Carbohydrates Definition

model of a glucose molecule
A model of a glucose molecule - one of the basic building blocks of carbohydrates. Carbohydrates are not foods, they are parts of foods. Science Photo Library - Miriam Maslo/Getty Images

Definition: A carbohydrate is a component of food that supplies energy (calories) to the body. Carbohydrates are one of the three macronutrients, along with proteins and fats.  Most foods contain some of each of these macronutrients in different proportions.

Traditionally, there are three broad categories of carbohydrates:

1) Sugars (also called simple carbohydrates) - These are either simply molecules of simple sugars such as glucose, fructose, or galactose (monosaccharides) or two of these molecules joined together (disaccharides).

  Examples of disaccharides are table sugar which is made up of molecules of glucose and fructose joined together, and lactose, which is  glucose and galactose joined together.

2. Starches (also called complex carbohydrates) - Starches (polysaccharides) are composed of long chains of glucose. They are broken down into glucose in the body, some more rapidly than others.  A special starch, called resistant starch, may be especially valuable to us. Learn more about starches, including resistant starch.

3. Fiber - Fiber essentially means a carbohydrate such as the cellulose in plants which cannot be broken down for energy use in our bodies. Learn more about fiber.

Bonus 4th. Oligosaccharides -  There is also a fourth category between sugars and starches, called oligosaccharides, many of which have positive effects in our colons by being so-called prebiotics.  Learn more about oligosaccharides and prebiotics.

Do We Need Carbohydrates to Be Healthy?

The primary use for carbohydrates in the body is energy, but carbohydrates are not the only dietary source of energy, as fats are also used for energy (and in fact are the main way the body stores energy).  The Institute of Medicine's Dietary Reference guide says, "the lower limit of dietary carbohydrate compatible with life apparently is zero, provided that adequate amounts of protein and fat are consumed."  The body can actually make what little glucose is strictly necessary (the Institute of Medicine reckons this to be about 22-28 grams per day) in a process called gluconeogenesis, primarily from proteins.

That said, foods that contain carbohydrate also contain important nutrients for us.  Happily for those of use who respond well to lower-carb diets, the vegetables and fruits richest in vitamins, minerals, fiber, and phytonutrients are also the lowest in carbohydrate, and with some attention we can eat a healthy diet that has much less carbohydrate than the starchy diet often recommended by professionals or the sugary/starchy diet often consumed by people today.

Pronunciation: kar bo HY drate

Also Known As: carb, carbs, carbos, sugar, sugars, starch, starches

Common Misspellings: carbohydate carbhydrate

Examples: Grains, fruits, cereals, pasta, breads, and pastries are foods which are primarily carbohydrate.


Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients) (2005), Institute of Medicine, Food and Nutrition Board, National Academy of Sciences.

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