Lactose is a sugar found in milk and its products. People with lactose intolerance can not digest dairy products well. This is because their digestive system produces not enough digestive enzyme called lactase. If a person with intolerance eat a lactose-containing food, they may have bloating, gas or diarrhea. Learn more about lactose intolerance and what you can do if you experience it.
Do not confuse lactose intolerance with milk allergies, because these are two different phenomena. In milk allergy, the body reacts to milk proteins, not milk sugar (lactose). Drinking milk or milk products with milk allergies can even lead to anaphylactic shock.
In turn, a person with lactose intolerance will also react badly to milk and its products, but it is not a threat to her life. Symptoms appear an hour or two after a meal. Their intensity depends on the amount of dairy consumed and the amount of lactase that the body produces intolerant people. They can be barely noticeable or very serious. Belong to them:
In more serious cases, diarrhea can lead to dehydration. 
The easiest way is if you go on a lactose-free diet for two weeks and see if your symptoms go away. Prepare for such a diet in advance. Throwing milk and its products out of the house (cheese, yoghurts, butter) is just the beginning. Read the compositions of all food products you eat every day. You will be surprised how many of them contain milk as an ingredient! Whey, milk powder, cheese, curd - under these names also lactose is hidden.
Typical products with lactose you must avoid are cakes, biscuits, ready-made sauces, creamy soups, pancakes, chocolate. Eating "out of town" will always involve asking the waiter about the dairy content of the dish you order. Do not be surprised if the waiter will not be able to answer your question and will have to go to answer the kitchen.
Also watch out for traces - in the composition will be listed after the slogan "may contain traces" - just enough to trigger a reaction! Trace amounts of lactose you will find, among others in bars, bread, breakfast cereals, margarines, powdered soups or mayonnaise.
If you are taking any medications permanently, check them for lactose content, which is a popular filler. Unfortunately, for many drugs, it is difficult to find a lactose-free alternative.
You already know what to avoid, but what can you eat then? Unless you replace milk and its products with healthy counterparts, a lactose-free diet can lead to nutritional deficiencies.
The most important ingredient that your body may lack is calcium. However, dairy is not the only source of calcium in the diet! You can also find them in highly mineralized water, nuts, seeds, kale, broccoli, oranges, beans, figs, quinoa, amaranth and products artificially enriched with calcium, such as plant milk.
Milk and its products are also a rich source of vitamin A. Its deficiency is supplemented by eating carrots, liver, broccoli, spinach, pumpkin, melon, eggs, papaya, mango, peas, apricot or drinking tran which is also a good source of vitamin D. You can get the best from the sun, but in Poland it is impossible for most of the year. The best sources of vitamin D are greasy sea fish and eggs.
Your ally will be products with a crossed milk symbol and the word "lactose-free". Prepare to be more expensive than your lactose counterparts. An alternative to classic milk is coconut, almond, rice, oat and soy milk. 
In this case, your ally will be digestive enzymes with lactase, which will help your body cope with lactose. How often should they be taken? It depends on the degree of your intolerance and the amount of lactose in the products you consume.
 Butler N. Lactose intolerance: What you need to know , https://www.medicalnewstoday.com/articles/180120.php