Lactose intolerance causes constipation

Lactose intolerance

Back to overview

27.03.2018 - Anja Proft

If symptoms such as abdominal pain, diarrhea and flatulence occur after consuming milk and dairy products, milk sugar - lactose - is often the culprit. Lactose intolerance affects more and more people, the suspicion should be clarified.

In Germany, around 15–20% of the population suffer from lactose intolerance. This means that they can no longer digest milk sugar properly and that milk and milk products can cause severe gastrointestinal complaints in those affected. The symptoms can appear relatively suddenly, as the activity of the lactose-splitting enzyme (lactase) gradually decreases and usually leads to intolerance in adulthood. In other cases, lactose intolerance is the result of an illness and is therefore only temporary.

If they suspect lactose intolerance, many people avoid milk and dairy products as a precaution. However, since these are particularly rich in nutrients, the risk of a deficit in important vitamins and minerals increases. A change in diet should therefore only be made if the diagnosis is clear. The hydrogen breath test is particularly suitable for this.

Lactose-free substitute products are now available in every supermarket and the range is constantly expanding, so that those affected can fall back on a wide range. However, the “free from” products do not offer any health benefits to the healthy. On the contrary: These products are usually significantly more expensive, so that unnecessarily large amounts of money are spent on them.

What is lactose?

Lactose, also called milk sugar, is a double sugar (disaccharide) made up of the two single sugars glucose and galactose. It occurs naturally in milk and dairy products. However, it is being added to more and more finished products industrially (e.g. ready-to-eat soup, cream vegetables, biscuits, pizza) for technological reasons, so that products also contain lactose that one would not suspect of. It makes sense to take a look at the list of ingredients in the food. Lactose can also be found in medicines. In order to use the lactose, the body needs the enzyme lactase. This is released through the mucous membrane of the small intestine and splits the lactose into its two simple sugars.

Which foods are particularly high in lactose?

The lactose contents of well-known foods are listed as examples:

FoodLactose (g / 100g)Lactose (g / portion)

Condensed milk, 10% fat

12.5 g

0.63 g / 5 g

Cow's milk, 3.5% fat

5.0 g

10 g / 200 ml


4.2 g

8.4 g / 200 ml

Whipped cream

3.3 g

0.83 g / 25 g

Yoghurt, natural 3.5% fat

3.2 g

5.6 g / 175 g

milk chocolate

9.5 g

3.8 g / 40 g

Milk powder

38.0-51.5 g

7.6-10.3 g / 20 g

Condensed milk, 4-10% fat

9.3-12.5 g

0.7-0.9 g / 7.5 g

Ice cream

5.1-6.9 g

3.8-5.2 g / 75 g

Edam, Gouda, Tilsiter

2-3 g

0.6-0.9 / slice (30g)

Brie, Camembert

1-2 g

0.3-0.6 / slice (30g)


<0.1 g<0.1 g / 30 g

The lactose content of cheese varies greatly. You can recognize this by the amount of "carbohydrates", since lactose is the main carbohydrate in cheese. The longer the cheese has matured, the harder it is and the less lactose is left. Hard parmesan cheese, for example, contains almost no lactose.

Lactose intolerance is triggered by a lactase deficiency

If the body produces too little or no lactase at all, the milk sugar in the small intestine cannot be used sufficiently and a lactose intolerance develops with corresponding symptoms. There are three causes of lactase deficiency.

Primary (hereditary) lactase deficiency

The primary lactase deficiency is genetic and the most common cause of lactose intolerance. By the way, humans are the only species that still consume milk in adulthood. And from another species too - have you ever thought about it? Therefore, the development of lactose intolerance is a natural process. Usually enough lactase is still produced in childhood, but the enzyme activity decreases with advancing age. This creeping process begins as soon as breast milk is no longer the main food. If the lactase activity is no longer sufficient, digestive problems occur. This is usually the case in adulthood, but sometimes even in childhood or adolescence. In Germany, an estimated 15 to 20% are affected by this form.

Secondary (acquired) lactase deficiency

The enzyme lactase is produced in the mucous membrane of the small intestine. If this is disturbed, no longer enough lactase can be produced. This secondary lactose intolerance may be caused by diseases of the small intestine (e.g. celiac disease or Crohn's disease), bacterial or fungal infections, gastrointestinal operations or medication (e.g. antibiotics). The lactose intolerance is usually limited in time. If the damage to the mucous membrane can be reversed, the mucous membrane of the small intestine can produce lactase again. Successful therapy of the underlying disease therefore usually normalizes lactase activity as well.

Congenital lactase deficiency (present from birth)

If the deficiency exists from birth, one speaks of a congenital lactase deficiency. This form of lactose intolerance is very rare. Due to a hereditary enzyme defect, no lactase is formed at all, which is why even newborns are severely intolerant. Even the smallest amounts of lactose can cause severe discomfort in babies. Only a special lactose-free diet prevents serious consequences (e.g. brain damage) from occurring.

Lactose intolerance is a digestive disorder

Lactose intolerance must be differentiated from a food allergy, which triggers an immune reaction in the body. In the small intestine, lactose is normally broken down into its two simple sugars with the help of the enzyme lactase. These are then absorbed through the mucous membrane of the small intestine. If the body produces too little or no lactase at all, the milk sugar molecules cannot be broken down or not in sufficient quantities and reach the deeper intestinal sections unchanged. In the large intestine, they are digested by the bacteria that live there. This process produces intestinal gases (methane, hydrogen and carbon dioxide) and organic acids, which are then responsible for digestive problems.

What are the typical symptoms of lactose intolerance?

Lactose intolerance manifests itself with a feeling of fullness, gas, diarrhea and cramps. These gastrointestinal complaints are caused by gases and short-chain fatty acids, which are formed from lactose by the intestinal bacteria. The symptoms can appear shortly after consuming lactose-containing foods, but sometimes not until hours later or the next morning. In addition, there are often unspecific symptoms such as headache and fatigue.

Geographical distribution of lactose intolerance

The majority of the world's population is lactose intolerant. This makes it the most common food intolerance worldwide. There are big differences between north and south. While only 3 to 8% of people in Scandinavia are affected by lactose intolerance, in the Mediterranean region this is already around 70% and in the regions around the equator in Africa even 98% cannot tolerate lactose. One explanation for this north-south divide is likely to be found in the cultural use of milk as food. If milk is consumed in certain population groups or if there is intensive cattle breeding, lactase production is more likely to be maintained and milk sugar is still tolerated.

Lactose Intolerance: Test Procedure

Since other food intolerances cause similar symptoms, it can be difficult to identify the underlying culprit. Complaints in connection with the consumption of milk and milk products can therefore only provide initial indications. You can read more about this in our article on the 4 most common food intolerances.
Avoiding dairy products as a precautionary measure without a confirmed diagnosis is not recommended. Not consuming milk and dairy products is often associated with a lower intake of nutrients (e.g. calcium, vitamin D, fluorine, iodine, vitamin B12).

There are various test methods that can be used to detect lactose intolerance. However, not all methods are equally useful.

H2 breath test

The hydrogen breath test is most commonly used to diagnose lactose intolerance. It can also be used to detect other intolerances, such as fructose intolerance. At the beginning, the affected person blows into a breathing device. After taking in the test liquid, which contains a defined amount of lactose, the patient then blows again into the breathing apparatus at intervals of 30 minutes. The amount of hydrogen is measured each time. An increase in the concentration above a certain limit value as well as the symptoms during the test procedure indicate a lactose intolerance. The measured hydrogen is a product that the intestinal bacteria form from the undigested lactose in the large intestine.

The simple breath test is also good to perform in children. No blood draw is required. This test is the method of first choice and it is inexpensive. The patient receives his result after the test.

The patient must prepare for the test (e.g. appear sober, stop certain medications). It usually lasts around 120 minutes. If the patient is lactose intolerant, symptoms may appear while the test is being carried out.

Lactose intolerance test

Genetic test

Primary lactose intolerance can be determined using a genetic analysis (blood test).

A single blood sample is sufficient, which is why the test is carried out particularly quickly. The patient does not have to be sober or otherwise prepare for the test. There is no intake of lactose as a test substance, which means that there are no symptoms of intolerance. If there is a confirmed lactose intolerance, the genetic test can differentiate between the primary and secondary form.

Secondary lactose intolerance is not detected by this test. This test is relatively expensive. The patient receives the result only after a blood analysis in the laboratory.

Lactose tolerance test (blood sugar test)

This test first measures the fasting glucose level in the blood. Then a defined amount of lactose is drunk in water. The glucose level in the blood is measured at intervals of 30 minutes. If there is an intolerance, the lactose cannot be split into glucose and galactose and the blood sugar does not rise. If gastrointestinal complaints such as flatulence and abdominal cramps also occur, the patient is very likely lactose intolerant.

The test is inexpensive. The glucose level can be determined with a simple blood glucose meter.

The patient must be sober when performing the test and plan several hours for performing the test. If you are lactose intolerant, you will usually experience symptoms while the test is being performed. This test is less accurate than the H2 breath test and is therefore not the method of first choice. The measured values ​​can be falsified in people with diabetes.

Provocation test

The provocation test is not a diagnostic test because it does not measure laboratory values. Rather, it is a self-test. The affected person refrains from lactose-containing products for a certain period of time and observes whether his symptoms go away. If this is the case, this is a first indication of the presence of a lactose intolerance. Then the person concerned drinks a glass of dissolved lactose. If the typical symptoms reappear, this indicates a lactose intolerance.

It is not advisable to make a diagnosis based on this self-test, as it is very error-prone. Lactose occurs “hidden” in some finished products, which is why it is not necessarily obvious to the layperson. The lactose-free diet is often not adhered to strictly enough. In large quantities, milk sugar can have a laxative effect. This effect can be misinterpreted as an intolerance if lactose is consumed again. Reliable evidence of lactose intolerance can only be provided by a doctor or a medical laboratory.

Diagnosis of lactose intolerance: what's next?

The interplay between the result of the lactose intolerance test and the symptoms is important. In addition, the age at the occurrence of the intolerance and its severity are decisive. Although it is usually the primary form of lactose intolerance, in some cases another disease, such as celiac disease, chronic inflammatory bowel disease (Crohn's disease, ulcerative colitis), is the cause of the lactose intolerance. If this secondary form is suspected, further examinations are required because the underlying disease must first be found and then treated. Successful therapy usually leads to the lactose being tolerated again.

If it is a hereditary form of lactose intolerance (primary form), milk and dairy products must first be avoided. In the first phase, foods containing lactose are completely avoided. In a subsequent test phase, it is determined which amounts of lactose can be tolerated by the patient by gradually increasing the milk sugar intake. The tolerable amount of lactose varies greatly from person to person. Sometimes small portions of milk are still tolerated, sometimes lactose-containing foods have to be omitted completely.

Individual portions of milk and dairy products are best tolerated if they are spread over the day and preferably added during the meal. A nutritionist is recommended to accompany the change in diet.
Sour milk products such as yoghurt or kefir are usually well tolerated, as the lactic acid bacteria they contain break down most of the lactose in these foods.

Lactose-free substitutes

An ever-increasing range of lactose-free alternatives (e.g. soy, almond, cereal milk and lactose-free milk) is available on the market today. It is important that the daily nutritional requirement (especially calcium) is covered. Enzyme preparations containing lactase are also commercially available. Taken shortly before a meal, these are supposed to ensure the complete digestion of lactose. However, so far there are no studies that confirm its effectiveness. Just like the dosage, this is individual and varies depending on the preparation. Regular consumption of these preparations is therefore not recommended. However, they can be helpful in certain exceptional situations (e.g. going to a restaurant or vacation).

Do you suspect lactose intolerance and do you have any further questions? Then please contact us to make an appointment.


Swell: Krankheiten/bauch-und-bauch-organe/laktoseintoleranz/verarbeitung-und-selbsthilfe/2528-kennen-sie-den-laktosegehalt- from-milk-chocolate-yogurt-ice-cream-or-kefir.html

About the author

I am responsible for the exciting marketing department in the Hamburg Stephansplatz Medical Laboratory. As an ecotrophologist, I am not only interested in a balanced diet, but also in new trends in sport and lifestyle. I love Hamburg's city life, but I also like to take time out from sporting activities in nature or traveling to foreign cultures with my backpack.