name of the term :


Short introduction

  • The term carbohydrates or saccharides comes from the Greek word sákkharon (sugar).
  • Saccharides are divided into four groups: monosaccharides, disaccharides, oligosaccharides and polysaccharides.
  • The monosaccharides and disaccharides, which are small carbohydrate units, are commonly referred to as sugars.
  • Monosaccharides are the simplest carbohydrates (smallest units) and cannot be hydrolysed (digested, broken-down) to smaller carbohydrates.
    • Glucose (blood sugar, grape sugar, dextrose)
    • Fructose (fruit sugar)
    • Galactose
  • Disaccharides: two joined monosaccharides hydrolysed by specific enzymes.
    • Sucrose (saccharose): glucose + fructose
    • Lactose (milk sugar): glucose + galactose
    • Maltose (malt sugar): glucose + glucose
  • Oligosaccharides: 3-10 monosaccharides linked together, which can be hydrolysed by specific enzymes. Examples:
    • GOS: galactooligosaccharides – produced out of lactose with the help of enzymes. Chemical structure: short chain of galactose compounds with a terminal glucose unit.
    • FOS: fructooligosaccharides, e.g. inulin is of vegetable origin and derived from chicory roots. Chemical structure: chain of fructose units with a terminal glucose unit.
    • Oligosaccharides are present in breast milk: human milk oligosaccharides (HMOS).
  • Polysaccharides are long chains consisting of >10 monosaccharides and sometimes even up to several thousands. Example:
    • Starch: the main reserve carbohydrate in vegetables and cereals. Examples of non-starch polysaccharides (main components of dietary fibre):
    • Cellulose: major component of plant cell walls.
    • Pectin: used in fruit jellies for its thickening and emulsifying properties.
    • Gums: such as galactomannans, e.g. carob bean gum, which is made up of long chains of galactose and mannose (related to glucose) and used for its thickening properties.
    • Glycogen: the main storage form of glucose in the body (liver and muscles).

Main natural sources

  • Glucose: found in grapes along with fructose.
    Fructose: fruits and fruit products.
    Galactose: component of lactose in milk and dairy products. Galactose also combines with sucrose in oligosaccharides; found in beans, lentils and peas.
  • Sucrose or saccharose: table sugar (in different forms), malt syrup, honey.
    Lactose: milk and milk products.
    Maltose: molasses – byproduct of the refining of sugarcane or sugarbeet into sugar.

Main function

  •  Source of energy: 1 g of carbohydrates provides 4 kcal (17 kJ).
    • After digestion, the small units (glucose, fructose, galactose) are absorbed in the small intestine and enter the bloodstream, where they travel to the liver. Fructose and galactose are converted to glucose. Glucose is transported, by the bloodstream, to the various tissues and organs and used as energy.
    • Brain tissue and red blood cells primarily use glucose as an energy source. A lack of glucose can result in weakness, dizziness, and low blood glucose (hypoglycaemia). Reduced blood glucose during exercise decreases performance and could lead to mental as well as physical fatigue.
    • If the body does not need glucose for energy, it stores glucose (as glycogen) in the liver and skeletal muscles. When glycogen stores are full, glucose is stored as fat. Glycogen stores are used as an energy source when the body needs more glucose than is readily available in the bloodstream (e.g. during exercise).
  • Carbohydrates prevent protein from being used as energy. Inadequate consumption leads to protein breakdown in order to make glucose and keep a constant blood glucose level.
  • Fibre plays a role in maintaining digestive health – important for healthy gut functioning.
    • Beneficial for overall human health and high fibre intake is linked with reduced risk of a number of chronic conditions. See: fibre. 
  • Sugar is used because of its sweetening properties. It has a sweet taste and is the reference against which other sweeteners are compared. Sugar provides structure and texture to foods (e.g. bakery products) and can act as a preservative (e.g. jam).

Deficiency disease

  • When carbohydrate intake is insufficient, blood glucose and glycogen stores (glucose reserve stores in liver and muscles) get depleted. Glucose synthesis (production) depends on breakdown of amino acids from body protein, dietary protein and the compound glycerol (from fat). Long-term carbohydrate inadequacy results in ketosis (high ketone levels lead to dehydration and change the chemical blood balance), acidosis (increased acidity in blood and other body tissues that may result in cell damage), and loss of cellular proteins. Protein breakdown may result in increased stress on the kidneys, where protein by-products are excreted into the urine.
  • Signs and symptoms include hypoglycaemia: drop in blood sugar levels (dizziness, fatigue, distress). Fatigue and decreased energy levels: non-availability of glucose in blood for energy production resulting in a dip in energy levels and fatigue. Muscle wasting: use of fat reserves and amino acids for energy production leading to loss of muscle mass and impairment of growth. Weight loss: loss of fat and muscle mass leading to weight loss. Dehydration and reduced body secretions: ketosis leads to loss of body fluids and may result in dehydration (dry eyes, and adjusted mucus production in salivary glands, respiratory airways, and gastrointestinal tract). Weakened immune system and susceptibility to infections, constipation, and mood swing: the brain may stop regulating the hormone serotonin causing mood swings and depression. Prolonged carbohydrate deficiencies can result in drastic weight loss and even starvation.

DRIs (Dietary Reference Intakes) have not been established for monosaccharides and disaccharides (sugars).

DRIs for carbohydrates have been established.

Recommended daily intake

Latest Dietary Reference Intakes  (DRIs) 
Institute of Medicine (IOM)

Age categoryPer day
175 g (RDA)
210 g (RDA)
Infants 6 – 12 months95 g (AI)
 1 – 3 years
 4 – 8 years
130 g (RDA)
130 g (RDA)
 9 – 13 years
14 – 18 years
19 – 30 years
31 – 50 years
50 – 70 years
> 70 years
130 g (RDA)
130 g (RDA)
130 g (RDA)
130 g (RDA)
130 g (RDA)
130 g (RDA)
 9 – 13 years
14 – 18 years
19 – 30 years
31 – 50 years
50 – 70 years
> 70 years
130 g (RDA)
130 g (RDA)
130 g (RDA)
130 g (RDA)
130 g (RDA)
130 g (RDA)

AI = Adequate Intake.
RDA = Recommended Dietary Allowance.

Synonyms : Saccharides

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