Carbohydrates are one of the three macronutrient compounds--the other two are protein and fat--meaning that they're nutrient molecules that you need in large quantities to fuel your cells and organ systems. You use carbohydrates as an important source of energy, and they help maintain brain and other organ system function.
Carbohydrates
There are three types of carbohydrates that you take in as part of your diet: sugars, starch and fiber. Of these, only sugars and starch provide energy. All carbohydrates consist of one or more building block molecules called monosaccharides, where sugars are made up of only one or two building blocks, and both starch and fiber are made of many. The most common monosaccharide is called glucose, which is a component of table sugar. Both starch and fiber also consist of long chains of glucose molecules.
Digestion and Absorption
Most carbohydrates have to be digested before you can absorb them, with the exception of single-unit sugars like glucose, and indigestible fiber. Enzymes in the saliva, stomach and intestine break down carbohydrates made of two or more monosaccharides into their building block units, which you then absorb into the bloodstream. From there, cells take up the monosaccharides and use them for energy or store them for later use.
Energy
Once you've taken up the monosaccharide components of carbohydrate, your cells can burn them for fuel. All carbohydrates aside from fiber, which doesn't provide you with energy, contain 4 calories per gram consumed. You can burn monosaccharides immediately in your cells or store them in the form of glycogen, a carbohydrate made by the liver and muscles. Alternately, you can convert monosaccharides to fat, which you can then burn later during periods of fasting.
Organ Function
Because all organs are made up of cells, and all metabolically active body cells need fuel, carbohydrates are important to the function of all your organs. The brain, in particular, depends upon carbohydrates. While most cells can burn carbohydrates, protein or fat for energy, the brain preferentially burns glucose. Your muscles also burn glucose preferentially during periods of particularly intense effort, such as during a sprint or if you're lifting a very heavy weight.
References
- "Human Physiology"; Lauralee Sherwood, Ph.D.; 2004
- "Anatomy and Physiology"; Gary Thibodeau, Ph.D.; 2007
- "Biochemistry"; Reginald Garrett, Ph.D. and Charles Grisham, Ph.D.; 2007
