Seafood Free Diet by Sue Kira

by sue

Seafood Free Diet

by Sue Kira, Naturopath & Clinical Nutritionist


This article is predominately about allergies and reactions to seafood, including fish, shellfish and crustaceans. Shellfish include scallops, mussels, clams and oysters; while crustaceans include shrimp, prawns, lobsters, crayfish and crab.

Some people have an allergy to just one category (fish or shellfish/crustaceans) or maybe just don’t like the taste of one of these groups.

Some people are sensitive or allergic to both shellfish, crustaceans, and fish. While others are sensitive or allergic to one, but not the other.

It is estimated that about 1% of the population have a seafood allergy, but there are many more who seem to have a sensitivity to seafood for many reasons, some of which we will cover in this article.

Symptoms of seafood reactions

For most, their reaction to seafood is mild, including symptoms such as a rash (hives/urticaria), some swelling of the face, lips, gums, tongue etc, or some get diarrhoea or vomiting. In more serious allergic reactions, some get a dramatic drop in blood pressure which can cause shock or even life-threatening anaphylactic reactions. Some people are even reactive to the smell of seafood being cooked.

Types of seafood that can trigger reactions

Seafood can be categorised into….

Vertebrates (fish with a backbone)
These include anchovies, cod, dory eels, haddock, herring, mackerel, rays, salmon, sardines, trout, tuna, and other fish.

Invertebrates (no backbone)
These include abalone, calamari, crab, clams, crayfish, lobster, mussels, octopus, oysters, pippies and other molluscs, prawns/shrimps, squid, sea slugs and yabbies.

Avoiding accidental exposure to seafood

If you react to fish or shellfish/crustaceans you can avoid those foods relatively easily when you have control, such as in your home. But there can be times when other foods can be contaminated with traces of fish or shellfish. This can happen when eating at a restaurant, a function, a friend’s house and so on.

It’s wherever you don’t have control over how your food is cooked, what it’s cooked with, or even where certain ingredients are used without the full knowledge of the cook, such as in sauces and substances like curry paste that may contain fish sauce, anchovies, fish/shellfish stock etc.

Other potential sources of exposure and cross-contamination may include:

  • Seafood platters with mixed shellfish and fish
  • Smorgasbords with mixed foods – may have been handled together
  • Seafood purchased from a shop where both fish and shellfish are sold. Fish can get contaminated with shellfish and vice versa
  • Asian foods commonly use various sauces and condiments with fish or shellfish including curry pastes, fish sauce etc
  • Takeaway food can be cooked in the same oil e.g. a hamburger patty may be cooked in the same oil as seafood or the same scoops, knives and spatulas used
  • Takeaway pizzas may be prepared alongside pizzas that have anchovies or prawns/shrimp etc
  • Anchovies are used in Caesar salads and as an ingredient in sauces like Worcestershire or fish sauces
  • Contaminated outdoor cooking venues like park barbeques
  • Beer and wine production uses a substance called ‘Isinglass’ as an agent to remove cloudiness which is made from collagen from certain species of fish. Although problems are rare from this substance, some people are sensitive to it. This ingredient isn’t required by law to be listed, so you don’t know if it has been used. A vegan organic product may have less chance of including Isinglass, but it can be difficult to be entirely sure.
  • Collagen from seafood can also be found in many skin care products and while it isn’t consumed, the collagen can cause localized skin reactions if there is an allergy to seafood.
  • Fish oil capsules rarely cause reactions, but if you have a severe allergy to fish then it is better to use other types of oils from things like flax seed or evening primrose oils. Some capsule casings are actually made from seafood, such as fish gelatine.
  • Glucosamine (from shellfish) and Chondroitin (from shark cartilage) is often used for conditions like arthritis, and most sources come from seafood. You can now buy vegan sourced glucosamine and chondroitin, but the chondroitin is algae based and the glucosamine is corn derived so care may still need to be taken as many people can also have reactions to these. Corn is a very common allergen and while not related to seafood allergies, is potentially allergenic.

Is a seafood allergy related to iodine allergy?

The short answer is ‘no’. Those with a seafood allergy react to the protein component of fish or shellfish and not the iodine part, even though there is iodine in seafood. Some people are definitely allergic to iodine, but many of them are not allergic to seafood. You can have an allergy to both, but for different reasons as they are not connected.

A reason I mention iodine is because it is often used as a contrast medium in CT scans (Computed Tomography) and in many supplements. Those with a seafood allergy may have concerns about using these, but in most cases there is no concern. However, if concerned about a potential iodine allergy, see your doctor or health practitioner and arrange for tests.

Reactions to seafood that resemble allergy (but are not)

You can get a reaction, mild or severe, from eating seafood that has nothing to do with an allergy to the protein in seafood, but rather from other toxins, chemicals or parasites commonly found in some seafood. Here are some to consider….

Scombroid fish poisoning
If fish are not refrigerated or frozen quickly after being caught, the bacteria on the fish break down the proteins in fish to develop histamines and many can have an allergic reaction due to the high level of histamine. This can happen more in fish with a high blood content which turns brown on cooking rather than white. Fish like tuna, marlin, mackerel, bluefish, king fish, sardines, herring, and anchovies are a higher risk of this happening, but any fish that is not fresh can create histamines.

The affected fish often taste more peppery or metallic and within 30 minutes of eating it you may experience symptoms of histamine overload such as itching, flushing, rash, heart palpitations, dizziness, belly cramps, wheezing, difficulty breathing, headaches or a drop in blood pressure. Antihistamines can help some people with this reaction, but medical attention is advised.

Scombroid poisoning could be suspected if allergy testing for seafood shows up as negative to fish protein. It is very important to ensure that your fish is either really fresh or snap frozen at sea to avoid histamine developing.

There is a fish parasite found in most of the world that can contaminate fish and create an infection in the human body that can cause vomiting, nausea, stomach pains and sometimes more severe conditions such as bowel blockage, bowel bleeding and even appendicitis. Most contamination occurs from undercooked or raw (sashimi) fish. Cooking above 60C/140F or snap freezing (industrial frozen preferable) for more than two days kills this parasite in fish.

Fish older than 48hrs from catching should be avoided, unless it had been frozen and eaten (cooked) soon after defrosting. In most cases our immune system can destroy this parasite within three weeks of consumption. You can also develop an allergic reaction to the parasite, so well cooked and frozen fish doesn’t exclude having a reaction to the parasite but does reduce the risk. A blood test can help discover what is happening if you suspect this has occurred.

Ciguatera, paralytic and diarrhoetic poisoning
Ciguatera poisoning comes from eating large reef fish (gets worse the higher up the food chain) that have fed on coral that has algae, which at certain times of the year contains this toxin. Paralytic shellfish poisoning and diarrhoetic shellfish poisoning is caused by a contamination of algae producing toxins in mussels and oysters. Each of these toxins are similar in that they are algae derived and create an interference with our nerve endings.

Symptoms can include tingling or itchiness of the lips, throat and/or tongue, and often include headache, muscle aches and pains, stomach upset, fever, and in ciguatera poisoning, also create changes in blood pressure and heart rhythm. Numbness, confusion, collapse, and even coma can result in severe reactions.

Symptoms usually start within two to three hours of eating the contaminated seafood. Most people recover well within a few days or weeks with supportive treatment. But many create a life-long reaction to the type of seafood they reacted to because an allergy can form from the poison. Anyhow, it’s quite probable you wouldn’t feel like eating the same again.

Metabisulfite/metabisulphite sensitivity reactions
Metabisulfite is a preservative often used to prevent fish and crustaceans from discolouring. It is also commonly used in salad bars, fresh meats on display in supermarkets/butchers, cold cuts of meat, dried fruits, wine and beer, so it’s not exclusive to seafood by any means. I even found some in a jar of horseradish paste.

If you react to these other foods except when they are ‘preservative free’, be aware that metabisulfite could be on your seafood as it doesn’t legally have to be listed (yet). It is a preservative that is designed to breakdown when the food is cooked and thereby not create a reaction. But some people can be sensitive to trace amounts left over, and worse still, if the food isn’t cooked as in some deli foods or wine for example.

Reactions to metabisulfite include itching or rash, headaches, heart palpitations, racing pulse, nausea, tummy pains, wheezing and tight chest (the latter is especially prevalent with asthmatics).

Several years ago one of my clients worked in a fish shop. One of her jobs was to dip fish and other seafood into a diluted mix of sodium metabisulfite and water into a bucket to help keep the seafood looking ‘fresh’. She developed a sensitivity to the solution and had a rash up her arms that stopped exactly at the line of the water level (and no other symptoms). When she stopped doing this, her rash cleared quickly.

Interestingly, I used to buy some of my fish from that same shop and my cat wouldn’t touch the raw fish but would eat it cooked – but he ate it raw from a different fish shop (that didn’t dip it). Cooking is said to destroy this chemical. But eating prawns that are cooked and then dipped in sodium metabisulfite to keep them looking a vibrant orange colour is probably not a good idea. Check with your seafood supplier to see if sodium metabisulfite is used. Food for thought?

The purpose of the above information is to let you know that if you can’t eat seafood due to allergic reactions, then you might be able to eat seafood if conditions are different. However, do not take a risk without first getting tested and cleared by an immunologist/allergist.


Before you commence a new diet, see your medical or health care professional for qualified guidance about what foods and supplements are best for your body. While on the diet do not stop any medications or supplements previously prescribed unless advised otherwise by your medical or health care professional.

During the early stages of a new diet, you may experience symptoms such as fatigue, headaches or body aches, which may occur because your body is detoxifying. However, if you are unsure about a symptom at any time, check immediately with your medical or health care professional.


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