@utoronto.ca
authors.forename: Thomas M S
authors.initials: TM
authors.lastname: Wolever
authors.forename: Jennie C
authors.initials: JC
authors.lastname: Brand-Miller
authors.forename: John
authors.initials: J
authors.lastname: Abernethy
authors.forename: Arne
authors.initials: A
authors.lastname: Astrup
authors.forename: Fiona
authors.initials: F
authors.lastname: Atkinson
authors.forename: Mette
authors.initials: M
authors.lastname: Axelsen
authors.forename: Inger
authors.initials: I
authors.lastname: Björck
authors.forename: Furio
authors.initials: F
authors.lastname: Brighenti
authors.forename: Rachel
authors.initials: R
authors.lastname: Brown
authors.forename: Audrey
authors.initials: A
authors.lastname: Brynes
authors.forename: M Cristina
authors.initials: MC
authors.lastname: Casiraghi
authors.forename: Murielle
authors.initials: M
authors.lastname: Cazaubiel
authors.forename: Linda
authors.initials: L
authors.lastname: Dahlqvist
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Delport
authors.forename: Gareth S
authors.initials: GS
authors.lastname: Denyer
authors.forename: Daniela
authors.initials: D
authors.lastname: Erba
authors.forename: Gary
authors.initials: G
authors.lastname: Frost
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Granfeldt
authors.forename: Shelagh
authors.initials: S
authors.lastname: Hampton
authors.forename: Valerie A
authors.initials: VA
authors.lastname: Hart
authors.forename: Katja A
authors.initials: KA
authors.lastname: Hätönen
authors.forename: C Jeya
authors.initials: CJ
authors.lastname: Henry
authors.forename: Steve
authors.initials: S
authors.lastname: Hertzler
authors.forename: Sarah
authors.initials: S
authors.lastname: Hull
authors.forename: Johann
authors.initials: J
authors.lastname: Jerling
authors.forename: Kelly L
authors.initials: KL
authors.lastname: Johnston
authors.forename: Helen
authors.initials: H
authors.lastname: Lightowler
authors.forename: Neil
authors.initials: N
authors.lastname: Mann
authors.forename: Linda
authors.initials: L
authors.lastname: Morgan
authors.forename: Leonora N
authors.initials: LN
authors.lastname: Panlasigui
authors.forename: Christine
authors.initials: C
authors.lastname: Pelkman
authors.forename: Tracy
authors.initials: T
authors.lastname: Perry
authors.forename: Andreas F H
authors.initials: AF
authors.lastname: Pfeiffer
authors.forename: Marlien
authors.initials: M
authors.lastname: Pieters
authors.forename: D Dan
authors.initials: DD
authors.lastname: Ramdath
authors.forename: Rayna T
authors.initials: RT
authors.lastname: Ramsingh
authors.forename: S Daniel
authors.initials: SD
authors.lastname: Robert
authors.forename: Carol
authors.initials: C
authors.lastname: Robinson
authors.forename: Essi
authors.initials: E
authors.lastname: Sarkkinen
authors.forename: Francesca
authors.initials: F
authors.lastname: Scazzina
authors.forename: Dave Clark D
authors.initials: DC
authors.lastname: Sison
authors.forename: Birgitte
authors.initials: B
authors.lastname: Sloth
authors.forename: Jane
authors.initials: J
authors.lastname: Staniforth
authors.forename: Niina
authors.initials: N
authors.lastname: Tapola
authors.forename: Liisa M
authors.initials: LM
authors.lastname: Valsta
authors.forename: Inge
authors.initials: I
authors.lastname: Verkooijen
authors.forename: Martin O
authors.initials: MO
authors.lastname: Weickert
authors.forename: Antje R
authors.initials: AR
authors.lastname: Weseler
authors.forename: Paul
authors.initials: P
authors.lastname: Wilkie
authors.forename: Jian
authors.initials: J
authors.lastname: Zhang
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D019540:Area Under Curve; D001786:Blood Glucose / Q000378:metabolism; D019411:Clinical Laboratory Techniques / Q000592:standards*; D018592:Cross-Over Studies; D004040:Dietary Carbohydrates / Q000378:metabolism*; D005260:Female; D005502:Food / Q000145:classification*; D005504:Food Analysis / Q000592:standards*; D005951:Glucose Tolerance Test; D038321:Glycemic Index; D006801:Humans; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D001786:Blood Glucose; D004040:Dietary Carbohydrates