Lactose Intolerance

In the case of lactose intolerance, the consumption of milk and milk products triggers symptoms. The cause is the absence or inadequate production of the digestive enzyme lactase. Lactase is produced in the mucous membrane of the small intestine and splits lactose into glucose and galactose.

Causes and symptoms

If the small intestine produces too little lactase or no lactase at all, the lactose cannot be split or is only partially split, and then moves to the large intestine, where it is broken down by intestinal bacteria into hydrogen, carbon dioxide, lactic acid and acetic acid. This causes diarrhea, bloating, nausea, flatulence and cramping abdominal pain.

Lactose intolerance should not be confused with a milk protein allergy. Here there is an allergic reaction with corresponding antibody production to the protein of the milk.


The diagnosis is carried out by means of a lactose load test. After taking 50 grams (1.7 ounces) of lactose, the hydrogen content in the breath or the blood sugar is measured.


The basic principle of lactose intolerance therapy consists in dispensing with or restricting the consumption of milk and milk products, depending on the degree of severity.

Severity of lactose intolerance

Severity Milk sugar (g) per day that is tolerated without discomfort
light 8 – 10 g (.2 - .3 oz)
medium bis 1 g (.03 oz)
heavy 0

Severity ranges from a complete intolerance to a mild intolerance. Ultimately, it is important for every person affected to know the amount of lactose at which they react with symptoms. Only rarely do very small amounts of lactose (less than 3 grams or .10 oz) cause intolerant reactions, so that foods with small amounts of lactose and consumed in small amounts are usually tolerated without problems.

Acidified milk products, such as yogurt and many cheeses, are often well tolerated despite the high lactose content, since the lactic acid bacteria contained in the yohurt itself break down most of the lactose.

In cases of severe lactose intolerance, the digestive enzyme lactase can also be prescribed. The simultaneous intake of lactase and milk products prevents the major symptoms.

Here you will find tables on lactose-containing foods and lactose-containing dairy products.