Paper: McQueen J, Loblay R, Swain AR, Anthony M, Lance J. A controlled trial of dietary modification in migraine. New advances in headache research. Smith-Gordom; 1989. p. 235–42.
Overview of paper: This trial follows on a study of food intolerance in 237 migraine patients presenting at a food allergy clinic [1]. In the original study (elimination diet/double blind placebo-controlled food challenges), 48% reacted to at least one chemical challenge, such as nitrates, preservatives, salicylate, amines, MSG, or tartrazine; four years later, a large number of these patients continued to follow an appropriately-restricted diet and considered themselves substantially improved.
In the current trial, participants were recruited from a migraine clinic instead of a food allergy clinic. Only 19 of 95 participants completed both the food challenge and the modified diet crossover trial (4 weeks normal diet, 1 week washout, 4 weeks trigger-free diet): “only half experienced a significant improvement on the appropriate [trigger-free] diet, and only three were headache-free altogether.”
The quote:
[E]ven in patients in whom dietary triggers may have been identified by double-blind challenge, long-term avoidance of the relevant foods is likely to be effective as a prophylactic measure only in a minority of patients. This should not be taken to mean that patients who incriminate particular foods as triggers must be mistaken. The situation is comparable to that in asthmatics where it has become abundantly clear that some patients are sensitive to the effects of salicylate, MSG and sulphite preservatives. Large doses may sometimes precipitate acute attacks, but regular avoidance of foods containing these substances does not usually produce measurable clinical improvements in the long term [2]. No doubt, in asthma as in migraine, this reflects the multitude of other intrinsic and extrinsic factors involved in the triggering of symptoms in predisposed individuals.
Significance of quote: This study has definite limitations, including a small sample size, a greater placebo response rate than normal, a short washout period (and possible order effect), and dietary compliance issues. The write-up is also short on experimental details, especially regarding the order of the two test diets. However, perhaps some of these problems mirror the real-life difficulties that people face when trying to manage migraines that can often be linked to food. Secondary triggers – lack of sleep, menstruation, bright lights, motion sickness, fragrances, etc. – can be at least as or even more important than food on any given day. This is not to say, though, that migraine (and asthma) sufferers should freely consume the foods that they know to be triggers, only that the complete avoidance of trigger foods may not be necessary for certain people.
2. “After 3 months on the restricted diet, four of 19 children on the MBS[metabisulfite]-free diet and one of six on the salicylate-free diet had objective signs of improvement, namely, reduction in asthma medications and/or improvement in lung function.”
Towns SJ, Mellis CM. Role of Acetyl Salicylic Acid and Sodium Metabisulfite in Chronic Childhood Asthma. Pediatrics. 1984 May 1;73(5):631–7.
Imagine that you are in a Chinese restaurant with your family. You’ll probably get a migraine later tonight (maybe from the amines in the soy sauce), but you’ve been craving Chinese food all week and you haven’t made the connection yet. Your daughter is drinking cup after cup of jasmine tea with her five spice stir fry, and this, combined with the other things she ate during the day, will give her hives again this evening. Your son asks you to read the fortune in his fortune cookie – “Knowledge is power,” it says, but it doesn’t warn you about the tartrazine in the cookie. He’ll be cranky tonight and distracted tomorrow morning. This is what you might experience if you suffer from food intolerance.
Lesson 1: What is food intolerance?
Is food intolerance real?
Yes. The existence of pharmacological food intolerance has been established by double blind placebo-controlled food challenges. The bulk of the research on food intolerance has been conducted in Australia, the UK, and Germany, and there is an increased awareness of food intolerance in these countries.
That said, two points should be kept in mind. First, even though food intolerance is real, it is relatively rare. These reactions are aptly categorized as ‘hypersensitivity‘ reactions, meaning that most people – perhaps 99% depending on the substance – will not experience any problems from food chemicals at normal amounts. Second, not all evidence carries equal weight when it comes to the different trigger chemicals, and many questions still need to be answered.
Food intolerance, as defined by the Allergy Unit at the Royal Prince Albert Hospital in Australia, is a sensitivity to chemicals found in a wide variety of foods. It is also known as pharmacological food intolerance, a type of non-allergic food hypersensitivity. Food intolerance does not involve the immune system.
The term ‘pharmacological’ is related of the nature of the substances that elicit food intolerance reactions. In addition to nutrients, foods contain chemicals that are foreign to our bodies (like benzoate in fruit or artificial colors in yogurt) or excess amounts of chemicals that our bodies normally produce (like tyramine or histamine in certain cheeses). This is obvious in the case of processed foods, but it is true for fresh or organic foods as well. The foreign or excess chemicals are processed in the body along the same lines as drugs, and in food intolerant people, they also produce drug-like effects. But why would such chemicals be present naturally in food? Because they are important to plants or because they are part of the normal ripening and aging processes.
Food intolerance is different in each person. Some people will be sensitive to certain trigger chemicals for their entire life, and these people will need to avoid foods that contain these chemicals in order to remain symptom-free. Others will only need to avoid their culprit foods for a time until they can resume eating them – perhaps in limited quantities – without seeing symptoms. Still others might only see problems when they eat large amounts of their offending foods or eat certain combinations of foods. But for everyone, the key to living life to the fullest is an accurate determination of which food chemicals are causing the problem. A registered dietitian or doctor can help you find your triggers through an elimination diet and food challenges.
Lesson 2: Food triggers linked to food intolerance
Table 1 contains the most commonly discussed food triggers linked to food intolerance. More than one trigger can be present in a given food, making it difficult to determine which foods contributed to your symptoms. Please be aware, though, that not all of the chemicals listed below are implicated in food intolerance by the same degree of evidence — for all the details, I recommend this recent open-access review:
Alcohol can modulate, for better or for worse, the effects of some food chemicals by increasing their absorption or altering their breakdown.
Lesson 3: Food intolerance symptoms
Food intolerance symptoms can arise hours or even days after eating a trigger food, and their severity depends on how much you ate, what you ate during the previous few days, and whether you have other health conditions. On top of this, symptoms can be aggravated by illness, environmental chemicals (like fragrances), medications, hormonal changes, or stress. The most common symptoms of food intolerance are given below.
System
Symptom
Skin
Hives (urticaria), swelling (angioedema), itching, aggravation of eczema
Migraine, vertigo, fatigue, muscle pain (myalgia), growing pains, behavioral changes in children
Generalized
Non-immune anaphylaxis
Lesson 4: Food intolerance as a food hypersensitivity
Adverse reactions like food intolerance and food allergy are classified as hypersensitivity reactions, where the concept of hypersensitivity has real meaning. Food hypersensitivities are reproducible reactions brought about by quantities of foods that most people can tolerate. In other words, to classify an adverse reaction as a food hypersensitivity, you must first think about the effect that a normal amount of that food would have on the average person.
Food hypersensitivities are divided into two main groups: those that are caused by the immune system (immune-mediated hypersensitivities) and those that aren’t (non-immune mediated hypersensitivities). If we consider food allergy – the poster child for immune-mediated food hypersensitivities – it is easy to see why hypersensitivity is an appropriate description. Allergies occur when the immune system overreacts to harmless proteins in foods, like milk, eggs, wheat, and soy, that lie at the heart of the Western diet. Only about 5% of the overall population is suffering from some type of food allergy, and the amount of food needed to trigger an allergic reaction can be much less than a typical portion.
There are more immune-mediated food hypersensitivities than just food allergies. These reactions involve other aspects of the immune system and may take a longer time to develop than a classic allergic reaction. Here I’m talking about problems like cow’s milk protein intolerance, soy protein intolerance and food protein induced entercolitis in children, celiac disease, and eosinophilic esophagitis — in some cases, asthma and eczema are also related to food. Notice that these conditions are occasionally lumped under food intolerance (and ‘intolerance’ even appears in a few of the labels), but strictly speaking, these are immune reactions.
The term food intolerance is used as the common name for non-immune mediated food hypersensitivities. The best-known type of food intolerance is lactose intolerance, the gastrointestinal discomfort that results from undigested lactose (milk sugar) in the colon. Roughly 75% of the world’s adults — 25% in the US and even fewer in northern Europe — do not produce enough lactase to digest all of the lactose they consume, but not all of these people will experience symptoms and, thus, lactose intolerance. In lactose intolerance, symptoms depend on a person’s gut bacteria and eating habits.
Pharmacological food intolerance, the focus of this primer, is also a non-immune mediated food hypersensitivity. For example, consider a person who has worked with their doctor to determine that their headaches and diarrhea are symptoms of histamine intolerance. In histamine intolerance, a person’s ability to break down histamine is impaired, so foods that are rich in histamine or that cause histamine to be released in the body can lead to symptoms. Histamine intolerance is a food hypersensitivity, because most people can tolerate normal quantities of histamine-rich or histamine-releasing foods.
That said, how do we gauge what “most people” can tolerate? As with food allergy and other immune-mediated food hypersensitivities, the non-immune hypersensitivities generally affect less than 10 or even less than 5% of the population. For example, less than 1% of adults are sensitive to food additives, at least 1% have histamine sensitivity, and around 6% suffer from food-induced migraines. This means that for any food hypersensitivity, perhaps 99% of people will experience no adverse reactions to those foods or food chemicals.
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Committee on toxicity of chemicals in food, consumer products and the environment. Adverse reactions to foods and food ingredients. London: Food Standards Agency; 2000.
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Joneja JMV. The Health Professional’s Guide to Food Allergies and Intolerances. Academy of Nutrition & Dietetics; 2012. 477 p.
