Understand Your Food Triggers

Why: The NHS says not to cut foods out of your or your child's diet without advice from a GP or dietitian, because you could miss vitamins and minerals. It also says to see a GP if you need to avoid lots of different foods to control IBS symptoms. A review of the low-FODMAP diet warns about nutritional adequacy when it is followed without dietitian support.

Who it applies to: Everyone, especially children, pregnant or breastfeeding people and older adults.

Try instead: Test one food or group at a time, for a set period, with a plan to reintroduce.

Why: NIDDK says doctors do not recommend starting a gluten-free diet before diagnostic testing because it can affect test results.

Who it applies to: Anyone who might have celiac disease, which can look like IBS or lactose intolerance.

Try instead: Ask your doctor about blood tests while you still eat gluten.

Celiac disease →

Why: For IBS the NHS suggests limiting fatty, spicy and processed foods, more than 3 portions of fresh fruit a day, more than 3 cups of caffeinated drinks, alcohol and fizzy drinks. NIDDK lists high-FODMAP foods such as some fruits, onions, garlic, beans, milk products, wheat and sweeteners ending in -ol. Triggers differ from person to person; these are candidates to check in your diary, not a list to avoid.

Who it applies to: People with IBS-type symptoms.

Try instead: Watch your own diary, test one at a time, and keep foods that do not bother you.

The low-FODMAP diet →

Why: The NHS lists delaying or skipping meals and eating too quickly among things not to do with IBS.

Who it applies to: Anyone with irregular or rushed meals.

Try instead: Regular meals eaten slowly; note this in your diary before blaming a food.

Why: The NHS says some tests you can buy that claim to diagnose food intolerances are not recommended, because there is limited evidence they give accurate results and they may suggest avoiding multiple foods, which can be harmful. The Canadian Society of Allergy and Clinical Immunology says there is no body of research supporting food-specific IgG testing, and that positive results are expected in healthy people.

Who it applies to: Anyone tempted by a mail-order or pharmacy test.

Try instead: Use a diary, a clinician and tests ordered by a doctor (such as celiac blood tests or a lactose breath test).

"Leaky gut", cleanses and gut tests: claim check →

Why: Allergy societies say IgG to a food is a marker of exposure and tolerance, and that someone with a true IgE allergy may not have raised IgG to that food. Two IBS trials of IgG-guided diets did find some benefit, but that does not make the test a diagnosis.

Who it applies to: Test marketing and social media.

Try instead: Look at your symptoms and results of removing and reintroducing a food.

Why: Outside celiac disease, a 2025 review found gluten-specific effects largely disappear once FODMAPs and expectation effects are controlled, and large nocebo responses undermine the label non-celiac gluten sensitivity.

Who it applies to: Diet books, packaging and online posts.

Try instead: Rule out celiac disease first; then probe gluten, if at all, with a dietitian.

Why: The NHS says an intolerance is not caused by the immune system overreacting and cannot cause a serious allergic reaction, whereas an allergy can be serious. Treating one like the other can be dangerous: a possible allergy needs proper assessment.

Who it applies to: Anyone describing reactions to food.

Try instead: If you have hives, swelling or breathing trouble after a food, see a doctor.

Why: A gastroenterology review in Gut says it is still unproven that restoring barrier function eases clinical features of gut or whole-body diseases, and that information on leaky gut in the public domain needs confirmation before endorsing dietary exclusions or supplements.

Who it applies to: Online programs and supplement marketing.

Try instead: Ask a clinician to look for diagnosable causes.

"Leaky gut", cleanses and gut tests: claim check →

Why: Food allergy can cause severe reactions, and the NHS advises seeing a GP who may refer you for skin-prick tests, blood tests or a supervised special diet. Allergy symptoms can start straight after eating.

Who it applies to: Anyone who has had hives, swelling or breathing symptoms after a food.

Try instead: See a GP before trying the food again.

Why: A review of the low-FODMAP diet describes restriction as one stage of three, and notes that reintroduction and personalisation have been studied less. The 2021 ACG guideline recommends only a limited trial.

Who it applies to: People who removed foods and felt better.

Try instead: Plan reintroduction from the start and aim to eat as broadly as you comfortably can.

Why: If you remove several foods, add a supplement and change your routine at once, you cannot tell what helped. Intolerance symptoms can start hours later, and allergy symptoms may start straight away or days later, so one meal rarely tells the story.

Who it applies to: Anyone doing their own experiment.

Try instead: One change, a set period, a diary entry each day.

Why: NIDDK lists anemia, rectal bleeding, black or bloody stools and weight loss as signs that may suggest a problem other than IBS, and the NHS says bowel cancer symptoms are common to other conditions but should be checked.

Who it applies to: Anyone with warning signs.

Try instead: Get checked first.

Digestive symptoms: red flags and when to get help →

The NHS does not recommend such tests, and the Canadian Society of Allergy and Clinical Immunology says there is no body of research supporting IgG testing for diagnosing food reactions; positive results are expected in healthy people. Two IBS trials found benefit from IgG-guided diets, but these were research studies in people with IBS.

It is recommended by the NHS and is a sensible first step, but We did not find trials testing diaries alone. It works best with a repeat-and-retest approach.

Evidence is inconsistent: gluten-specific effects largely disappear once FODMAPs and expectation are controlled.

A guideline recommends a limited trial and an umbrella review found moderate-certainty benefit over short follow-up; a 2026 meta-analysis found no difference versus other diets.

Intestinal permeability is real, but it is unproven that restoring barrier function eases symptoms or disease.

The NHS says intolerance is not an immune reaction and cannot cause a serious allergic reaction; food allergy can be serious.