Do you have a food intolerance?

Jo Williams – Registered nutritionist

Published: June 7, 2024 at 12:25 PM

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Information about food allergy and intolerance is plentiful, but so are the myths. Self-diagnosing has become more commonplace, but how can you really tell if you have a food intolerance?

Food sensitivities are increasingly common, with an estimated 20% of the world’s population potentially having a food intolerance or allergy. Many more experience issues, including bloating and gastric discomfort, and choose to eliminate foods from their diet in an attempt to alleviate their symptoms.

However, restricting your diet without proper medical guidance is not a sustainable way to eat and may lead to nutrient deficiencies. Read on to discover more.

What is the difference between a food allergy and an intolerance?

Food allergies causes an acute, almost immediate reaction, the worst of which is anaphylaxis. Food intolerances are less severe but more difficult to diagnose. Intolerances typically occur because the body is lacking an enzyme that is needed to properly digest something. Symptoms may be delayed and might include bloating, headaches or skin rashes. Skin-prick testing and lab blood tests are available, but the most effective, accepted and accurate way of identifying problem foods is via an elimination diet.

Discover more about intolerance and whether you should invest in a food intolerance test as well as lots of recipe inspiration for those with a food intolerance, including gluten- and dairy-free diets.

What is an elimination diet?

An elimination diet is a free, non-invasive way of working out if you have a sensitivity to a certain food. You don’t need any pills or potions, just a fair amount of will power because compliance and commitment are key to getting accurate results.

An elimination diet should be followed for the shortest period of time to bring about symptom improvement. Before you start an elimination diet, arm yourself with all the information you need. Consult a qualified health professional to check your nutritional requirements will be met and to address any other considerations. For example, where testing for coeliac disease, it's very important you don't eliminate any foods from your diet until all tests have been completed.

How do I follow an elimination diet?

The NHS suggests the most appropriate way to diagnose a food intolerance is to monitor your symptoms when you eat certain foods. Once you identify the possible culprit(s) you can restrict them one at a time to see if there is any improvement to your symptoms; then you can carefully reintroduce them. This trial-and-error approach can help narrow down suspect foods and you may find out that you can tolerate a certain amount of the food without symptoms.

Common food intolerance foods: milk, eggs, seafood, wheat flour and nuts

An elimination diet is best performed using the 'three Rs’ approach:

Record – without altering your usual diet, record in a diary or on a smartphone tracker what, when and how you were eating, plus any symptoms, when they occur and how long they last. Be thorough and include condiments, treats, drinks and snacks – this is best done in real time so you don’t forget things. Do this over a 7- to 14-day period and assess your findings to decide which food or drinks, if any, may be causing you a problem. If at the end of this step you think the culprit maybe wheat or gluten, speak to your GP in case they feel it appropriate to test you for Coeliac disease – this is important before proceeding to step two. Similarly, if you suspect a problem with dairy (lactose) or fructose, your GP may suggest a hydrogen breath test.
Restrict – once you have identified the suspect food(s), familiarise yourself with alternatives and then restrict the suspect food while monitoring and recording how you feel. Do you still get symptoms? If step one identified several foods, you should refer to a dietician for guidance to avoid the risk of nutritional deficiencies. Step two may take some time, so don’t be tempted to rush this stage.
Reintroduce – this step helps confirm your suspicions and may help you understand your tolerance threshold. On day one, reintroduce the suspect food, but only a third of your normal portion – you can increase the amount gradually over time. If you do get symptoms, wait until you are symptom-free before you try the next test food.

An elimination diet should be used for as short a time as possible, and be followed by reintroduction of the food to establish your tolerance levels, if any. This helps to ensure a balanced, varied diet and minimises any detrimental impact on levels of beneficial gut bacteria.

If you believe your symptoms are the result of a classic allergy rather than a food intolerance, speak to your GP for referral to an NHS-approved diagnostic IgE testing facility, which also offers professional dietetic support.

A woman reading a food label in a supermarket

What are the most likely foods to cause intolerance?

Fructose

This is a natural sugar found in fruit, honey and some syrups. If you suspect you have a sensitivity to fructose, you should also try to avoid sucrose (table sugar), high-fructose corn syrup, fruit and fruit juices, sorbitol and sweetened juices. Common signs of fructose intolerance include abdominal pain, gas and bloating and diarrhoea. The FODMAP diet is a new approach to managing IBS which may be helpful in this circumstance.
Wheat

Wheat is one of the most commonly cited foods for causing digestive upsets including bloating. When trying to decipher wheat intolerance, it is important to eliminate flour and flour-based products entirely as well as other foods which may contain wheat or wheat-derived ingredients. Wheat intolerance varies between individuals, with some people able to tolerate alternative grains. If you suspect you have a wheat intolerance, try eliminating wheat entirely. You may find that you are able to tolerate small amounts of older varieties of grains such as spelt or kamut; these grains are higher in fibre, lower in gluten and nutritious.
Gluten

Gluten is the glue-like protein found in many grains but especially in wheat, rye and barley. Its elasticity makes it a key part of many bakes. Some people are intolerant to the gluten in all of these grains, others just find wheat the trigger. A diet high in refined carbohydrates may contain significant quantities of gluten. If you have discovered you cannot tolerate any gluten-containing grains, try rice, corn or potato flour. Before you embark on any elimination diet, be sure to consult your GP. It is essential that, if you suspect gluten to be a problem, you make no changes to your diet until you have completed all of the appropriate tests. If you eliminate gluten before tests are completed you risk a false negative result. Learn more about a gluten-free diet and some common foods that you might think are gluten-free but aren’t.

Glucose

Glucose intolerance is the umbrella term given to metabolic conditions which cause elevated blood glucose levels. If you have impaired glucose tolerance (IGT) or impaired fasting glucose (IFG), your body is not using glucose (sugar) properly. This may result in higher than normal blood sugar levels – a condition known as hyperglycemia. Diagnosis of either IGT or IFG requires medical assessment. Symptoms include excessive thirst, dry mouth, fatigue, blurred vision and frequent urination. It is important to seek medical advice if you suspect you have an intolerance to glucose.
Lactose

All animal milks contain a sugar called lactose and the body produces an enzyme in our gut called lactase to digest it. Without sufficient lactase, the sugar is left to ferment and may lead to symptoms such as bloating, wind and diarrhoea. Many adults lose the ability to produce enough lactase, resulting in lactose intolerance. Those who are intolerant to lactose may be able to tolerate a little butter, cheese or yogurt, while others avoid dairy products completely.
Alcohol

Intolerance may be caused by alcohol or the food the alcohol is made from (e.g. grapes from wine, grains from whisky). Alcohol can affect the integrity of the gut, which may explain why some people experience digestive discomfort when they drink alcohol with food. Red wine is a common trigger, as are whisky and beer. Alcohol intolerance may also cause symptoms such as nasal congestion and skin flushing. Once again, intolerance is linked to an enzyme deficiency which makes it hard for the body to break down alcohol. Intolerance may also be due to other ingredients commonly found in alcoholic beverages (especially beer and wine) including sulphites, preservatives or chemicals.
Histamine

This substance occurs naturally in certain foods and some foods act as histamine liberators, effectively stimulating our body to release histamine. We produce an enzyme called diamine oxidase which helps break down histamine and manage our overall load. Many people don't produce enough of this enzyme, so when they eat histamine-containing foods they may suffer symptoms such as headaches, skin rashes, itching, diarrhoea and abdominal pain. Foods that are particularly high in histamine include wine, beer, cider, pickled foods, cheese, tofu, soy sauce, processed meats, smoked fish and chocolate. More information on histamine intolerance can be found at allergyuk.org.
Yeast

Yeast is present in foods including bread, baked products and alcoholic beverages. Yeast intolerance has a wide range of symptoms including flatulence, bad breath, fatigue, irritability, cravings for sugary foods, stomach cramps, bad skin and indigestion. If you suspect you are intolerant to yeast, try eliminating it from your diet for a few weeks. If there is a significant improvement then you may have found your culprit.
Salicylates

These are natural chemicals made by plants, found in foods as varied as prunes, broccoli and cumin. Although a less common intolerance, people who have it cannot tolerate even small amounts without experiencing side effects. A low-salicylate diet may be helpful.

For more information on food intolerances visit allergyuk.org.

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Do you have a food intolerance?

What is the difference between a food allergy and an intolerance?

What is an elimination diet?

How do I follow an elimination diet?

What are the most likely foods to cause intolerance?

Fructose

Wheat

Gluten

Glucose

Lactose

Alcohol

Histamine

Yeast

Salicylates

Read more on this topic…

Comments, questions and tips

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