Carbs, or carbohydrates, are molecules that have carbon, hydrogen and oxygen atoms.

In nutrition, “carbs” refers to one of the three macronutrients. The other two are protein and fat.

Dietary carbohydrates can be split into three main categories:

  • Sugars: Sweet, short-chain carbohydrates found in foods. Examples are glucose, fructose, galactose and sucrose.
  • Starches: Long chains of glucose molecules, which eventually get broken down into glucose in the digestive system.
  • Fiber: Humans cannot digest fiber, although the bacteria in the digestive system can make use of some of them.

The main purpose of carbohydrates in the diet is to provide energy. Most carbs get broken down or transformed into glucose, which can be used as energy. Carbs can also be turned into fat (stored energy) for later use.

Fiber is an exception. It does not provide energy directly, but it does feed the friendly bacteria in the digestive system. These bacteria can use the fiber to produce fatty acids that some of our cells can use as energy.

Sugar alcohols are also classified as carbohydrates. They taste sweet, but usually don’t provide many calories.