The IgG antibody test: Vital for optimising nutrition? Part 1

 I wanted to write about something that was brought to my attention recently by a friend.
She was approached by a client of hers (a professional rugby player), who had been told by the team's nutritionist that he should have an IgG test. This test involves taking a small blood sample and then testing the blood to see if there are any IgG antibodies specific to certain foods. The theory is that IgG antibodies while not being involved in allergy (more on that in a second), can lead to "food sensitivities", abdominal pain, bloating, diarrhoea etc.

We all know that optimising diet is essential if we want to get the most out of our training. "You can't out-train a bad diet", whilst being one the most overused catchphrases in the health and fitness industry,  is essentially correct. You certainly won't be performing at your best if your diet is awful.
So, is the IgG test an essential tool to get the most out of your diet or a waste of time and money?

Unfortunately in the world of nutrition there is a lot of, shall we say, nonsense that lacks any backing by scientific literature.Even more annoying is that usually this brand of pseudo-science gets the most attention. So I wanted to check if this was one of those situations or it actually had some merit to it.
I thought it would be best to split this post into 2 parts to prevent it from being too long.
The first part is going to be a bit of background on what allergy is (and isn't). This is important so you don't get caught up in the grey areas that exist in this topic. I'm not going to go into too much depth with the immunology just a quick overview.
The second part will be a review of the literature on IgG antibodies and their role in food intolerances.
With this being a blog and not a theses I'll keep it as concise as possible, hopefully you find it useful and if you like you can delve further into the topic.

So what is a food allergy? 

Good question.
I think there is a general misunderstanding and confusion between a true allergy, an intolerance or even a person just not liking a food. It's these grey areas that can often lead to someone thinking they have an allergy, self diagnosing and then consuming a sub-standard diet.

When defining allergy it is first useful to familiarise yourself with the term Hypersensitivity. 
Simply put, a hypersensitivity causes objective, reproducible symptoms to something that the "normal" population would be fine with.
An allergy is a hypersensitivity that is driven by "immunological mechanisms".
Clear as mud? Well, the most important thing to remember is that allergy must involve the immune system. If the immune system isn't involved then it's not an allergy.
Another important thing to remember is that you cannot be allergic to something if you have never been in contact with it before. So people who say they had an allergic reaction the very first time they ate a certain food, are either mistaken and the reaction wasn't allergic, or they have been in contact with that food and just can't remember or didn't realise.
In the simplest of terms our immune system is our body's protection against harmful foreign invaders (bacteria, viruses etc). Using peanut as an example. The "normal" immune system when it comes into contact with the peanut (which if you think about it is a foreign invader) realises that it is not harmful and does not mount a response. With an allergy however, the immune system mistakenly thinks this peanut is harmful and responds.
The first response isn't an allergic reaction (remember you can't have an allergic reaction first time round) but is to create antibodies specific to peanut. The next time this person comes into contact with a peanut they will have a reaction.
There are several classes/types of antibody and the antibody responsible for allergy is the IgE (Immunoglobulin E) antibody, they sit on top of the Mast cells and Basophils (cells from our immune system) and cause them to release various chemical nasties, one of which is histamine. It's these chemicals that cause your typical allergy symptoms, runny nose and eyes, urticaria, breathing difficulties and in severe cases anaphylaxis. Just to confuse matters you can have an allergy that does not involve the IgE antibody but the symptoms are different and I will touch on that in part 2 of the post.

What are food intolerances and sensitivities?

These can be thought of as "non-allergic hypersensitivities".
Food intolerances do not involve the immune system. Probably the most well-known of these is lactose intolerance. Here the individual is lacking the necessary enzyme (lactase) to digest lactose and so when ingested it causes them problems.
The term "food sensitivity" appears to be interchangeable with intolerance so essentially it is 2 different names for the same thing.
Hopefully you are starting to get the picture. But it all comes crashing down when looking at the website of one of the companies that offers IgG testing.

On the website they list everything under the umbrella of food sensitivity/intolerance

• Enzyme deficiencies (like above),
• Chemical sensitivities  
• Reactions to histamines in foods

So far so good and that is what I would class as intolerance/sensitivity

But then they also include in their list

• Allergy
• Coeliac disease  
• IgG mediated reactions  

I disagree here and it is this lumping everything together under the title of "intolerance" that is unhelpful and leads to the confusion I mentioned at the start of this post. The fact food is involved is pretty much where the similarities start and end.
Both allergy and Coeliac involve the immune system so need to be separated from conditions such as lactose intolerance. IgG is a grey area within a grey area and after part 2 I will tell you where I would categorise it.

So that's it for the first part. Hopefully I have gone some of the way to clearing up the confusion around definitions and you now have a clearer picture of what is meant by food intolerance or sensitivity. And that we are clear that we are not talking about allergy (or Coeliac disease). But if you want to delve a little further the website below is what I used for the definitions. It's a bit wordy and medical but I would recommend that you take a look, especially if nutrition and immunology is an area of interest for you.

 http://www.worldallergy.org/professional/allergic_diseases_center/nomenclature/english.php


Coming up in part 2 I will discuss the evidence for IgG tests and food related symptoms. So hopefully by the end you will be able to decide if an IgG test is something worthwhile or not.

If you have any questions/comments please stick them below.

Thanks