How do food allergies and intolerances impact our health, and how to detect them?

First of all, it’s important to distinguish food allergies from food intolerances.

Confusingly enough, both are immune-related, meaning the body reacts to a food that it mistakenly recognises as a foreign protein. As a result, the body produces antibodies to attack these “offenders” (IgE antibodies for allergies, IgG for intolerances). However, symptoms are very different whether it’s an allergy or an intolerance.

Food allergy vs. food intolerance


Food allergies (i.e. IgE mediated) are usually relatively easy to identify as the reaction occurs instantly, or within minutes of eating the offending food.

Symptoms would include sneezing, rashes, difficulty breathing, and more rarely, anaphylactic shock, which can be fatal.

People with food allergies should totally exclude the food(s) in question. Sometimes, food allergies in children resolve themselves overtime, but for some people, the offending food will need to be strictly avoided for their entire life.

Food intolerances (i.e. IgG mediated) are less obvious to detect as they can occur within hours, and up to several days after an offending food has been ingested.

They’re caused by the gradual formation of antigen/antibody complexes that get deposited in tissues, which in turn causes chronic inflammation and delayed symptoms.

These symptoms include digestive issues. In fact, IBS has been associated with food intolerances (references upon request).

Perhaps less expectedly, food intolerances can also cause anxiety, depression, headaches/migraines, hypertension, atopic conditions (e.g. eczema, asthma, rhinitis), joint pain, arthritis, weight problems, fatigue and fibromyalgia.

Other (non IgG mediated) food intolerances

Not all intolerances are IgG mediated, some occur because the body can’t digest some foods properly. This is the case when someone doesn’t produce enough of the enzymes responsible to break down certain proteins, for instance when lacking the enzyme lactase to digest the protein lactose that’s contained in milk and dairy products. Symptoms are mostly of digestive nature, but can also compromise gut health and create other inflammation-related symptoms on the long term.

How to identify food allergies and intolerances?

Food allergies

In most cases, people know to which food(s) they are allergic, due to the immediate reaction they cause. This said, sometimes reactions are mild and then ingredients may be present in processed foods, making their identification more difficult. In this case, it’s a good idea to do a laboratory test to understand which foods cause an IgE immune reaction. These are blood tests and costs between around £100 to £200, depending on the number of foods (and inhalants) tested.

Food intolerances

Where lactose intolerance is suspected (so not an IgG mediated reaction), based on the symptoms reported, excluding dairy products for a few weeks would be my recommendation of choice, over testing. That’s obviously for clients who feel confident they can stick to this restrictive diet. The result would be unequivocal, and come at no financial costs. Else, lab tests are available in the form of blood, breath or stool tests. I usually recommend breath test for their sensitivity and specificity (i.e. how reliable they are), and because they’re easy to perform. Lactose breath tests tend cost around £80.

Exclusion diet isn’t always an easy option though. For IgG meditated intolerances, it’s really not easy to know which food to start with, plus, the probability of being intolerant to only one type of food is quite low. So whilst it’s not an impossible choice, the process may be time-consuming and tedious, and the answer to our question inaccurate.

Where there’s suspicion of IgG mediated food intolerance, my recommendation would therefore be a laboratory test, which is a blood/serum test that can be performed at home. I won’t lie, getting enough blood from a finger prick is not a pleasant experience, or at least it wasn’t for me, so if that’s an issue, nurse visits can be organised. Test prices vary depending on the number of foods tested, and range from around £120 to £300. Luckily, there’s no need for follow-up tests. 



Does food intolerance mean total food exclusion, for ever?


The short answer is: Maybe, but probably not.

After excluding the offending foods for a few months, people with food intolerances may be able to reintroduce some foods, in small or larger quantities.

I apologise for the vague answer here; there are so many factors that would impact where your immune reaction threshold is; only a personalised approach can tell what foods would be helpful, or less helpful for you, and in which amount.

It all depends on how many foods you have an immune reaction to, and perhaps some other reactions, what’s your level of reaction to these (every food creates a different level of IgG antibodies, from low to elevated and high), how much symptoms you’d be ready to endure, whether you’d want to live with a certain level of chronic inflammation knowing the risks associated with it, etc.

If my clients are up for a food reintroduction challenge, I fully support them as my role is to help them reach their health goals as they define them, not as I do.

Can foods triggering IBS symptoms be detected with food intolerance test?

Sadly not. Whilst the exact causes of Irritable Bowel Syndrome aren’t fully understood, several causes have been identified, and so investigating each of them would be my recommendation in order to try and get on top of IBS symptoms. This said, IgG food intolerances may play a role in IBS symptoms, so finding out about them, and consequently excluding them for at least a few months might improve symptoms.

Once again, there’s no one-fits-all answer, a personalised approach is required to get to the bottom of what causes digestive symptoms in an individual.

What other factors can impact our digestive health?


When a client sees me to get on top of their digestive symptoms, food intolerances are one of the possible root causes I’d investigate in the first place.

Beside food intolerances, there are other root causes I’d want to exclude when working with clients with digestive issues, such as poor chewing (digestion starts in the mouth!), lack of stomach acid, dilution of gastric juices, Coeliac disease (which is an auto-immune condition), inappropriate hydration, a diet low in dietary fibre and/or high in sugar, dysbiosis (an imbalance in the gut bacteria), intestinal permeability, chronic low-grade inflammation, gut hypersensitivity to certain foods (mostly those high in a certain type of sugar called fructo-oligosaccharides or FOS), and the presence of unhelpful bacteria, viruses, fungi and yeast in the digestive tract.

Usually, with a clear understanding of the client’s symptoms, diet, lifestyle, antecedents, medical history as well as possible triggering events, the investigation quickly moves to the most likely root causes for the symptoms. As in, not all of the above possible factors would be investigated in the first instance.


I may also refer my clients to a GP for them to exclude more serious digestive conditions, such as Inflammatory Bowel Disease (IBD), pancreatitis, etc.

I hope this short article has shed some light on questions you may have about food allergies and intolerances. For any questions, don’t hesitate to reach out, I’d love to hear what your health goals are, and help you find your glow.

N.B.: A special thanks to CNS Labs for their educational webinars and literature on food intolerances; they’re a very valuable partner and I’m grateful for their continuous support.