Consumers and Health

ISO 26642:2010: a scientific and legal guide to the glycaemic index

September 11, 2025

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ISO 26642:2010 provides a standardised methodology for glycaemic index testing and recommends criteria for classifying foods into low, medium, and high GI categories.

This international standard, developed in collaboration with the FAO and WHO (Flavel et al., 2021), is the definitive reference for food manufacturers, researchers, and regulatory bodies.

Beyond its scientific application, this article uniquely clarifies the EU regulatory framework for GI labelling, arguing that the mere mention of a food’s GI value is neither a nutrition nor a health claim.

What is Glycaemic Index?

The glycaemic index (GI) is a scale from 0 to 100 that indicates how quickly a carbohydrate-containing food raises blood glucose levels. Pure glucose is set at 100 and used as the reference point. GI is calculated by measuring the incremental area under the two-hour blood glucose response curve (Area Under the Curve, AUC) after a 12-hour fast and ingestion of a fixed amount of available carbohydrate (usually 50 g).

In simple terms, foods with a low GI release carbohydrates slowly, helping to maintain steady blood sugar and prolong satiety, while high-GI foods are absorbed more quickly, leading to sharper rises in blood glucose. Understanding GI can therefore guide healthier food choices, support dietary planning, and play a crucial role in medical nutrition therapy, particularly for individuals managing diabetes or seeking improved metabolic health.

What is Glycaemic Load?

While the glycaemic index (GI) measures how quickly the carbohydrates in a food raise blood glucose, it does not account for the amount of carbohydrates in a typical serving. Glycaemic load (GL) addresses this limitation by combining the GI with the available carbohydrate content per portion, providing a more practical estimate of a food’s overall impact on blood sugar. It is calculated as:

GL = (GI × available carbohydrate (g)) ÷ 100

GL values are generally classified as low (10 or less), medium (11–19), or high (20 or more). Unlike GI, which reflects the quality of carbohydrates, GL reflects both quality and quantity, offering a more realistic measure of a food’s total glycaemic effect and making it particularly useful for dietary planning and nutritional assessment.

Glycaemic index classification system

According to ISO 26642:2010 and established scientific literature, foods are classified into three distinct categories based on their glycaemic index values:

Low GI foods (≤55)

Low glycaemic index foods (GI ≤55) play an important role in a low GI diet designed to support blood sugar control and reduce postprandial glucose spikes. This category includes most fruits, vegetables, legumes, minimally processed whole grains, dairy products, and pasta.

Such foods are rich in healthy carbohydrates that provide a slow and steady release of energy, contributing to improved satiety and better long-term metabolic health. Consistent research shows that these foods maintain low GI values across different populations and regions (Atkinson & Brand-Miller, 2021).

Medium GI foods (56-69)

Foods with a medium glycaemic index (GI 56–69) include whole grain breads, brown rice, and certain types of breakfast cereals.

These foods cause a moderate rise in blood glucose levels, making them suitable for balanced diets when consumed in appropriate portions.

They can serve as a useful middle ground between low-GI foods that provide sustained energy release and high-GI foods that lead to quicker glucose spikes.

High GI foods (≥70)

Foods with a high glycaemic index (GI ≥70) typically include refined carbohydrates such as white bread and many processed products. Most varieties of potato also fall into the high-GI category, although some lower-GI varieties have recently been identified (Atkinson & Brand-Miller, 2021).

These foods cause a rapid rise in blood glucose levels, which can be useful for quick energy replenishment after intense physical activity but are generally less desirable for long-term glycaemic control.

For this reason, dietary guidelines often recommend limiting their frequent consumption in favour of lower-GI alternatives.

Detailed methodology for measuring glycaemic index

Participant requirements

The average glycaemic index (GI) value is derived from data obtained in at least 10 human subjects. Typically, enrolling a minimum of 15 eligible healthy participants per laboratory allows for a reduction of the margin of error associated with each estimate by 95% (Wolever et al., 2019). Therefore, participants who withdraw prematurely are replaced to ensure that at least 15 evaluable subjects complete the trial.

The standard requires participants to:

be healthy individuals without diabetes or glucose intolerance;

fast for 12 hours prior to testing;

avoid strenuous physical activity before the test;

maintain consistent dietary patterns leading up to the study.

Reference food standards

Section 5.4.1 of the ISO:2010 standard states ‘The acceptable reference foods shall be as follows:

anhydrous glucose powder (50 g);

dextrose (glucose monohydrate, 55 g); and

commercial solution used for the oral glucose tolerance test (OGTT) containing glucose (50 g)’ (Flavel et al., 2021).

The current validated methods use glucose as the reference food, giving it a glycemic index value of 100 by definition. Alternative reference standards include white bread, though this requires conversion to glucose equivalents for final reporting.

Testing protocol and blood sampling

The ISO 26642:2010 methodology follows a rigorous protocol:

Pre-test preparation: participants fast for 12 hours and avoid alcohol, caffeine, and strenuous exercise;

Baseline measurement: fasting blood glucose is measured before food consumption;

Food administration: test food containing 50g of available carbohydrate is consumed within 10-15 minutes;

Blood sampling schedule: blood glucose response curve (AUC) following a 12-hour fast and ingestion of a food with a certain quantity of available carbohydrate (usually 50 g) is monitored over 2 hours, with samples typically taken at 15, 30, 45, 60, 90, and 120 minutes;

Reference testing: each participant consumes the reference food (glucose) on separate occasions under identical conditions.

Calculation methodology

The Area Under the Curve (AUC) of the test food is divided by the AUC of the standard (either glucose or white bread, giving two different definitions) and multiplied by 100.

The final glycaemic index value represents the mean response across all participants, providing a standardised measure that can be compared across different foods and laboratories.

Quality assurance and variability considerations

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 in relation to the international standard for critical aspects of GI testing methodology (Flavel et al., 2021).

The ISO 26642:2010 protocol employs an in vivo test that requires the participation of multiple volunteers and is inherently time-intensive (Li et al., 2022). Furthermore, the requirement for ethical approval may represent an additional constraint, limiting its feasibility for rapid, iterative testing of foods during the developmental phase.

Applications and significance

Nutritional and clinical applications

The glycaemic index serves as a fundamental tool in evidence-based nutrition practice and clinical interventions, with extensive applications across multiple wellness and healthcare domains:

weight management strategies. The glycaemic index plays a crucial role in appetite regulation and satiety mechanisms (Bornet et al., 2007). Low-GI foods have been associated with prolonged satiation, reduced subsequent food intake, and improved weight loss maintenance. The sustained release of glucose from low-GI carbohydrates helps prevent rapid blood glucose fluctuations that can trigger hunger signals and promote overeating behaviours. A systematic review and meta-analysis found that low-GI diets resulted in small but significant improvements in body weight, with studies achieving a difference in GI of 20 points or more resulting in larger reductions in body weight (Zafar et al., 2019). The PREVIEW study, a large-scale randomised trial, demonstrated that a high-protein, low-GI diet was superior in preventing increases in hunger during 3-year weight loss maintenance compared with a moderate-protein, moderate-GI diet (Christensen et al., 2021). Clinical trials have demonstrated the efficacy of low-GI interventions in supporting sustainable weight reduction and preventing weight regain;

diabetes mellitus management. The glycaemic index provides critical guidance for individuals with type 1 and type 2 diabetes in selecting carbohydrate foods that promote optimal blood glucose control (Brand-Miller et al., 2003). Low-GI foods have been demonstrated to improve glycated haemoglobin levels, reduce postprandial glucose excursions, and enhance insulin sensitivity in systematic reviews and meta-analyses of randomised controlled trials (Zafar et al., 2019). Healthcare professionals utilise GI values to develop personalised meal plans that support long-term diabetes management whilst maintaining dietary variety and palatability. A comprehensive meta-analysis of intervention studies found that low-GI diets were effective at reducing glycated haemoglobin (HbA1c), fasting glucose, BMI, total cholesterol, and LDL cholesterol in individuals with diabetes and prediabetes (Zafar et al., 2019);

cardiovascular disease prevention. Prospective cohort studies have established significant associations between high-GI diets and increased risk of cardiovascular disease mortality (Dwivedi et al., 2022). Low-GI dietary patterns contribute to improved lipid profiles, reduced inflammation markers, and enhanced endothelial function. The mechanism involves the modulation of postprandial glucose responses, which influence HDL-cholesterol concentrations, triglyceride levels, and oxidative stress parameters. Meta-analyses of observational studies have demonstrated that high dietary glycaemic load is associated with an overall 23% increase in risk of stroke and a specific 35% increase in risk of ischaemic stroke (Ma et al., 2012). A systematic review and meta-analysis of prospective cohorts found an 11% increased relative risk of coronary heart disease for the highest versus lowest quantile of GI and a 27% increased relative risk for glycaemic load, with effects predominantly observed in women (Mirrahimi et al., 2012);

sports nutrition and performance optimisation. Athletic performance and recovery strategies increasingly incorporate glycaemic index principles to optimise carbohydrate utilisation (O’Reilly et al., 2010). Sports nutritionists utilise GI classifications to develop periodised nutrition strategies that align carbohydrate intake with training demands and competition schedules. Evidence suggests that the glycaemic index may be more beneficial for longer-term dietary strategies rather than acute pre-exercise interventions (Moitzi & König, 2023). At the biochemical level, research consistently shows that choosing foods with different glycaemic index (GI) values can influence how the body breaks down fat, the levels of free fatty acids in the blood, and how the body uses fat and carbohydrates for energy during exercise (Mondazzi & Arcelli, 2009).

Food industry applications

Food manufacturers rely on ISO 26642:2010, which provides a validated methodology for determining and labelling low-GI foods (Li et al., 2022), to:

develop healthier formulations and processes with verified glycaemic properties;

ensure accurate information on food labels;

comply with regulatory requirements;

facilitate standardized, comparable nutritional research.

Research and development

The availability of new data on the GIs of foods will facilitate wider research and application of the twin concepts of GI and GL. Although the 2021 edition of the tables improves the quality and quantity of GI data available for research and clinical practice, GI testing of regional foods remains a priority (Atkinson & Brand-Miller, 2021).

Limitations and considerations

Individual variability

Glycaemic responses vary between individuals and can also fluctuate within the same person from day to day, influenced by factors such as fasting blood glucose, insulin sensitivity, and metabolic status. Consequently, glycaemic index values reflect population averages rather than precise predictions of an individual’s response. In practice, this means that while GI can guide healthy carbohydrate choices and blood sugar management, individual responses may differ, highlighting the importance of personalised dietary adjustments.

Methodological factors

Glycaemic index (GI) tables, providing values for a wide range of foods, are readily available (see the following paragraph). However, numerous intrinsic and extrinsic factors can significantly influence glycaemic index values and must be considered when interpreting GI data:

food processing and manufacturing variables. Industrial processing techniques fundamentally alter carbohydrate structure and accessibility. Mechanical processing, such as grinding or milling, increases surface area for enzymatic digestion, generally raising GI values. Similarly, thermal treatments, including extrusion and high-temperature cooking, gelatinise starch, also increasing its digestibility and consequently the GI. Conversely, certain processing techniques, such as parboiling in rice or sourdough fermentation in bread, can create resistant starch formations that lower glycaemic responses;

culinary preparation methods. Cooking techniques and duration exert a profound effect on carbohydrate bioavailability. Extended cooking times generally increase starch gelatinisation and reduce food structure integrity, leading to higher GI values. The degree of mechanical breakdown during preparation, cooking temperature profiles, and moisture content during heating all influence the final glycaemic response. For example, cooking pasta ‘al dente’ or other starchy foods until just firm preserves the starch structure, leading to lower GI values compared with extensively cooked, softer products;

botanical and maturation factors. Natural variation in carbohydrate composition occurs throughout plant maturation processes. Fruit ripeness represents a critical determinant, as enzymatic conversion of complex carbohydrates to simple sugars during ripening substantially increases glycaemic index values. Seasonal variations, cultivar differences, and growing conditions can introduce significant variability even within identical food varieties;

food matrix interactions and meal context. The presence of co-consumed nutrients significantly modulates glycaemic responses through various physiological mechanisms. Dietary fibre content can physically entrap carbohydrates and slow digestion, whilst protein and fat components delay gastric emptying and alter absorption kinetics. Mixed meal consumption typically produces lower glycaemic responses than isolated carbohydrate consumption due to these synergistic effects;

storage and post-harvest conditions. Post-harvest storage conditions, including temperature, humidity, and duration, can alter carbohydrate structure through enzymatic activity and physical changes. Starch retrogradation during storage can form resistant starch, potentially lowering GI values, whilst prolonged storage may lead to structural breakdown that increases glycaemic responses.

Current status and future developments

The fourth edition of the International Tables of Glycemic Index and Glycemic Load Values was compiled by Atkinson and Brand-Miller from the University of Sydney, Australia, along with international collaborators Foster-Powell (Australia), Buyken (Germany), and Goletzke (Germany) and published as a systematic review in The American Journal of Clinical Nutrition in 2021. The tables are freely available to all readers regardless of subscription status as supplemental materials through the journal’s online platform.

This edition of the tables lists over 4000 items, a 61% increase in the number of entries compared to the 2008 edition. The data have been separated into two lists based on methodological quality and adherence to ISO 26642:2010 standards. The first list (Supplemental Table 1) provides the most reliable glycaemic index values, as it is based on the methodology recommended by the International Organization for Standardization (ISO) and includes approximately 2,100 food items. In contrast, the second list (Supplemental Table 2) reports values obtained through less robust approaches, such as studies with small sample sizes or large standard errors of the mean (SEM), covering about 1,900 food items (Atkinson & Brand-Miller, 2021). For research and dietary applications, Supplemental Table 1 should be considered the definitive reference.

The comprehensive data compilation spans 12 years of research since the last major update, during which time the number of scientific publications including ‘glycemic index’ or ‘glycaemic index’ in the title, abstract, or keywords has tripled from approximately 2500 to approximately 7500 studies. The continuous expansion of glycaemic index databases reflects the growing importance of this nutritional tool in public health, clinical practice, and food technology. Ongoing research focuses on improving testing methodologies, understanding individual variability, and developing more personalised approaches to dietary recommendations based on glycaemic response.

EU regulatory framework for glycaemic index labelling

Within the European Union, the glycaemic index (GI) of a food, when indicated on labels or in advertising, cannot be classified either as a nutrition claim or as a health claim, for the reasons explained below.

Exclusion from nutrition claims

Nutrition and Health Claims Regulation (EC) No 1924/06, NHCR, defines a nutrition claim as: ‘any indication that states, suggests or implies that a food has particular beneficial nutritional properties, due to:

a) to the energy (caloric value) that it contributes, contributes at a reduced or increased rate, or does not contribute, and/or

b) to nutrients or other substances it contains, contains in reduced or increased proportions, or does not contain‘ (Article 2.2.4).

The glycaemic index, which simply indicates the rate at which a food’s carbohydrates are absorbed, does not concern its energy value or nutrient content. It therefore cannot be classified as a nutrition claim under EU law.

Exclusion from health claims

The same European Regulation defines a health claim as:

‘any indication that affirms, suggests or implies the existence of a relationship between a food category, a food or one of its components and health‘(Article 2.2.5).

The mere indication of a food’s glycaemic index, in the absence of any suggestion of nutritional or health benefit, cannot be qualified as a health claim either.

As a result, the indication of a food’s glycaemic index is neither a nutrition nor a health claim. While not prohibited, it is not expressly regulated, leaving a regulatory gap.

Beyond claims: legal clarity and scientific standards

Certain interpretations – most notably those put forward by former European Commissioner Vytenis Andriukaitis (2019) – wrongly suggested that GI indications could fall within the scope of nutrition and health claims, despite offering no supporting legal rationale. Such positions are not only devoid of any official authority but also risk creating regulatory confusion, whereas the binding definitions of Regulation (EC) No 1924/2006 provide unambiguous clarity on the matter.

In the author’s view, food business operators who wish to indicate the GI of a product on labels or in advertising, in full compliance with Food Information Regulation (EU) No 1169/11 and to ensure responsible communication, must observe the following conditions:

duty to measure. The GI must be determined for the specific food item each time it is communicated, using the internationally recognised methodology set out in ISO 26642:2010. This is particularly important because GI can vary widely within the same food category depending on factors such as variety, processing, and preparation;

prohibition on health claims. Operators are strictly prohibited from implying, directly or indirectly, that the GI value itself confers any nutritional or health benefit, as this would constitute a health claim subject to the authorisation requirements of Regulation (EC) No 1924/2006.

Conclusion

ISO 26642:2010 represents the gold standard for glycaemic index determination, providing a scientifically robust methodology that enables consistent, reproducible measurements across laboratories worldwide.

This standard continues to play a crucial role in advancing nutritional science, supporting evidence-based dietary recommendations, and facilitating the development of healthier food products.

Understanding and implementing this methodology correctly is essential for researchers, healthcare professionals, and food industry stakeholders working to improve public health through better nutritional choices.

Dario Dongo

References

Atkinson, F. S., & Brand-Miller, J. C. (2021). International tables of glycemic index and glycemic load values 2021: A systematic review. The American Journal of Clinical Nutrition, 114(5), 1625-1632. https://doi.org/10.1093/ajcn/nqab233

Bornet, F. R. J., Jardy-Gennetier, A. E., Jacquet, N., & Stowell, J. (2007). Glycaemic response to foods: Impact on satiety and long-term weight regulation. Appetite, 49(3), 535-553. https://doi.org/10.1016/j.appet.2007.04.006

Brand-Miller, J., Hayne, S., Petocz, P., & Colagiuri, S. (2003). Low-glycemic index diets in the management of diabetes: A meta-analysis of randomized controlled trials. Diabetes Care, 26(8), 2261-2267. https://doi.org/10.2337/diacare.26.8.2261

Christensen, P., Henriksen, M., Bartels, E. M., Leeds, A. R., Emery, P., Sandbaek, A., Raben, A., & Astrup, A. (2021). A high-protein, low glycemic index diet suppresses hunger but not weight regain after weight loss: Results from a large, 3-years randomized trial (PREVIEW). Frontiers in Nutrition, 8, 685648. https://doi.org/10.3389/fnut.2021.685648

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Flavel, M., Jois, M., & Kitchen, B. (2021). Potential contributions of the methodology to the variability of glycaemic index of foods. World Journal of Diabetes, 12(2), 108-123. https://doi.org/10.4239/wjd.v12.i2.108

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Li, H., Dhital, S., Gidley, M. J., & Gilbert, R. G. (2022). A review of in vitro methods for measuring the glycemic index of single foods: Understanding the interaction of mass transfer and reaction engineering by dimensional analysis. Processes, 10(4), 759. https://doi.org/10.3390/pr10040759

Ma, X. Y., Liu, J. P., & Song, Z. Y. (2012). Glycemic load, glycemic index and risk of cardiovascular diseases: Meta-analyses of prospective studies. Atherosclerosis, 223(2), 491-496. https://doi.org/10.1016/j.atherosclerosis.2012.05.028

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Zafar, M. I., Mills, K. E., Zheng, J., Regmi, A., Hu, S. Q., Gou, L., & Chen, L. L. (2019). Low-glycemic index diets as an intervention for obesity: A systematic review and meta-analysis. Obesity Reviews, 20(2), 290-315. https://doi.org/10.1111/obr.12791