Common Food Intolerance Symptoms (and What to Do About Them)

What is a food intolerance?

A food intolerance is a difficulty digesting certain foods. Unlike a food allergy, which involves the immune system and can be life-threatening, an intolerance is a digestive reaction. Your body either lacks the enzymes needed to break down a particular food, or reacts to natural chemicals within it.

Food intolerances are common. The NHS estimates that they affect far more people than food allergies, though exact figures are hard to pin down because many people self-diagnose or don't seek medical advice. What we do know is that the symptoms can significantly affect quality of life — even if they aren't dangerous.

The tricky part is identifying the culprit. Because symptoms can appear hours or even days after eating, people often blame the wrong food — or assume their symptoms are just "normal."

Common food intolerance symptoms

Most food intolerance symptoms are digestive, though some people experience broader effects. According to the NHS and Allergy UK, the most commonly reported symptoms include:

• Bloating — A feeling of fullness, tightness, or swelling in the abdomen, often after meals. This is the single most common intolerance symptom.
• Stomach cramps — Intermittent abdominal pain, sometimes mild, sometimes sharp. Often worse after larger portions of the trigger food.
• Diarrhoea — Loose or watery stools, sometimes urgent. Particularly associated with lactose and fructose intolerances.
• Constipation — Less commonly reported than diarrhoea, but some intolerances (especially gluten sensitivity) may slow digestion.
• Excessive gas (flatulence) — Produced when undigested food is fermented by gut bacteria. Especially common with lactose, fructose, and FODMAP intolerances.
• Nausea — A feeling of sickness that may or may not lead to vomiting. Often accompanies other digestive symptoms.
• Headaches — Some people experience headaches or migraines after consuming trigger foods, particularly those high in histamine, tyramine, or caffeine.
• Fatigue — Persistent tiredness or feeling "wiped out" after eating certain foods. This is commonly reported but harder to link to specific triggers.
• Skin reactions — Some people report eczema flare-ups, itching, or rashes, though this is more commonly associated with allergies. If you experience hives or swelling, seek medical advice promptly as this may indicate an allergy.

Common food intolerances in the UK

Some foods cause intolerance reactions more frequently than others. The table below covers the most common types seen in the UK, based on data from Allergy UK, the British Dietetic Association, and NHS sources.

FODMAPs deserve special mention. The term stands for Fermentable Oligosaccharides, Disaccharides, Monosaccharides, and Polyols — a group of short-chain carbohydrates that are poorly absorbed in the small intestine. A low-FODMAP diet, developed by Monash University, is now widely recommended by NHS dietitians for people with IBS. However, it should only be followed under professional guidance as it involves careful phased elimination and reintroduction.

How food intolerance differs from food allergy

People often use "intolerance" and "allergy" interchangeably, but they are fundamentally different conditions. Understanding the distinction matters — both for your safety and for getting the right help. For a deeper look, see our full guide on food allergy vs food intolerance.

How to identify your food intolerance triggers

Because intolerance symptoms are delayed and can be caused by multiple foods, identifying your specific triggers requires a systematic approach. The gold standard method recommended by the NHS, NICE, and the British Dietetic Association is the elimination diet.

The elimination diet approach

1. Speak to your GP first. Before eliminating any foods, see your doctor. They can rule out more serious conditions (coeliac disease, inflammatory bowel disease, bowel cancer) that share similar symptoms. This step is non-negotiable.
2. Identify suspected foods. Using your food diary (see below), work with your GP or a registered dietitian to identify the 1-3 foods most likely causing your symptoms.
3. Remove suspected foods for 2-4 weeks. Eliminate the suspected trigger completely from your diet. Continue keeping your food diary throughout this period.
4. Monitor your symptoms. If symptoms improve significantly during the elimination phase, the removed food may be a trigger. If there's no change, it probably isn't.
5. Reintroduce gradually. Bring the food back in small amounts over 2-3 days while monitoring for returning symptoms. This is the confirmation step.
6. Repeat if needed. If you suspect multiple triggers, test one food at a time. Rushing this process leads to unclear results.

The role of a food diary

A food diary is the single most useful tool for identifying food intolerances. Both the NHS and Allergy UK recommend keeping one before and during an elimination diet. The more detail you record, the clearer the patterns become.

Here's what to record in your food diary:

• What you ate and drank — Be specific. "Sandwich" is less useful than "wholemeal bread, cheddar cheese, butter, lettuce, tomato."
• Time of each meal or snack — This helps you calculate the gap between eating and symptoms.
• Any symptoms experienced — Bloating, cramps, gas, headache, fatigue, skin reactions, etc.
• Severity of symptoms — A simple 1-5 scale helps you spot patterns over time (1 = barely noticeable, 5 = significantly affects your day).
• Timing of symptoms — When did symptoms start relative to your last meal? This is crucial for narrowing down the trigger.
• Other factors — Stress, sleep quality, exercise, and menstrual cycle can all affect digestion. Note anything relevant.

Keeping a food diary for at least 2 weeks before starting an elimination diet gives you a baseline. You can then take this diary to your GP appointment, which makes the conversation far more productive than trying to recall what you ate from memory.

A food tracking app like NutraSafe can make this process significantly easier — logging meals with timestamps and noting symptoms as they occur, rather than trying to remember everything at the end of the day.

Warning: unregulated food intolerance tests

Other unvalidated tests to be cautious about include hair analysis testing, kinesiology (muscle testing), Vega testing, and cytotoxic food testing. None of these have sufficient scientific evidence to support their use for diagnosing food intolerances.

When to see your GP

While food intolerances themselves aren't dangerous, the symptoms can overlap with more serious conditions. See your GP if you experience any of the following:

• Persistent symptoms lasting more than a few weeks, even after dietary changes
• Unexplained weight loss
• Blood in your stool
• Difficulty swallowing
• Persistent vomiting
• Severe abdominal pain
• Symptoms that significantly affect your daily life — missing work, avoiding social situations, constant discomfort
• Symptoms that started after age 50 — new digestive symptoms in older adults warrant investigation

Your GP may refer you for blood tests (to check for coeliac disease), a breath test (for lactose or fructose malabsorption), or to a gastroenterologist for further investigation. Getting a proper diagnosis is important — self-diagnosing can mean missing something treatable.

Living with food intolerances

Once you've identified your triggers (with medical support), managing a food intolerance usually means reducing or avoiding the problem food. The good news is that many intolerances are dose-dependent — you may tolerate small amounts even if larger portions cause symptoms.

Some practical tips:

• Learn to read food labels. In the UK, the top 14 allergens must be highlighted in bold on ingredient lists. While this is primarily for allergies, it helps with intolerances too (especially lactose and gluten).
• Find alternatives, not just exclusions. Lactose-free milk, gluten-free pasta, and dairy-free cheese have improved significantly in quality and availability in UK supermarkets.
• Know your threshold. If you're lactose intolerant, you might tolerate a splash of milk in tea but not a bowl of cereal. Understanding your limits means less restriction.
• Keep tracking. Intolerances can change over time. Periodic food diary check-ins help you stay informed about whether your thresholds have shifted.

For more on what causes bloating after eating and how to manage it, see our dedicated guide. You can also use our food intolerance symptoms checklist to review your own symptoms against common intolerance patterns.

Frequently asked questions

What are the most common food intolerance symptoms?

The most common symptoms are digestive: bloating, stomach cramps, diarrhoea, constipation, nausea, and excessive gas. Some people also experience headaches, fatigue, or skin reactions. Symptoms typically appear 30 minutes to 48 hours after eating the trigger food, which makes identifying the cause more difficult than with allergies.

How is a food intolerance different from a food allergy?

A food allergy involves the immune system and can cause severe, rapid reactions including anaphylaxis. A food intolerance is a digestive issue — the body struggles to break down certain foods, causing discomfort but not life-threatening reactions. Allergies appear within minutes; intolerances may take hours or days. For a full comparison, read our guide on food allergy vs food intolerance.

Are IgG food intolerance tests accurate?

No. The NHS, NICE, British Dietetic Association, and Allergy UK do not recommend IgG food intolerance tests. IgG antibodies are a normal part of the immune response to food and their presence does not indicate intolerance. These tests can lead to unnecessary dietary restriction, nutritional deficiencies, and wasted money. The recommended approach is a supervised elimination diet with your GP or a registered dietitian.

How long does it take for food intolerance symptoms to appear?

Symptoms usually appear between 30 minutes and 48 hours after eating the trigger food. This delayed onset is why keeping a detailed food diary is so important — it helps you connect symptoms to specific meals that might be hours apart. The severity can also vary depending on how much of the trigger food was eaten.

When should I see a GP about food intolerance symptoms?

See your GP if symptoms are persistent or worsening, if you experience unexplained weight loss, blood in your stool, difficulty swallowing, persistent vomiting, or if symptoms significantly affect your daily life. Your GP can rule out more serious conditions such as coeliac disease, inflammatory bowel disease, or bowel cancer before you begin an elimination diet.

Related articles

• Food Allergy vs Food Intolerance: What's the Difference?
• How to Track Food Intolerances with a Food Diary
• What Causes Bloating After Eating?
• Food Intolerance Tracker UK
• Food Intolerance Symptoms Checklist
• Elimination Diet Tracker UK

Last reviewed and updated: 7 February 2026