Lactose Intolerance (Milk Sugar Intolerance)

What is lactose (milk sugar)?

Milk sugar (lactose) is a natural component of milk and a so-called disaccharide sugar, i. e. it consists of two separate monosaccharides – glucose and galactose. For milk sugar to be absorbed in the small intestine, it must first be broken down into these two components. Usually the enzyme lactase (beta-galactosidase), which is found in the mucosa of the small intestine, breaks down milk sugar.

What is lactose intolerance?

Persons who are intolerant to lactose cannot break down milk sugar into its separate components. A lactase deficiency reduces the ability to break down sugar. As a result the milk sugar remains in the bowel, binds water, and ultimately causes diarrhoea. In addition, intestinal bacteria digest the unsplit sugar, causing flatulence.

Prevalence

The majority of the world’s population is not able to completely digest milk sugar after infancy. In other words, lactose intolerance is normal in those cases. Moreover, the sugar splitting enzyme is hardly ever found in Asians. You will therefore not find any milk or cheese products in the diets of people from Asian regions. In Central Europe an estimated amount of more than 15 % of the population suffers from lactose intolerance. Milk sugar intolerance must not be confused with an allergy to dairy products.

There are different types of lactose intolerance:

Primary lactose intolerance This is the most frequent type of lactose intolerance. It is congenital and found most of all in warmer, sunny regions. It occurs from around the age of five and becomes worse with age. Consequently 70 % of Europeans aged 60 cannot digest lactose.

Secondary lactose intolerance This is not a genetic defect, but a disorder of the intestinal mucosa. The enzyme lactase is formed in the epithelium of the small intestine. This layer of the intestine is the first to be damaged by other diseases or external influences. Such influences include taking antibiotics for a longer period of time, for instance. This form of lactose intolerance is reversible, i.e. it can be cured.

Depending on the remaining beta-galactosidase activity in the above described groups of consumers suffering from lactose intolerance, there are significant differences in the amount of lactose that can be tolerated. The advice given by the German Nutrition Society (DGE) takes this fact into account. As a result the majority of persons intolerant to lactose are free of symptoms if they keep to a diet low in lactose (8 – 10 g per day). Very sensitive persons are advised by the DGE to limit lactose consumption to a maximum of 1 g per day. Individuals suffering from galactosaemia, however, should follow a diet practically free of galactose and also free of indirect galactose sources such as lactose.

How much lactose can be found in food?

Average Lactose Contents  of Selected foods	per 100 g	per potion	Portion Size
Milk chocolate	9.5 g	2.9 g	30 g
Ice cream (milk-based)	6.7 g	8.4 g	125 g
Milk	4.7 g	11.8 g	250 ml
Latte Macchiato	4.1 g	6.2 g	150 ml
Yoghurt	3.2 g	4.8 g	150 g
Chocolate spread	1.9 g	0.3 g	15 g
Camembert cheese (50 % FDM)	0.1 g	0.03 g	30 g
Emmentaler cheese (45 % FDM)	< 0.05 g	< 0.05 g	30 g
Source: Souci/Fachmann/Kraut "Food Composition and Nutrition Tables", 7th revised and completed edition (April 1st, 2008), Wissenschaftliche Verlagsgesellschaft mbH, Stuttgart

Labelling

In Germany the Society of Food Chemistry Division’s working group ”Nutritional Issues” published a policy document in 2005 specifying the labelling of foods containing lactose (Lebensmittelchemie 59, 45[2005]).

low in lactose Lactose content not exceeding 1 g / 100 g (mI) or 10 g/ kg (l)

strictly low in lactose Lactose content not exceeding 100 mg / 100 g (mI) or 1000 mg / kg (l)

lactose-free Lactose and galactose content not exceeding 10 mg / 100 g (mI) or 100 mg / kg (l)