Simply put, carbohydrates are compounds made of different concentrations of carbon and water. Carbohydrates are sometimes referred to as saccharides. Classified by increasing size, they exist as monosaccharides, disaccharides, oligosaccharides, and polysaccharides. ‘Simple’ carbohydrates usually refer to monosaccharides and disaccharides while ‘complex’ carbohydrates typically represent oligosaccharides and polysaccharides.
We consider the small, simple carbohydrates as sugars. We use them as fuel for energy, and to build many of the important compounds that our bodies need. Glucose is the most important monosaccharide that we use for metabolism. A common disaccharide is sucrose (made of two monosaccharides, glucose and fructose). When we ingest more glucose than our body needs, we combine the monosaccharides into polysaccharides for more efficient storage (glycogen in animals, starch in plants; glycogen is sometimes referred to as ‘animal starch’). We store most of our glycogen in liver and muscle for later use during times of need.
Sometimes polysaccharides are used as structural compounds (chitin, cellulose). Cellulose is an important part of cell walls in plants. It is the most abundant organic molecule on earth, and we commonly use it to make paper and textiles, convert it to cellophane, or use it as feedstock for the production of rayon. We occasionally use chitin in surgical sutures.
Dietary fiber, or roughage, is simply non-starch polysaccharide. We do not digest fiber, and it helps to move waste through our intestinal tract. It decreases the pressure in our intestines, lowers our cholesterol levels, and even helps to protect our heart.
Foods rich in carbohydrates include fruits, grains (barley, oat, wheat), soft drinks, beans, potatoes, bran, and rice. Simple carbohydrates such as sugar are found in candies, jams, and many different desserts. Complex carbohydrates are typically found in bread, cereal, and pasta.
We commonly use carbohydrates as a source for energy; however, they are not an essential nutrient in human beings. Our brain and nerves need glucose or ketones (byproducts of fat metabolism when glucose is not available) for fuel, and we derive much of the fuel from our diet. Interestingly, however, we are also able to make glucose during times of need through a natural process called gluconeogenesis. Occurring mostly in our liver, this process makes glucose from non-carbohydrates such as amino acids, lactate, and glycerol.
You will often hear that our bodies digest complex carbohydrates (i.e. starches) slower than simple carbohydrates (i.e. sugar), suggesting that they are healthier for us. In truth, we metabolize some simple carbohydrates (fructose) slower than many complex ones. It is more accurate to gauge carbohydrates by their glycemic index (GI) and glycemic load (GL). A measure of nutrient behavior during digestion, foods with higher glycemic index cause a greater rise in our blood glucose (‘blood sugar’) levels. The glycemic load combines the quality and quantity measurements together by considering the glycemic index as well as the amount of carbohydrate consumed (GL = GI X the amount of carbohydrate available in a 100 gram serving / 100). Watermelon is an example of food with high GI, but because it does not contain much carbohydrate, the GL is relatively low. A GL of less than 10 is considered low, 11 to 19 is medium, and greater than 20 is considered high.
Here is a Table of Common Foods with Associated GI and GL. Choose and balance wisely!