Protein and glucose, which is a carbohydrate, represent two of the three classes of macronutrients that humans need in the diet -- the third is fat. While both protein and glucose are important to normal, healthy human function, there are significant chemical differences between the two, both structurally and in terms of how they're processed in the body.
Function
Both protein and glucose can serve as sources of cellular nutrition and energy, though through slightly different metabolic mechanisms. Unlike glucose, which doesn't serve significant functions in the body that aren't energy-related, protein is broken down into its constituent compounds -- called amino acids -- and is used for several other purposes. In their book "Biochemistry," Reginald Garrett, Ph.D., and Charles Grisham, Ph.D., explain that amino acids are used to synthesize other molecules, like neurotransmitters, and to build new body proteins.
Glucose Structure
Glucose and proteins differ significantly in their chemical makeup. Glucose is a monosaccharide, or sugar unit. It's composed of six atoms of carbon, 12 atoms of hydrogen and six atoms of oxygen. In the diet, it's most commonly linked to the sugar fructose in the form of table sugar, or linked to other glucose molecules in the form of starch. Garrett and Grisham note that glucose can be unlinked from other sugars to which it is chemically connected and absorbed from the digestive tract.
Protein Structure
Proteins are made up of long chains of amino acids, chemically bonded to one another and folded into an overall shape -- often a ball-like or fibrous shape. It's not possible for the body to absorb whole proteins from the gut, explains Dr. Lauralee Sherwood in her book "Human Physiology." Instead, enzymes in the gut separate amino acids from one another, and they're absorbed individually. Amino acids consist of various numbers of carbon atoms, hydrogen atoms, oxygen atoms and nitrogen atoms. Some even include sulfur.
Metabolism
The cells take up glucose from the bloodstream and either store it for later use in the form of a molecule called glycogen or burn it for energy. The process through which glucose is burned involves many chemical reactions and yields a significant amount of energy per molecule of glucose. Amino acids, if they're burned for energy, enter the same series of reactions that burns glucose, though amino acids enter the process much later in the series, note Garrett and Grisham.
Expert Insight
While both glucose and protein are important components of a healthy diet, glucose has the potential to cause trouble for diabetics, while protein does not. This is because diabetics lack or can't respond to the enzyme responsible for moving glucose into the body cells, explains Dr. Gary Thibodeau in his book "Anatomy and Physiology." As such, diabetics can experience very high blood sugar, or hyperglycemia, after a glucose-rich meal. This is associated with a variety of symptoms and can be quite serious. Protein causes no such effect.
References
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
