Food Intolerance

Overview

Food intolerance means your body has trouble breaking down or handling a certain food. It is not the same as a food allergy. An allergy involves your immune system and can be dangerous, while an intolerance is about digestion. With an intolerance, you may feel bloated, gassy, or get a sore tummy or loose stools after eating that food. The amount you eat often matters, so a small taste may be fine but a large portion causes trouble. Food intolerance is not life-threatening, but it can be uncomfortable and annoying.

Yes. Food intolerance is very common. Many people notice a food or drink that does not agree with them at some point in their life.

It can affect anyone at any age. Some types are more common in certain groups — for example, trouble digesting milk sugar (lactose) is more common in people of East Asian, African, South American and Southern European descent, and becomes more common as people get older. Children can have intolerances too, and some of them improve as the child grows.

Symptoms

Common symptoms

• Bloating and a full, tight feeling in the tummy
• Wind and gas
• Tummy pain or cramps
• Diarrhoea or loose stools, sometimes constipation
• Feeling sick or needing to rush to the toilet
• Headaches or tiredness after certain foods
• Flushing, itching, or a rash in some people (for example with wine or cheese)

Symptoms in children

• Tummy aches, wind and loose stools after certain foods or drinks
• Being clingy or unsettled after feeding in babies
• Refusing certain foods or being very fussy at mealtimes
• In babies: crying a lot, drawing legs up, and frequent watery stools (see your doctor if there is poor weight gain)

Symptoms in older adults

• Symptoms may become more noticeable with age, as digestion slows and milk sugar is broken down less well
• Diarrhoea can lead to dehydration more quickly, so drink plenty of fluids
• Tummy symptoms can overlap with other conditions, so it is worth getting them checked
• Unintentional weight loss or a change in bowel habits should always be checked by a doctor

Causes

Main causes

• Not enough of a digestive enzyme — for example, many people have less lactase, the enzyme that breaks down milk sugar (lactose)
• Carbohydrates in foods that are hard to fully digest and ferment in the gut, such as beans, lentils, onions, garlic, wheat and some fruit
• Natural chemicals in foods, such as histamine in cheese, wine and cured meats, or caffeine in coffee and tea
• Food additives such as some colourings and flavourings, or sweeteners that can cause wind and loose stools
• Irritable bowel syndrome (IBS) and other gut conditions, which can make the gut more sensitive to certain foods
• A changed gut bacteria mix (the community of germs that live in your bowel), which can be affected by illness, antibiotics, or diet

Risk factors

• Getting older, which can lower how much of some digestive enzymes you make
• Your ethnic background and family history
• A recent bout of food poisoning or a gut infection
• Having irritable bowel syndrome or another long-term gut condition
• Taking some medicines that affect the gut
• Eating very large amounts of a particular food or drink regularly
• Stress, which can make gut symptoms feel worse

When to see a doctor

See a doctor urgently if:

• Blood in your stool
• Severe tummy pain that does not settle
• Unintentional weight loss
• Vomiting blood
• Signs of dehydration
• Suddenly finding you cannot swallow, or your face, lips or tongue swell — this needs emergency care straight away

Book a routine appointment if:

• Tummy symptoms that keep coming back, even if you change your diet
• Finding you are cutting out more and more foods, so your meals feel limited
• Symptoms in a child, especially if they are not growing well
• A change in your bowel habits lasting more than a few weeks
• Feeling worried or anxious about eating, or avoiding social meals
• Before you start a strict diet or stop eating a whole food group

Diagnosis

Your doctor will start by asking about your symptoms and your eating and drinking habits, and may suggest keeping a food diary for a few weeks. They will want to rule out a food allergy, coeliac disease (a condition where gluten damages the gut), and other gut problems, because these need different care. A common next step is trying a short, planned cut-out of a suspected food, then adding it back while watching your symptoms.

Tests that may be done

• Physical examination and a careful history of your symptoms
• A food and symptom diary kept over 2 to 4 weeks
• A trial of removing a suspect food and then reintroducing it (guided by your doctor or a dietitian)
• A breath test, which can check how well you break down lactose or other sugars
• Blood tests to rule out coeliac disease or allergy (these conditions are not the same as intolerance)
• Stool tests, if there is diarrhoea or bleeding
• A camera test of the bowel (endoscopy) only in some cases, if other tests do not explain your symptoms

What to expect at your appointment

It can take a few weeks of gentle detective work. You may not get a quick answer, and you may be referred to a dietitian, especially if a strict diet is being considered. Be patient with yourself, and avoid cutting out many foods on your own so you keep getting the nutrients you need.

Treatment

There is no cure for food intolerance, but most people manage it well by finding their trigger, eating less of it, or swapping to foods they tolerate better. The goal is to feel comfortable without making your diet unnecessarily narrow.

Self-care at home

• Keep a simple food and symptom diary so you can spot patterns
• Try one change at a time so you know what actually helped
• Reduce the amount of the trigger food rather than always cutting it out completely — many people can handle a small portion
• Eat smaller meals more slowly, and take your time over food
• Try lactose-free or reduced-lactose milk and dairy if milk sugar seems to be the problem — these are widely available
• Spread dairy or trigger foods through the day instead of having a lot at once
• Stay well hydrated, especially if you have loose stools
• Try supermarket milk alternatives fortified with calcium if you avoid dairy — check the labels

Medical treatments

Your doctor or pharmacist can advise on options that may help you digest certain foods or ease symptoms, and there are limited choices available without a prescription. A dietitian can also guide you through a structured food plan, such as a low-fermentable-carbohydrate diet, for a set number of weeks, followed by careful reintroduction so your diet stays varied. Never take a new medicine or supplement, or start a strict diet, without checking with your doctor or pharmacist first, especially if you have other health conditions or take regular medicines.

Living with this condition

Once you know your trigger, life usually gets easier. You learn which foods to enjoy freely, which to have in smaller amounts, and how to handle eating out. Many people find they can still eat most things — just not always a large plateful.

Lifestyle tips

• Read food labels, but do not let shopping become stressful — look at the ingredients you care about
• When eating out, look at menus online first and ask about ingredients if you are unsure
• Keep a small snack with you that you know suits you
• Tell friends and family about your trigger so meals together are easier
• Try not to skip meals, as an empty stomach can make symptoms feel worse
• Build a short list of safe meals you enjoy so busy days feel simpler

Diet and exercise

Aim for a varied diet with plenty of fruit, vegetables, whole grains you tolerate, and protein. If you cut out a food group such as dairy, replace the nutrients it gave you — for example, choose calcium-rich alternatives. Regular gentle exercise, like walking, can help your gut and your mood. If you are unsure whether your diet is balanced, ask your doctor to refer you to a dietitian.

Mental health and emotional wellbeing

Tummy symptoms can be embarrassing and tiring, and eating out may feel worrying. Some people feel anxious about food or low in mood. This is very common, and it is okay to ask for help. If you feel very low, hopeless, or have thoughts of harming yourself, contact your local emergency number or a crisis service straight away, and reach out to a trusted person or your doctor.

Prevention

You cannot always prevent a food intolerance, especially the type linked to getting older. But you can often stop symptoms from taking over your life by noticing your triggers, not eating very large amounts of one food at a time, and getting advice before starting a strict diet.

Screening programmes

There is no routine screening test for food intolerance. If you have a close family member with coeliac disease, or you have ongoing gut symptoms, talk to your doctor about whether testing for other conditions is right for you.

Complications

If left untreated

• Ongoing discomfort, wind and loose stools that affect work, sleep and social life
• Cutting out too many foods, which can lead to missing important nutrients like calcium, iron or certain vitamins
• Poor growth or slow weight gain in children if their diet is very limited
• Dehydration from ongoing diarrhoea
• Worry and stress around food and eating
• Missing another condition, such as coeliac disease, that needs its own treatment

Long-term outlook

The outlook is good. Most people with food intolerance feel much better once they understand their trigger and find a way of eating that suits them. You can still enjoy food and meals out — it just takes a little planning at first.

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