Food intolerance is an adverse reaction to a particular food that does not involve the immune system (unlike food allergy), often develops over a few hours, and is not life threatening; it is also much more common than food allergy affecting up to 20% of the population (compared to 2-5% for food allergy). Recognized causes of food intolerance include fructose and lactose and sensitivity to food additives such as monosodium glutamate, sulphites, caffeine and tyramine. The issue of non-celiac gluten sensitivity (NCGS), non-allergic gluten sensitivity in those who do not have celiac disease, is a more controversial potential cause of food intolerance; persons with this disorder are not allergic to gluten, the main cereal protein allergen in celiac disease, but may be sensitive to another component of gluten-containing grains, FODMAPS (fermentable oligosaccharides, disaccharides, monosaccharides and pyrols), which can cause abdominal discomfort and bloating.
The symptoms of food intolerance, irrespective of cause, are often similar to those associated with food allergy including respiratory symptoms, runny nose, itchiness, facial swelling, abdominal discomfort, fatigue, headaches and muscle aches. What differentiates food intolerance from the allergy symptoms is the relatively slow onset over hours and prolonged duration, the reduced severity and the absence of any detectable antibody levels to food in the blood; the symptoms of food intolerance are also dose-dependent, the more you consume the worse you feel, whereas consumption of minute quantities of a food allergen may have very serious consequences.
A less well-know food intolerance is to members of the allium family (garlic, onions, scallions, chives, leeks, shallots) which I am aware of and interested in primarily because I suffer from it. I did not have any obvious sensitivity to this food family in my teens or early adulthood, but when I was in my mid thirties I noticed that eating food with a lot of garlic for dinner was associated with hangover symptoms the following morning including difficulty getting out of bed, lethargy, headache and vague abdominal discomfort. If I consume a dish with garlic during the day after about an hour I become somnolent, and feel vaguely unwell; a lunch loaded with garlic may ruin the rest of my day. Although, I am most sensitive to garlic (closely followed by leeks), other members of this food family cause similar symptoms in a dose dependent manner; for example, a single onion as an ingredient in a beef stew is not a problem but I will be miserable after a good helping of caramelized onions or a bowel of French onion soup. There appears to be a genetic component to allium intolerance as my daughter and one of my sisters are also intolerant.
It is likely that there is an overlap between food intolerance and food allergy. Immunological reactions in humans, including specific antibodies in the blood, have been documented for more than a 100 common foods but for many of these foods the prevalence of an immunological reaction is very low. The European Union has identified 14 common food allergens and mandated that they be specifically listed when included in manufactured food products or in restaurant menus. These allergens include: cereals containing gluten, crustaceans, eggs, fish, peanuts, soybeans, milk, nuts, celery, mustard, sesame seeds, sulphur dioxide/sulphites, lupin, molluscs.
Sensitivity to members of the allium family including allergic hypersensitivity to garlic and onions has been found in approximately 3% of food hypersensitivity patients in a cross-sectional observation study conducted at an allergy clinic in Spain (1). In a retrospective study on a smaller number of suspected food allergy patients in Saudi Arabia specific antibodies to garlic and onions were detected in 13.8% (2).
In summary, sensitivity to members of the allium family is relatively common and largely underappreciated among food producers and restauranteurs as well as in the general population.
(1) Armentia A, Martín-Armentia S, Pineda F, Martín-Armentia B, Castro M, Fernández S, Moro A, Castillo M. Allergol Immunopathol (Madr). 2020 May-Jun;48(3):232-236.
(2) Almogren A, Shakoor Z, Adam MH. Afr Health Sci. 2013;13(septiembre de (3)):689-93.
