ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.

The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote.

Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights.

ISO 26642 was prepared by Technical Committee ISO/TC 34, Food products.

The development of this International Standard originated from a recognized need to standardize the determination of glycaemic index (GI) of foods for practice and research purposes, particularly with its increasing use as a nutrition claim, illustrating the importance of GI within human nutrition.

The objective of this International Standard is to establish the recognized scientific method as the standard method for the determination of the GI of foods.

This International Standard is intended for use by:

This International Standard is based on a Joint FAO/WHO Expert Consultation, Carbohydrates in human nutrition (Reference [6]).

Additional recommendations have been taken from References [1] to [3].

The GI is a property of the carbohydrates in different foods, specifically the blood glucose-raising ability of the digestible carbohydrates. It compares carbohydrates on a mass for mass basis in single foods or food items, in the physical state in which they are normally consumed (Reference [1]). Low GI foods are those containing carbohydrates that have less impact on blood glucose levels, because their digestion and absorption is slowed or because the sugars present (e.g. fructose, lactose) are inherently less glycaemic. When combined in actual meals, low GI foods produce less fluctuation in blood glucose and insulin levels than high GI foods. The clinical and practical value of the GI continues to be studied and there is growing consensus that there are benefits to health when low GI foods replace high GI foods in a balanced diet (Reference [2]).

Historically, not all GI values on food labels have been reliable (Reference [4]). Some claims have been based on extrapolation or inappropriate methodology. While a digestibility or hydrolysis index can be obtained by in vitro methods of assessing the rate of carbohydrate digestion (Reference [5]), the results should not be referred to as GI values. The method set out in this International Standard should be applied to ensure that GI values are determined by recognized methodology.

GI testing is appropriate only when the food in question contributes physiologically relevant amounts of digestible carbohydrate to a meal or diet. For the purposes of this International Standard, the minimum amount is specified as 10 g or more of glycaemic carbohydrate per serving. Low-digestibility or non-digestible carbohydrates (resistant starch, some sugar alcohols, polydextrose, etc.) are not to be intentionally counted in the specified carbohydrate portion (50 g or 25 g) used in GI testing.

Small amounts of resistant starch may be inadvertently included because the methods of assay of starch are not yet adequate to clearly differentiate between digestible and non-digestible starch. Foods containing large amounts of low-digestibility carbohydrates or resistant starch are not suitable for GI testing if the amounts consumed during the test are likely to provoke gastrointestinal discomfort.

Caution should be exercised with foods containing significant amounts of low-digestibility carbohydrates. By definition, a low GI food contains glycaemic carbohydrate, i.e. “providing carbohydrate for metabolism” (Reference [6]). Distinguishing between low-GI carbohydrate-containing foods and sources of low-digestibility carbohydrate or low carbohydrate content is important.