What is the difference between food allergies and food intolerances?

The most essential difference between the two is whether the immune system is involved - food allergy is a symptom caused by the immune system mistaking normal food as an invading pathogen and initiating an immune attack. In severe cases, it may be fatal.； Food intolerances are mostly caused by problems with digestion and metabolism, and have little to do with the immune system, and are generally not life-threatening. To put it bluntly, allergies are a contagion of your immune system. It doesn’t matter if you don’t eat good food. If you have to treat it as a foreign enemy and fight, in the end, even your own body tissues will be accidentally injured. ； Intolerance means that your gastrointestinal or metabolic enzymes are too weak to digest something, and can only make a fuss and embarrass you.

Last year, when I was following up in the allergology department, I met two patients with similar but completely different symptoms in the morning: One was a junior high school student. He ate half a peanut cookie given by his deskmate. Within ten minutes, his lips swelled into sausages, his throat became tight and he couldn't breathe. He was pulled from the emergency department and diagnosed with IgE-mediated peanut allergy. From now on, let alone peanuts, he cannot touch processed foods containing peanut ingredients, and he must carry an epinephrine pen with him to save lives.； The other was a girl in her twenties who said she had diarrhea whenever she drank milk. She thought she was allergic to milk and wanted to get a certificate stating that she would not drink milk for life. The results showed that the IgE related to allergy was completely normal. After taking a lactose breath test, she found out that she was lactose intolerant. In the future, drinking Shuhua milk or fermented yogurt will be basically no problem, and there is no need to restrict the food at all.

Many people think that as long as they feel uncomfortable after eating something, it is an allergy. In fact, it is really far from the truth. For example, if someone feels itchy around the mouth after eating a freshly picked kiwi fruit, it is most likely that the protease in the kiwi fruit has stimulated the mucous membranes. It is neither an allergy nor an intolerance. Just wash it, peel it, and let it ripen before eating. Some people blush and feel dizzy after eating leftover seafood that has been stored for two or three days, thinking that they are allergic to seafood. In fact, it is because the histamine in the seafood has not been completely metabolized, and they are intolerant to histamine. If they eat fresh food, there will be no problem.

It’s not difficult to make a preliminary distinction on your own. Allergies are mostly of an “explosive” nature. Even eating a few micrograms of allergenic ingredients can cause illness. The onset is quick, with symptoms basically appearing within a few minutes to 2 hours. Moreover, it is not only diarrhea and rash, but severe cases can affect the respiratory tract and cardiovascular system, cause breathlessness and drop in blood pressure. This is what we often call anaphylactic shock, which can really kill people. Intolerances are more "tolerant" and most of them have to eat enough to cause symptoms. For example, people with lactose intolerance may be fine if they drink a sip of milk. The bloating will only start after drinking half a cup. The onset is also slow. It may take several hours or even a day or two before the stomach upset occurs after eating. It is basically limited to the digestive tract. There are few systemic symptoms, and there is no sudden death. Of course, there are exceptions. For example, in a few non-IgE-mediated delayed-type allergies, the onset may be as slow as a few hours or even a day or two, and the symptoms may only be diarrhea. At this time, it is difficult to distinguish by oneself. You must ask a doctor to do a special food challenge test to confirm the diagnosis. As an aside, I have met someone before who said he was allergic to rice. After a long search, it turned out that he was allergic to preservatives put in rice from restaurants outside. This is quite outrageous.

There is also a lot of controversy about the diagnosis of food intolerance. For example, the "food IgG test" has been popular on the Internet for many years. Many institutions say that through this test, you can find out intolerable foods, and that as long as you avoid foods, you can solve the problems of eczema, irritable bowel and even hair loss. The mainstream allergology community currently does not recognize the diagnostic value of this test. They believe that food-specific IgG can only mean that you have eaten this food before and your body has produced a normal immune response. It does not mean that you are intolerant, nor does it mean that you should avoid it. ； However, some doctors in functional medicine and gastroenterology believe that this indicator can be used as a reference in conjunction with a food diary. If a certain food is indeed high in IgG and makes you feel uncomfortable every time you eat it, you can try a short-term food restriction instead of just following the test report to avoid dozens of foods, which may lead to malnutrition.

When I usually help patients identify themselves, the most recommended method is not to do a bunch of hundreds or even thousands of tests at first, but to keep a food diary. Write down everything you eat every day, the amount you eat, and the body's reaction in the next 24-48 hours. Keep a record for 2-4 weeks. Most of the time, you can find the food responsible, which is more effective than any other test. There was a patient who always said that he was allergic to seafood when he ate it. However, after keeping a diary for a week, he discovered that he only had diarrhea when he ate fried clams from a food stall. He was fine even if he ate steamed crabs and shrimps at home. Later, he found out that the clams from the food stall were not washed properly. Also, every time he ate clams, he had cold beer with them. The cold and unkilled bacteria stimulated diarrhea and had nothing to do with allergies.

In fact, we ordinary people don’t need to be obsessed with the academic definitions of the two. If you really feel uncomfortable after eating something, don’t blindly label yourself an “allergy” on Baidu, and don’t blindly follow the online test packages and blindly follow the food taboos. Just find a specialist in a regular hospital. If you are really diagnosed with an allergy, you should strictly avoid food and carry emergency medicine with you. This is no joke. ； If it's just intolerance, it can mostly be improved by eating small amounts more often and changing processing methods. You don't have to completely isolate yourself from your favorite foods. After all, being able to happily eat what you want is the most important thing in life.