Carbohydrates are organic compounds made up of carbon, hydrogen, and oxygen. They contain two atoms of hydrogen for each atom of oxygen in the same ratio as water. Carbohydrate means carbon with water.

Can we make carbs in our body?

Plants and some bacteria have the capability of making energy-producing carbohydrates from two non-energy producing molecules carbon and water. The process is known as photosynthesis. Humans do not have the capacity to make carbohydrates hence we eat carbohydrate filled foods for energy. Carbohydrates are the primary sources of energy.

Food sources of carbohydrate

Fruits, vegetables, and milk are sources of simple carbohydrates. Carbohydrates are one of the macronutrients that supply energy. Complex carbohydrates are found in grains, tubers, and legumes.

  1. Grains
  2. Fruits
  3. Vegetables
  4. Legumes

Carbohydrates classification based on sugar units

Carbohydrates are classified as monosaccharides, disaccharides, oligosaccharides, and polysaccharides based on the number of sugar units they contain.


The simplest or basic form of carbohydrates are the monosaccharides, these form the building blocks of other carbohydrates. You cannot further breakdown these monosaccharides into simpler carbohydrates.  There are more than one hundred monosaccharides found in nature. The monosaccharides are white, crystalline solids which are subdivided into two classes aldoses and ketoses.

Monosaccharides are classified based on the number of carbons they contain into

  1. Trioses (3 carbon)
  2. Tetroses (4 carbon)
  3. Pentoses (5 carbon)
  4. Hexoses (6 carbon)
  5. Heptoses (7 carbon)

Examples of monosaccharides

  1. Glucose (dextrose)
  2. Fructose
  3. Galactose
  4. Xylose
  5. Mannose
  6. Ribose

Hexoses (glucose, fructose, galactose, mannose) are the monosaccharides which are found in significant amounts in foods.


The disaccharides are made up of two units of monosaccharides. The most common disaccharides we come across are sucrose, maltose, and lactose. Sucrose is derived from sugar cane and beet. Lactose is the sugar present in milk and maltose is a breakdown product of starch.

Disaccharide               Monosaccharide

Sucrose                        Glucose + Fructose

Maltose                       Glucose + Glucose

Lactose                        Glucose + Galactose


Oligosaccharides are made of three to ten monosaccharides. The most important oligosaccharides found are alpha-galactosides and fructo-oligosaccharides. Oligosaccharides raffinose, stachyose, and verbascose are soluble oligosaccharides found in legumes.


As the name suggests they contain a large number of monosaccharide units. Polysaccharides are long chains of monosaccharides attached by glycosidic linkages. The three most important polysaccharides, glycogen, starch, and cellulose, are all polymers of glucose. They are usually bland in taste.

Simple and complex carbohydrates

Carbohydrates can also be classified as simple and complex carbohydrates.

Simple carbohydrates

Monosaccharide made out of single sugar unit and disaccharide composed of two sugar units are called simple sugars. For example, monosaccharides such as glucose, fructose, and disaccharides such as sucrose and lactose. These simple sugars are easily digested and absorbed.

Complex carbohydrates

Complex carbohydrates such as starch and fiber are composed of a long chain of monosaccharides. Starch and fiber are found only in plant sources. These take more time to digest or are not digested.

Carbohydrates form an important and essential part of a balanced diet. There is a difference between how different carbohydrates are used in the body. Make sure that simple sugars are limited in the diet and include more of complex carbohydrates.