How to distinguish food allergies and adverse food reactions

First, let’s look at the relationship between onset and intake – food allergies are mediated by the immune system, and may occur if you are exposed to even trace amounts of allergens (such as cake crumbs mixed with peanut crumbs, chopsticks stained with mango juice)； Adverse food reactions do not involve the immune mechanism. Either there is something wrong with the food itself (stale, irritating, toxic), or the intake reaches a threshold that the body cannot handle. Secondly, look at the pattern of symptoms. As long as the allergy triggers the same allergen, the core symptoms of each attack will be basically the same. You will not have diarrhea this time and eczema for no reason the next time. ； The symptoms of adverse reactions will change according to the intake and food status, and there is no fixed pattern.

I just met a girl who is a sophomore in high school in the clinic last week. As soon as she came in, she said she was allergic to strawberries and would have diarrhea every time she ate it. After careful questioning, I found out that every time she ate strawberries, she bought a pound of ice cream after school on weekends and stood on the roadside to show off the strawberries in ten minutes. Later, she was asked to go home and try two strawberries at room temperature. Nothing happened - it was just that eating too much raw and cold strawberries irritated the gastrointestinal tract, which is the most common adverse food reaction and has nothing to do with allergies.

To put it bluntly, it’s easy to understand. Allergy is equivalent to your immune system “recognizing the wrong person” and mistaking a specific protein in a certain food for an invading germ. As long as a tiny bit leaks in, the whole body will sound the alarm, ranging from itchy skin and wheals to laryngeal edema and anaphylactic shock. It doesn’t matter how much you eat or how little you eat. Adverse food reactions are more like carrying half a bucket of water upstairs and you are wheezing and coughing. It is not that you are allergic to the bucket, but simply that you are not strong enough to carry it: either you are lactose intolerant and lack enzymes and have bloating after drinking milk, or you are poisoned by eating uncooked beans, or you are like that little girl who eats too much iced fruits and your stomach cannot bear it. In essence, it has nothing to do with the immune system being excited.

Of course, we should also mention here a controversial point that has not been completely unified in the academic community: for non-IgE-mediated delayed-type allergy, the judgment standards of different departments are quite different. This type of allergy has a slow onset, and symptoms often appear 24 to 72 hours after exposure to the allergen. Most of them are atypical manifestations such as chronic diarrhea, repeated eczema, and growth retardation. They are especially easy to be confused with food intolerances. Most doctors in the allergology department will ask for a comprehensive judgment based on the results of specific IgE testing and skin prick testing, and are less likely to recognize the results of individual IgG testing. ； However, many doctors in the gastroenterology department will give priority to the symptom correlation in the diet diary, and will even refer to the abnormal IgG results to give staged dietary adjustment suggestions. This is why sometimes you go to two departments and get completely different conclusions. There is no one who is right or wrong, but the entry point for judgment is different.

Ordinary people can actually do a preliminary check at home, and there is no need to spend hundreds of dollars on a full set of tests right away. Just take a small book and keep a food diary. Focus on writing down exactly what you ate at each meal, how much you ate, how long it took for symptoms to appear, and what the specific symptoms were. If you touch something with milk every time, even if it is a biscuit with milk powder, you will get hives within half an hour. Don't worry about the high probability of being allergic to milk. ； But you will only become bloated if you drink more than 200ml of iced milk. There is nothing wrong if you drink warm milk or 100ml at a time. That is lactose intolerance, which is a common adverse reaction. There is no need to avoid milk altogether. Buying low-lactose milk or taking lactase tablets can solve the problem.

I also encountered a particularly unfortunate case two years ago. My mother bought a food intolerance test for several hundred yuan online. It was found that wheat IgG was high, so she stopped eating pasta for almost half a year. When she came to see a doctor, her child was half a head shorter than his peers. Later, we did an oral challenge test and found that the child had no problem after eating a whole white steamed bun. He just felt a little bloated when he ate too much at one time. It was not an allergy at all. He missed half a year of carbohydrate intake for no reason. How unfair. One more thing to say here is that most of the tests on the market that claim to be able to detect hundreds of food allergies detect IgG. Currently, the mainstream allergist community generally believes that this indicator is not directly related to food allergies. Don’t blindly avoid food if the test is positive. It is really unnecessary.

If you are really not sure, go to the hospital to do an oral food challenge test. This is currently the recognized gold standard for identification, but it must be done in a regular hospital with emergency facilities, especially for people who have had severe allergic reactions before. Do not try it blindly at home, as it is really life-threatening.

In fact, to put it bluntly, whether it is an allergy or an adverse reaction, the core is that you feel uncomfortable after eating something, so there is no need to diagnose it yourself. If you are really allergic, you have to strictly avoid food and carry emergency medicine with you. If it is just a common adverse reaction and you avoid so many delicious foods for no reason, it is not a loss. If you are not sure, it is much more reliable to see a doctor than to search online for a long time and get more and more panicked.