Lactose intolerance: everything you need to know!

The term ‘lactose intolerance' is thrown around so much these days, and sometimes you just want a straight answer as to what it is, and why it exists. We have those answers right here! 🐄

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The term ‘lactose intolerance’ is thrown around so much these days, and sometimes you just want a straight answer as to what it is, and why it exists. We have those answers right here! 🐄

Is lactose intolerance caused by cow’s milk?

Cow’s milk is a great source of protein and provides calcium and other minerals essential for bone development. But for some people, cow's milk (and cow’s milk products) lead to gastric discomfort, skin rashes and in severe cases, anaphylactic shock. Two main causes of these negative reactions include lactose intolerance and cow’s milk protein allergy. These two conditions may have overlapping symptoms but follow different pathways in the body. It’s important to know the difference, so the right treatment can be administered.

pouring milk in a glass

Lactose intolerance 

Lactose intolerance is a condition resulting from a physiological decline in lactase enzyme activity in the intestinal cells after weaning from breast milk. Lactase breaks down lactose–which is the sugar found in mammalian milk– into glucose and galactose. If the lactose isn’t broken down it moves to the colon and gets broken down by bacteria which leads to excessive gas formation, bloating, belching, stomach cramps and diarrhoea.  

Secondary lactose intolerance presents as a result of mucosal damage, usually following severe gastroenteritis but also when the epithelium is damaged such as in coeliac disease and cow’s milk allergy. It is usually reversible once the epithelial lining has repaired.  

What does a lactose intolerance diagnosis mean?

The diagnosis of adult-type hypolactasia is by definition based on:

1. The measurement of activity of:

2. the lactase to sucrase (L:S) ratio in intestinal biopsies.

The invasive technique of using intestinal biopsies is not suitable for primary screening of abdominal complaints. 

Jejunal biopsy (the removal of a piece of the lining –mucosa– of the upper small intestine. This can be done by a surgical operation but is usually performed by an enteroscope), is considered one of the most reliable methods to detect lactose malabsorbers and many researchers use it as gold standard in comparison studies. However lactase activity from jejunal biopsies was speculated as not being a gold standard, owing to the uneven dissemination of lactase activity throughout the small intestine mucosa. 


The diagnosis is usually based on the lactose tolerance test (LTT) for which specificity has been reported to range from 77–96% and sensitivity from 76–94%. For the breath hydrogen test the specificity is observed to be 89–100% and sensitivity 69–100%.  

Data is scarce for the reliability of the routine diagnostic tests of lactose malabsorption during childhood. The incidence of false positive results in LTT in children has been reported to be as high as 30%, reducing its value in clinical use.

Genetic testing of the Lactase gene (LCT) is the most accurate test that can diagnose lactose intolerance. The genotype CC is associated with adult-type hypolactasia. Genotypes CT and TT are associated with lactase persistence. DNAfit tests for the LCT gene, and would, therefore, be a valuable investment. 

Sometimes cow’s milk protein allergy gets confused for lactose intolerance. That’s why it’s important to know exactly what Cow’s Milk Protein Allergy is and how is occurs in the body.

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What is Cow’s Milk Protein Allergy?

Cow’s milk protein allergy (CMPA) is an allergic reaction to cow’s milk protein and this involves the immune system. The body produces antibodies against the protein to elicit an allergic response whenever these proteins are ingested. A high percentage of children and adults do not show circulating IgE (immunoglobulin E) specific for cow’s milk proteins and their skin prick test and serum specific IgE antibodies result negative.

 This occurs for the development of a non-IgE-mediated allergic disease. These reactions are characterized by a delayed set up, associated with the onset of symptoms after one hour or many days after the ingestion of cow’s milk proteins. For this reason, these reactions are classified as “delayed hypersensitivity”.  

Often, when people rule out a CMPA based on a negative IgE test, a possible explanation for their symptoms would then be a protein sensitivity which also involves the immune system through a different pathway such as T lymphocytes. 

Milk allergy can be either immunoglobulin E (IgE) or non-IgE mediated. IgE-mediated reactions typically occur immediately after ingestion whereas non-IgE mediated are delayed and take up to 48 hours to develop, but still involve the immune system. It’s the symptoms of non-IgE mediated disease, which are commonly wrongly labelled as symptoms of intolerance, using either the terms ‘lactose intolerance’ or ‘milk intolerance’. 

For the diagnosis of IgE-mediated CMPA, the use of skin prick tests (SPT) or specific serum IgE tests are recommended. There are no validated tests for the diagnosis of non-IgE CMPA, apart from the planned avoidance of cow’s milk and foods containing cow’s milk. This is then followed by reintroduction of cows milk as a home challenge, to confirm the diagnosis. 

Casein vs Whey Protein Sensitivity

Cow’s milk contains around 30–35 g of proteins per litre and includes more than 25 different proteins, but only some of them are known to be allergenic. 

Through the acidification of raw skim milk to pH 4.6 at 20°C two fractions can be obtained: 

The casein fraction consists of four proteins which account for different percentages of the whole fraction: 

The most important allergen of the casein fraction is aS1-casein.

 Allergens found in the whey fraction are: 

The most important allergens of the whey fraction are a-lactalbumin and b-lactoglobulin, accounting for 5% and 10% of the total milk proteins. There are only a few reports describing allergies to minor whey proteins such as immunoglobulin, BSA or lactoferrin.

A major problem of CMPA is the fact that the human IgE response to cow’s milk proteins is characterized by a great variability and that no single allergen or particular structure has been identified that accounts for a major part of allergenicity in milk. 

Sensitization to several proteins occurs in approximately 75% of patients with cow’s milk allergy, with great variability of the IgE response in specificity and intensity. The most frequently recognized allergens seem to be those which are most abundant in cow’s milk, namely caseins, b-lactoglobulin and a-lactalbumin.

What to do if you’re diagnosed lactose intolerant or have cows milk protein allergy?

The most accurate way of knowing the root cause of digestive discomfort on cow’s milk ingestion is either by doing either 

If the diagnosis is lactose intolerance, individuals can include lactose-free milk and fermented products such as yoghurt and cheese. 

If the diagnosis is a cow’s milk protein allergy, the individual should determine which proteins they are specifically sensitive towards; if its casein protein, they can still include whey containing products in their diets. 

It’s therefore important not to self-diagnose as this can result in eliminating milk products unnecessarily from the diet. 

Are you lactose intolerant? Not sure? Find out if you're lactose tolerant with a genetic test.

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