The Glycemic Index

With carbohydrate calories making up on average 65% of most Americans total daily caloric intake, any modification in the variety and volume of carbohydrate intake might have a profound impact on long-term health and weight management. Numerous popular diets have targeted the lowly carbohydrate, leading the charge in what will surely be remembered as the “low carb” diet era.

However, without a deeper understanding of the role carbohydrates play in normal physiology, in gut physiology, in the prevention of heart disease and cancer, and more globally, the role they play in long-term health promotion—cutting carbs may or may not be a desirable goal depending on which carbs are being eliminated. This series will attempt to demystify and unravel the popular notions of carbohydrate intake as well as the glycemic index and glycemic load and add insight into the relationship between carbohydrate intake and health.

A basic presentation of carbohydrate terminology will be presented first—which is an admittedly dry subject—but will naturally lead into some current controversies related to carbohydrate intake. The basic science and vocabulary of carbohydrates is critical to understanding not just the glycemic index and glycemic load, but numerous other aspects of carbohydrate physiology. Ultimately, the distillation of the following sections is the impact carbohydrates may have on weight management, health, and longevity.

The glycemic index and glycemic load are measures of glucose absorption and the concomitant blood glucose level resulting. In very basic terms, glucose is the fundamental building block of most carbohydrate molecules. The basic sugars are broken down into

monosaccharides

1. Glucose (glue-kose) Grape sugar
2. Fructose (frook-tose) Fruit sugar
3. Galactose (Galak-tose) Component of Milk Sugar

And disaccharides . . .

4. Sucrose (Sue-krose) Table sugar
5. Lactose (Lak-tose) Milk sugar
6. Maltose (Mall-tose) Malt sugar

The glycemic index asks the question: if I eat a food containing carbohydrates, how will it impact my blood sugar over the next two to three hours? Thus taking that approach, the disaccharides cannot be absorbed until broken down in the gut to allow the glucose (and fructose and galactose) to travel through the intestinal mucsoa into the blood.

Honey is primarily fructose and since we don't measure blood fructose levels, the glycemic index of honey is low. Again, when blood sugar is measured, we measure glucose, not fructose. Honey is gram for gram sweeter than table sugar, but the resulting glycemic index is lower. Confused? Don't be, fructose triggers those papillary taste buds with waves of sweetness and the resulting blood glucose elevation is minimal. Fructose is absorbed from the intestine and taken up by cells, with some being metabolized for the energy needs of cells, and some fructose is altered (metabolized) in reverse to produce glucose and enter the blood stream. Thus fructose containing foods have a low glycemic index. Numerous foods are flavored with fructose and high fructose corn syrup (HFCS). It hardly seems fair, but Cola drinks usually have a lower glycemic index than certain vegetables because they're sweetened with HFCS. More tomorrow.