Allergy to starchy foods

The vast majority of people who claim to be "allergic to starchy foods" are not allergic to starch (that is, the pure carbohydrate polysaccharide itself), or are allergic to impurities such as proteins, additives, pesticide residues, etc. associated with starchy foods, or they are confusing carbohydrate intolerance with allergic reactions. There are less than a hundred cases of true medical diagnosis of allergy to starch itself in the world, and it is an extremely rare immune disease.

When I worked as a science popularization volunteer in the allergy department of a tertiary hospital two years ago, I met a 22-year-old girl who called in three times to confirm whether she was "starch allergic" - she would get rashes all over her body when she ate steamed buns, noodles, roasted sweet potatoes, and even drank commercially available corn juice. In severe cases, her throat would become edema. During that time, she only ate boiled vegetables and chicken breasts, and her face turned sallow. After a full set of allergen screening + oral provocation tests, it was discovered that she was actually allergic to gluten in wheat (what we often call celiac disease), specific mucin in sweet potatoes, and edible glue added to commercially available corn juice. The doctor made her a cup of cornstarch paste that was purified to 99.9% on the spot. After drinking it, she had no problem at all, and she stopped eating staple food for more than three months.

Many people feel uncomfortable when eating rice, noodles and potatoes, and their first reaction is to think of "starch allergy". In fact, they are most likely confusing two completely different problems. Allergy is a reaction mediated by the immune system. Most symptoms include skin rash and respiratory symptoms. In severe cases, it may induce anaphylactic shock. ； What we often say about "bloating and diarrhea after eating starch" is mostly due to digestive intolerance. For example, people with congenital insufficient secretion of α-amylase eat too much high-starch food and cannot digest it in time, which will ferment the intestines and produce gas, resulting in bloating and diarrhea. This has nothing to do with immune response. In fact, the judgment logic of different clinical departments is different here. When gastroenterologists encounter this kind of situation, they usually ask the patient to adjust their diet and supplement digestive enzymes for investigation. Most doctors in the allergology department will give priority to IgE antibody testing to rule out real allergic risks first. Both ideas are actually correct, but they come from different angles.

Of course, this does not mean that there is no possibility of starch allergy. There are currently more than 60 confirmed cases publicly reported in the world, almost all of which are infants and young children. Most of them have an immune response to the amylose fragment in the starch molecule. Eating pure starch will cause rashes and vomiting. However, more than 80% of the children will tolerate it on their own by the age of 6. There are only three cases of pure starch allergy in adults reported in the world so far.

In fact, you need to find out whether you are really allergic to starch, and you don't have to cut out all staple foods at all. In a case I came across, a young man who was working out said that he was allergic to rice. In order to build muscle, he stocked up on prepackaged brown rice so as not to cook it himself. As a result, every time he finished eating, he developed a red rash on his forearm, which was so itchy that he thought he was allergic to rice and did not even dare to drink porridge. In the end, it was found out that I was allergic to the sodium dehydroacetate preservative in the prepackaged brown rice. I ate my own steamed white rice and brown rice without any problems. I lost 4 pounds of muscle, which was a huge loss. If you have similar troubles, you might as well keep a food diary for a week, and write down clearly the specific ingredients, processing methods, and reactions after eating each food you eat. Many times, you will find the real culprit after sifting through it. If you are really unsure, go to the hospital to do an oral provocation test. This is the current gold standard for allergy diagnosis. However, it must be done in a hospital with emergency measures. Don’t try it blindly at home.

As for how to adjust your diet in the future, doctors in different fields currently have different opinions. For safety reasons, most allergist doctors will recommend avoiding all suspicious foods first. If the allergen cannot be found, it is not impossible to try a low-carbohydrate diet in the short term. ； However, nutrition doctors usually recommend precise avoidance. For example, if you are only allergic to wheat protein, it is perfectly fine to eat purified wheat starch, corn starch, and sweet potato starch. There is no need to cut off all carbohydrates. Otherwise, it is easy to be deficient in B vitamins and dietary fiber, which will affect immunity. I have been doing science popularization for so long, but I still recommend the latter. After all, it would be too uncomfortable to not eat staple food at all, right?

To put it bluntly, "allergy to starchy foods" is actually an over-exaggerated problem. You don't have to feel uncomfortable when eating staple foods. Most of the time, you can find the right cause. There is no need to insulate yourself from delicious noodles, sweet potatoes, and freshly baked bread. After all, days when you can eat carbohydrates steadily are delicious enough.