Lactose Intolerance – Back to the Basics

Written by: AllergySense

What exactly causes lactose intolerance?
Unlike allergies, which start in the immune system and can affect the respiratory and digestive system as well, lactose intolerance only affects the digestive system. Lactose intolerance occurs when the small intestine is not producing sufficient lactase, an enzyme that breaks down lactose, the primary sugar in milk, into its components – glucose and galactose. The incompletely digested lactose travels into the large intestine, where friendly bacteria (microflora) that live in our colon converts the lactose into short-chain fatty acids and gases (mostly hydrogen), causing stomach cramps, bloating, and flatulence, and in some cases, diarrhea. The degree of a person’s lactose intolerance is dependent on their remaining lactase activity, the amount of lactose consumed, the microflora activity in their colon, and the irritability of their digestive tract.

Lactose intolerance is usually confirmed using a hydrogen breath test – after an overnight fast, the subject is given a sample of pure lactose (usually 50 g) dissolved in water. If the lactose is not digested, then hydrogen produced by microflora in the colon will be detected in the breath about 2-3 hours later.
There are two main types of lactose intolerance – primary lactose intolerance and secondary lactose intolerance.
Primary lactose intolerance occurs when lactase activity decreases after children are weaned off of milk. It is more common in certain racial or ethnic groups, such as Africans, Asians, and Aboriginals, who historically did not consume dairy in their traditional diets. It is estimated that 75% of adults worldwide experience a decrease in lactase activity, with statistics ranging from as low as 5% amongst northern Europeans, and over 90% in some African and Asian countries.
Secondary lactose intolerance occurs when another gastrointestinal disorder causing damage to the small intestine, such as Crohn’s disease, celiac disease, gastroenteritis (stomach flu) and exposure to parasites, causes a temporary disruption in lactase production. Lactase production usually resumes after the causative factor is corrected, though in some cases the lactose intolerance becomes permanent.
A third cause of lactose intolerance is congenital lactase deficiency, which is a genetic disorder that prevents the production of lactase and therefore presents at birth. It is usually diagnosed in early infancy, and is treated similarly to primary lactose intolerance.
What are some foods/ingredients that people with lactose intolerance need to watch out for?
Although it is imperative for people with milk allergies to avoid all milk products and foods containing milk products, people with lactose intolerance are often encouraged to consume increasing amounts of lactose in order to test their individual tolerance and to help their colonic microflora adapt to breaking down the lactose, thereby increasing tolerance.  Hard, aged cheeses (i.e. Swiss, cheddar) and soft, ripened cheeses (i.e. brie, camembert) are very low in lactose content due to the fermentation process. Yogurt and kefir, a fermented dairy drink, may also be tolerable as the bacterial cultures used in the products produce some lactase. Some people with lactose intolerance find that taking lactase supplements (i.e. Lactaid ®) helps, but individuals will need to experiment with the timing and dosage of them to find out what works best with different foods.
While lactose is not naturally present in non-dairy foods, it is a common food additive that can be found in processed foods, including processed meats, margarine, bread, cereal, protein bars, meal replacements. People with lactose intolerance may need to watch out for foods containing lactoserum, whey, milk solids, or modified milk ingredients.
What are some nutritional implications of having a milk allergy or being lactose intolerant?
As mentioned above, people who are lactose intolerant may still be able to tolerate dairy products, and are thus able to enjoy a balanced diet that includes all of the food groups. For those who cannot tolerate dairy products, you may want to refer to my previous article on non-dairy sources of calcium and vitamin D to ensure you are meeting your needs for optimal bone health. Ask your doctor to refer you to a registered dietitian to assess whether you are meeting all your dietary needs and to make any necessary recommendations.

This article was written by Vincci Tsui, a Registered Dietitian based in Calgary, Alberta, Canada. She obtained her Bachelor of Science in Nutritional Sciences from McGill University, where she also completed her dietetic internship, which included placements in Montreal, Calgary and Hong Kong. She is currently practicing in a collaborative care clinic where she meets with clients with a variety of health and nutrition issues, including food allergies and sensitivities.Vincci is as passionate about food as she is about healthy eating and nutrition, and she strives to provide solutions that are healthy, yet tasty and easy to incorporate into busy lifestyles.

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