Seven Steps to Identifying a Food Intolerance

(Last Updated On: June 24, 2019)

Do you ever get the feeling that something you’re eating is making you ill? You know you aren’t imagining those symptoms – that bloating, headache or fatigue is very real, but simply not normal. If your doctor can’t find anything wrong, it may be time to consider the possibility that you have a food intolerance.


Food Intolerance under the microscope

If you do indeed have a food intolerance, the good news is that you don’t have to soldier on with your symptoms. With just a little patience and some clever sleuthing on your part, you can identify whatever food is causing your symptoms, eliminate it and then experience the joy of being symptom-free.


This goal can be achieved in seven easy steps. You can start the process by thinking about the foods you consume most regularly, and the ones you crave the most. Your diet is peppered with clues; it is cruelly ironic that the foods we love most – and eat most of – are often the ones that cause the most trouble.

 Here’s your seven-step guide to nailing that culprit.


Food intolerance has been associated with a myriad of chronic symptoms including headaches, intestinal and skin symptoms, behavioural changes and respiratory disorders. Currently, the best accepted method for diagnosing and confirming food intolerance is empirical, by elimination diet and subsequent challenge.

Hardman and Hart 2007


Step 1

Keep a food diary for five days. Write down everything you eat and drink throughout each day. Make sure that these days are truly representative of your typical diet, and be honest with yourself.


 Step 2

Read through your diary, and use highlighters to mark the foods you consume the most. This exercise can be quite a revelation – you may be shocked by the amount of bread you eat or the number of biscuits that accompany each cup of tea or coffee.


Once you have identified the foods you eat most often, make a list of them. Bear in mind that if your symptoms occur every day, the food intolerance culprit is most likely to be something you eat every day.


Step 3

You will now strictly avoid the food item that tops your list, for seven full days. Remember, any food can cause a reaction; everyone is an individual and this individuality is reflected in health and symptoms. Having said that, there are certain foods that are regarded as common culprits – see below.


Gluten grains (wheat, rye, barley, spelt)
Nuts - all or some


Gluten is a protein found in wheat, barley and rye. Some people are sensitive to all the gluten grains, and others are only sensitive to the gluten in wheat.


Step 4

Keep a symptom diary during the seven-day exclusion period. Make a note of any changes to your health and symptoms during this period. What has improved, gone away or stayed the same? How do you feel generally?


Step 5

Here’s the best part – the challenge. When the seven exclusion days are up, you can enjoy a feast of the food you have so stoically avoided. For example, if you have been avoiding wheat, you could take the opportunity to savour a large bowl of pasta with your favorite sauce, perhaps with a bread roll on the side. 

Enjoy this meal, but do not have the challenge food again for at least three days.


Step 6

Keep a record of any symptoms that emerge after reintroducing the challenge food, over the next three days.

Step 7

Avoid the offending food item. You will almost certainly have no problems recognising the food in question, because once reintroduced it will reveal itself as the guilty party quite clearly, usually within just a couple of hours. Your symptom diary will also provide evidence of your food intolerance.


If some, but not all of your symptoms disappeared during the avoidance phase, it is possible that you have more than one food intolerance. If that is the case, you should consider repeating the exercise with the next food on your frequency list.


Common Food Intolerance Offenders

There’s every chance that you selected wheat-based foods as your first choice to carry out the challenge.


Not for nothing is wheat often cited as the most common offender. After all, it is a recent addition to the human diet (we only began cultivating wheat, and other grains, at the start of the Agricultural Revolution 10-11,000 years ago). Therefore our genetic make-up has not had time to adapt to something that has effectively become a staple. What’s more, the wheat we eat today has been genetically engineered to contain a great deal more of the protein gluten than the wild wheat that once grew in pre-agricultural times.


It is this gluten (responsible for making bread more doughy and elastic) that causes so many health problems.  Each of the gluten grains – wheat, rye and barley – contains a different type of gluten, with wheat gluten (gliadin) being the most common offender. Some people are sensitive to all gluten, and others to wheat gluten only.


Be careful if you think you may be wheat intolerant. Wheat often hides in plain sight, so watch out. Bread and pasta are well known, but less obvious are muesli, biscuits (sweet and savoury), cakes, pastries, cous cous, and semolina.


The second most likely culprit is probably dairy food. Many people are lactose intolerant, meaning they lack the enzyme to digest the lactose (milk sugar) in milk. The result is usually digestive problems: bloating, pain and diarrhoea are not uncommon, and neither are eczema and asthma, especially in children. But even if you are not lactose intolerant, you could still be dairy intolerant, meaning that you react to one of the proteins in dairy foods. Therefore if dairy features regularly in your diary, it is worth carrying out the challenge.


Food Intolerance – It’s Not an Allergy

Food intolerance is no figment of your imagination; it may be tricky to identify, but that doesn’t make it any less real. This elusive affliction often takes on a chameleon quality – one day a headache, the next day a bloated stomach.


The same cannot be said for an allergy.


If you have a true allergy, you probably already know it. The reaction, whether it be a rash, stomach pain or itchy tongue, tends to be immediate, making the offending food relatively easy to identify. A true allergy is a rare thing: it is believed that less than five per cent of people are affected. An extreme allergy can invoke an extreme reaction, known as anaphylactic shock, a threat to life that requires immediate medical intervention.


Allergies often occur in families, passing from parent to child. These are known as atopic families, and they commonly experience the same symptoms – often asthma, eczema and hay fever. Food allergies are fairly easy to identify, and a medical doctor can arrange for appropriate testing.


A Happy Ending

Blood tests for a food intolerance are much less reliable.  For that reason, the best way to identify an intolerance is to do the challenge test.


The percentage of patients reporting noticeable improvement suggests that such specified elmination diets are a valid intervention in the relief of certain symptoms.

Hardman and Hart 2007


Having to avoid a beloved food item may feel painful, but happily there is a silver lining to this cloud. After a long period of avoidance (usually two or three months) there is every chance that you will have built up a degree of tolerance to the food in question. You may find that you can start eating it occasionally (no more than once or twice a week), without experiencing any symptoms. You get to eat the food you love, and still feel great – and stay in control of your health.


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