All About Fish, Shellfish Allergies
So why is it that a food you’ve always been able to tolerate suddenly starts wreaking havoc? There is no firm answer, but scientists theorize that it could have something to do with the fact that the main allergen in shellfish, the muscle protein tropomyosin, is very similar to the tropomyosin found in dust mites and cockroaches, which are some of the most allergenic pests.
So exposure to those insect proteins might actually increase a person’s odds of developing a seafood allergy. (This would also explain why studies in which orthodox Jews, who have never eaten shellfish, end up with positive results for shellfish allergy in medical tests.)
Another hypothesis is that many adults eat seafood on occasion rather than regularly, and that may affect their tolerance. In other words, the immune system may in effect forget that the food is not a problem, and may instead treat it like a harmful invader.
Pass the Caviar
It’s important to note that the key allergens in fish and shellfish are unrelated, so people who can’t eat salmon might be just fine with crab, and someone who can’t tolerate even the tiniest amounts of shrimp may be able to eat whole helpings of fresh cod.
To further complicate matters, some people only react to very specific foods: so they may be able to eat crab but not oysters, or they may be allergic to the roe (eggs) of the fish, but not to its meat. Others who cannot tolerate fresh tuna or salmon may be just fine with the same fish canned, which has led some researchers to believe that the method of food preparation could have something to do with seafood’s allergenicity.
Seafood Allergy Myths
There is some confusion about the safety of both fish oils and iodine for people with shellfish allergy.
Fish oils are popular as nutritional supplements, because they are very rich in essential omega-3 fatty acids – but are they safe for people with allergies? According to Health Canada, most of the oils are so highly refined that they no longer contain the allergenic protein, and they should be safe to consume.
However, if you have a seafood allergy, it’s important to discuss any fish products with your allergist before trying them out; it may also be a good idea to contact the company and ask them about the processes they use.
Because many types of shellfish are rich in iodine, some shellfish-allergic people are told that they must avoid iodine – a common ingredient in everything from table salt to x-ray dyes. This is incorrect: the allergen in shellfish is in the flesh of the food, and not in the iodine, so iodine should be safe to consume. (Some people cannot tolerate iodine, but this is a separate issue.)