Glucose is a carbohydrate, which is one of the three macronutrient classes. The human body requires macronutrients--carbohydrates, fats and protein--to maintain normal cellular function. In food, glucose serves two purposes. Digestible sources of glucose provide for cellular energy requirements, while indigestible sources of glucose improve digestive function.
Features
The glucose molecule is made up of six atoms of carbon, 12 atoms of hydrogen and six atoms of oxygen. In food, glucose is most often found combined with other molecules of glucose or other sugar molecules, though sugar units must be separated from one another through digestive processes before the intestines can absorb glucose. The glucose molecule, note Drs. Reginald Garrett and Charles Grisham in their book "Biochemistry," is slightly less sweet than common table sugar, of which it is a component.
Function
In the body, glucose from digestible sources provides for cellular energy requirements. Common digestible sources of glucose include table sugar and starch. Though starch--such as that found in grains, rice and potatoes--doesn't taste sweet on the tongue, it's nevertheless broken into glucose units by the digestive tract, say Garrett and Grisham. The glucose absorbed by the digestive tract ends up in the bloodstream, and from there, it's taken up by the liver and other body cells.
Considerations
Not all glucose in food is in a digestible form. Explain Drs. Mary Campbell and Shawn Farrell in their book "Biochemistry," glucose units linked together in a particular way, as they are in dietary fiber, can't be separated from one another by the human digestive system. As such, dietary fiber passes undigested through the intestines. While the glucose in fiber can't be absorbed and used for energy, it's nevertheless important to digestive function and decreases the risk of heart disease.
Effects
One of the effects of glucose in the blood, which is where it is found after absorption by the digestive tract, is to initiate insulin release from the pancreas. Insulin, explains Dr. Lauralee Sherwood in her book "Human Physiology," is a hormone that causes the body cells to absorb glucose from the bloodstream for use in metabolic processes that ultimately result in energy generation. Glucose-containing meals temporarily raise blood sugar, but insulin quickly causes cells to remove much of the excess sugar from the blood.
Expert Insight
Cells can burn glucose for energy under either of two conditions. When oxygen is plentiful, as in most body cells and in resting muscle, glucose is burned in the presence of oxygen. This, explain Campbell and Farrell, results in significant energy production from each glucose molecule. Under low-oxygen conditions, as in working muscle, glucose is often burned through a different process that results in production of about 15 times less energy. Low-oxygen glucose metabolism is much less efficient, which is why most cells use oxygen to burn the majority of glucose that they use.
References
- "Biochemistry"; Reginald Garrett and Charles Grisham; 2007
- "Biochemistry"; Mary Campbell and Shawn Farrell; 2005
- "Human Physiology"; Lauralee Sherwood; 2004
