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Sugars, starches and the glycaemic index

A group of people consumed two test meals, each containing the same amount of total carbohydrate, on two separate occasions. The graph shows the average changes in blood glucose concentration over 4 hours after each meal.

glucose response

Can you account for the differences?

What would you expect to see if the subjects had consumed an equivalent amount of glucose?

The carbohydrate in meal 2 is obviously more rapidly and completely digested than that in meal 1.

Glucose does not require digestion, and is rapidly absorbed, so the response of blood glucose to a test dose of glucose would be similar to that after test meal 1 - or perhaps a higher peak achieved slightly more rapidly.

What is meant by the term glycaemic index?

The glycaemic index of a food is the extent to which it raises the blood concentration of glucose (i.e. the area under the curve in the graph shown above), compared with that for a test dose of the equivalent amount of glucose or a standard carbohydrate food that is rapidly digested, such as freshly boiled mashed potato or white bread.

Would you expect to see different results for measurement of serum insulin after these two test meals?
If so, why? If not, why not?

insulin response Insulin is secreted in response to increasing blood glucose concentrations, so you would indeed expect to see a lower concentration of serum insulin at each time point after meal 1, which causes less increase in blood glucose, than after meal 2.