Lactose Intolerance: A harmless but irritating condition

Find out why certain people cannot consume dairy products and what happens when they do. Also, learn about the alternative options that lactose intolerant individuals have available. 

Lactose Intolerance, also called hypolactasia, is the most prevalent food intolerance in the world (>70% people have it). This condition is caused by the deficiency and sometimes absence of an enzyme known as lactase. This enzyme is produced by intestinal cells called enterocytes in order to break down lactose into simple sugars, which can then be absorbed and used by the body to produce energy. Lactose is a disaccharide, a sugar molecule composed of two smaller sugar residues: glucose and galactose. Lactase essentially acts like a pair of scissors, cleaving the sugar lactose to produce glucose and galactose, which can then be absorbed.



Figure 1. Lactose is broken down by the action of lactase into two simple sugars: glucose and galactose.

Because lactose intolerant individuals have deficient levels of lactase, when they ingest lactose, this sugar molecule doesn’t get broken down, meaning it cannot be absorbed. The body then moves lactose to a section of the large intestine known as the colon. Most of the symptoms that lactose intolerant individuals have are due to what happens to lactose in this part of the gut. In the colon, there are groups of bacteria that ferment lactose to produce energy, but they also release short chain fatty acids such as methane. Fermentation produces gas and results in the cleavage of lactose into glucose and galactose. Unfortunately, these simple sugars cannot be absorbed in the colon and a lot of fluid gets drawn in by osmosis. Bacterial lactose fermentation results in a substantial increase in gas and fluid in the bowel which causes a number of uncomfortable symptoms: abdominal pain, flatulence, cramping, bloating, diarrhoea (caused by the osmotic effect of lactose).


Figure 2. Lactose is absorbed in the small intestine after being decomposed into glucose and galactose by the actions of the enzyme lactase. However, in lactose intolerant individuals, lactose is not broken down and remains as a disaccharide (complex sugar), thereby it doesn’t get absorbed. Lactose passes to the colon in the large intestine, where it is a substrate (food-source) for colonic acid bacteria.

Most people with lactose intolerance don’t have to completely avoid lactose containing foods. They still produce small amounts of lactase, meaning they can usually consume a glass of milk without eliciting symptoms. Dairy products are better tolerated if they are spread throughout the day and if they are consumed in combination with other food e.g. yoghurt with cereals. What tends to be quite difficult for lactose intolerant individuals is the avoidance of lactose containing products. Things like dairy products are pretty obvious, but there are many unexpected sources of lactose: bread, many prepared foods and even medical tablets!

Since dairy products are a rich source of many minerals and vitamins, lactose intolerant individuals must look for alternative nutrient sources. Milk tends to be the richest source of calcium in our diets and it is essential for building strong and healthy bones. Other nutrients found in dairy products that must be considered are Vitamin A, B2, B5 and B12 and the mineral iodine. There are many calcium fortified beverages: soy, coconut, almond, oat, rice etc. Fortunately, people with lactose intolerance don’t have to choose alternative sources to milk anymore. Milk can now be rendered lactose-free by pretreating it with lactase or by genetic engineering. Lactose intolerance is easier to manage than ever before, though it can still be tricky to avoid lactose in some unexpected foods.


Figure 3. The best substitute for lactose intolerant individuals is simply milk that has been rendered lactose free. This way they don’t have to worry about missing any important nutrients found in dairy products. This milk has higher levels of glucose and galactose because all the lactose has been broken down into these two simple sugars.



Mattar, R., de Campos Mazo, D.F. & Carrilho, F.J. (2012). Lactose intolerance: diagnosis, genetic, and clinical factors. Clinical and Experimental Gastroenterology, 5, 113-121.

Swagerty Jr, D.L., Walling, A.D. & Klein, R.M. (2002). Lactose intolerance. American Family Physician, 65(9), 1845-50.




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