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Recognizing food chemical intolerances

Despite allergies and intolerances being frequently grouped together, there are fundamental differences between the two. A true food allergy is defined as an abnormal immune response to a food protein which is directly mediated by immunoglobulin E (IgE), causing almost immediate and often life-threatening reaction to the allergen.

On the other hand, a food intolerance is a non-immune mediated reaction to a food protein, carbohydrate or chemical. These reactions appear over a prolonged period of time and leave no chemical or physical trace, making them extremely difficult to diagnose.

Under the umbrella of food intolerances, the attention of the media and available literature tends to restrict itself to carbohydrates (such as FODMAPS) and proteins (such as gluten), with food chemical intolerances frequently overlooked. For many, this means their symptoms go unrecognised and undiagnosed for quite some time. As such, it is important for healthcare professionals to be familiar with the signs and symptoms of food intolerances so that they can appropriately and safely offer recommendations and referrals.

What is a food chemical intolerance?

Food chemical intolerances are widely misunderstood. The term ‘chemical’ gets a bad rap in the public eye, conjuring up the idea of artificial additives and pre-packaged junk food. Yet, naturally occurring food chemicals, endogenously produced by plants and animals appear everywhere in nature and have the potential to provoke distressing symptoms in sensitive individuals. These natural chemicals include salicylates, amines and glutamate, and they are predominantly found in fresh, whole foods and are therefore consumed in greatest quantity in a healthy, well-balanced diet.

Unlike carbohydrate and protein intolerances where symptoms are usually localised and confined to the abdomen where malabsorption occurs, food chemicals are absorbed which means their symptoms are systemic and can appear anywhere in the body.2 Due to the lack of controlled studies, the precise mechanism of action is poorly understood.2 Current literature suggests that in sensitive individuals food chemicals irritate nerve endings in different parts of the body and trigger a histamine-type response in a similar way that certain drugs can cause side effects in sensitive people.

The most commonly reported symptoms include:

• skin irritations such as hives, swelling, rashes or eczema

• sinus irritations and/or breathing problems

• nervous system irritations such as headaches, migraines,fatigue, flu-like aches and pains, mood changes

• gastrointestinal irritations such as reflux, nausea, mouthulcers, bloating, cramps, diarrhoea and/or constipation.


Salicylates are a major plant hormone that acts to regulate stress. It is essentially a naturally occurring pesticide that prevents plants from rotting and against potentially harmful pathogens, such as insects, bacteria and fungi. Given the paramount role of salicylates in nature, it is the most widely distributed food chemical in fresh fruits and vegetables and is mostly found in the outer layers and skin. According to available research, the most common symptoms of salicylate intolerance are respiratory and skin irritations, with gastrointestinal discomfort possible but far less documented.

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Amines are formed from the natural breakdown of proteins during fermentation, storage and ripening. They include phenylethylamine, tyranime, tryptamine, putrescine, cadaverine, spermine, spermidine and perhaps the most frequently intolerable—histamine. Foods like meat, cheese and fish increase in amines as they age or mature, and in fruits and vegetables as they ripen or ferment. According to available research, headaches are the most common complaint for patients with amine intolerance.


Glutamates are non-essential amino acids present in all protein foods in one of two forms: bound or free. When bound, glutamate is attached to a complete protein that allows for it to be digested and absorbed slowly. In free form, glutamate is not tied to any other amino acid molecule which means it is absorbed quickly. It is when glutamate exists in free form that individuals will be more likely to experience problems.6 Freeform glutamate enhances the flavour of foods, which is why it is commonly found in umami rich foods such as cheese, tomatoes, mushrooms and meat/yeast extracts. Current studies link glutamate intolerance to asthma, headaches and skin irritations.

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Identifying & managing food chemical intolerances

Food chemicals are found in a wide variety of foods in varying amounts and in many cases more than one food chemical is present in a single food item. When a patient experiences an intolerance, they are able to tolerate a particular food chemical up until they reach a threshold, meaning the onset of symptoms rarely implicates the irritant. And because they do not cause physical damage or result in any internal chemical release, they are impossible to credibly identify through any currently available diagnostic tests. It is for these reasons that food chemical intolerances are incredibly difficult to identify.

So, unlike other well-established nutrition guidelines, identifying food chemical intolerances is based on trial, error and observation.3 Currently, the gold standard for both identifying and managing food chemical intolerances is through the Royal Prince Alfred Hospital (RPAH) Diagnostic Elimination Diet.

This diet is broken into two phases: an elimination phase and a re-challenge phase. In the elimination phase, salicylates, amines and glutamates are highly restricted for several weeks until symptoms are controlled. If eliminating food chemicals from the diet helps, this is then followed by a re-challenge phase.

In this phase, patients re-introduce individual foods high in particular food chemicals to identify food triggers which may need to be avoided in the future.

Due to the restrictive nature of the elimination diet and potential negative consequences for nutritional adequacy, it is imperative that patients are supervised by a dietitian during the initial elimination phase as well as the re-challenge phase.


Patients who present with symptoms that may implicate a food chemical intolerance should be discouraged from conducting any at-home IgG or antibody tests as they are not validated or recommended by the scientific community. Instead, patients should be encouraged to visit their doctor to review their symptoms and conduct legitimate tests to rule out other conditions. If an elimination diet is required, patients should be referred to an Accredited Practising Dietitian with experience in food intolerances.


Food intolerances are a highly individualised and ambiguous phenomenon that is difficult to both research and identify. Despite being a tricky area for health professionals to navigate, it is imperative that we do not overlook food chemicals as a possible trigger for patients experiencing distressing symptoms.

SalicylatesFruit: soft avocado, tomato, berries, banana, cherry, citrus fruit, grapes, kiwi fruit, pineapple, guava

Vegetables: broad beans, capsicum, eggplant, zucchini, mushrooms, spinach, pickled vegetables

Herbs & spices: chilli, curry, cayenne, turmeric, ginger, mustard, oregano, peppermint

Other: coffee, tea, truffles, olives, dates, peanuts
AminesFruit: bananas, soft avocado, ripe tomatoes

Vegetables: eggplant, mushrooms, spinach, legumes

Other: fish, meat products, aged cheese, aged wine, pickled and fermented food products
GlutamatesFruit: tomatoes

Vegetables: mushrooms, spinach, sweet corn, pickled vegetables, fermented vegetables

Other: soups and stocks, soy sauce, vegemite, parmesan cheese, cured meats, seafood, chicken, beef
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