Food Allergy, Food Intolerance and Food Sensitivity: Clearing the Confusion

Surveys consistently find that far more people believe they react to foods than can be confirmed on testing. Some have genuine allergies, some intolerances, some other digestive conditions, and some have attributed symptoms to foods that are not the cause. The words used to describe these reactions, allergy, intolerance and sensitivity, are often used interchangeably, but they describe different mechanisms, carry different risks and require different approaches. Clearing up the confusion protects patients from both danger and unnecessary restriction.

3 categories

Food allergy

IgE mediated allergy

In IgE mediated allergy, the immune system produces IgE antibodies against a food protein. On re exposure, the food cross links IgE on mast cells, releasing histamine and other mediators within minutes. Symptoms include hives, swelling, vomiting, wheeze, and in severe cases anaphylaxis with breathing difficulty or collapse. Common triggers include peanut, tree nuts, milk, egg, fish, shellfish, wheat, soy and sesame, with regional variation.

Diagnosis requires an allergist and rests on a clear history supported by skin prick testing or specific IgE blood tests. A crucial point is that a positive test indicates sensitisation, not necessarily allergy. Many people have positive tests to foods they eat without problems. Broad panels of IgE tests without a supporting history therefore produce many misleading results. The oral food challenge, supervised in a clinical setting, is the definitive test.

People with IgE mediated allergy need an allergen avoidance plan, education about reading labels and, where indicated, adrenaline auto injectors and an emergency plan. Suspected allergens should never be reintroduced at home.

Prevention in infants

The understanding of allergy prevention has reversed in recent years. A landmark trial found that early introduction of peanut to infants at high risk of peanut allergy substantially reduced the development of allergy compared with avoidance. Guidance in many countries now supports introducing common allergenic foods in infancy, alongside other solids, rather than delaying them.

Non IgE mediated reactions

These involve other immune mechanisms and tend to cause delayed, mainly gastrointestinal symptoms. Examples include food protein induced enterocolitis syndrome in infants, eosinophilic oesophagitis and cow’s milk protein allergy presenting with gut symptoms in infancy. Coeliac disease is an immune mediated enteropathy triggered by gluten and is usually considered separately. Standard allergy tests are often negative in these conditions, and diagnosis relies on history, specific investigations and supervised elimination and reintroduction.

Food intolerance

Lactose intolerance

Most of the world’s adults, particularly in Asia, Africa and parts of the Americas, produce less lactase after childhood. Many people with reduced lactase tolerate moderate amounts of lactose, especially with meals and in fermented dairy such as yoghurt and hard cheese. Symptoms of bloating, gas and diarrhoea follow larger amounts. Diagnosis is usually clinical, sometimes supported by breath testing. Complete avoidance of dairy is rarely necessary and can reduce calcium intake.

Fermentable carbohydrates

Fructose, fructans, galacto oligosaccharides and polyols can cause bloating and discomfort, especially in people with irritable bowel syndrome, through fermentation and water drawn into the gut.

Pharmacological reactions

Caffeine, alcohol and some food additives can cause symptoms in susceptible people. Sulphite sensitivity can trigger asthma symptoms in some people with asthma. Histamine intolerance, attributed to reduced breakdown of dietary histamine, is widely discussed but its diagnosis and prevalence remain uncertain.

Food sensitivity and non coeliac gluten or wheat sensitivity

Non coeliac gluten or wheat sensitivity describes gastrointestinal and sometimes other symptoms related to wheat or gluten in people without coeliac disease or wheat allergy. Its existence is supported by some blinded challenge studies, but in many people the trigger may be fructans in wheat rather than gluten itself. A blinded crossover study in people with self reported gluten sensitivity found that symptoms were provoked more by fructans than by gluten. Expectation effects are also significant: symptoms often occur with placebo in blinded studies. Coeliac disease must be excluded while the person is still eating gluten before this label is used.

Tests that are not validated

Several widely marketed tests claim to identify food reactions but lack validation.

These tests can lead to extensive and unnecessary dietary restriction, nutritional inadequacy and anxiety about food, and may delay diagnosis of other conditions.

A practical approach

1. Take a careful history: what food, how much, how quickly, what symptoms, how consistent.
2. Suspect IgE allergy with rapid symptoms such as hives, swelling, wheeze or vomiting, and refer to an allergist.
3. Exclude coeliac disease and other conditions with appropriate tests before dietary change.
4. Consider intolerance with dose related digestive symptoms, and use targeted elimination and reintroduction.
5. Avoid unvalidated tests.
6. Protect nutrition and watch for anxiety about food and disordered eating.
7. Aim for the broadest diet the person can comfortably eat.

An illustrative case

A 30 year old woman brings an IgG food panel listing reactions to 27 foods, including wheat, dairy, eggs and several fruits. She has removed them all, has lost weight and is anxious about eating out. Her symptoms are bloating and irregular bowel habit.

The practitioner explains what the IgG test measures. Coeliac serology, tested after gluten is reintroduced, is negative. Her history suggests irritable bowel syndrome. A supervised low FODMAP approach with structured reintroduction follows, identifying larger amounts of wheat fructans and onion as her main triggers, while she tolerates dairy, eggs and most fruits. Her diet expands substantially, her weight stabilises and her anxiety about food eases.

Words that matter

Distinguishing allergy, intolerance and sensitivity is not pedantry. It separates reactions that can be fatal from those that are merely uncomfortable, determines who needs specialist care and protects people from restrictions that reduce their quality of life without benefit.