Carbohydrates are categorized as either simple or complex. The simple carbohydrates are made of a single unit of various arrangements of the three elements (carbon, hydrogen, oxygen). Each unit has the same number of carbon, hydrogen, and oxygen atoms; the different arrangements of them account for their distinct properties, such as sweetness and solubility. Complex carbohydrates are made of different arrangements of these single units that are linked together in various patterns that can be from two to tens of thousands of units long. The more units linked, the more complex the carbohydrate. Simple carbohydrates are sugars; complex carbohydrates are starches, fiber, glycogen, and dextrin.
the food, such as the lactose in milk and fructose in fruits, as well as sugar that's been added to the food, such as table sugar, corn syrup, and dextrose.
There are two kinds of simple carbohydrates: monosaccharides and disaccharides. Each type is quite easily broken down by the body to create the glucose the body uses for energy.
Monosaccharides. These are the simplest form of carbohydrate ("mono" means one, "saccharide" means sugar). Glucose, fructose, and galactose, the monosaccharides that are found in fruits, vegetables, and milk, make up approximately 10 percent of the carbohydrate in our diet. Glucose is often called blood sugar because it is the main form of carbohydrate that travels through the bloodstream to provide energy to the body's cells. It's found naturally in fruits, vegetables, and honey. Fructose, also known as fruit sugar, is found naturally in many different fruits as well as honey. Galactose is a monosaccharide that is the end result of the digestive breakdown of a disaccharide called lactose (the sugar found in milk).
Disaccharides. These are made of two single sugar units (monosaccharides) that are linked together. The different types of disaccharides ("di" means two) are created through various combinations of monosaccharides. Here are some examples of disaccharides you might recognize and how they are formed:
glucose + fructose = sucrose (disaccharide)
glucose + galactose = lactose (disaccharide)
glucose + glucose = maltose (disaccharide)
Sucrose is the most common disaccharide; it's commonly known as table sugar. Lactose is the disaccharide found in milk. Maltose is the least common disaccharide; it's created during digestion by enzymes that break down large molecules of starch and is a product of cereal grain germination.
Complex carbohydrates are assembled from single sugar units, including glucose, fructose, and galactose, or pairs of single sugars (the disaccharides, including sucrose, lactose, and maltose) that are linked together. Here's how complex carbs are formed:
Polysaccharides. Polysaccharides ("poly" means more than one) are also known as complex carbohydrates and include starch, fiber, glycogen, and dextrin. Although complex carbohydrates are built from many single sugar units, they don't taste sweet. Joining these sugar units together creates the new, complex carbohydrate-either starch, glycogen, or cellulose (fiber). Starch is found in plants (starch is their storage form of carbohydrate), glycogen is the storage form of carbohydrate in humans and animals, and cellulose, an indigestible form of carbohydrate that's better known as fiber, provides structure for all plants. A fourth type of polysaccharide, dextrin, is produced as a result of breaking down long chains of starch into shorter chains during digestion. All of these complex carbohydrates are more stable and less soluble than the simple carbohydrates. However, the body can still break them down fairly easily into simple sugars and finally into glucose, the simple sugar that the body uses directly for energy.
The chemical composition of carbohydrates is a nice starting point, but the real information you probably want to know about carbs is how they are used by the body. In the next section, we'll examine what happens when we eat simple and complex carbohydrates.