The glycaemic index

The glycaemic index (GI) of a foodstuff or a food component is defined as the ratio, expressed as a percentage, of the area under the blood glucose time plot to that produced by consuming a standard glucose drink containing 50g of anhydrous glucose.

Individuals respond differently to both glucose and foodstuffs. To minimise the impact of such differences the GI is stated as the average of ten measurements.

Another way of looking at the index is to say that the glucose response is set at 100 and the GI of foodstuffs is expressed as a number, which is usually less than 100.      

Foods or food components are classed as follows according to their GI:

  • 0 to 55: low GI
  • 56 to 69: medium GI
  • 70 or higher: high GI

There is evidence that low-GI diets may be beneficial for people with certain medical conditions, such as:

  • Diabetes
  • Heart disease
  • Obesity
  • Metabolic syndrome

You can read more below.

Diabetes
There is an emerging body of evidence that low-GI diets lead to improved glycaemic control in both type 1 and type 2 diabetes.

Examples of research
Brand-Miller JC, Petocz P, Colagiuri S. Meta analysis of low glycaemic index diets in the management of diabetes; response to Franz. Diabetes Care  2003; 26: 3363-3364.

Rizkalla SW, Bellisle F, Siama G. Health benefits of low glycaemic index foods, such as pulses, in diabetic patients and healthy individuals. Br J Nutr 2002; 88 (suppl 3): S255-262.

Schultze MB, Liu S, Rimm EB et al. Glycaemic index, glycaemic load and dietary fibre intake and incidence of type 2 diabetes in younger and middle aged women. Am J Clin Nutr 2004; 80: 348-356.

Heart disease
There is strong epidemiological evidence and data from randomised controlled trials that demonstrate that low-GI diets have a positive effect on a number of cardiovascular risk factors.

Examples of research
Brand-Miller JC. Glycaemic index in relation to coronary disease. Asia Pac J Clin Nutr 2004; 13: S3.

Rizkalla SW, Bellisle F, Siama G. Health benefits of low glycaemic index foods, such as pulses, in diabetic patients and healthy individuals. Br J Nutr 2002; 88 (suppl 3): S255-262.

Patel VC, Aldridge RD, Leeds A et al. Retrospective analysis of the impact of low glycaemic index diet on hospital stay following coronary artery bypass grafting; a hypothesis. J Hum Nutr Diet 2004; 17: 241-247.

Leeds AR. Glycaemic index and heart disease. Am J Clin Nutr 2002; 76: 286S-289S.

Liu S, Willett WC, Stampfer MJ et al. A prospective study of dietary glycaemic load, carbohydrate intake and risk of coronary heart disease in US women. Am J Clin Nutr 2000; 71: 1455-1461.

Frost G, Leeds AA, Dore CJ et al. Glycaemic index as a determinant of serum HDL-cholesterol concentration. Lancet 1999; 27: 1045-1048.

Obesity
There is a growing body of evidence that demonstrates a relationship between low-GI diets and both appetite regulation and changes in body composition.

Examples of research
Young PC, West SA, Ortiz K et al. A pilot study to determine the feasibility of the low glycaemic index diet as a treatment for overweight children in primary care practice. Ambul Paediatr 2004; 4: 28-33.