Difference Between Glucose and Galactose

As many know, glucose and galactose are two types of sugar, the latter being understood as the solid, white, water-soluble organic substance that constitutes an important part of the energy reserves of animal and plant cells.

Despite being two types of sugar, there are differences between glucose and galactose, which are basically determined by their origin and chemical composition. The objective of this article is to point out the differences between these two types of sugar based on their definitions.


Glucose is a type of simple sugar that living things use as an energy source. It is the most abundant organic element in all of nature, since it is present in different natural elements. In this sense, all vegetables and plants obtain it from photosynthesis, in which different inorganic elements such as water or sunlight are transformed into food.

Its molecular formula is C 6 H 12 O 6 , this means that it is made up of six carbon atoms, being a hexose molecule and also a monosaccharide (carbohydrate that cannot be broken down into a simpler one), twelve hydrogen molecules and six oxygen molecules. Its appearance is that of a whitish powder after processing and refinement. Among other characteristics we have that its melting point is 146 °C (419 °K) and its energy yield is 3.75 kilocalories per gram under standard conditions.

In animals and humans, glucose is synthesized in the liver as an energy source. Also, it is worth noting that all natural fruits have some amount of glucose, often combined with fructose, which can be extracted and concentrated. On an industrial level, glucose is obtained from the enzymatic hydrolysis of cereal starch (generally wheat or corn).


Galactose is a type of sugar present in nature that many living beings use as an energy source and is also a monosaccharide compound. It comes from milk and is synthesized by the mammary glands to produce lactose, which is a disaccharide formed by the union of glucose and galactose, therefore, the greatest contribution of galactose in nutrition comes from the intake of lactose from milk. .

Its chemical formula is the same as glucose (C 6 H 12 O 6 ) but with a different biochemical structure, that is, the orientation of the functional groups of the entire fourth carbon varies in relation to the structure of glucose, therefore , its melting point is 167 °C (440.15 °K).

As can be seen, there are important differences between glucose and galactose, which are indicated below:

  • The main sources of glucose are fruits, fruit juices and sweeteners such as honey while the main source of galactose is foods containing lactose, such as dairy products, although it also occurs naturally in honey and the beet
  • Glucose is used by the body for fuel or is stored in the liver and muscles as energy reserves while galactose can be used for fuel or stored for reserve but is also a component of fatty acids in the nervous system.
  • High levels of glucose in the blood can be harmful and cause type 1 and 2 diabetes, resulting in cardiovascular diseases, retinopathy, nephropathy, chronic kidney disease, and in acute cases, hypoglycemia and hyperglycemia, while high levels of galactose in the blood can lead to galactosemia, which can cause cataracts.

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