Most carbohydrate-containing foods have large quantities of glucose, and as you digest your food, you absorb the glucose into the bloodstream. In most cases, you can't absorb glucose directly from your food -- you have to break larger molecules down into smaller molecules using digestive enzymes. As such, the activity of digestive enzymes directly influences your blood glucose level.
Glucose Chemistry
Glucose is chemically classified as a monosaccharide, meaning that it's a single sugar unit. In nature, it can occur on its own or can be chemically bonded to additional molecules of glucose or other monosaccharides. If you consume sources of free or unbonded glucose, you can absorb the glucose directly into your bloodstream without the use of digestive enzymes. Much more commonly, however, you consume glucose linked to other molecules, then depend on digestive enzymes to separate the monosaccharides from one another.
Glucose in Food
There are many common sources of glucose in food. For instance, when you consume starch, you're taking in the chemical amylose. Amylose, explain Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry," consists of long chains of glucose molecules chemically bonded together. You need digestive enzymes called amylases to split the glucoses apart so that you can absorb them. Additionally, table sugar contains glucose linked to a monosaccharide called fructose. You need the enzyme sucrase to split the monosaccharides apart.
Blood Glucose
When you consume glucose-containing food, you digest the food and absorb the glucose. Eventually, you'll absorb nearly all of the glucose from your food into the bloodstream, but the rate at which you absorb the glucose varies slightly depending on the chemical composition of the food. Interestingly enough, digestive enzymes work so fast that regardless of whether you consume unbonded glucose or glucose bonded to other monosaccharides, your blood glucose goes up at the same rate.
Slower Absorption
In some cases, digestive enzymes slow down and blood glucose levels increase more slowly when you consume glucose-containing food. This occurs if you eat a source of glucose in combination with dietary fiber. You can't digest fiber, explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry," but it gets in the way of the amylase and other carbohydrate-digesting enzymes, slowing them down and decreasing the rate at which you absorb blood sugar.
Healthy Foods
In general, it's better for your body to absorb glucose slowly rather than quickly. Absorbing glucose from the digestive tract very quickly can lead to excess fat storage and unstable blood sugar. The healthiest foods are those that contain glucose -- either as starch or as sugar -- in combination with fiber. These foods absorb much more slowly than very starchy or sugary foods that don't contain fiber, helping to keep blood sugar stable and prevent fat storage.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Biochemistry"; Mary Campbell, Ph.D. and Shawn Farrell, Ph.D.; 2005
