Types of Sugar

There are several types of sugar. This page mentions some specific sugars but concentrates on the main categories of sugars (monosaccharides and disaccharides) and the relationship between these and certain larger carbohydrates.

What is Sugar ?

Definition of sugar :

A sugar is a carbohydrate that is soluble in water. Sugars are usually crystalline and have a sweet taste.

Chemicals that are sugars often have names ending in "-ose".
For example, note the suffix "-ose" in fructose, glucose, galactose, sucrose, lactose, and maltose.

The word-ending "-saccharide" does not necessarily indicate that the chemical or group or category of chemicals is a sugar. See more examples of prefixes and suffixes used in biology - general biology, not all medical terms.

The two main categories of sugars are monosaccharides and disaccharides. They are often described together with polysaccharides, and sometimes also oligosaccarides, due to the chemical relationship between these types of carbohydrates:

  • Categories of sugars:
    • Monosaccharides are simple ('unit') sugars.
    • Disaccharides consist of molecules whose form is that of two monosaccharide molecules joined together.

  • Categories of larger carbohydrate molecules formed from sugars:
    • Oligosaccharides consist of molecules formed from a few (i.e. more than 2, but not 'many') monosaccharide molecules joined together.
    • Polysaccharides consist of molecules formed from many monosaccharide molecules attached together in the form of long chains.


Courses covering the human digestive system and human diet and nutrition often include the following information about:

    1. Monosaccharides
    2. Disaccharides
    3. Oligosaccharides, and
    4. Polysaccharides

1. Monosaccharides

Chemical Structure:

Monosaccharides are also called 'simple sugars'.
Monosaccharides are the common base unit of all carbohydrate molecules.

Remember: ' Mono ' ' One (1) '


  • Soluble in water
  • Sweetness varies (with individual monosaccharide)

3 Common Monosaccharides:


Fructose (Fruit Sugar)

  • Also known as 'Fruit Sugar'
  • Main sources are many kinds of fruits, as well as honey.



  • Very important in animal (including human) physiology, diet and nutrition -
    because glucose is the form of sugar that is used by the body for energy.
  • All other carbohydrates, including all other sugars, are converted into glucose within the digestive system (digestive processes)
  • Present in various forms of vegetation including many ripe fruits as well as onions and beetroot.



  • Present in mammals' milk
    (see also the disaccharide Lactose, which is composed of glucose and galactose)

2. Disaccharides

Chemical Structure:

Disaccharides consist of (exactly) TWO (2) monosaccharides joined together.

Remember: ' Di ' ' Two (2) '


  • Soluble in water
  • Must be broken-down into monosaccharides before they can be absorbed into the body

3 Common Disaccharides:



  • Chemically, Sucrose (molecule) = Glucose (molecule) + Fructose (molecule)
  • Common form of sugar obtained from sugar cane or sugar beet
  • Also present in some fruits and vegetables



  • Chemically, Lactose (molecule) = Glucose (molecule) + Galactose (molecule)
  • Present in mammals' milk, hence associated with diary products
  • Provides mammilian infants with a source of energy



  • Chemically, ONE Maltose molecule consists of TWO Glucose molecules attached together
  • Present in cereals e.g. barley
  • Also known as "Malt Sugar"

3. Oligosaccharides

Chemical Structure:

Oligosaccharides consist of a small number of monosaccharides joined together.

Some sources say that oligosaccharides consist of 2 - 10 monosaccarides but as chemicals whose molecules that consist of two monosaccharides joined together are disaccharides, it is clearer to think of oligosaccarides as 3 "or a few more" so up to around 10 monosaccharides attached together, but not very many (as in long chains) of monosaccharide units joined together (because many monomers joined together forming long chains are polymers, in this case polysaccharides - see below).

Remember: ' Oligo' ' Few ' or in some cases "deficiency", i.e. too few (of something)


  • In many cases only partially digestible by humans.
  • The undigested part of oligosaccarides may help support intestinal microflora (i.e. microorganisms living in the digestive tract, many of which perform useful functions, though under certain conditions some species are considered potentially harmful). Some studies have indicated that FOS or GOS can increase the quantity of 'friendly bacteria' in the colon while also reducing the quantity of harmful bacteria.

3 Types of Oligosaccharides:

1. Fructo-oligosaccharides (FOS)

  • Chemically, consist of short chains of fructose molecules
  • Present in certain plants e.g. some artichokes, burdock, chicory, leeks, onions, asparagus.
  • Can also be synthesized by enzymes of the fungus Aspergillus niger acting on sucrose.

2. Galactooligosaccharides (GOS)

  • Chemically, consist of short chains of galactose molecules
  • Naturally occurring in soybeans
  • Can be synthesized from lactose (a disaccharide - see above)

3. Mannan Oligosaccharides (MOS)

  • Used in some animal feeds - for digestive health, energy, & performance
  • Unlike other oligosaccharides, MOS are not fermentable

4. Polysaccharides

Chemical Structure:

Polysaccharides consist of polymers of chains (in some cases very long chains) of monosaccharide or disaccharide units all joined together.

Remember: ' Poly ' ' Many '


  • Tasteless
  • Insoluble in cold water

5 Main Groups of Polysaccharides:

1. Starch

  • Chemically, consists of long chains of glucose (a monosaccharide, see above) molecules
  • Formed by plants during photosynthesis
  • Present in many plant-based food sources, such as root vegetables. e.g. potatoes, cereals e.g. and pulses.

2. Dextrin

  • Formed when starchy foods (i.e. foods that contain starch, such as bread or potatoes) are baked or toasted. Dextrin is formed as part of the dry 'crust'
  • Dextrin is more soluble than starch

3. Cellulose

  • Chemically, consists of long chains of glucose (a monosaccharide - see above) molecules
  • Forms the structure of some plants
  • Indigestible by humans but digestible by some other animals.
  • Valuable in human diet as source of dietary fibre - which used to be known as 'roughage'

4. Pectin

  • Present in the roots and / or fruits of certain plants e.g. types of plums and apples
  • Pectin forms a gel in water and has uses for setting jam and making various sweet foods.
  • Sometimes used as a vegan alternative to gelatin (also known as gelatine) in the preparation of 'set' or glazed foods because the beef (cow) or pork (pig) origin of gelatin is not acceptable to some people.
  • Pectin forms a complex polysaccharide

5. Glycogen

  • The stored form of glucose (glucose is a monosaccharide - see above) present in animals including humans.
  • Energy store within the body, stored within muscles and the liver and brain
  • Humans store sufficient glycogen for 24 hours
Re-cap examples of monosaccharides, disaccharides and polysaccharides:

Examples of some types of sugars (which are also types of carbohydrates) and some larger carbohydrates:


Examples of Monosaccharides:

  • Fructose ( 'Fruit Sugar')
  • Glucose
  • Galactose
  • Ribose
  • Deoxyribose - and many others

Examples of Disaccharides:

  • Sucrose
  • Lactose
  • Maltose
  • Isomaltose
  • Trehalulose - and many others

(Larger) Carbohydrates

Types of Polysaccharides:

  • Starch
  • Dextrin
  • Cellulose
  • Pectin
  • Glycogen

See also the effects of overnutrition, carbohydrates, fatty acids, fats and proteins.

More about Nutrition

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Veterinary Science Textbook Statistics for Field Biology

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