Lactose What is lactose intolerance?Dairy products contain the milk sugar lactose. Some people are unable to digest lactose because they lack the enzyme lactase which splits the lactose into in parts (galactose and glucose).Lactose that is not digested enters the colon and is fermented by the action of bacteria in colon. This produces wind (bloating and flatulence) and loose bowel motions and perhaps abdominal cramps as a result of the distension from increased gas production.A lack of the lactase enzyme is more common in Asian, African and Middle Eastern populations. This is actually the normal state. The mutation, affecting the majority of the European population, leads to persistence of the lactase enzyme into adulthoodTemporary lactose intolerance is common after a gastroenteritis illness.Lactose intolerance is not the same as having irritable bowel syndrome but may be an aggravating factor for IBS. How can the diagnosis be made?The association of symptoms with dairy food intake may not be obvious and there will need to be a one-month trial of dairy food exclusion to see if there is any improvement. Often there does not need to be complete dairy food exclusion in the long-term to maintain a benefit seen after a trial of exclusion.There are tests available for testing the level of lactase enzyme activity. The most accurate test is a hydrogen breath test. This requires the collection of a sample of exhaled air every 30mins over a 3-hr period after having ingesting a large amount of lactose. Some symptoms may be caused by the lactose load if there is a genuine intolerance.The other method is to take a biopsy sample from the small bowel (duodenum) at the time of a gastroscopy. In practice this has not proved to be very accurate.I have adopted the pragmatic approach of trying a dairy-free diet rather than trying to prove a problem with lack of lactase enzyme. In general it is the lactose levels in foods that determines intolerance but there are probably other parts of dairy products that can cause symptoms. Tips about a lactose-free diet. Soft cheese has much more lactose than hard cheese. Lactose levels in yoghurt and generally low and often tolerated when other dairy foods give symptoms. The presence of acidophilus and lactobacillus in natural yoghurt may ease some bowel symptoms. Milk - as drinks or on cereal - is the source most likely to be giving the highest lactose load - use soya-based or rice-based milk on cereal. Calcium intake can be maintained by taking yoghurt or by using soy milk enriched with calcium (So Good). Some UHT milks are the lactose levels reduced. Lactose-free ice-cream is also available.