Measuring the glycemic index and insulin index of dairy products

At the moment GI is one of the main targets of nutritional research to explain
its role in the rising levels of obesity. Since fat intake has probably
decreased over the last couple of years while prevalence of obesity did not,
the focus of research has been changed towards the carbohydrate intake and in
particular high GI carbohydrates like sugar. Readily digestible carbohydrates
give higher postprandial blood glucose and insulin concentrations than do less
digestible carbohydrates. McCarron et al (1984) pointed for the first time on
the inverse relation between dairy intake and more in particular calcium intake
and body weight. Dairy products have a very low GI and except for cheese, all
diary products have shown potent insulinotropic properties [6]. The
International table of glycemic index from Foster and Powell et al (2002)
included analyses of dairy products. However the GI of some common used Dutch
dairy products is missing and also the II is nog measured in these products.
Before setting up experimental studies with different GI and II diets,
inclusive dairy products, it is necessary to analyze some typical Dutch dairy
product on GI and II.

The presently proposed study aims to investigate the effects of different dairy
products, which are frequently used in the Netherlands and not yet analyzed, on
Glycemic Index and Insulin Index in humans. This will be investigated by
analyzing postprandial venous blood samples for glucose and insulin
concentrations.

Different dairy products will be selected and given in the fasted state to the
subjects. Subjects will come to the testing laboratory in the morning, after
10- to 14-hour overnight fasts, and consume in random order four of the test
meals.
The GI and II of these foods will be determined according to standard and
accepted protocols. To calculate the GI and II the test foods will provide the
same amount of available carbohydrates (25 gram). For each test, subjects will
come to the university in a fasting state, which means that they will receive
instructions not to eat from 22:00 the evening before, while only water or tea
will be allowed in the morning before blood sampling. At arrival, an indwelling
cannula will be inserted into an anticubital vein for the withdrawal of blood
samples. Blood (5 mL) will be sampled immediately before ingestion of the
experimental meal (0 min), and 15, 30, 45, 60, 90 and 120 postprandially.
Samples will be coded and will be destroyed after publication of the results.
Maximum storage however will be five years. Only the main investigators (MJMM
and WHMS) have access to the code. Samples from one subject will be analyzed
for glucose and insulin within one run at the end of the study under strict
quality control. Plasma will be obtained by low-speed centrifugation within one
hour after venipuncture and stored as appropriate.

The GI of some Dutch dairy products was missing; therefore 8 Dutch dairy
products will be analyzed in this study. Experimental products that will be
tested are dairy products including semi-skimmed milk, buttermilk, soft curd
cheese, custard, breakfast drink, yogurt drink, and dairy drink. As reference,
a glucose solution will be used. Each person consumes 4 times a dairy product
and 2 times the glucose drink at the 6 test days.

The dairy products are obtained from the convenience store, therefore totally
safe. Also a hematomme could occur after taken the blood-samples.