Review
Copyright ©The Author(s) 2021. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Diabetes. Feb 15, 2021; 12(2): 108-123
Published online Feb 15, 2021. doi: 10.4239/wjd.v12.i2.108
Potential contributions of the methodology to the variability of glycaemic index of foods
Matthew Flavel, Markandeya Jois, Barry Kitchen
Matthew Flavel, Barry Kitchen, Bioactive Division, The Product Makers, Keysborough 3173, Victoria, Australia
Matthew Flavel, Markandeya Jois, Barry Kitchen, School of Life Sciences, La Trobe University, Bundoora 3086, Australia
Author contributions: Flavel M searched the literature and drafted initial manuscript; Kitchen B and Jois M provided further editing and comments.
Conflict-of-interest statement: Flavel M and Kitchen B are both employees of The Product Makers Pty. Ltd., the manufacturer of patented glycaemic index lowering plant extracts.
Open-Access: This article is an open-access article that was selected by an in-house editor and fully peer-reviewed by external reviewers. It is distributed in accordance with the Creative Commons Attribution NonCommercial (CC BY-NC 4.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/Licenses/by-nc/4.0/
Corresponding author: Matthew Flavel, PhD, Honorary Research Fellow, Bioactive Division, The Product Makers, 50-60 Popes Road, Keysborough 3173, Victoria, Australia. mflavel@tpm.com.au
Received: October 28, 2020
Peer-review started: October 28, 2020
First decision: November 16, 2020
Revised: December 3, 2020
Accepted: December 23, 2020
Article in press: December 23, 2020
Published online: February 15, 2021
Abstract

Glycaemic index (GI) testing provides a useful point of comparison between carbohydrate sources. For this comparison to be meaningful, the methods used to determine GI values need to be rigorous and consistent between testing events. This requirement has led to increasing standardization of the GI methodology, with an international standard developed in joint consultation with FAO/WHO (ISO 26642:2010) currently the most up to date document. The purpose of this review is to compare the international standard to methods of published studies claiming to have performed a GI test. This analysis revealed that the international standard permits a wide range of choices for researchers when designing a GI testing plan, rather than a single standardized protocol. It has also been revealed that the literature contains significant variation, both between studies and from the international standard for critical aspects of GI testing methodology. The primary areas of variation include; what glucose specification is used, which reference food is used, how much reference food is given, what drink is given during testing, the blood sampling site chosen and what assay and equipment is used to measure blood glucose concentration. For each of these aspects we have explored some of the methodological and physiological implications of these variations. These insights suggest that whilst the international standard has assisted with framing the general parameters of GI testing, further stan-dardization to testing procedures is still required to ensure the continued relevance of the GI to clinical nutrition.

Keywords: Glycaemic index, Blood glucose, Nutritional guidelines, Food classifications, ISO 26642:2010

Core Tip: This review highlights major areas of variation that are currently permitted under the international glycaemic index (GI) testing standard and explores the significant influence these choices may have on the final GI value attributed to a food. This review also reports a summary of the range of choices researchers have made across a large set of published GI papers.