Measuring the glycemic index of foods: interlaboratory study
Thomas M S Wolever, Jennie C Brand-Miller, John Abernethy, Arne Astrup, Fiona Atkinson, Mette Axelsen, Inger Björck, Furio Brighenti, Rachel Brown, Audrey Brynes, M Cristina Casiraghi, Murielle Cazaubiel, Linda Dahlqvist, Elizabeth Delport, Gareth S Denyer, Daniela Erba, Gary Frost, Yvonne Granfeldt, Shelagh Hampton, Valerie A Hart, Katja A Hätönen, C Jeya Henry, Steve Hertzler, Sarah Hull, Johann Jerling, Kelly L Johnston, Helen Lightowler, Neil Mann, Linda Morgan, Leonora N Panlasigui, Christine Pelkman, Tracy Perry, Andreas F H Pfeiffer, Marlien Pieters, D Dan Ramdath, Rayna T Ramsingh, S Daniel Robert, Carol Robinson, Essi Sarkkinen, Francesca Scazzina, Dave Clark D Sison, Birgitte Sloth, Jane Staniforth, Niina Tapola, Liisa M Valsta, Inge Verkooijen, Martin O Weickert, Antje R Weseler, Paul Wilkie, Jian Zhang, Thomas M S Wolever, Jennie C Brand-Miller, John Abernethy, Arne Astrup, Fiona Atkinson, Mette Axelsen, Inger Björck, Furio Brighenti, Rachel Brown, Audrey Brynes, M Cristina Casiraghi, Murielle Cazaubiel, Linda Dahlqvist, Elizabeth Delport, Gareth S Denyer, Daniela Erba, Gary Frost, Yvonne Granfeldt, Shelagh Hampton, Valerie A Hart, Katja A Hätönen, C Jeya Henry, Steve Hertzler, Sarah Hull, Johann Jerling, Kelly L Johnston, Helen Lightowler, Neil Mann, Linda Morgan, Leonora N Panlasigui, Christine Pelkman, Tracy Perry, Andreas F H Pfeiffer, Marlien Pieters, D Dan Ramdath, Rayna T Ramsingh, S Daniel Robert, Carol Robinson, Essi Sarkkinen, Francesca Scazzina, Dave Clark D Sison, Birgitte Sloth, Jane Staniforth, Niina Tapola, Liisa M Valsta, Inge Verkooijen, Martin O Weickert, Antje R Weseler, Paul Wilkie, Jian Zhang
Abstract
Background: Many laboratories offer glycemic index (GI) services.
Objective: We assessed the performance of the method used to measure GI.
Design: 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.
Source: PubMed