On this page, we discuss the differences between intolerance and allergy, symptoms of intolerance, and the role of genesCan people be intolerant to foods they eat?

The short answer is yes. Though often confused with allergy (even by health professionals), food intolerances are rather different. 

If you are allergic to a food, exposure will predictably and quickly trigger symptoms. You'll often be able to identify the trigger. You might develop a rash. Or vomiting. Or an uncomfortable sensation in the mouth. Or something more serious still. Allergy involves a branch of the immune system known as IgE. While these Immunoglobulin E (IgE) antibodies were vital for protecting us against parasites, in the developed world they are mostly known for their role in allergy. Think of it; there's an entire medical specialty devoted almost entirely to the malfunctioning of this tiny immunoglobulin!

Food intolerance is different. It doesn't have a medical specialty but its multiple effects overlap several, most especially gastroenterology and neurology. There is also overlap with allergy, notably for skin and respiratory symptoms*. As it lacks ownership by a single medical or scientific specialty, the terminology is less well-defined and even conflicting. 

For example, in Northern Europe and North America, lactose intolerance is viewed as an illness. Yet most of the world doesn't; they just don't drink milk after infancy. As children, they stop producing the lactase enzyme required to break down the lactose sugar in milk. They can still, if they wish, tolerate fermented dairy produce in the form of cheese or yoghurt. In these paragraphs when I speak of milk intolerance, I am referring to milk protein intolerance.

'Intolerance' also covers a range of unrelated chemical reactions to substances like MSG or preservatives in wines. Again, that is beyond the scope of these pages. I will be speaking of a specific, but increasingly common range of reactions associated with raised levels of IgG antibodies (a different branch of the immune system!) against common food proteins. These food protein intolerances respond well to elimination of the food and relapse when the food is taken again. So how do they differ from food allergy?

Firstly, it is less clear-cut. With intolerances it is not just a question of 'yes or no' but of 'how much'. 

That 'how much' might be little or none. Or it or might be once or twice a week. 

It varies from person to person. More confusingly, after a gap, it can take several days of exposure to trigger the old level of symptoms again. This inconsistency leads some to dismiss the existence of food intolerances at all. It is not uncommon for sufferers to have been told 'it's all in the mind'. 

With intolerances it is often hard to pinpoint the food that gives rise to symptoms. Especially if it's more than one food. Or if there are other more obvious complicating factors, like stress. For example, IBS sufferers may not have identified which foods trigger their symptoms, but they know that stress will predictably worsen things. This fact may lead IBS to be labelled as psychosomatic (produced by the mind without a physical basis). 

Food intolerances aren't immediately life-threatening. But they may be life-changing. Flare-ups of Irritable Bowel Syndrome, Crohn's Disease, Migraines or a range of respiratory and skin conditions have substantial consequences for the sufferer. 

Elimination. Rechallenge. Re-program

When I began trialling blood testing for food intolerances, the results (of modifying the diet) were sometimes so stark that I wondered how I had missed the link in the past. However, there is a proper process of diagnosis which must be followed. Following a 12-week strict Elimination Diet comes a careful Re-challenge with individual foods. 

Most people who offer diagnostic testing for treating food intolerance logically focus on the Elimination part. After all, Elimination is what makes you feel better. Some of my most fulfilled professional moments have come from people saying 'I'm like a new person' or 'you've given me back a new child'. The Elimination phase also exposes you to new and improved dietary choice - of fresh, varied and nutrient-rich foods.

But don't stop there. The Re-Challenge is still important, if sometimes uncomfortable. It tells you if, and how often, you may be able to take the foods in future. And whether different forms of a food - cooked or processed - have a different impact. And whether certain combinations are worse than the individual ingredients (e.g. pizza). 

Re-Challenge joins the dots, re-programs your diet and, importantly, confirms the diagnosis.  

What are the symptoms of food intolerance?

There are many. Austrian research by Prof Martie Truschnigg at the University of Graz showed that high levels of IgG antibodies against foods were associated with increased inflammation. The marker of inflammation used in the study was CRP (C-Reactive Protein) - a routine test during a health check-up. 

As the name suggests, inflammation is not just a local thing. It can affect many, indeed most, parts of the body. It can aggravate, trigger, a broad variety of symptoms and conditions and cause knock-on effects on other functions, such as fertility and mental clarity. 

And, as if aging wasn't enough punishment, older bodies tend to produce more inflammatory cytokines, making problems easier to trigger.

Food intolerance has been linked to aggravation of a wide variety of symptoms, including:

Anxiety (acute or chronic), Arthritis, Asthma, Ataxia, Attention Deficit Disorder, Bed wetting, Bronchitis, Coeliac Disease, Chronic Fatigue Syndrome, Constipation, Depression, Diarrhoea, Fatigue, Fibromyalgia, Gastritis, Headaches, Hyperactivity Disorder, Inflammatory Bowel Disease, Insomnia, Irritable Bowel Syndrome, Itchy skin problems, Malabsorption, Migraines, Nasal congestion or a runny nose*, Sleep Disturbances, Water retention

That's a long list. But it's not because 'milk causes sinus problems' or 'gluten causes IBS', it's because the circulating inflammatory chemicals and immune complexes can get to many places. 

Is it hereditary?

I normally explain this as follows: Every one of us has a variety of genetic 'buttons', inherited from our parents and grandparents, which can trigger particular problems.

We may never press the buttons, or we may press lots of them. We may start to press them gradually, or some trauma or shock may push a serious one (e.g. psoriasis). Inflammation makes these buttons easier to press.

What we do know is that modern diets and lifestyles play an important role. It is the price of affluence. 

For example, comparisons between neighbouring (and ethnically-related) areas on the Finnish-Russian border showed that coeliac disease was 8 times more common on the Finnish side, even though the poorer Russian side consumed more bread. 

Think about that. Coeliac is generally viewed as a genetic disease, yet the genes are clearly just one (albeit vital) part. Being born in Russia saved 7 of 8 coeliacs from this fate. That is why I advise people to never accept that a particular condition 'runs in my family'. Not without a fight.

Even before inflammation becomes a definable disease, sufferers of food intolerance may complain of lethargy, brain fog, and a general feeling of unwellness, symptoms that can persist over years. 

In the early stages, these symptoms cannot be easily diagnosed medically. Health checks like blood pressure, routine blood chemistry, cholesterol or even endoscopy may give normal results. Paradoxically, the doctor's reassurance that there's nothing dangerous happening may make the sufferer feel that their suffering is being dismissed as insignificant. This is one of the reasons that people turn to alternative therapies - some good, some not. My discussions with a very wide range of practitioners shows that many are converging on the importance of diet. Their Continuing Professional Development (CPD) programmes are more likely to feature new findings on nutrition and bowel bacteria than CPD for my own health profession.

It is ironic that the stage at which it is most possible to change your future health and wellbeing - when you are still low-risk - is the stage when our medical system is weakest. 

Finnish research (again!), showed that more lives were saved (from death due to heart disease) by lifestyle change amongst the low-risk population than high risk patients. And at far lower cost. 

While it may be possible to manage symptoms well with medication, it is better to join the dots and learn what you can do to prevent and control them. And if diet and lifestyle eventually prove inadequate, you'll still have a wide range of well-tested medical treatments left to try.  

* nasal symptoms or wheeze can also be provoked by so-called "true allergy" an IgE antibody reaction against dust mites, pollens, cat or dog dander, or a combination of these. Symptoms of "true allergy" may tend to be worse in the summer (during pollen season) or in the mornings (if dust-mites are involved).



REPLACE AND IMPROVE

Carrying out an Elimination Diet involves replacing one food by others, Eliminating a food can be hard. But it should also be an opportunity to improve things. Very few of us eat a nutritionally complete diet. When replacing, say, milk, don't just focus on calcium. Also look at important bone-health nutrients that are not adequately available from milk, especially magnesium. So you might choose to add more green vegetables like cabbage or broccoli. But also consider almonds, brazil nuts, quinoa. And don't be afraid to drink water.