Do you have a food intolerance?
Information regarding food allergy and intolerance is plentiful, but so are the myths. Self-diagnosed, food sensitivities have become more common place, but how can you really tell if you have a food intolerance?
What is the difference between a food allergy and an intolerance?
Food intolerances differ to food allergies. An allergy elicits an acute, almost immediate reaction, the worst of which is anaphylaxis. Food intolerance is less severe and as a result more difficult to diagnose. An intolerance typically ocur because the body is lacking an enzyme that is needed to properly digest and eliminate a food or substance. Symptoms may be delayed and might include bloating, headaches or skin rashes. Skin prick testing and laboratory 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 embark on an elimination diet, arm yourself with all the information you need. Consult a qualified health professional to ensure your nutritional requirements are met and to address any other considerations. For example, where testing for coeliac disease is recommended, it is very important that you do not 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 food culprit(s) you can restrict them one at a time to see if you have any improvements in your symptoms before carefully re-introducing them. This trial-and-error approach may help narrow down suspect foods and allow you to discover that you can tolerate a certain amount of the food without symptoms.
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This ‘elimination diet’ is best performed using the 3 ‘R’ approach:
1. Record – without altering your usual diet, record in a diary or on a smartphone tracker what, when and how you were eating, along with any symptoms you experience and when those symptoms 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 seven 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 may be 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.
2. Restrict – once you have identified the suspect food(s), familiarise yourself with alternatives that you can include in your diet 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, for example three to six months, so don’t be tempted to rush this stage because it’s important that you address one food at a time rather than compromising your diet.
3. Re-introduce – this step helps confirm your suspicions and may help you understand your tolerance threshold. On day one, re-introduce the suspect food but only a third of your normal portion – you can increase the amount gradually overtime. 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 re-introduction of the food to establish your own tolerance levels, if any. Performing the food challenge in this way helps to ensure a balanced, varied diet and minimises any detrimental impact on levels of your 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.
What are common causes of intolerance?
Fructose
This natural sugar is 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
This is one of the most commonly cited foods for causing digestive upsets including abdominal 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, and some people are 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 some grains such as spelt or kamut, these grains are higher in fibre, lower in gluten and nutritious.
Gluten
This 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, which effectively ‘glue up’ the digestive system. 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. If you suspect gluten to be a problem, it’s essential that you make no changes to your diet until you have completed all of the appropriate tests to determine what the problem may be. This is because if you eliminate gluten before tests are completed then you risk a false negative result. Read more about how to follow a gluten-free diet.
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 and as a result experience what is known as 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 food is coupled with drinking alcohol. Red wine is a common trigger, followed by whisky and beer. Alcohol intolerance may also cause unpleasant symptoms such as nasal congestion and skin flushing. Once again, intolerance is linked to an enzyme deficiency making 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 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 to help break down the histamine in certain foods and manage our overall histamine load. Some people do not produce enough of this enzyme and consequently, when they eat histamine-containing or liberating foods, they 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, soya sauce, processed meats, smoked fish and chocolate. More information on histamine intolerance can be found at allergyuk.org.
Yeast
Yeast is present in a variety of foods, commonly 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 following a yeast free diet (through elimination) for a few weeks. If there is a significant improvement then you have found your culprit!
Salicylates
These are natural chemicals made by plants and are found in foods as varied as prunes, broccoli and cumin. Although less common than other intolerances, people with an intolerance 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.
Read more on this topic…
What is a dairy-free diet?
What is a gluten-free diet?
20 foods you think are gluten-free but aren’t
Top 10 tips for a gluten-free diet
What is the candida diet?
Top 20 low-histamine foods
This article was last reviewed on 27 March 2024 by Kerry Torrens.
Kerry Torrens is a qualified Nutritionist (MBANT) with a post graduate diploma in Personalised Nutrition & Nutritional Therapy. She is a member of the British Association for Nutrition and Lifestyle Medicine (BANT) and a member of the Guild of Food Writers. Over the last 15 years she has been a contributing author to a number of nutritional and cookery publications including BBC Good Food.
Jo Williams is a registered nutritionist (RNutr) with the Association for Nutrition with a specialism in public health.
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