I’ve devoted several past blogs to gluten sensitivity, but people report trouble with a variety of different food ingredients – from soy to seafood.

The trouble seems to differ though. Some people must avoid peanuts due to severe, life-threatening reactions. But others have gastrointestinal (GI) symptoms, ranging from bloating to throwing up, that seem to be associated with milk or gluten.

Out of curiosity, I decided to take a quick look at what scientists and doctors know about situations where food becomes the opponent.

Food Allergy:

The traditional “food allergy” is one major way specific foods can cause problems. The term is typically used to refer to an abnormal reaction produced by the body’s immune system in response to a food – specifically an immune reaction involving proteins called IgE antibodies.

In this situation, the immune system mistakes a food molecule as an invader and creates these IgE antibodies that recognize the molecule, as it would do for a bacteria or virus. The next time a person is exposed to the food, the immune system generates the IgE antibodies, leading immune cells to release the chemical histamine. An allergic reaction results. Symptoms can range from mild, such as a tingling in the mouth, to severe, such as the life-threatening breathing problems and loss of consciousness that can occur with anaphylaxis.

Eight foods – milk, eggs, peanuts, tree nuts, fish, shellfish, soy and wheat – are the culprit for over 90 percent of food allergies, according to the CDC.

However, other food-related conditions exist that involve other aspects of the immune system, as a recent Mayo Clinic review notes. They’re classified separately because they require different treatments than IgE-mediated food allergies. Some of them are still considered “food allergies,” such as food protein-induced enterocolitis syndrome (FPIES) – a condition with symptoms that can appear similar to severe stomach bug. Others, like the gluten-related celiac disease, involve the immune system but aren’t categorized as an allergy.

Food Intolerances:

When foods cause negative symptoms without involving an immune response, they’re typically known as food intolerances. Here are some of the common ones:

Food additives – Products like monosodium glutatmate (MSG) and sulfites are added to some foods to provide color or flavor, or to protect against pathogens. These extras may cause issues like headaches or breathing issues, depending on the additive.

Lactose intolerance – Lactose intolerance is an adverse reaction to milk products containing the sugar lactose. People with this issue don’t have the enzyme needed to break down the sugar, so lactose is broken down by bacteria in the gut. The bacteria produce gas, which leads to bloating and other unpleasant GI symptoms.

Gluten intolerance – Gluten can still be a problem for people without a gluten food allergy or celiac disease. Less is known about these intolerances or sensitivities and whether or not they involve the immune system.

If you’re interested in what’s going on in the world of research and treatments for food allergies, check out this interesting New York Times Magazine article from last year.