Many Europeans and some populations in Africa, the Middle East and Southeast Asia can digest lactose throughout life thanks to the presence of the enzyme lactase in the small intestine. This is called lactase persistence. Most people who cannot tolerate lactose can digest about 12 grams of lactose per day. This is equal to a large glass (250 ml) of milk. Yoghurt contains less lactose and semi-hard cheeses hardly contain any lactose.
Lactase converts lactose into glucose and galactose in the small intestine. A part of the world population no longer produces the enzyme lactase or to a lesser degree after childhood. This results in the lactose remaining in the large intestine partially undigested. Bacteria in the large intestine then ferment the lactose causing flatulence and may also cause gastrointestinal discomfort.
The treatment of lactose intolerance consists of omitting lactose from the diet. Usually, it is not necessary to eat completely lactose-free. Small amounts of lactose usually cause no discomfort and are not harmful. Although some people do have complaints with an intake of less than 6 g of lactose most people with diagnosed lactose intolerance can digest about 12 g of lactose per day (about 250 ml of milk) with little to no symptoms. This is especially so if consumption is spread throughout the day, taken with meals and using products with a low lactose content. As lactose is partially converted by lactic acid bacteria, fermented dairy products, for instance yoghurt, contain less lactose. Semihard cheeses, such as Dutch-type cheese and cheddar, hardly contain any lactose after six weeks of ripening time.
FIGURE 1 Adults with lactase persistence
Light = in these areas the prevalence of lactose intolerance is higher. Generally, these populations have a lower lactase production and lactose digestion is more difficult.
Dark = in these areas the prevalence of lactase persistency is higher. Generally, these populations can digest lactose throughout life thanks to the presence of the enzyme lactase. Source Itan, Y et al (2009)
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