Understanding Food Intolerances




One of the main complaints I hear from people I work with is that they are becoming more and more intolerant to foods, but they are having trouble pinpointing which foods are causing the problem.

So this post is all about how you can begin to understand your food intolerances, and how to identify them.


Firstly, I think it’s important to point out that there is a huge difference between food intolerances and allergies, as the terms are often used interchangeably, when they are in fact very different.


Food allergies are classified by an exaggerated immune system response to a food protein and the body triggers an allergic reaction as a result. They usually develop in childhood, and are not necessarily something you can overcome, although some people do seem to grow out of them.

On the other hand, food intolerances are an adverse reaction to a food that does not involve the immune system. Reactions can be immediate or delayed up to 20 hours after a food is eaten...hence being difficult to pinpoint the culprit in many cases. The good thing about food intolerances is that they can be temporary, and are more a sign of dysfunction in the digestive system. The key to overcoming them, is to identify why you have lost the ability to digest certain foods in the first place. Avoiding them in the short term helps a lot with reducing symptoms, but it’s not a good long-term solution, as most people will slowly become intolerant to more and more foods over time and end up on a very limited diet which isn’t fun, or beneficial for your health in the long term.


The only accurate way to identify food intolerances is through an elimination diet. Unfortunately tests that claim to identify food intolerances are not reliable and often leave you with a long list of random foods to exclude from your diet, which in many cases is unnecessary, and misses the foods that are actually problematic.

Why are the common food intolerance tests not helpful? Let's take a look.

ELISA and ALCAT are both blood tests that claim to identify food intolerances. They look at how your blood responds when exposed to a specific food. ELISA measures IgG antibody reactions. ALCAT measures white blood cell reactions. These sound like plausible theories, right? Antibodies and white blood cells are part of your immune system. If your immune system reacts to a food, that would obviously signify intolerance. It turns out that some studies show that an IgG response to a food actually indicates tolerance. And white blood cells constantly change shape and activity anyway, so if they do that in the presence of a food, that doesn’t mean the food was the trigger. Not surprisingly, both tests are notorious for inconsistent results.


The most common causes for food intolerances are related to dysfunction in the gut. You may have an overgrowth of bacteria in the small intestine (SIBO), which means that when you eat foods that are normally broken down by gut bacteria in the large intestine, this starts to happen in the small intestine. The result is gas production, and when this happens in the small intestine, it can result in extreme bloating, uncomfortable gas and changes to bowel movements.

Another common cause for developing food intolerances is nervous system dysfunction, which is generally driven by stress and anxiety. To put it simply, your nervous system may often be in a state of ‘fight or flight’, which results in your digestion being “switched off”, leading to lower production of HCl in the stomach, and pancreatic enzymes, needed to break down the foods you eat, as well as changes to motility, causing your digestion to either slow down (constipation), or speed up (diarrhea).


As you can see, it is really important to address the underlying issue, rather than stop at simply eliminating foods you are intolerant to. However, working out your food intolerances can help to reduce your symptoms in the short term, and reduce inflammation in the gut.

As I mentioned before, the only accurate way to do this is to work through an elimination diet, and starting with the most common foods that people with digestive issues are intolerant to is a great place to start.


I recommend beginning with gluten, dairy, and FODMAPs. It is important to note that gluten is not a FODMAP, but it is common for those with digestive issues (even if you don’t have celiac), to become intolerant to it. Dairy can be problematic for several reasons. The first being that it can lead to inflammation due to the proteins in it (specifically A1 protein), and the second being that some dairy products are high in lactose, which is a FODMAP. If you don’t know what FODMAPs are, Put simply, FODMAP is an acronym for a collection of short-chain carbohydrates (sugars) that aren’t absorbed properly in the gut, and which gut bacteria breakdown for you. FODMAPs are found naturally in many foods and food additives.

The recommended time frame to eliminate these foods is 5-6 weeks. After this time, you should begin to reintroduce each food group one by one to test your tolerance. FODMAP elimination diets can be quite difficult to do alone, which is why I always recommend working alongside an experienced professional who will be able to give you clear instructions on how to do this. The reason being, that many foods that are classified as high FODMAP, are dependent on the amount. For example, broccoli is considered low FODMAP at a typical serving of 1 cup, if you consume the head only, but high in excess fructose if you’re consuming the whole vegetable (stalk included), but low at a smaller serving size of ½ cup. See how this could get confusing? To make things even more confusing, even if you’re eating the right amount and it is considered low FODMAP, if you combine this with other foods that have the potential to be high FODMAP at various serving sizes, you may experience symptoms because the FODMAPs add up. This is called FODMAP stacking.

I have had many clients who have been diagnosed with IBS, and advised to follow a low FODMAP diet, with little instructions on how to do it correctly. They then give up because it was too confusing to do without a proper plan to follow. If you are not in a position to hire a Nutritionist to help you with this process, the next best option is to download the Monash University FODMAP app.


Following a FODMAP/gluten/dairy elimination diet correctly can reduce symptoms like bloating, gas and pain within 1 week in most cases and is a great place to start for anyone who has recently received an IBS diagnosis. However, it is not the long-term solution and will not fix the underlying cause. It is also very important that you don’t follow a diet like this indefinitely, as most people do not have intolerances to all of these food groups. Elimination diets are designed to remove the food, then reintroduce after a period of time to test your tolerance and work out which are problematic for you, so that you can have relief from the daily symptoms, while working on the underlying cause. Eliminating FODMAPs indefinitely is actually detrimental for your gut health as FODMAPs are the main fuel source for your beneficial bacteria. Your long-term goal should be to correct the underlying imbalances that led you to becoming intolerant to these foods in the first place, so that you can eventually enjoy them freely.


If you have recently been diagnosed with IBS, or suspect you have IBS, and have no idea where to start, I can help. Book in a free 20 minute introductory consultation with me, and we can discuss your symptoms, likely underlying cause, and how you can get started on a personalised plan that doesn’t just stop at eliminating foods, and instead aims to correct the underlying imbalances that have lead you to becoming intolerant to foods in the first place.


Chrystie x


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© 2021 The Gut Health Nutritionist

DISCLAIMER. As each person is different, individual results cannot be guaranteed.

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