How to tell if you have a food intolerance (and what to do about it)

Many people experience uncomfortable symptoms after eating certain foods. If you’re not sure what’s causing them, it can feel stressful to manage day-to-day life around meals. 

Food intolerances are common and often manageable once you know what you’re dealing with, but the signs can be easy to overlook or mistake for something else.

This guide explains what a food intolerance is, the symptoms to look out for and what you can do if you think specific foods are affecting your health.

What is a food intolerance?

A food intolerance happens when your body has difficulty digesting or processing a certain food. This is different from a food allergy.

Food allergies involve the immune system and can cause fast and sometimes serious reactions. Food intolerances usually affect the digestive system, with symptoms that are uncomfortable and often delayed rather than dangerous.

Common food intolerances include:

• Lactose (a natural sugar in dairy)
• Gluten (a protein in wheat, barley and rye)
• Certain carbohydrates found in foods like onions, beans and wheat
• Food additives such as preservatives or flavour enhancers
• Caffeine

A food intolerance can develop at any age. Some people notice symptoms gradually, while others find that a food becomes a problem after illness, antibiotics, hormonal changes, dietary changes or even stress.

If your symptoms are recurring, affecting daily life or difficult to make sense of, it’s sensible to

speak to a healthcare professional. They can help rule out other conditions, such as coeliac

disease or irritable bowel syndrome (IBS), inflammatory bowel disease (IBD) and advise whether further assessment is needed.

Speak to your GP or a specialist

Your symptoms may be caused by other health conditions, such as coeliac disease. These need proper assessment and the right tests.

Understanding the difference between an allergy and an intolerance matters because it guides the right tests, treatment and support. At King Edward VII’s Hospital, we offer consultant-led diagnostics for both, helping patients gain clarity and manage their health confidently from the start.

Main signs and symptoms of food intolerance

Food intolerances often cause unwanted symptoms that build over hours, not minutes. Many people don’t realise their symptoms are linked to food at all. Keeping a simple food and symptom diary can help you spot patterns.

Digestive symptoms

Digestive symptoms are the most common and often the most disruptive to daily life. They may include:

• Bloating or abdominal swelling 
• Excess wind
• Diarrhoea
• Constipation
• Stomach cramps
• Nausea

These symptoms typically appear several hours after eating the food that triggers them. They can vary from mild to severe, depending on portion size or factors such as stress.

General discomfort or fatigue

Some people feel unusually tired, foggy or generally unwell after eating certain foods. This happens because the digestive system works harder or struggles to break down a particular ingredient.

Other possible symptoms

Food intolerances can affect the body beyond digestion. Some people notice:

• Headaches
• More frequent migraines
• Skin rashes, bumps or worsening eczema
• Heart palpitations
• Joint pain

These signs alone don’t confirm a food intolerance, but they can be helpful clues when they appear alongside digestive health changes or discomfort.

Food intolerance symptoms aren’t always predictable. A small portion may be fine, while a larger portion triggers discomfort. While common, many people find this inconsistency frustrating and seek professional guidance.

What to do if you think you have a food intolerance

Noticing symptoms is the first step. Understanding what’s causing them is next. It can be tempting to cut out several foods on your own, but this can lead to confusion and unnecessary restrictions. A guided, structured approach is the safest way to get clear answers and protect your long-term health.

If your symptoms are recurring, affecting daily life or difficult to make sense of, it’s sensible to speak to a healthcare professional. They can help rule out other conditions, such as coeliac disease or irritable bowel syndrome (IBS), and advise whether further assessment is needed.

For those who need specialist support, King Edward VII’s Hospital provides rapid access to consultants in gastroenterology, nutrition and allergy care. A specialist can offer clarity, reassurance and a personalised plan, helping you move from uncertainty to a better understanding of your symptoms and how to manage them.

Managing your food intolerance symptoms

When symptoms start affecting your daily life, it’s helpful to take a structured approach. Finding out what’s triggering them and getting the right guidance can make the process clearer and less overwhelming.

Keep a simple food and symptom diary

Tracking what you eat and how you feel for two to four weeks can reveal helpful patterns. Write down:

• Everything you eat and drink
• Time of meals
• Any symptoms that develop
• How long symptoms last

This diary gives your doctor or dietitian valuable information when discussing possible triggers.

Speak to your GP or a specialist

Your symptoms may be caused by other health conditions, such as coeliac disease. These need proper assessment and the right tests. 

Your doctor may recommend:

• Blood tests
• Breath tests for lactose intolerance
• A referral to a gastroenterology or allergy consultant
• Allergy tests
• Endoscopy (a diagnostic test that uses a small camera to assess the small intestine)

At King Edward VII’s Hospital, you can access these assessments quickly with consultants who specialise in digestive and dietary conditions. They’ll look at the full picture and guide you safely through the next steps.

Avoid online intolerance testing kits

Many home testing kits available online lack scientific evidence and aren’t recommended by the NHS. They can lead to unnecessary food restrictions, which can create more problems than they solve. Choosing clinically approved testing ensures you get reliable results.

Try an elimination and reintroduction plan if advised

If a consultant or dietitian suspects a food intolerance, they may guide you through a structured elimination diet. This involves removing a specific food for a set period, then reintroducing it slowly to see if symptoms return. 

This type of plan should always be carried out under professional supervision to make sure your diet remains balanced.

Consider treatment options

Treatment depends on the type of intolerance. Common approaches include:

• Reducing rather than completely removing the food
• Using alternatives, such as lactose-free dairy
• Enzyme supplements for conditions like lactose intolerance
• Dietitian support to ensure you’re eating a healthy, complete diet

If you’re diagnosed with a condition such as coeliac disease, your consultant at King Edward VII’s Hospital will help you understand how to manage it safely long term.

Getting food intolerance support at King Edward VII’s Hospital

Living with ongoing digestive symptoms can feel draining and isolating. You may find yourself second-guessing what you can eat or avoiding social events to prevent feeling unwell. With the right assessment and guidance, most people begin to understand their triggers and make confident food choices.

At King Edward VII’s Hospital, our consultants specialise in identifying the causes of symptoms like bloating, abdominal pain and food reactions. You’ll receive clear explanations, honest advice and a plan that works for your lifestyle.

Book your consultationwith King Edward VII’s Hospital today and get the support you need to manage food intolerances effectively.