What is Lactose Intolerance?

Lactose intolerance is extremely common - it’s super likely that if you don’t have it yourself, you know somebody that does. What exactly is it, though? How is it caused? How do you get it diagnosed? All this and more, right here!

What is Lactose Intolerance?

Lactose intolerance is exactly what it says on the tin, an intolerance to lactose. Lactose is a type of sugar found in milk and dairy products, and the body has trouble digesting it if you are lactose intolerant.1

Lactase is an enzyme produced in the small intestine that is needed in order for us to digest lactose. Lactose intolerance is usually caused by a shortage of the enzyme lactase in the body, making it difficult to digest.2 

If the body does not have enough lactase, the lactose passes undigested into the colon and is broken down by the colon bacteria in a process known as fermentation.

This breakdown process results in carbon dioxide, hydrogen gases, organic acids and other molecules being produced, leading to unpleasant symptoms.3

What are the Types of Lactose Intolerance?

There are 3 different forms of lactose intolerance:3

Acquired Lactase Deficiency is the most common version of lactose intolerance and is what people usually refer to when discussing lactose intolerance. This condition occurs due to the normal lactase decline as we age.

Primary Lactase Deficiency is the rarest form of lactose intolerance. It occurs when babies are born with the absence of any lactase, and this is an inherited condition caused by receiving one gene from each parent. These babies require a specialised formula that includes alternative sugar, which is digestible to them, as lactose is not.

Secondary Lactase Deficiency is a temporary form of lactose intolerance in babies and young children caused by an infection that impacts the gastrointestinal tract and causes damage to the lining of the small intestine.

This can also be caused by Coeliac disease and Crohn’s disease when either of these conditions causes damage to the gastrointestinal tract. Once the disease is treated, the secondary lactase deficiency will usually go away within a month or so.

What are the Symptoms of Lactose Intolerance?

If somebody that is lactose intolerant doesn’t consume any lactose, they won’t have any symptoms. The symptoms only occur when lactose is consumed and can involve:1 

  • Excess gas
  • Diarrhoea
  • Bloating
  • Stomach cramps
  • Stomach pain
  • Stomach rumbling
  • Nausea

Symptoms can range from mild to severe, depending on the severity of the intolerance. For some, it may be as simple as mild discomfort, whereas, for others, it can be unbearable. Symptoms will usually occur a few hours after the lactose is consumed. 

How Common is Lactose Intolerance?

It is estimated that 68% of the world’s population has some degree of lactose intolerance.2 Lactose intolerance usually worsens with age because we naturally have less lactase as we age. Some that may not have previously suffered from lactose intolerance may develop symptoms at any age.

Lactose intolerance most commonly affects African Americans; 85% of adult African Americans in the US are lactose intolerant, versus 15% of adult Caucasians.3

People of Asian, Hispanic, native American or Jewish descent are also more likely to have lactose intolerance. It can have a genetic link - for example, if lactose intolerance runs in your family, your chances of developing it are higher.3

Where is Lactose Found?

Most commonly, lactose is found in milk and other dairy products such as cheese, ice cream and yoghurt. It can also be found in bread, pastries, processed breakfast cereals, pre-prepared potatoes, soup, lunch meats, sweets, sauces, dressings and pre-made baking mixes.3

It is also found in breast milk and infant formula milk, so if your baby seems to be having an unpleasant reaction to feeding time, it is important to get them checked for lactose intolerance.

How is Lactose Intolerance Diagnosed?

A doctor can perform a lactose intolerance test to determine if you are lactose intolerant. You drink a lactose solution in this test, and a blood sample will be taken. The blood is then tested to see how much blood sugar it contains. If you are lactose intolerant, your blood sugar levels will either not rise at all or will rise slowly.4


Although lactose intolerance isn’t deadly, it can be very uncomfortable and unpleasant. If you think you or your child may be suffering from lactose intolerance, contact your doctor for a test so you can begin to eliminate this trigger from your diet. 

References → 1

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