Food intolerance can cause symptoms such as bloating, abdominal pain, diarrhoea and gas, but it is different from a food allergy and should not automatically be treated as an allergic reaction.
Food intolerance generally involves difficulty digesting a particular food or ingredient. Lactose intolerance, for example, occurs when the body cannot properly digest lactose, the sugar found in milk and other dairy products.
Food allergies involve an immune response and can, in some cases, cause a severe reaction known as anaphylaxis. Symptoms may include swelling of the lips, mouth or throat, breathing difficulties, wheezing, dizziness or fainting and require urgent medical attention.
Symptoms can have different causes
Common symptoms associated with food intolerance include bloating, abdominal pain, diarrhoea, constipation, gas and nausea. Headaches and tiredness can also occur, although these symptoms can have many other causes.
Because similar symptoms can occur with several digestive conditions, experiencing a symptom after eating a particular food does not by itself establish an intolerance or allergy.
A doctor may ask about what a person ate, when symptoms appeared, how long they lasted and whether the reaction happens repeatedly. Keeping a record of foods and symptoms can also help identify possible patterns.
Testing depends on the suspected condition
There is no single blood test that can diagnose every form of food intolerance.
Depending on the suspected problem, assessment can include an elimination diet followed by reintroduction, blood tests or a breath test. For example, breath testing can be used when lactose intolerance is suspected. Such dietary changes are best undertaken with medical or dietetic guidance, particularly when several foods are being removed.
Commercial food-sensitivity tests that claim to identify numerous intolerances are not considered reliable diagnostic tools. The American Academy of Allergy, Asthma & Immunology says IgG food panels have not been scientifically established for diagnosing food allergies or food intolerances and warns that they can lead to unnecessary dietary restrictions.
Specific IgE testing has a different role. It can help investigate suspected food allergies, but a positive result does not by itself prove that eating the food will cause an allergic reaction. Test results need to be interpreted alongside a person’s medical history and symptoms.
ImmunoCAP is among the laboratory methods used to measure allergen-specific antibodies, including specific IgE. It should not be described as a test that establishes food intolerance by measuring IgG antibodies.
Gluten requires a separate approach
People who develop symptoms after eating wheat or other gluten-containing foods may have several different conditions, including coeliac disease, wheat allergy or non-coeliac gluten sensitivity.
Coeliac disease is an immune-mediated condition triggered by gluten. It is not the same as a food allergy and does not cause anaphylaxis.
Testing for coeliac disease generally begins with blood tests and may require further investigation, including a small-intestinal biopsy. Importantly, a person should normally continue eating gluten while being tested because removing gluten beforehand can make the results inaccurate.
That means a 14-day gluten elimination period should not be presented as a test that can determine whether someone has coeliac disease.
Nor should symptoms such as fatigue, headaches, skin problems or digestive complaints automatically be attributed to gluten. Such symptoms have numerous possible causes and require appropriate assessment.
Avoid unnecessary dietary restrictions
Eliminating large groups of foods without establishing the cause of symptoms can create nutritional problems and make it harder to identify the actual trigger.
The NHS advises against removing foods from a person’s diet without appropriate medical or dietetic advice, particularly when several foods are being excluded. It also warns that some commercially available home intolerance tests have limited evidence behind them and can lead people to avoid unnecessary foods.
There is also no established medical basis for recommending a Paleo diet as a general treatment or prevention strategy for food intolerance. The appropriate diet depends on the condition involved and the foods actually causing symptoms.
Anyone with recurring symptoms after eating should discuss them with a healthcare professional rather than relying on an unvalidated food-sensitivity test or making extensive dietary changes based only on symptoms.
If symptoms suggest a serious allergic reaction, particularly sudden swelling of the mouth or throat, difficulty breathing, fainting or severe dizziness, urgent medical care is required.
