What Are Carbohydrates?

Carbohydrates are any of a group of organic compounds that includes sugars, fiber, starches, celluloses, and gums and serves as a major energy source in the diet of animals. They are found in a wide array of foods—bread, beans, milk, popcorn, potatoes, cookies, spaghetti, soft drinks, corn, and cherry pie. These compounds are produced by photosynthetic plants and contain only carbon, hydrogen, and oxygen, usually in the ratio 1:2:1, which unite into a simple union of sugar molecule, as the basic building block of every carbohydrate. Starches and fibers are essentially chains of sugar molecules. Some contain hundreds of sugars. Some chains are straight, others branch wildly.

Carbohydrates Categorizations

According to the Length of Their Molecule Chains:

• Simple carbohydrates, which have no more than two molecule chains, include sugars such as fruit sugar (fructose), corn or grape sugar (dextrose or glucose), and table sugar (sucrose).
• Complex carbohydrates include everything made of three or more linked sugars.

Complex carbohydrates were thought to be the healthiest to eat, while simple carbohydrates weren't so great. It turns out that the picture is more complicated than that.

The digestive system handles all carbohydrates in much the same way—it breaks them down (or tries to break them down) into single sugar molecules, since only these are small enough to cross into the bloodstream. It also converts most digestible carbohydrates into glucose (also known as blood sugar), because cells are designed to use this as a universal energy source.

Dividing carbohydrates into simple and complex makes sense on a chemical level. But it doesn't do much to explain what happens to different kinds of carbohydrates inside the body. A new system, called the glycemic index, aims to classify carbohydrates based on how quickly and how high they boost blood sugar compared to pure glucose.

According to the Glycemic Index:

• Carbohydrates with a high glycemic index, like in white bread, causing rapid spikes in blood sugar. Foods with a score of 70 or higher are defined as having a high glycemic index
• Carbohydrates with a low glycemic index, like in whole oats, are digested more slowly, causing a lower and gentler change in blood sugar. The score is 55 or below.

Fiber

Fiber is another kind of carbohydrate. It can't be broken down into sugar molecules, and so it passes through the body undigested. Fiber comes in two varieties:

• Soluble fiber dissolves in water. It binds to fatty substances in the intestines and carries them out as a waste, thus lowering low-density lipoprotein (LDL, or bad cholesterol). It also helps regulate the body's use of sugars, helping to keep hunger and blood sugar in check
• Insoluble fiber does not dissolve in water. It helps push food through the intestinal tract, promoting regularity and helping prevent constipation.

Adults need at least 20 to 30 grams of fiber per day for good health. But most Americans get only about 15 grams a day.