Lactose intolerance is a physiological response to undigested lactose in the large intestine, resulting from lactase enzyme inactivity or deficiency in the small intestine. Lactose itself is a disaccharide sugar, composed of two units: glucose and galactose, which, when digested normally by lactase, then enters the blood stream via tiny blood vessels. Predominantly found in mammalian milks – human, cow, goat, sheep and products like yoghurt. Cheese, butter and double cream contain very low levels of lactose and are often tolerated by adults and older children with established lactose intolerance. It’s worth noting the different types of lactose intolerance.

Secondary Lactose intolerance
Is the most common type and is usually temporary; the term secondary meaning as a result of something else. Secondary lactose intolerance occurs when the small intestinal lining suffers damage or inflammation eg. after a gastro-intestinal infection or surgery.   A lactose free diet should be followed for 6 weeks or until the symptoms have settled before reintroducing lactose back into the diet. This allow the intestine time to repair itself and for the return of normal lactase enzyme production.

Primary Lactose intolerance
Is less common and refers to a permanent reduction in lactase enzyme activity. Worldwide it affects 70% of the population, with large variations in ethnic groups with around 2% of Northern Europeans affected. In people of Asian, African and Indian decent, children as young as 2 – 3 years can loose lactose activity, but this is not normally seen in the UK. However teens may not recover their lactase activity following a gut infection, especially if they are not habitual milk drinkers.  Lactase enzyme activity reduces progressively with age. Careful trial of varying amounts of lactose using guidance on lactose content of dairy foods will determine the amount of lactose that can be tolerated.

The most obvious symptoms are diarrhoea and loose stools, abdominal pain and bloating and flatulence and wind.

  • Diarrhoea and loose stools – caused by lactose in the large intestine where water and salts are drawn into the gut by osmosis causing urgency and increased volume of watery stools
  • Abdominal pain and bloating – caused by bacterial fermentation of lactose in the large intestine where gases and short-chain-fatty-acids are produced.  Effects are nappy rash or sore bottom
  • Flatulence and wind – caused by excessive gas production

What about cows milk allergy?
Cows Milk Allergy (CMA) is an immune response to the proteins found in cow’s milk giving rise to symptoms which can affect the skin, gastrointestinal tract or respiratory system. It is more common in families with atopic conditions such as asthma, eczema or hayfever and is often confused with lactose intolerance, due to similar symptoms. Secondary lactose intolerance is associated with prolonged gastrointestinal symptoms in CMA, resulting from gut inflammation.