Rumbling that starts an hour after a glass of milk, bloating that lasts until evening after a plate of pasta, flushing and a headache after a glass of wine… Complaints like these are usually explained with a single phrase: food intolerance. Yet very different causes can lie behind the same symptoms, and each of them calls for a different response at the table.
On this page you will find what food intolerance is, how it differs from allergy and coeliac disease, which tests are useful and which are misleading, and how an elimination diet is carried out step by step. The aim is not to shrink your diet with bans, but to find the food that really bothers you and the amount you can tolerate.
What is food intolerance?
Food intolerance is the body’s difficulty in digesting, breaking down or clearing a food or a component of a food. It is not a condition in which the immune system sounds the alarm; the problem usually starts in the digestive tract and stays there. Symptoms are generally proportional to the amount eaten: a small portion causes no trouble, while complaints grow as the amount increases.
There are three main mechanisms behind intolerance:
- Enzyme deficiency: The enzyme that breaks down the food is insufficient. The best-known example is lactose intolerance, which appears when lactase, the enzyme that breaks down milk sugar, declines.
- Poor absorption and fermentation: Some carbohydrates that are not fully absorbed in the small intestine reach the large intestine, where bacteria ferment them and produce gas. Fructose, sugar alcohols such as sorbitol, and certain carbohydrates in onions, garlic and pulses belong to this group.
- Sensitivity to active compounds in food: Histamine, caffeine or some additives can cause headache, palpitations, flushing or digestive complaints in people who clear them slowly.
The difference between food intolerance and food allergy
Although the two terms are used interchangeably in everyday speech, they are not the same thing, and the distinction matters for your safety.
- Food allergy is a reaction of the immune system. Symptoms usually begin within minutes; hives, swelling of the lips and tongue, shortness of breath and vomiting may occur. Even a very small amount can trigger a severe reaction. It is diagnosed and monitored by an allergy specialist; a food you are allergic to should never be eaten at home as a trial.
- Food intolerance is mostly limited to the digestive system. Symptoms appear over a period ranging from half an hour to several hours, sometimes into the next day; they are not life-threatening and depend on the amount eaten.
- Coeliac disease is a separate matter: an autoimmune disease that develops against gluten and damages the small intestine. It is not an intolerance, and the idea that a little will not hurt does not apply to it. It is diagnosed by a doctor with blood tests and, where necessary, an endoscopic biopsy.
For this reason, if there is any sign suggesting allergy or coeliac disease, you should see the relevant doctor before cutting foods out on your own.
What are the symptoms of food intolerance?
Symptoms vary from person to person, and most of them are also seen in other digestive problems. The most commonly described are:
- Bloating and a feeling of tightness in the abdomen that increases after meals
- Gas, rumbling and cramp-like abdominal pain
- Diarrhoea, loose stools or alternating diarrhoea and constipation
- Nausea, early fullness, belching
- In some people, headache, facial flushing, a runny nose or marked tiredness
There is an important note here: not every case of bloating is an intolerance. Eating quickly, skipping meals and then eating a lot at once, constipation, suddenly increasing fibre, fizzy drinks, sugar-free gum, stress and lack of sleep can all cause the same complaints. A stomach that is flat in the morning and swollen by evening usually has to do with the gas and stool that build up during the day; looking for a single culprit food does not always lead to the right answer.
The most common food intolerances
Lactose intolerance
Lactase, the enzyme that breaks down the milk sugar lactose, declines in many people in adulthood. Undigested lactose is fermented in the large intestine; gas, bloating and diarrhoea follow milk, ice cream or milk-based desserts. Lactose intolerance rarely means giving up all dairy products. Yoghurt, kefir and matured cheeses contain less lactose and are generally better tolerated; taking milk in small amounts and with a meal can also ease symptoms. Lactose-free dairy products are similar to other dairy products in calcium and protein.
Fructose and other fermentable carbohydrates (FODMAPs)
In some people, absorption of fructose, the sugar in fruit, is limited. Honey, apples, pears, fruit juice and products containing fructose syrup may trigger complaints. Fructose, lactose and sugar alcohols, together with certain carbohydrates in onions, garlic, wheat and pulses, are collectively known as FODMAPs. The low-FODMAP approach, used especially in irritable bowel syndrome, is based on temporarily reducing this group and then reintroducing it in sequence.
Gluten sensitivity
Some people find that their symptoms increase with gluten-containing foods even though coeliac disease and wheat allergy have been ruled out; this is called non-coeliac gluten sensitivity. In some of them the real trigger is not gluten but the fermentable carbohydrates in wheat. The critical rule here is: do not cut out gluten before coeliac tests have been done. Tests carried out after starting a gluten-free diet can come back falsely normal, and the diagnosis is delayed.
Histamine intolerance
Histamine increases in foods that have been stored for a long time, matured or fermented. Mature cheeses, processed meats such as salami and cured sausage, tinned or stored fish, pickles and wine are the main examples. In people whose histamine-degrading enzyme does not work well enough, these foods may be followed by flushing, headache, a runny nose, palpitations or digestive complaints. It is difficult to diagnose and its symptoms overlap with many other conditions, so it should be addressed together with a medical assessment.
Caffeine, sugar alcohols and additives
People who clear caffeine slowly may experience palpitations, restlessness or stomach complaints after a single cup of coffee. Sugar-free gum, sweets and products labelled “sugar-free” that contain sugar alcohols such as sorbitol, xylitol and maltitol are also frequently overlooked causes of gas and diarrhoea.
Food intolerance tests: which ones work and which mislead?
“I had a food intolerance test and forty foods came up” is a sentence often heard in consultations. It is important to be clear on this subject, because a misinterpreted test result can lead to years of unnecessary restriction.
- Hydrogen breath test: A test requested by a doctor to assess lactose and fructose malabsorption.
- Coeliac blood tests and, if needed, endoscopy: Requested by a doctor when coeliac disease is suspected, and they must be done while gluten is still being eaten.
- Allergy tests: Skin tests and specific IgE measurement in the blood are interpreted by an allergy specialist together with your history when allergy is suspected.
- IgG-based food intolerance panels: These tests, which measure IgG against dozens or sometimes hundreds of foods, are not recommended for diagnosing intolerance by specialist allergy and immunology societies. The presence of an IgG antibody mostly shows that the food has been eaten and that the body recognises it; it does not show the cause of the complaint.
At present there is no single laboratory test that reveals most food intolerances. The most reliable method is still a planned process of elimination and reintroduction.
What is an elimination diet and how is it done?
An elimination diet is a method in which suspected foods are removed from the diet for a limited period and then reintroduced one by one in measured amounts. It is not a weight-loss diet, nor a lifelong list of bans; it is a controlled trial that proceeds in four stages.
1. Food and symptom diary
For the first week or two you record what you eat, how much, at what time and how you feel afterwards. Sleep, stress, the menstrual cycle and bowel habits are also noted. The diary often reveals an unexpected picture: the complaint may turn out to be linked not to a particular food but to days when meals are skipped or to large portions eaten late in the evening.
2. Elimination phase
The suspect foods that emerge from the diary and your history are removed from the diet, usually for a few weeks. Rather than cutting everything out at once, we begin with the strongest candidates. During this period we plan together how to read labels, how to choose when eating out and what to put in place of the removed food, because every food that is not replaced means a nutrient that goes missing.
3. Reintroduction
If symptoms have eased, foods are added back one by one. Only one food is tested at a time, starting with a small portion; the amount is increased over a few days and symptoms are recorded. This is the stage most often skipped and yet the most valuable part of the process: only this stage shows which food causes trouble and in what amount.
4. Your personal eating pattern
At the end of the process you have a map of your own: foods you can eat freely, foods you tolerate up to a certain amount and foods you need to avoid. Your long-term eating pattern is built on this map. Because tolerance can change over time, retrying some foods later is also part of the plan.
Common mistakes on an elimination diet
- Cutting out many foods at once: Even if symptoms improve, it is impossible to tell which food was responsible, and the diet narrows unnecessarily.
- Skipping the reintroduction stage: Saying “it helped, so I won’t touch it again” turns a temporary trial into a permanent ban.
- Not replacing the removed food: Calcium and protein may fall when dairy is removed; fibre and B vitamins may fall when grains are restricted.
- Giving up gluten without being tested: This makes coeliac disease harder to diagnose.
- Stretching the process over months: The elimination phase is time-limited; the longer it lasts, the more both dietary variety and your relationship with food can suffer.
- Blaming a food for a single bad day: A stressful day, a sleepless night or the days before a period also affect the gut. Decisions are not made on a single trial.
When should you see a doctor?
In the following situations you should see a doctor without waiting for dietary changes:
- Swelling of the lips, tongue or throat, widespread hives, shortness of breath or feeling faint shortly after a food (this requires emergency care)
- Unintentional weight loss
- Blood in the stool, or black, tar-coloured stool
- Abdominal pain or diarrhoea that wakes you at night
- Prolonged diarrhoea, repeated vomiting or difficulty swallowing
- Unexplained iron deficiency and anaemia
- A family history of coeliac disease, inflammatory bowel disease or bowel cancer
Frequently asked questions
Can food intolerance develop later in life?
Yes. Lactase can decline with age, and a gut infection, prolonged antibiotic use or another bowel disease can also lead to temporary or lasting intolerance. It is therefore not surprising when a food you have eaten without trouble for years starts to disagree with you.
Does food intolerance go away?
It depends on the cause. Intolerances that develop after an infection may ease as the gut recovers. Those due to low enzyme levels are mostly permanent; however, once the tolerated amount is found, they have little effect on daily life.
How long does an elimination diet take?
The elimination phase generally lasts a few weeks; the reintroduction stage takes longer depending on the number of foods to be tested. The total length varies from person to person.
If I have lactose intolerance, do I have to give up dairy completely?
Usually not. Yoghurt, kefir and mature cheeses are generally well tolerated, and lactose-free products are also an option. If you do need to give up dairy altogether, how your calcium needs will be met from other sources should be planned.
Is an elimination diet used in children?
In growing children, any food restriction must be done with a paediatrician’s assessment and under close monitoring. Self-imposed restrictions can affect growth.
