Difference Between Lactose and Lactase

Lactose vs Lactase

Lactose and lactase although they sound very similar, are two very different things in structure and role. These two words are commonly heard together with lactose intolerance, a certain health condition some people experience.


Lactose (C12H22O11) discovered in 1619 and identified as a sugar in 1780, belongs to the bio-molecular group of carbohydrates. Carbohydrates are mainly divided into monosaccharide, disaccharide and polysaccharide out of which lactose belongs to disaccharide. As the name implies, this sugar is made up of two simple sugars glucose and galactose. Cyclic forms of glucose and galactose, which are also known as pyranose forms, release a water molecule and bind with each other via a glycosidic bond; a typical connection present in sugar polymers. Since glucose and galactose are 6 Carbon sugars, the linkage can also be named as a 1-4 glycosidic linkage, where 1 stands for the Carbon-1 of galactose and 4 stands for the Carbon-4 of glucose and the connectivity is between the mentioned carbons through an oxygen atom. The systematic name for lactose is β-D-galactopyranosyl-(1->4)-D-glucose.

Lactose is a common sugar in our diet because 2-8% of the weight of milk is due to the presence of lactose. Lactose is also present in dairy products such as butter, cheese, ice cream etc. Lactose content is high in mammalian milk; it is one of the first tastes we experience as babies.


Lactase is an enzyme (“ase”- stands for enzyme). Enzyme is a substance which catalyzes and carries out biological reactions in our body. Enzymes come under the bio-molecular class of proteins. This particular enzyme, which is a member of β galactosidase enzyme family, is responsible for the catabolism also known as degrading or hydrolysis of lactose. In the small intestine, lactase enzyme gets secreted into the digestive track out of the intestinal villi present in the intestine’s wall. Then the enzyme cleaves lactose from 1-4 glycosidic linkage by adding a water molecule and breaking lactose into its two original parts. That is into galactose and glucose, which are readily absorbed by the cells for cellular respiration and energy production. When proper lactase action does not take place, lactose travels to the colon undigested and due to the bacterial action and fermentation people may experience diarrhea, cramps and stomach pain. This is what we refer to as “Lactose intolerance” or “lactase deficiency”.

What is the difference between Lactose and Lactase?

• Lactose is a carbohydrate-sugar, and Lactase is a protein.

• Lactose is an energy source for the body and lactase is not used as an energy source.

• Lactose is taken in from the diet rich in dairy products (from outside the body), but lactase is naturally produced inside our bodies.

• Lactose is made up of two simple sugars, but lactase is made up of amino acids chains folding into 3D structure.

• In the digesting reaction, lactose is the substrate, and lactase is the catalyst for this reaction.

• In a lactose intolerant person, presence of lactose or absence of lactase worsens the condition.