Measuring the glycemic index of foods: interlaboratory study.
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.
Wolever
Thomas M S
TM
Department of Nutritional Sciences, University of Toronto and Glycemic Index Laboratories, Inc, Toronto, Ontario, Canada. thomas.wolever@utoronto.ca
Brand-Miller
Jennie C
JC
Abernethy
John
J
Astrup
Arne
A
Atkinson
Fiona
F
Axelsen
Mette
M
Björck
Inger
I
Brighenti
Furio
F
Brown
Rachel
R
Brynes
Audrey
A
Casiraghi
M Cristina
MC
Cazaubiel
Murielle
M
Dahlqvist
Linda
L
Delport
Elizabeth
E
Denyer
Gareth S
GS
Erba
Daniela
D
Frost
Gary
G
Granfeldt
Yvonne
Y
Hampton
Shelagh
S
Hart
Valerie A
VA
Hätönen
Katja A
KA
Henry
C Jeya
CJ
Hertzler
Steve
S
Hull
Sarah
S
Jerling
Johann
J
Johnston
Kelly L
KL
Lightowler
Helen
H
Mann
Neil
N
Morgan
Linda
L
Panlasigui
Leonora N
LN
Pelkman
Christine
C
Perry
Tracy
T
Pfeiffer
Andreas F H
AF
Pieters
Marlien
M
Ramdath
D Dan
DD
Ramsingh
Rayna T
RT
Robert
S Daniel
SD
Robinson
Carol
C
Sarkkinen
Essi
E
Scazzina
Francesca
F
Sison
Dave Clark D
DC
Sloth
Birgitte
B
Staniforth
Jane
J
Tapola
Niina
N
Valsta
Liisa M
LM
Verkooijen
Inge
I
Weickert
Martin O
MO
Weseler
Antje R
AR
Wilkie
Paul
P
Zhang
Jian
J
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
D001786:Blood Glucose; D004040:Dietary Carbohydrates