In a very real sense, everybody has direct reactions to foods. Direct reactions are reactions caused directly to cells by chemicals in foods. Among the most obvious direct reactions are those caused by alcohol. If you drink alcohol, you are almost certain to experience sedative effects, due to the direct effect of alcohol on your brain cells.
Often, people with Asian heritage react quite negatively to alcohol, and the common belief is that they're allergic to it. Technically, though, they don't have an allergy; they have a sensitivity — because this is a direct reaction, which doesn't involve the immune system. I believe that it's clearer and more sensible to say simply that Asians often have a food reaction to alcohol, since food reactions include both allergies and sensitivities.
Direct reactions, however, can eventually involve the immune system, because sooner or later the immune system is called in to repair the mess that direct food reactions cause. Therefore, the symptoms of direct reactions can feel much like allergies. Because of this, direct food reactions are sometimes called false food allergies.
Alcohol has obvious direct actions, but most direct food reactions are more subtle. Often, direct reactions occur when chemicals in foods bind with the cells that produce histamine; these cells are called mast cells. When this happens, it can cause the release of histamine. The food chemicals that are most likely to do this are lectins, which are most often found in wheat, peanuts, and beans. Another cause can be certain partial proteins, or peptides, that are found in tomatoes, strawberries, shellfish, pork, chocolate, and eggs.
Other foods that often seem to cause direct food reactions are mustard, pineapple, papaya, buckwheat, and sunflower seeds. Ironically, one patient of mine had terrible digestive symptoms, including severe heartburn, and took large amounts of digestive enzymes to help the problem. However, his enzymes were full of papaya, which he later found he was reactive to. When he stopped taking the digestive aids, his digestion improved immeasurably. Moral of the story: don't trust common knowledge about what's healthy — trust your own experiences. Everyone is different.
Other foods that sometimes cause direct reactions are those that contain high levels of natural histamines. Histamines are formed in foods that are allowed to age and ferment. Therefore, histamines are often found in aged cheese, sausage, and salami.
Other foods that can cause direct reactions are those that contain the partial proteins tyramine, phenylethylamine, and octopamine. These chemicals, like histamines, can cause blood vessels to expand and contract, which causes tissue swelling. In the head, blood vessel constriction and expansion can cause migraine headaches. That's why people who get migraines often shun the foods that are high in these partial proteins, such as wine, aged cheese, citrus fruit and yeast.
Another common foodstuff that often causes direct reactions is the artificial sweetener aspartame. Aspartame is mostly composed of the partial protein, or amino acid, called phenylalanine. In some people, it acts directly on brain cells, causing symptoms such as agitation and depression. In other people, it causes blood vessels to contract and expand, triggering migraines. In most people, though, it causes no reaction at all.
Many people also react to MSG, or monosodium glutamate, with headaches, nausea, dizziness, heart palpitations, and confusion. Others react to various additives, including nitrates, sulphites, and artificial food colours.
Another name for direct food reactions is pharmacologic reactions. That's a good description, because it implies an important point: foods, like drugs, are chemicals. Not all drugs are good for you — and not all foods are, either.
Now let's look at the last type of food reaction: immune complex reactions. This type of reaction is not well known. But it should be. It can be a killer.
Foods, like drugs, are chemicals. Not all drugs are good for you, and not all foods are, either.