Food Intolerance - a Health Concern?

Adverse reactions to food have become far more commonly reported in recent years. Some of that is better recognition, some is genuine increase — but a great deal of confusion surrounds the terminology, and getting the distinction right genuinely matters for your safety.

Intolerance, allergy and sensitivity are not the same thing

These terms are used interchangeably in everyday speech, but clinically they describe very different processes.

Food allergy is an immune system reaction. The body mistakenly identifies a food protein as a threat and mounts a response, typically involving IgE antibodies. Reactions are usually fast — minutes to two hours — and can include hives, swelling of the lips, face or throat, vomiting, wheezing and, at worst, anaphylaxis. Allergy can be life-threatening.

Food intolerance does not involve the immune system. It arises when the digestive system cannot properly process a food component, usually because of an enzyme shortfall. Symptoms are uncomfortable rather than dangerous, are often delayed by hours, and are typically dose-dependent — a small amount may be fine where a large amount is not.

Coeliac disease sits in neither category and is often misfiled as gluten intolerance. It is an autoimmune condition in which gluten triggers damage to the small intestine. It requires proper diagnosis and strict lifelong gluten avoidance — and, critically, you must still be eating gluten when tested, or the test will be falsely negative.

Symptoms of food intolerance

• Bloating and abdominal distension
• Stomach cramps and pain
• Wind
• Diarrhoea or loose stools
• Nausea
• Headaches and fatigue in some people

Because reactions are often delayed by several hours, identifying the trigger can be genuinely difficult. These symptoms also overlap substantially with IBS, coeliac disease and inflammatory bowel disease — conditions that need ruling out.

Common types

Lactose intolerance. Insufficient lactase enzyme means lactose is not broken down and ferments in the bowel, causing cramps, bloating and diarrhoea. Determined largely by variants near the MCM6/LCT genes.

Caffeine sensitivity. The CYP1A2 gene influences how quickly caffeine is cleared. Slow metabolisers experience stronger and longer-lasting effects — jitteriness, palpitations, disrupted sleep — from the same amount.

Alcohol intolerance. Variants in ALDH2 and ADH1B affect how alcohol is broken down. Reduced ALDH2 activity causes acetaldehyde to accumulate, producing facial flushing, nausea and rapid heartbeat.

Histamine intolerance. Reduced activity of the DAO enzyme, which breaks down dietary histamine, can cause headaches, flushing and digestive symptoms after aged cheese, wine and fermented foods.

FODMAP sensitivity. Certain fermentable carbohydrates trigger symptoms in many people with IBS.

Get a proper diagnosis first

This is the most important point in the article. If you are having reactions to food:

• See your GP before eliminating foods. Cutting out gluten before coeliac testing makes accurate diagnosis impossible without a lengthy gluten reintroduction.
• Rule out the serious things. Unexplained weight loss, blood in stool, persistent vomiting, anaemia or a change in bowel habit lasting more than a few weeks need proper investigation — they are not intolerance symptoms.
• Be sceptical of IgG food sensitivity panels. Widely sold online, these are not supported by allergy or immunology bodies as a means of diagnosing food intolerance. IgG antibodies generally indicate exposure, not intolerance, and acting on them can lead to unnecessarily restricted diets.
• Keep a food and symptom diary. Unglamorous, but often the single most useful diagnostic tool.
• Get dietitian support before any long-term elimination, to avoid nutritional gaps.

Seek urgent help for swelling of the lips, tongue or throat, difficulty breathing, or widespread hives — that is a possible allergic reaction, not intolerance. Call 999.

Where genetic testing fits

Genetic testing can indicate a predisposition — for example, whether you carry variants associated with lactase non-persistence or slow caffeine metabolism. This is useful context, but it is not a diagnosis of a clinical food intolerance and does not replace assessment by a GP or dietitian.

Rightangled's DNA tests assess relevant genetic markers, and our blood tests can check for related deficiencies. Results are reviewed by our clinical team, which includes GPhC-registered independent prescribers, with medical oversight from our doctor, Dr Abdullah.

For symptom relief, see our IBS, bloating and abdominal pain range.

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This article is for general information and does not replace personalised medical advice. Speak to your GP before eliminating any food group long-term.