I've recently been learning about special dietary restrictions that affect some people. For example, my dad has developed somewhat of a lactose intolerance. Here is an article from Medical News Today that I think might be helpful/insightful.
In theory, any food can cause a food allergy. But in fact just a handful of foods are to blame for 90% of allergic reactions to food. These common foods are known as the 'big eight'. They are:
-- peanuts (groundnuts)
-- nuts from trees (including Brazil nuts, hazelnuts, almonds and walnuts)
-- shellfish (including mussels, crab and shrimps)
In children, most allergic reactions to food are to milk, peanuts, nuts from trees, eggs, soya and wheat. Most children grow out of most allergic reactions to food in early childhood. In adults, most allergic reactions are to peanuts, nuts, fish, shellfish, citrus fruit and wheat.
This section mainly describes foods that can cause food allergy, but it also includes lactose intolerance and gluten intolerance/sensitivity (coeliac disease). These are types of food intolerance, but they aren't allergies. Remember, if you think you have a food intolerance, you should contact your GP.
Cereal allergy: A number of cereals have been reported to cause allergic reactions in sensitive children and adults. These include wheat, rye, barley, oats, maize (corn) and rice. Sometimes people can react to more than one type of cereal.
Coconut allergy: Allergy to coconut is rare in the UK, but coconut can cause allergic reactions (including anaphylaxis) in people who are sensitive. A small number of people who are allergic to nuts have reacted to coconut. It might also cause reactions in people who are allergic to latex.
Egg allergy: Like most food allergies, egg allergy is more common in childhood and about half the children who have it will grow out of it by the age of three. In a few cases, egg allergy can cause anaphylaxis. Egg allergy is mainly caused by three proteins in the egg white called ovomucoid, ovalbumin and conalbumin. Cooking can destroy some of these allergens, but not others. So some people might react to cooked eggs, as well as raw eggs. Occasionally someone might react to egg because they have an allergy to chicken, quail or turkey meat, or to bird feathers. This is called bird-egg syndrome.
Fish allergy: Fish allergy can often cause severe reactions, including anaphylaxis. Adults are more likely to have an allergic reaction to fish and shellfish than children, which is probably because adults will have eaten these foods more often. People who are allergic to one type of fish, such as cod, often react to other types of fish such as hake, haddock, mackerel and whiting as well. This is because the allergens in these fish are quite similar. Cooking doesn't destroy fish allergens. In fact, some people with fish allergy can be allergic to cooked but not raw fish.
Fruit and vegetable allergy: Allergic reactions to fruits and vegetables are usually mild and often they just affect the mouth, causing itching or a rash where the food touches the lips and mouth. This is called oral allergy syndrome. A number of people who react in this way to fruit or vegetables will also react to tree and weed pollens. So, for example, people who are allergic to birch pollen are also likely to be allergic to apples. Cooking can destroy a number of the allergens in fruits and vegetables, so cooked fruit often won't cause a reaction in people with an allergy to fruit. Pasteurised fruit juice might not cause an allergic reaction either, for the same reason. However, the allergens in some vegetables, such as celery, aren't affected by cooking. Some fruits and vegetables, such as tomatoes, are more likely to cause a reaction as they get riper.
Gluten intolerance: Gluten is the mixture of proteins found in some cereals, including wheat, rye and barley. Gluten intolerance, or coeliac disease, is a lifelong disease, which is caused by sensitivity to gluten. It can damage the lining of the small intestine, which stops the body from absorbing nutrients, causing diarrhoea and eventually malnutrition. Coeliac disease can sometimes run in families, but we don't know exactly what causes it. The only way to avoid the symptoms is not to eat foods containing gluten, such as wheat, rye, barley, malt, malt extract, malt flavouring, beer and lager. Processed food can often contain hidden gluten, but a large number of gluten-free products, such as bread, cakes and pasta are now available.
Lactose intolerance: Lactose is a sugar found naturally in milk. It's important to distinguish between lactose intolerance and milk allergy, because milk allergy can cause severe reactions. See the section on milk allergy for more information. Lactose intolerance is caused by a shortage of the enzyme lactase, which is needed to break down lactose so it can be absorbed into the bloodstream. When someone doesn't have enough of this enzyme, lactose isn't absorbed properly from the gut, which can cause symptoms such as bloating and diarrhea.
Latex-food syndrome: Latex allergy is caused by a reaction to a number of allergens found in natural rubber or latex. In recent years, the number of people with latex allergy has increased, particularly among healthcare workers and people with spina bifida, because they come into contact with lots of latex products. Latex contains lots of allergens that are similar to the allergens in some foods. So people who are allergic to latex might also find they react to foods such as banana, mango, kiwi, chestnut, paprika, celery, apple, carrot, cherry, coconut, strawberry and avocado. This is called latex-food syndrome. In the same way, people who are allergic to these foods may also react to latex.
Lupin allergy: Lupins are common garden plants, which are related to legumes such as peas, lentils and beans. Many types of lupin seed are poisonous, because they contain bitter-tasting toxins. But sweet lupins don't contain these toxins and they can be eaten by humans or livestock. Sweet lupin seeds are being used more and more to replace cereal grain in many food products, for example flour and pasta. The major allergens in lupin are also found in peanut, so people who are allergic to peanuts could react to lupin. The Anaphylaxis Campaign in the UK has advised people with peanut allergy to avoid lupin. It's mainly used in flour-based products such as pastry.
Maize allergy: Maize (or corn) allergy isn't common in the UK, although there have been reported cases. For people who are sensitive to maize, avoiding it can be very difficult, because maize is commonly used in a wide variety of food products.
Meat allergy: People with a meat allergy might react to beef, mutton, pork or chicken. Sometimes people who are allergic to one type of meat or poultry might also react to other types. Cooking destroys some of the allergens in meat, but some people will still react to cooked meat. Processed meats, such as frankfurters, luncheon meats and pates, sometimes contain other ingredients, particularly milk products, as emulsifiers or flavour enhancers. So it's possible for someone who is allergic to milk to react to a meat product because it contains milk. For example, milk is sometimes used in chicken nuggets to stick the breadcrumbs to the chicken pieces.
Milk allergy: Allergy to cows' milk is the most common food allergy in childhood, and affects 2-7% of babies under one year old. It's more common in babies with atopic dermatitis. A reaction can be triggered by small amounts of milk, either passed to the baby through the mother's breast milk from dairy products she has eaten, or from feeding cows' milk to the baby.
Milk protein intolerance: Intolerance to cows' milk protein is a type of intolerance that is common in babies and children, and symptoms start from the time when cows' milk is first introduced into the diet. There is no cure for it and the only way to stop the symptoms is to avoid cows' milk products. Cows' milk protein intolerance is different to lactose intolerance and milk allergy. See the sections on lactose intolerance and milk allergy for more information.
Nut allergy: Allergy to nuts from trees is usually lifelong. The nuts that are most likely to cause allergic reactions are walnuts, hazelnuts, almonds, pecans, Brazil nuts, pine nuts, macadamia nuts and cashew nuts. On rare occasions, all these nuts can cause anaphylaxis in people who are sensitive. Sometimes people with an allergy to one type of nut will also react to other nuts. So if you have a nut allergy, you need to be very careful to avoid nuts and unrefined (crude) nut oil. Talk to your GP for advice.
Peanut allergy: Allergy to peanuts (also known as groundnuts and monkey nuts) is often lifelong, but research suggests that, in a very few cases, young children diagnosed with peanut allergy may grow out of it. Peanuts are one of the most common causes of food allergy and can cause severe reactions, including anaphylaxis. They contain a number of allergens that are not destroyed by cooking or roasting.
Pine nut allergy: Pine nuts can cause severe allergic reactions, including anaphylaxis, in people who are sensitive. People who are allergic to pine nuts might also react to peanuts and nuts such as almonds.
Quorn allergy: Quorn is a type of protein, which is made from a fungus. It has been available in the UK since 1985, and is often used as a meat substitute. There have been some reports of intolerance to Quorn, but this is not surprising, because it has a high protein content (allergens are usually proteins). Intolerance to Quorn is much less frequent than to other foods such as soya and dairy products. As Quorn is made from a fungus, some people who react to other fungi or moulds (including by inhalation) may also react to Quorn.
Rice allergy: Rice allergy is common in countries in Eastern Asia, such as Japan, where rice is commonly eaten, but it isn't common in the UK. People who are allergic to rice can react when they eat it or when they inhale its pollen. Rice can cause hayfever symptoms in areas where it's grown commercially.
Sesame allergy: We don't know how many people in the UK suffer from sesame allergy, but it's quite common in countries such as Australia and Israel. We think that sesame allergy is increasing, possibly because it's now more commonly used.
Shellfish allergy: Allergy to shellfish is quite common, and a number of different types of shellfish can cause reactions in people who are sensitive, for example shrimps, prawns, lobster, crab, crayfish, oysters, scallops, mussels and clams.
Soya allergy: Soya allergy is a common childhood allergy. Most people grow out of it by the age of two, but occasionally adults are allergic to soya. The symptoms of soya allergy are similar to milk allergy, and they include rashes, diarrhoea, vomiting, stomach cramps and breathing difficulties. Some people with soya allergy might also react to milk. Very rarely, soya can cause anaphylaxis.
Spice allergy: Allergic reactions to spices are rare and usually mild, but severe reactions can happen occasionally. Some people react to mustard, coriander, caraway, fennel, paprika or saffron and, less frequently, to onions, garlic or chives. Reactions to mustard have been reported to cause anaphylaxis, particularly in mainland Europe, where mustard is used more. The allergens in spices are similar to those in pollens and vegetables, and people who are allergic to mugwort and birch are more likely to be sensitive to spices for this reason.
Vegetable oil allergy: Vegetable oil is usually a blend of oils. In the UK, the oils used the most to make up vegetable oil are soya, rapeseed, sunflower, maize, palm, coconut and palm kernel oils. Where they appear in pre-packed food, these oils will have been refined. The refining process removes proteins from the oil. Since it's the proteins in oils that can cause allergic reactions, sensitive people probably won't react to refined oils. Some speciality oils, such as sesame and walnut, aren't refined, so they are best avoided by people who are sensitive to the nuts or seeds they are made from.
Wheat allergy: Wheat allergy is common, particularly among babies. One of the main allergens in wheat is a protein called gliadin, which is found in gluten. Because of this, people with a wheat allergy are sometimes recommended to eat a gluten-free diet.