A protein shake with milk after training, a fruit yogurt in the afternoon, and a little later your stomach starts rumbling. If this happens often, it is easy to suspect lactose intolerance and cut out all dairy products. That is rarely necessary and can mean you fall short on protein and calcium. This article explains what happens in the gut with lactose intolerance, how common it is in Switzerland and how a meaningful breath test works. You will also learn how to find your personal tolerance threshold and which dairy products and alternatives are suitable.
What happens in the gut with lactose intolerance
Lactose, also known as milk sugar, is a double sugar (disaccharide) found in milk and dairy products. The small intestine, however, can only absorb single sugar molecules. That is why the enzyme lactase first has to split milk sugar into its two building blocks: glucose and galactose. In lactose intolerance, there is a lactase deficiency. Some of the lactose remains unsplit and moves on into the large intestine.
There, the gut bacteria take over. They ferment the milk sugar, in other words they break it down, producing gases such as carbon dioxide, hydrogen and methane. Short-chain fatty acids are also formed, and these cause water and sodium to be released into the gut. More gas and more water in the gut explain the two most common symptoms: bloating and diarrhoea.
Typical symptoms
- Bloating and flatulence (wind)
- Diarrhoea
- Constipation
- Abdominal pain and cramps
Many people are surprised that milk sugar can also cause constipation. People who mainly react in this way appear to have more methane-producing bacteria in their gut, and methane can slow down the movements of the intestine. Lactose intolerance must be clearly distinguished from an allergy. Its symptoms are unpleasant but not life-threatening. A food allergy, by contrast, involves the immune system and can cause severe reactions, up to and including respiratory arrest.
How common lactose intolerance is and which forms exist
Prevalence varies greatly from country to country. In Switzerland, about one in five people is affected, which is around 20 percent. In countries further south, such as Spain or Italy, the proportion rises to as much as 70 percent, and in Asia practically everyone is affected. Worldwide, the figure is about two thirds of the population.
Three forms can be the cause:
- Primary lactose intolerance: Lactase activity decreases during childhood or adolescence. This form is genetic and particularly common in countries where dairy products have traditionally been eaten very rarely or not at all.
- Secondary lactose intolerance: It develops as a result of an intestinal disease such as coeliac disease, Crohn's disease or a bacterial infection. This damages the lining of the small intestine, more precisely the so-called brush border, where lactase is produced.
- Congenital genetic defect: This form is very rare.
Primary and secondary lactose intolerance usually persist. That does not mean, however, that dairy products are off limits altogether. Depending on how much enzyme activity remains, people with lactose intolerance can still tolerate smaller or larger amounts of lactose. Avoiding lactose completely is only indicated in the case of the congenital genetic defect.
Testing for lactose intolerance: how the hydrogen breath test works
A reliable diagnosis requires a hydrogen (H2) breath test and a detailed medical history, that is, a thorough record of your symptoms. For the breath test, you drink a lactose solution, and the hydrogen in your breath is then measured. Hydrogen is not produced by the body's cells but almost exclusively by bacteria that ferment carbohydrates in the large intestine. If undigested lactose arrives there, production rises markedly and quickly, so an increase can already be measurable within the first few hours. The threshold is an increase of 20 ppm (parts per million) above the baseline value.
The test dose is crucial. The recommended amount is 25 grams of lactose, which corresponds to about half a litre of milk and therefore to an amount within the normal range of consumption. In practice, tests are sometimes carried out with 50 grams. This dose is above usual consumption, and even people who have no symptoms in everyday life can respond to it with incomplete absorption. The result is then a false positive. Lactose intolerance can therefore only be assumed if the test with 25 grams is positive and symptoms occur at the same time.
False negative results also occur. If the test is too short and intestinal transit is slow, the test solution only reaches the large intestine after the test has ended. In addition, some gut bacteria mainly produce methane instead of hydrogen. This also causes symptoms but cannot be detected with a test that measures hydrogen only.
Preparation includes twelve hours of fasting (water is allowed up to one hour beforehand) and one to two days without high-fibre foods. Whether you also need to stop taking medication or fibre supplements for a while is something to clarify with your doctor. If no breath test is available or you would rather not have one, an intolerance can also be uncovered through targeted elimination and reintroduction alone.
Finding your personal tolerance threshold in three steps
A low-lactose diet can reduce symptoms. Cutting out lactose completely is usually not necessary. To find out how much lactose you can tolerate, a three-step approach makes sense. It follows the same principle as an elimination diet: first leave it out, then test in a targeted way.
- Avoid: For about two weeks, you leave out all products containing lactose in order to become symptom-free.
- Test: You then reintroduce small amounts of products containing lactose and check how you react to them.
- Eat a balanced diet in the long term: Knowing your threshold, you put together a balanced diet that covers your needs.
Record everything in a food and symptom diary: what you ate, when and in what quantity, and which symptoms occurred. The composition of the meal also plays a part. Combined with foods rich in fat and protein, the stomach empties more slowly, which can promote absorption in the small intestine. The same amount of lactose may then be better tolerated.
Lactose, incidentally, is one of the so-called FODMAPs. The abbreviation stands for fermentable oligosaccharides, disaccharides, monosaccharides and polyols, in other words short-chain carbohydrates that ferment rapidly and are poorly absorbed. A low-FODMAP diet is mainly relevant for irritable bowel syndrome. Whether lactose in particular is one of your triggers can be clarified specifically with a medical history and a breath test.
Lactose content: what is in cheese, yogurt and convenience foods
Dairy products vary greatly in their lactose content. Some guideline values per 100 grams:
- Whey powder: 75 g
- Milk powder: 35 g
- Cow's, goat's or sheep's milk: 4 to 5 g
- Yogurt or kefir: 3 to 6 g
- Cottage cheese: 3 g
- Soft cheese: 1 g
- Semi-hard and hard cheese: less than 0.1 g
Thanks to its ripening process, hard cheese is practically lactose-free. Butter, too, is naturally free of lactose or very low in it. Both are therefore usually well tolerated. Soft cheese contains less lactose than milk or yogurt, and smaller amounts are often tolerated. Yogurt, in turn, is often well tolerated because the bacteria it contains help to break down the lactose. Fresh, unprocessed foods that are not made from milk are generally lactose-free.
Hidden lactose in convenience foods
Lactose is also found where you might not immediately expect it: in chocolate, plaited bread (Zopf) or bagels, cakes and waffles, sports bars, muesli mixes, spreads, and instant soups and sauces. Even sausages and cold cuts can contain 1 to 2.5 grams of lactose per 100 grams. It is therefore worth checking the list of ingredients. Ingredients containing lactose must be highlighted there, for example in capital letters, in bold or underlined. Common names are milk sugar, milk product, dried milk, skimmed milk powder, whey powder, sweet whey product, condensed milk, cream, cream powder, yogurt powder and chocolate preparation.
Lactose-free products, plant-based alternatives and lactase
If you eat fewer dairy products, you may also take in less protein and calcium, especially if you follow a vegetarian diet. According to the Swiss dietary recommendations issued by the Swiss Society for Nutrition (SSN) and the Federal Food Safety and Veterinary Office (FSVO), dairy products are an important source of protein, calcium, iodine and vitamins B2 and B12. Two to three portions a day are recommended. One portion corresponds, among other things, to 30 grams of semi-hard or hard cheese, a food that contains practically no lactose. These points help to ensure an adequate supply:
- Continue to eat low-lactose dairy products to the extent that you tolerate them.
- Include special lactose-free products such as lactose-free milk or lactose-free yogurt. They are widely available in larger supermarkets and, provided there is no allergy to milk protein, can be eaten even in large quantities.
- Check plant-based alternatives made from soya, oats or nuts carefully. Compared with dairy products, they contain more sugar, which is often added, and less protein. Soya drinks are equivalent to cow's milk in terms of protein, whereas drinks made from oats, rice or almonds contain hardly any protein.
- Pay attention to calcium: Choose alternatives fortified with calcium. If their protein content is lower than that of the original, combine them with protein-rich ingredients such as nuts, seeds or kernels.
Also check regularly whether your diet is balanced overall. A separate article shows how you can calculate your protein requirements. If you eat a mainly plant-based diet and train regularly, you will find further advice in the article on vegan sports nutrition.
Lactase as a tablet or capsule
Lactase supplements are another option. They supply the missing enzyme as a tablet or capsule, work like the body's own lactase and make the lactose in a meal easier to tolerate. Timing is important: you take them immediately before or together with the meal, as they only work for that one meal. They are available in pharmacies and sometimes in supermarkets. If lactose intolerance has been confirmed by a breath test, health insurers often cover part of the cost.
Course tip from update Akademie: Lactose intolerance is only one of several intolerances that nutrition professionals deal with in counselling. In the Ernährungscoach (nutrition coach) course, you study functional gastrointestinal complaints and intolerances to lactose, fructose, histamine and gluten. Assessment and nutritional counselling are also covered, including consultation skills.
Frequently asked questions about lactose intolerance
How can I tell if I have lactose intolerance?
Typical signs are bloating, flatulence, diarrhoea, abdominal pain and sometimes constipation after consuming milk or dairy products. The cause is a deficiency of the enzyme lactase, so that unsplit milk sugar is fermented by bacteria in the large intestine. Whether lactose really is the cause is shown by a medical assessment with a detailed history and a hydrogen breath test. What counts is a positive test combined with symptoms occurring at the same time.
How much milk can I drink with lactose intolerance?
This varies from person to person and depends on the remaining enzyme activity. Avoiding lactose completely is usually not necessary, except in the case of a very rare congenital genetic defect. You can find your threshold by avoiding all products containing lactose for about two weeks and then gradually reintroducing small amounts. A food and symptom diary helps with the evaluation.
Which dairy products are well tolerated with lactose intolerance?
Semi-hard and hard cheese contain less than 0.1 grams of lactose per 100 grams and are considered lactose-free because of the ripening process. Butter, too, is free of lactose or very low in it. Soft cheese contains about 1 gram per 100 grams, and smaller amounts are often tolerated. Yogurt is often well tolerated because its bacteria help to break down lactose.
Are plant-based drinks a good milk substitute for lactose intolerance?
Plant-based products made from soya, oats or nuts are a possible alternative but differ in nutritional value. They often contain more sugar and less protein. Soya drinks are equivalent to cow's milk in terms of protein, while oat, rice and almond drinks contain hardly any protein. Choose products fortified with calcium. Lactose-free dairy products are another option.
Do lactase tablets help with lactose intolerance?
Lactase supplements provide the missing enzyme as a tablet or capsule and make the lactose in a meal easier to tolerate. You take them immediately before or together with the meal, as they only work for that meal. They are available in pharmacies and sometimes in supermarkets. If lactose intolerance has been confirmed by a breath test, health insurers often cover part of the cost.
Conclusion
Lactose intolerance rarely means that you have to give up cheese, yogurt and milky coffee altogether. A proper assessment is what matters: only a positive breath test with 25 grams of lactose together with symptoms points to the diagnosis. A short avoidance phase followed by reintroduction then shows you how much lactose you can tolerate. Hard cheese, butter, lactose-free products and well-chosen alternatives help you keep an eye on protein and calcium. Have symptoms checked by a doctor before you cut out entire food groups.
