What is lactose? All about this carbohydrate

Lactose is a carbohydrate (or “sugar”) naturally present in dairy products (from cows, goats or ewes). It is composed of glucose and galactose and is digested with an enzyme called lactase. When this enzyme is absent or insufficiently produced, it is called lactose intolerance.

Characteristics of lactose:

  • It is a carbohydrate and provides energy
  • Its digestion is possible thanks to an enzyme, lactase
  • Lactose is found in milk, cheese and dairy products
  • Lactose intolerance is quite common and results in digestive disorders

Why consume foods rich in lactose?

What to do in case of lactose intolerance?

Depending on the severity of the lactose intolerance, a partial or total reduction or eviction of the dairy products can be carried out. Some dairy products on the market are available in delactosed version (lactose-free milk, lactose-free cheese or lactose-free yoghurt), which may be an alternative for people with lactose intolerance who wish to continue consuming dairy products. Symptoms of lactose intolerance often occur a few hours after the ingestion of lactose. They are usually very uncomfortable and painful: abdominal cramps, bloating, diarrhea, gas, or headache and nausea.

Attention, we often speak wrongly lactose allergy. However, true allergy to cow’s milk protein is very infrequent and involves the immune system whereas lactose intolerance results only from lactase deficiency.

Should we eat gluten-free and lactose-free?

More and more people are adopting gluten-free and lactose-free diets because they think they are intolerant. If they are poorly conducted these particular diets may however lead to shortcomings, it is better to be accompanied by a health professional for their implementation. Eating gluten-free and lactose-free is not always the solution, but reducing their intake can sometimes reduce digestive discomfort significantly.


Lactose is a carbohydrate, so it has a nutritional and energetic interest in bringing calories to the body.

20 foods rich in lactose

Lactose is contained in all dairy products, whether from cows, goats or ewes.

Foods Portion Amount of lactose (g)
Whey100ml39 to 75
Milk powder100g36 to 52
Skim milk (cow, goat, sheep)100ml4 to 5
Whole milk (cow, goat, sheep)100ml4 to 5
Fresh cream100ml4
Yogurt with whole milk100g4
Ice cream100ml3 to 8
Semi-skimmed milk yogurt100g2-7
Ricotta100g1 to 5
Fresh cheese spread100g1 to 3
Mozzarella100g1 to 3
Butter100g0.5 to 1
Brie100g0.1 to 1
Camembert100g0.1 to 1
Parmesan100g0.1 to 1
Emmental100g0 to 3
Gruyère100g0.1 to 1
Raclette cheese100g0.1

How to use lactose properly?

Use of lactose

There are no nutritional recommendations for daily lactose needs. It is recommended, however, to consume 3 dairy products per day in healthy adults to promote good intakes of protein, calcium and phosphorus.

Lactase food supplements

More and more laboratories market lactase-based dietary supplements, the intake of which increases the tolerance to lactose. It is recommended to take them before meals containing lactose to facilitate digestion and reduce unpleasant digestive symptoms.

Undesirable effects of lactose

Consequence of lactose deficiency

Lactose can be totally absent from the diet without any adverse health consequences. Special attention should still be paid to calcium intake which is often covered by dairy products.

Consequences of an excess of lactose

There are no studies evoking the harmful consequences of an excess of lactose (apart from lactose intolerance).

Chemical Properties

The crude formula of lactose is C12H22O11 and its molar mass is 342.2965 g / mol. It is a carbohydrate found in mammalian milk. Lactose is composed of two oses, galactose and glucose. This is called a diholoside. It is a reducing sugar because it contains a hemiacetal function. Its sweetening power is relatively low (0.16). Digestion of lactose in the body involves an enzyme, hydrolase, also called lactase. This hydrolysis releases one molecule of glucose and one of galactose, which is then taken care of separately.

Nutrient History

A third of adults on Earth would be able to digest lactose properly. In all mammals the production of lactase at birth is very important. Fortunately, milk is the basis of any newborn’s diet. Then the production of this enzyme will decrease gradually to make room for weaning and a more diversified diet. Several hypotheses exist regarding the evolution and prevalence of lactose intolerance. It appears, however, that this decrease in lactase production in the majority of individuals poses problems of digestion.


  • Food Content in Lactose, Food intolerances,
  • Composition of lactose, CNESST,
  • Lactose intolerance, Swagerty DL Jr, Walling AD, Klein RM, American Family Physician, 2002.