Understanding lactose intolerance

There are three main types of lactose intolerance:

  • Congenital lactose intolerance – evident from birth1
  • Primary lactose intolerance – normally becomes apparent after 5 years of age2-4
  • Secondary lactose intolerance – can occur following damage to the gut2

Sufferers display gastrointestinal symptoms, which can be confused with other conditions such as delayed cows’ milk allergy (CMA)4. Treatment depends on the type of lactose intolerance but generally involves reducing or removing lactose from the diet5.

What is lactose intolerance?

Lactose intolerance is a digestive problem where the body is unable to digest lactose, a sugar mainly found in milk and dairy products2,5 This is usually as the result of an absence or deficiency of lactase, an enzyme that breaks down lactose into glucose and galactose, which are more easily absorbed into the bloodstream1-3.

The three main types of lactose intolerance

Congenital lactose intolerance (extremely rare)

This rare condition is caused by the absence of lactase from birth . Babies born with congenital lactose intolerance cannot tolerate any breastmilk or infant formula3.

Primary lactose intolerance (genetically inherited)

Associated with a developmental decline of the lactase enzyme which gradually occurs after weaning4,8. Primary lactose intolerance is uncommon before 2–3 years of age and normally becomes apparent after 5 years of age2-4. It is also uncommon in white Northern Europeans, who are more used to dairy in their diet, whereas it is very prevalent in some ethnic groups who historically have eaten little dairy2-4. In the UK, it’s more common in people of Asian or African-Caribbean descent1.

Secondary lactose intolerance (more common, but temporary)

Occurs after damage to the brush border of the gut where lactase is produced, e.g. during acute gastroenteritis, persistent diarrhoea or coeliac disease. This type of lactose intolerance can occur at any age but is more common in infancy. It is usually temporary and once the underlying problem is resolved, lactose can be reintroduced1-4.

In addition to these three main types of lactose intolerance, there is also ‘developmental lactose intolerance’. This occurs in premature infants, when lactase is deficient in the gut until 34 weeks’ gestation2-4.

Recognising the symptoms

Lactose intolerance causes gastrointestinal symptoms such as diarrhoea, cramping and bloating. These are the result of any undigested lactose passing into the large gut. The undigested lactose has an osmotic effect, drawing in water, leading to diarrhoea. It is then fermented by the bacteria in the gut, producing gas, which causes bloating and cramping2,5,7.

Lactose intolerance has some similar symptoms to delayed cows’ milk allergy (CMA), so the two conditions are often mistaken for each other1,2,8. Take a look at our article ‘The differences between lactose intolerance and CMA’ to find out more.

Treating lactose intolerance

There are no official UK guidelines on the treatment of lactose intolerance in infants or adults. Depending on the type of lactose intolerance, treatment can either involve the reduction or removal of lactose in the diet, while achieving optimal nutritional intake1. Even if lactase levels are reduced by 50%, individuals can still digest a significant amount of lactose3,9.

Treating congenital lactose intolerance

Lactose must be completely removed from the diet and a lactose-free formula must be used for infants3,5.

Treating primary lactose intolerance

Children may be able to consume small amounts of lactose without experiencing symptoms.
In other cases, where lactose may need to be avoided completely, care should be taken to ensure that their diet is still nutritionally balanced. For formula fed infants under one year, a lactose free formula may be used1.

Treating secondary lactose intolerance

Opinion on the treatment of secondary lactose intolerance varies. The American Academy of Pediatrics suggests that it “generally does not require elimination of lactose from the diet but, rather, treatment of the underlying condition”2. Other healthcare professionals recommend total lactose avoidance until lactase production resumes after the underlying cause has been resolved5.

Foods and ingredients that contain lactose

Here are three lists covering foods and ingredients which contain lactose, foods which may contain lactose and some low-lactose alternatives:

Foods and ingredients which contain lactose
Milk Solids
MargarineDairy Yoghurt
Condensed MilkCreamWhey Powder
Modified MilkArtificial CreamLactose
Evaporated MilkIce CreamLactoglobulin
Skimmed Milk PowderCheese 
  • Milk, milk solids, condensed milk, modified milk, evaporated milk, skimmed milk powder
  • Butter, buttermilk, margarine
  • Cream, artificial cream, ice cream
  • Cheese, quark, curd, dairy yogurt
  • Whey powder, lactose, lactoglobulin

Foods which may contain lactose

  • Processed meats and foods, e.g. ham
  • Bread and bread products
  • Breakfast cereals
  • Cakes
  • Biscuits

How low dairy intake affects bone health

Avoiding lactose by restricting dairy foods in the diet can lead to an insufficient intake of calcium and other key nutrients, impacting on healthy bone development.

At birth, the skeleton has only 20–30g of calcium and approximately 150mg of calcium is deposited in the bones each day until the age of about 20. If calcium intake is insufficient when bones are growing and developing, they may never reach full strength or peak bone mass. Other nutrients key to bone health are phosphorus, magnesium, vitamin D, and protein10,11.

It is therefore important to ensure these nutrients are supplied through other foods or supplements.


Lactose intolerance is a condition that can have a serious effect on an infant’s health and development. However, by understanding its symptoms and the treatment options available, healthcare professionals can help parents manage their children’s condition effectively.

  1. NHS. Lactose Intolerance [Online]. 2011. Available at: http://www.nhs.uk/Conditions/lactose-intolerance [Accessed April 2013].
  2. Heyman MB. Pediatrics 2006;118(3):1279-86.
  3. Lomer ME et al. Aliment Pharmacol Ther 2007;27:93-103.
  4. Swallow DM. Annu Rev Genet 2003;37:197-219.
  5. Wright T, Meyer R. Milk and eggs. In: Skypala I, Venter C (eds). Food Hypersensitivity. Oxford: Wiley-Blackwell, 2009. p.117-35.
  6. Bhatnager S, Aggarwal R. BMJ 2007;334:1331-2.
  7. European Food Safety Authority Panel on Dietetic Products, Nutrition and Allergies. EFSA Journal 2010;8(9):1777.
  8. Bahna SL. Ann Allergy Asthma Immunol 2002;89(Suppl):56-60.
  9. Du Toit G et al. Arch Dis Child Educ Pract Ed 2010;95:134-44.
  10. Greer F et al. Pediatrics 2006;117(2):578-85.
  11. The Dairy Council. Dairy and Health: Bones [Online]. 2013. Available at: http://www.milk.co.uk [Accessed May 2013].


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