Determination of the glycaemic index of foods: interlaboratory study

Abstract

Objective: Practical use of the glycaemic index (GI), as recommended by the FAO=WHO, requires an evaluation of the recommended method. Our purpose was to determine the magnitude and sources of variation of the GI values obtained by experienced investigators in different international centres. Design: GI values of four centrally provided foods (instant potato, rice, spaghetti and barley) and locally obtained white bread were determined in 8 -12 subjects in each of seven centres using the method recommended by FAO=WHO. Data analysis was performed centrally. Setting: University departments of nutrition. Subjects: Healthy subjects (28 male, 40 female) were studied. Results: The GI values of the five foods did not vary significantly in different centres nor was there a significant centre  food interaction. Within-subject variation from two centres using venous blood was twice that from five centres using capillary blood. The s.d. of centre mean GI values was reduced from 10.6 (range 6.8 -12.8) to 9.0 (range 4.8 -12.6) by excluding venous blood data. GI values were not significantly related to differences in method of glucose measurement or subject characteristics (age, sex, BMI, ethnicity or absolute glycaemic response). GI values for locally obtained bread were no more variable than those for centrally provided foods. Conclusions:The GI values of foods are more precisely determined using capillary than venous blood sampling, with mean between-laboratory s.d. of approximately 9.0. Finding ways to reduce within-subject variation of glycaemic responses may be the most effective strategy to improve the precision of measurement of GI values.

Are the glycemic and insulinemic index values of carbohydrate foods similar in healthy control, hyperinsulinemic and type 2 diabetic patients?

“…The sample size was determined based on previous studies , Wolever, 2003, with a power of 80% and Po0.05. The AUC for glucose, insulin, C-peptide and GLP-1 were calculated using the trapezoid rule (Wolever et al, 1991).…”

Effect of breakfast glycemic index on metabolic responses during rest and exercise in overweight and non-overweight adolescent girls

“…Capillary rather than venous blood sampling is preferred for reliable GI testing (Wolever et al, 2003). Duplicate 25-ml aliquots of whole blood was deproteinised in 250 ml of ice cooled perchloric acid (2.5%), centrifuged for 4 min at 2415 Â g and stored at À20 1C for blood glucose analysis.…”

Effects of two different types of fast food on postprandial metabolism in normal and overweight subjects

“…It has also been reported that there is quite a substantial inter-laboratory difference in GI estimates (for example, 30 GI unit difference between rice and spaghetti), showing methodological difficulties in the measurement of GI and in turn potentionally leading to erroneous food table data. [42][43][44] Our study shows that the effects of different meals on postprandial glucose metabolism can be considerably different despite a similar energy, carbohydrate, protein and fat contents of the meals and thus a conscious choice might help to control postprandial blood glucose and blood insulin.…”