Food Intolerances

Food intolerances – are they real? On one hand, we have always known that the same diet does not suit everyone. A Roman poet said, “One man’s meat is another man’s poison”, and ancient traditions such as Ayurveda recommend different diets for different constitutions. However, the vast array of “free from” products on supermarket shelves bears witness to how many people now consider that they have an intolerance, and this was certainly not the case a generation ago. Are there legitimate reasons for some people to avoid certain foods, or is this merely a fad? In this post, I aim to explain why food intolerances occur and why they might be on the increase, tell you a little of my own experience and suggest a way to determine what your intolerances might be.

Food intolerances are different from allergies. An allergic reaction causes particular immunoglobulins (IgE) to be released into the blood, and the response is usually immediate, making the allergy relatively easy to identify. Blood tests can accurately identify IgE to allergens, so the concept of allergies is not disputed. Food intolerances, on the other hand, result in a different immune response (IgG). This is often delayed by as much as 3 days after the food is eaten. When you consider how many different foods you may eat over a 3 day period, you can begin to realise how difficult it can be to identify a food causing an intolerance! To make the situation worse, symptoms of intolerance can be vague and non-specific, such as headaches, brain fog, digestive upset and skin problems, and the identification of food intolerances by blood testing is not well supported by scientific evidence.

This doesn’t mean, however, that food intolerances don’t exist. In some cases, such as lactose intolerance, the intolerance is due to the absence of an enzyme (lactase) which breaks down the lactose molecule in dairy. As much as 75% of the world’s population lacks the gene for this enzyme (1), particularly populations outside northern Europe and Africa. (In fact, at one point in our evolution, all humans were lactose intolerant after early childhood – some farming communities later evolved to be able to break down lactose.) My son has seen remarkable improvements in sinus congestion purely from removing lactose from his diet.

Another reason for multiple intolerances is intestinal permeability, or ‘leaky gut’. Think of the body as having a tube all the way through the middle – this is the gut. Food in the gut is still “outside” our bodies – it is only when food is digested and then absorbed through the intestinal walls that it enters our bloodstream. The cells of the intestinal walls have tight junctions between them so that large, partially digested pieces of food cannot get through. However, these junctions can become “leaky”, and when they do, large particles of food can get into the bloodstream, where they are not supposed to be. The incredible immune system, which is on constant surveillance, sees these particles as foreign invaders and (mistakenly) attacks them (2).

The immune system attack creates inflammation, which can become chronic if you are continually eating foods which trigger an immune response. And chronic inflammation is bad news – it is the driver of chronic diseases, from arthritis, diabetes and cardiovascular disease to autoimmunity and even cancer (3). It can also cause typical symptoms of food intolerance such as joint pain and brain fog. What’s more, as the immune system attacks food particles, it is possible that tissues of the body might be damaged at the same time. This is one of the theories for the development of autoimmunity.

The leaky gut theory would explain why food intolerances seem to be on the rise. Factors which contribute to leaky gut include alcohol, drugs such as ibuprofen, the Western diet, and stress (4, 5) – factors which are an intrinsic part of many people’s lives in modern times.

For years, I thought that I didn’t have any food intolerances. However, I changed my diet radically a few years ago and was eating a lot more plant protein such as pulses and nuts and seeds. Much as I thought this was good for me, I eventually had to admit that it was causing me a lot of bloating, digestive discomfort and low energy. Although my “healthy” diet may have suited some people, it was clearly not right for me. As I have an autoimmune condition (and autoimmunity is linked to intestinal permeability) I had to accept that I must have a leaky gut, and that in all likelihood I had multiple food intolerances. However, I had no idea what foods might be triggers for me.

And so we come to the best way of determining food intolerances: an elimination diet. All foods which are likely to cause an adverse reaction are removed from the diet, usually for a period of at least 30 days, but sometimes for longer. The list of foods to eliminate may vary somewhat from one health condition to another. After the foods have been out of the diet for a while symptoms (such as eczema, digestive issues, joint pain or brain fog) should improve.

This is the time to try to heal the gut! When trigger foods are being eaten, the continual inflammation can itself perpetuate a leaky gut, but with the offending foods removed, inflammation reduces. Foods such as bone broth contain nutrients for the cells of the gut and can be very healing to consume during the elimination phase.

You can then reintroduce foods one at a time, only adding a new food every 3 days so that if a reaction occurs it is easy to identify the culprit. If a particular food causes a reaction, it should be left out, but it is encouraging to consider that as the gut continues to heal, you might tolerate it in the future.

An elimination diet can be a real challenge. Sometimes it can feel as though there is little left to eat, especially at the start! But, with support and careful meal planning, in time you can get used to a new way of eating. And as you continue, the benefits can make it all worthwhile. In my case my eczema (which I have had for 20 years) has completely cleared up and my digestion is so much better than before. A source of chronic inflammation in my body has been eliminated too, and this can only be good for my health.

Working with a nutritional therapist can ensure that your diet still includes all the nutrients you need while you are on an elimination diet.





  • Silanikove, Leitner and Merin (2015). ‘The Interrelationships between Lactose Intolerance and the Modern Dairy Industry: Global Perspectives in Evolutional and Historical Backgrounds’, Nutrients, 7(9), pp7312-7331. [Online]. Available at (Accessed 3 August 2017).
  • Fasano, A. (2011). ‘Zonulin and Its Regulation of Intestinal Barrier Function: The Biological Door to Inflammation, Autoimmunity, and Cancer’, Physiological Reviews, 91(1), pp151-175. [Online]. Available at (Accessed 4 August 2017).
  • Dubois, R.N. (2015). ‘The Jeremiah Metzger Lecture: Inflammation, Immune Modulators, and Chronic Disease’, Transactions of the American Clinical and Climatological Association, 126, pp230-236. [Online]. Available at (Accessed 4 August 2017).
  • Leclerq, S., Matamoros, S., Cani, P.D. et al. (2014). ‘Intestinal permeability, gut-bacterial dysbiosis, and behavioral markers of alcohol-dependence severity’, Proceedings of the National Academy of Sciences of the United States of America, 111(42), E4485-93. [Online]. Available at (Accessed 4 August 2017).
  • Konturek, P.C., Brzozowski, T. and Konturek, S.J. (2011). ‘Stress and the gut: pathophysiology, clinical consequences, diagnostic approach and treatment options’, Journal of Physiology and Pharmacology, 62(6), pp591-599. [Online]. Available at (Accessed 4 August 2017).