Food allergies
Food allergens
Plant-derived food: Common food allergens are fruits of the Rosaceae family including apples, peaches, cherries, and almonds. Cross-reactivities to pollen (eg birch) are frequent. The heat-labile allergens (PR-10 proteins and profilins) are degraded by cooking or through acidity in the stomach and consequently rarely cause systemic symptoms. Other plant-derived allergens that are heat- and acid-resistant (lipid transfer and storage proteins, LTPs) occur in nuts (ie cashew and hazelnut), seeds (eg sesame and pine), legumes (eg peanuts and soy), vegetables (eg celery), and grains (eg wheat and corn flour).Animal-derived food: Animal-derived food allergens include eggs, cow’s milk, seafood (eg fish, shrimps and mussels), and, more rarely, poultry and red meat (eg chicken and pork or beef). Allergens encompass various proteins – albumins or tropomyosins are common examples. In red meat, the carbohydrate galactose-alpha-1,3 galactose (alpha-Gal) is a rare but important elicitor. Most of these allergens are heat stable and acid resistant and are therefore more likely to cause systemic symptoms.Clinical manifestations of food allergies
Food allergies mediated by IgE antibodies may result in local to severe systemic allergic symptoms. The symptoms depend on the food type and on how resistant the food is to increasing temperature (cooking) or acidity (ie decreasing pH). Easily degradable foods (heat and acid-sensitive), eg raw fruits and some vegetables, often cause local symptoms, while more resistant foods (eg roasted peanuts and shrimps) are likely to cause systemic symptoms. Some cofactors may aggravate the symptoms of food allergies, particularly to wheat, nuts, and shellfish. These include stress, exercise, high or low temperature, or concurrent intake of alcohol or some drugs (eg aspirin or some medications to treat hypertension). This condition, requiring several factors, is called food-dependent exercise-induced anaphylaxis or FDEIA.
Food intolerance
Food intolerances are more common. They frequently occur when eating carbohydrates (eg lactose or fructose). Food intolerances are not triggered by an immune reaction. For example, the common lactose intolerance in adults is caused by an acquired deficiency of the enzyme lactase in the gut. Ingested lactose is consequently digested by intestinal bacteria. The thereby generated water and gas lead to indigestion, nausea, bloating, pain, and diarrhoea. There is a close dose-response relationship: the higher the dose, the more severe the symptoms. Although impacting on quality of life, life-threatening reactions do not occur in these food intolerances.Case study
Let’s now consider the case of a 21-year-old man who ate various foods from a buffet and drank several beers at a Chinese restaurant. While eating, his palms and soles turned itchy, he began to sweat, and had colics. He then had sudden diarrhoea and collapsed. He was brought to the hospital, where disseminated wheals were observed and low blood pressure was measured. Anti-allergic therapy abolished his symptoms. He has never had any previous allergic symptoms. His older brother had hay fever. Skin tests were positive for house dust mites and shrimps. Specific IgE blood tests were positive for the house dust mite of the species Dermatophagoides pteronyssinus, shrimps, and the muscle protein tropomyosin.Allergies: When the Immune System Backfires

Our purpose is to transform access to education.
We offer a diverse selection of courses from leading universities and cultural institutions from around the world. These are delivered one step at a time, and are accessible on mobile, tablet and desktop, so you can fit learning around your life.
We believe learning should be an enjoyable, social experience, so our courses offer the opportunity to discuss what you’re learning with others as you go, helping you make fresh discoveries and form new ideas.
You can unlock new opportunities with unlimited access to hundreds of online short courses for a year by subscribing to our Unlimited package. Build your knowledge with top universities and organisations.
Learn more about how FutureLearn is transforming access to education