Lactose Intolerance

Lactose intolerance is when a person has difficulties digesting the mik sugar lactose. This can lead to digestive issues such as bloating and discomfort. Avoiding lactose in the daily diet is recommended. Lactose intolerance doesn’t involve the immune system and shouldn’t be confused with cow’s milk protein allergy.

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In Europe up to 40% of the population suffer with lactose intolerance, in the UK, the prevalence is about 5%.  Symptoms vary from individual to individual - some can tolerate small amounts of lactose, while others have to avoid it altogether. For those seeking lactose free choices, plant-based products are ideal as they’re naturally free from lactose.

People who are unable to digest the lactose from dairy products in their diet can suffer distressing, often severe, complaints. On the other hand, some individuals have such a low dairy intake that they often have no problems and they are not aware that they are lactose intolerant. Calcium and vitamins enriched soya-based dairy alternatives are naturally free from lactose and are ideal dairy substitutes in the diet.

Lactose is the sugar naturally found in human breast milk and the milk of other animals (such as cow’s milk, goat’s milk and sheep’s milk). Lactose, or milk sugar, is a disaccharide consisting of glucose and galactose. When ingested, lactose is normally broken down in the small intestine into absorbable monosaccharides (glucose and galactose) by the enzyme lactase.
If levels of the lactase enzyme are low or absent, unabsorbed lactose reaches the colon and comes into contact with the colonic bacteria. These bacteria ferment the lactose producing hydrogen and methane gases and small organic molecules. These can cause a number of problems, such as abdominal pain, flatulence, bloating and diarrhoea.

After weaning, the amount of lactase in the small intestine decreases, and the speed at which this occurs is genetically determined. This explains why the prevalence of lactose digestion problems varies among different ethnic groups. As well as the loss of lactase through genetic differences and aging, it can also occur when the cells lining the small intestines are damaged (e.g. coeliac disease).

Lactose intolerance does not involve the immune system and so is completely different to cow's milk protein allergy
Prevalence of lactose intolerance varies widely across the world: some races, particularly those whose diet has been traditionally non-dairy based, are more susceptible e.g. in South-East Asia and parts of Africa. It’s particularly high in people of Chinese and Japanese descent, with 90% thought to suffer some degree of lactose intolerance.. On average, the age at which lactose intolerance starts to manifest is around 5 years.

Figure: Prevalence of Lactose Sensitivity in the World

Did you know that 20,000 years ago we were all lactose intolerant?

DNA analyses of skeletons from archeological sites in Europe show that early Neolithic European populations (5480 BC – 5000 BC) were unable to digest lactose because they lacked the gene that produces lactase. This suggests that lactase persistence alleles were rare until the advent of dairying early in the Neolithic period. Following the growth and development of dairy farming, these then rose rapidly in frequency through the process of natural selection.

Everyone has a threshold of how much lactose they can tolerate. In some people this is very low, about as much as in a cup of coffee, whereas others can tolerate a litre of milk with no problem.
Lactose intolerance can cause abdominal discomfort, usually within a few hours or a few days of consuming milk or dairy products containing lactose.

Gut complications
Abdominal pain

As well as abdominal discomforts, some research suggests that lactose intolerance can also cause other non-gut symptoms.

Possible Non-gut complications
Loss of concentration
Muscle and joint pain Eczema
Hearth palpitation
Mouth ulcers
Lactose intolerance results in undigested lactose arriving in the large intestine, the colon, where it is fermented by the enormous range of bacteria present here. This fermentation results in the production of gases and small organic toxins. The gases, hydrogen and methane, cause the distension and pain. It’s been suggested that the other non-gut discomforts are due to the bacterial ‘toxins’ being absorbed into the blood where they then reach the brain causing headaches; the heart to cause palpitations; the muscles and joints resulting in pain; and the immune system exacerbating allergies and other problems.
  1. If lactose intolerance is suspected a good clinical history can show a clearer link between the symptoms and the ingestion of lactose. A challenge test may then be recommended. This involves a strict lactose-free diet for 2 weeks followed by the reintroduction of dairy products. Recurrence of symptoms can confirm the diagnosis, but in some cases this method is still inconclusive. The benefit of this test is that individuals can determine their own sensitivity threshold to lactose.
  2. A lactose tolerance test involves measuring glucose levels in the blood after an oral administration of lactose. However results can be influenced by an individual’s insulin response, giving rise to false negative results in people with diabetes, and can also be affected by bowel motility. It should be noted that this procedure can cause some discomfort.  
  3. The most frequently used test is the hydrogen breath test. This measures the hydrogen concentration in expired air after taking an oral dose of lactose. The increase in hydrogen is a measure of the fermentation of lactose by the bacteria in the colon.
  4. Although this is the most reliable test, false negative results can arise in around 10-20% of the world's population as they have a bacterial composition unable to produce hydrogen. Furthermore the use of antibiotics can change the gut flora causing false negative results.
  5. A biopsy of the small intestine can determine lactase activity in the small intestine, although this is an invasive method.
  6. Genetic test: this test analyses a polymorphism at C/T13910. In a Northern European Caucasian a CC pattern at this locus always leads to lactose intolerance. Alternative tests are required in different populations due to other polymorphic variants. These genetic tests are not yet freely available.
For anyone suffering with lactose intolerance, it’s generally recommended that lactose should be completely eliminated  to begin with (by following a lactose free diet) and then to gradually reintroduce small amounts to determine tolerance levels.

Soya-based dairy alternative (drinks, desserts, plant-based alternatives to yoghurt, plant-based alternatives to cream) are naturally free from lactose. Subsequently the calcium and vitamin enriched soya-based dairy alternatives are ideal dairy substitutes in the diet. Other plant based drinks such as almond drink, hazelnut drink and rice drink can also be used as they contain no lactose.
Matthews SB, Waud J, Roberts A and Campbell AK. Systemic lactose intolerance: a new perspective on an old problem. Post Grad. Med. J. 2005;81:167-173.
Campbell AK, Jenkins-Waud J and Matthews SB. The Molecular Basis of Lactose intolerance. Science Progress 2005;88:157-202.
Waud JP, Matthews SB and Campbell, AK. Measurement of Breath Hydrogen and Methane, together with Lactase Genotype, Defines the Current Best Practice for Investigation of Lactose Sensitivity. Annals of Clinical Biochemistry 2008;45:50-8.