Food intolerance
Food intolerance is what happens when the body cannot cope with digesting a particular food, or a substance inside it.
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Food intolerance is what happens when the body cannot cope with digesting a particular food, or a substance inside it. The immune system plays no part, there is no risk of anaphylaxis and life is not in danger, yet the gut answers with bloating, gurgling, pain and a disturbed bowel habit, and quality of life genuinely suffers. The real difficulty lies elsewhere: illnesses that need entirely different treatment hide behind the label of intolerance, which is why cutting foods out at random is a poor idea.
Why a food stops being digested
There are several causes, and they have little in common.
- A missing enzyme. The commonest version: too little lactase in the small bowel, so milk sugar reaches the colon undigested and the bacteria there deal with it. Hence the wind, the bloating and the loose stools.
- Poorly absorbed sugars. Fructose, sorbitol, xylitol and some of the carbohydrates in pulses, onion, cabbage and wheat draw water into the bowel and ferment readily. In some people this passes unnoticed and in others it does not.
- A substance acting like a drug. Caffeine, histamine, tyramine and alcohol act directly on blood vessels, the nervous system and gut movement, with no immune involvement whatsoever.
- A reaction to an additive. Sulphites in wine, cider and dried fruit can trigger an attack in someone with asthma.
Lactose intolerance in adults deserves a paragraph of its own. The ability to digest milk beyond early childhood did not become fixed in every population: around the Mediterranean and in southern Europe far more adults tolerate milk poorly than in the north, and that is the norm rather than a disease. There is also a temporary version: after a bout of gastroenteritis lactase takes weeks to recover, and throughout that time milk causes trouble before becoming acceptable again.
What it feels like
Symptoms usually appear a few hours after eating and last from several hours to a couple of days.
- bloating, a feeling of fullness, loud gurgling;
- excessive wind;
- cramping or dull abdominal pain;
- loose stools or, just as often, constipation;
- nausea.
Less often there are complaints nobody links to the gut straight away: headache, exhaustion, aching joints, a vague rash, irritability. A diary helps here far more than trying to work it out from memory.
One feature matters above all: everything depends on the amount. A spoonful of cream in coffee often passes unnoticed, while a glass of milk on an empty stomach floors you. The practical conclusion is that the aim is rarely total avoidance but finding your own threshold.
How it differs from an allergy
The words look alike, the substance does not, and the confusion is costly.
- Mechanism. Allergy is an immune error; intolerance is a digestive difficulty.
- Timing. Allergy unfolds in minutes; intolerance takes hours.
- Dose. In allergy traces of the food can set off a severe reaction; in intolerance a small portion usually goes unpunished.
- Symptoms. Allergy involves the skin and the breathing: weals, swollen lips and eyelids, wheezing. Intolerance keeps everything in the abdomen.
- Danger. Intolerance wears you down but does not kill. Allergy can end in anaphylaxis.
If after a meal the lips or tongue swell suddenly, the voice goes, breathing or swallowing becomes hard, the skin turns blue or pale, or sudden weakness sweeps in, that is not intolerance. That is a severe allergic reaction and it needs an ambulance: in Spain, Italy, Portugal, Poland and Ukraine the single European number is 112.
The usual culprits
The list of suspects is familiar to almost everyone.
- Lactose — milk, cream, soft cheeses, ice cream. Hard matured cheeses and yoghurt are tolerated far better because they contain very little of it.
- Fructose and sugar alcohols — honey, apples, pears, fruit juice, and also sugar-free chewing gum and sweets, since sorbitol and xylitol loosen the bowels even in healthy people.
- Caffeine — coffee, tea, energy drinks, cola: palpitations, anxiety, poor sleep and a gut in a hurry.
- Histamine and related substances — matured cheese, cured meat, fermented vegetables, red wine, smoked fish. Flushing, headache and a blocked nose are possible.
- Alcohol — irritates the lining and speeds up transit, and in some people of East Asian descent also causes facial flushing because of how it is metabolised.
- Sulphites — wine, cider, beer, dried fruit; risky above all in asthma.
- Wheat — here conclusions need caution, because there are three possible causes: coeliac disease, wheat allergy, and a reaction to the poorly absorbed carbohydrates it contains. These are different conditions handled in different ways.
On monosodium glutamate it is worth being honest: in studies where participants did not know whether the dish contained the additive, no link with headache or fatigue could be confirmed. The symptoms people describe are real, but the cause is most likely somewhere else.
When an illness hides behind the intolerance
This is the most important part of the subject. A similar picture appears in conditions that do not settle on their own.
- Coeliac disease. Immune damage to the small bowel caused by gluten. It gives the same bloating and loose stools, but over time adds weight loss, anaemia, iron deficiency and, in children, poor growth. The only treatment is a gluten-free diet for life, not occasional restriction.
- Inflammatory bowel disease. Crohn's disease and ulcerative colitis begin insidiously and need treatment.
- Giardiasis and other gut infections. Prolonged diarrhoea with bloating after travel or after drinking doubtful water.
- Irritable bowel syndrome. The diagnosis is made once everything else has been ruled out.
- Shortage of pancreatic enzymes. Bulky, greasy stools and weight loss.
- An overactive thyroid. Frequent stools together with palpitations, sweating and weight loss.
Some signs mean the trouble must never be put down to food alone:
- blood in the stool, or black stools;
- weight loss without trying;
- pallor, breathlessness on exertion, signs of anaemia;
- pain and diarrhoea that wake you at night;
- a fever lasting weeks;
- persistent bowel symptoms appearing for the first time in later life;
- bowel cancer or coeliac disease in close relatives.
One more rule is worth knowing in advance: coeliac testing is done before gluten is removed. On a gluten-free diet the tests turn negative, so the diagnosis is missed for years or bread has to be put back on the menu just to repeat the investigation.
How to work out what does not suit you
The order is this: rule out illness first, then hunt for the food.
The doctor usually arranges blood tests including ferritin and inflammatory markers, a stool test and, where suspicion exists, coeliac screening. After that come:
- A food and symptom diary kept for two or three weeks: what was eaten, how much, how long before symptoms began, how long they lasted. It is the cheapest and the most useful tool there is.
- A trial exclusion. One suspect food is removed for two to four weeks and then brought back. Bringing it back is compulsory: without that step there is no telling whether the food was to blame.
- A breath test where lactose intolerance or bacterial overgrowth in the small bowel is suspected.
- Work with a dietitian when a lot has to come out, chiefly so that the diet does not lose its substance.
What is not worth doing is buying home kits that promise a list of intolerant foods from a drop of blood, a strand of hair or a gadget. A class G antibody test only shows that you have eaten the food. The lists that come out of such testing are long, the diet gets thinner, and the cause remains unfound.
How to keep eating well
The point is not to ban things but to find the portion you tolerate.
- cut down rather than cut out: half the usual amount is often enough;
- eat the suspect food alongside other food rather than on an empty stomach;
- with lactose intolerance choose hard cheese, yoghurt and lactose-free milk; lactase preparations are taken together with the dairy food;
- read the ingredients: lactose turns up in sausages, sauces and bread, sorbitol in chewing gum and diet sweets;
- never drop a whole food group for good without discussing it with a doctor.
That last point matters most for children. Giving up dairy without a replacement hits calcium; giving up grains hits fibre and the B vitamins; giving up pulses hits protein and iron. Substitutes are not hard to find, but they need thinking about in advance, not once fatigue and brittle hair have appeared.
And one more thing: intolerance is not always permanent. After a gut infection it clears by itself, and in irritable bowel syndrome the threshold rises as the condition comes under control. The list of banned foods deserves reviewing at least once a year.
Online consultation
In an online consultation the doctor goes through your food diary, judges whether the picture fits an intolerance or calls for another illness to be excluded, and advises which tests to arrange, in what order, and which of them must be done before any diet begins. You will also get help planning a trial exclusion with reintroduction, so that the result can be read without ambiguity and the diet keeps what it needs.
This material is for information only and does not replace medical advice.
Consult with a doctor about Food intolerance
Discuss your symptoms and possible next steps with a doctor online.
Online doctors for Food intolerance
Discuss your symptoms and possible next steps for Food intolerance with a doctor online.
