Food Intolerance


The comments of those who have recovered from food intolerance after many years of ill-health are always memorable. ‘It’s like getting my life back again,’ said one woman. ‘I had actually forgotten what it felt like to be well,’ said another, ‘the effect of cutting out certain foods was just amazing.’ For most of those with food intolerance, the disease begins very subtly and gradually – first one symptom (persistent and unexplained diarrhoea, perhaps) then, some years later, another (migraine or headaches) and then, when a few more years have passed, another symptom (such as joint pain or muscle aches). Steadily increasing levels of irritability, ‘fuzzy-headedness’ or inexplicable tiredness may accompany this decline in health.
Most patients have no idea that all these symptoms are connected until they try an elimination diet, and everything clears up at once, quite dramatically.
As one former sufferer described it:
‘Some of the stuff that got better – well, I’d been like that so long I thought it was just the way I was – grumpy and exhausted, and feeling terrible if I didn’t eat meals on time. It was an absolute revelation to feel completely OK again.’
Woman suffering from food intolerance having a terrible heachace and stomach avhe

Photo by Anh Nguyen on Unsplash

What does ‘food intolerance’ mean?

In article, food intolerance means any reaction to food where the immune system has no proven central role. All the people I have described so far have idiopathic food intolerance, which means, food intolerance with no established mechanism – in other words, doctors can’t say exactly how it is caused. This is a highly controversial area.
The definition of food intolerance used in this book means that it also includes metabolic abnormalities, which do have a well-established cause. These are due to defective enzymes. The question of what words mean is a key part of the debate over idiopathic food intolerance. At one extreme, you may come across doctors who call this problem ‘food allergy’, using the original meaning of the word ‘allergy’. (Some of these doctors use terms such as delayed food allergy and masked food allergy, to point up the distinction from true food allergy, but not all do).
Using the word ‘allergy’ in this context causes a lot of aggravation and confusion, so the term ‘food intolerance’ has, for a long time, been widely accepted as a useful one that avoids unnecessary conflict. You will also hear the term ‘food intolerance’ used to mean idiopathic food intolerance only – this is probably the most common usage. When the term is used in this way, metabolic abnormalities are being thought of as a separate entity altogether.
A new twist has recently been added to this long-standing wrangle over meanings. When mentioning food intolerance in their literature, some of the major medical organisations (those who dispute the very existence of idiopathic food intolerance) now say simply ‘food intolerance e.g. lactase deficiency’ . To anyone familiar with this field, it looks suspiciously like an attempt to redefine ‘food intolerance’ so that it means nothing more than ‘metabolic abnormalities ‘.
The idea seems to be that, if you deny a disease a name, it will go away!

In the medical wilderness

The main text of this article is about idiopathic food intolerance, a disease with a distinctly dubious reputation among doctors. Because it is so controversial, few doctors actually look at the evidence that it exists – which is in fact quite strong (see box on this page – The evidience). Such evidence is simply ignored in most of what is written by the major medical organisations debunking idiopathic food intolerance.
This lack of medical recognition is very unfortunate for patients with idiopathic food intolerance, whose debilitating symptoms could be eliminated, rather than simply being treated (usually to little effect) with drugs. This prejudiced attitude to idiopathic food intolerance also plays into the hands of those offering bogus diagnostic tests and phoney treatments, often at a very high price.
These practitioners
– who have moved in to fill the gap left by conventional medicine
– are a considerable part of the problem, helping to give idiopathic food intolerance a bad name.
The waters are muddied even more by the fact that some people who believe themselves to have food intolerance are actually suffering from psychological problems, which they prefer to attribute to food. Many more have picked up on food intolerance as something rather glamorous to suffer from, inspired by all the media reports about food intolerance among celebrities. All these patients are a good source of revenue for the less scrupulous fringe practitioners and are unlikely, therefore, to be discouraged from their beliefs. Fortunately there are enough conventional but open-minded doctors, often GPs, who have come to realise, through experience with their own patients, that elimination diets have a remarkable curative effect for some people. The ones who benefit are often the doctor’s ‘old faithfuls’ – those with long-term multiple symptoms, who have been referred to innumerable specialists and treated with all kinds of drugs, but who never get much better. The conventional view of such patients is that they have psychological problems that are being expressed as physical symptoms. This may well be true for some – but others have idiopathic food intolerance.


The symptoms of idiopathic food intolerance come on slowly after eating the offending food, and the foods to blame are often those eaten very regularly, such as wheat or milk. Consequently, the symptoms from one meal tend to overlap with those from the previous meal and people with idiopathic food intolerance are more-or-Iess unwell for most of the time. It is usually not obvious that food is at fault. All the symptoms of idiopathic food intolerance are common ones that can be caused in other ways. And no two patients have exactly the same set of symptoms.
(As far as doctors are concemed, neither of these attributes gives the disease a respectable air.)

These are some of the symptoms commonly reported

Headache or migraine

diarrhoea, sometimes with bloating and wind; this is often diagnosed as irritable bowel syndrome (IBS)

in children, stomach aches

occasionally constipation

nausea and indigestion

joint pain

aching muscles

a constantly runny or blocked nose (this could be perennial allergic rhinitis linked to food)

glue ear

fatigue and a general feeling of vague ill-health. Asthma and eczema, triggered by specific foods, can also be part of the picture.

In babies, colic is often caused by food intolerance, including
foods the mother is eating which come through into the breast
milk in tiny amounts.

Less common symptoms include:

recurrent mouth ulcers

stomach or duodenal ulcers

chronic urticaria

swelling (angioedema)

The following diseases have also been linked to idiopathic food

intolerance in some patients:

Crohn’s disease

palindromic rheumatism (intermittent episodes of joint inflammation)

rheumatoid arthritis

Psychological problems such as depression, anxiety, or hyperactivity in children can sometimes be due to food but it is rare for such psychological effects to occur without any physical symptoms. Remember that every single one of these symptoms and conditions can be caused in some other way. However, the constellation of migraine/headache, joint pain and diarrhoea is highly characteristic of idiopathic food intolerance.

Photo by Karly Gomez on Unsplash

The evidence

The evidence for idiopathic food intolerance is more substantial than its opponents would have you believe.
One very well-conducted and interesting study involved children with severe migraine who were investigated by a research team at Great Ormond Street Hospital in London. These are children who are very difficult to treat successfully by normal means. On an elimination diet, 88% of those children got better – an astonishing number. Not just their migraine, but all sorts of other symptoms as well, including aching limbs, runny noses, asthma, eczema, diarrhoea, wind, mouth ulcers and hyperactivity. Some of these children also had epileptic fits, and even this symptom cleared up on the diet, recurring when culprit foods were tested. A notable feature of this study is that, of the five researchers involved, four were deeply sceptical at the outset. Their report notes that they embarked on this study believing that any favourable response, such as that claimed to substantiate the dietary hypothesis, could be explained as a placebo response. The positive double-blind controlled trial … provides clear evidence that a placebo response was not the explanation.’
Other studies with good scientific credentials have demonstrated a role for idiopathic food intolerance in adults with migraine, and for sufferers from irritable bowel syndrome and Grohn’s disease. There are also good studies of individual patients with rheumatoid arthritis and palindromic rheumatism (an episodic form of inflammatory arthritis) who have responded dramatically to avoidance of a particular food. Some of these patients were given several double-blind challenges and showed changes in certain immunological tests, as well as joint symptoms, when challenged with the offending food. This suggests that the immune system could be playing some part in these food reactions.

The text on this page is used with permission from Linda Gamlin and Professor Jonathan Brostoff