Millions of people rely on seafood for their protein but what are the health benefits and the risks?
13 Nov 2014 - 2:53 PM  UPDATED 13 Nov 2014 - 3:11 PM

Millions of people in the world rely on seafood as their primary source of protein.

There are health benefits to eating seafood, but what about the risks?

In light of sustainability issues, it may be wise to have a look at our seafood eating habits.

This is one of the issues explored in the new SBS documentary series "What's the Catch?"

There are several reasons why seafood is good for you.

It provides a good source of protein, but contains less fat than other animal protein sources.

Seafood is generally low in cholesterol, which is important for heart health.

It’s rich in vitamins and minerals including iodine, zinc, potassium, and vitamin B.

One of the major seafood health benefits comes from their abundance of Omega-3 fatty acids, a type of polyunsaturated fat.

Nutritionist Dr Rosemary Stanton explains why these Omega-3 fats are good for us.

“The Omega-3s, and there's not just one, there are many of them, and we need to keep that in mind, they do seem to have some anti-inflammatory properties, and these can work against an excess of what we call Omega-6 fatty acids, which are found in vegetable oils and some seeds.”

Omega-6 fats are essential nutrients found in most vegetable oils, made from plants like sunflower, sesame, and corn.

But Dr Stanton says consuming too much of these Omega-6 fats can promote inflammation in the body.

An excess of some Omega-6 fats is associated with diseases such as arthritis, as well as inflammatory diseases like asthma.

On the other hand, Omega-3 fats found in seafood can help counter this negative effect.

Dr Stanton says if you don't eat seafood, avoiding bad fats becomes even more important.

“If you're a vegetarian, it's probably a good idea to use as your cooking oil something like olive oil or canola oil which are not high in the Omega-6 fatty acids.”

There are vegetarian sources of some Omega-3 fats such as linseeds, chia seeds, walnuts and soybeans however seafood is the most common source.

Spokesperson for the Dieticians’ Association of Australia Natasha Meerding says some fish contain more healthy fats than others.

“Oily fish, ones that are commonly eaten in Northern America and Scandinavia, so things like salmon and mackerel and sardines, those really oily fish will be higher in Omega-3 oils.”

Still, nutritionists agree that all seafood has health benefits, even octopus.

Dr Stanton says that in general, Australian seafood contains good levels of Omega-3.

“If we look at things like swordfish, salmon, mackerel, sardines - those sorts of fish have much higher levels of the Omega-3 fatty acids. But, in fact, all of the Australian seafoods have been analysed, and all of them contain enough of the Omega-3 fatty acids to legally be listed as a source of them.”

It’s interesting to discover that you don't need to eat that much seafood to get its health benefits.

Our national dietary guidelines recommend we eat from one-point-four to two-point-eight servings of fish per week.

Dietician Natasha Meerding explains how much fish that is.

“In terms of grams, that's about 140 to 280 grams of fish per week, that's for adults. Obviously proportionally less for adolescents and children. The dietary guidelines just list fish and seafood as part of the lean meat and poultry and egg, and legume food group. So they don't specify any particular type.”

Eating significantly more seafood than the guidelines recommend doesn't seem have any advantage.

In fact, it may cause problems.

Heavy metal mercury is a pollutant generated by coal plants and other industrial activity.

It settles into oceans, where bacteria convert it into methyl mercury, a form readily absorbed by the human body.

This mercury builds up in fish, particularly large predators at the top of the food chain, such as tuna, swordfish and sharks.

Mercury is particularly dangerous for pregnant women and small children, because it can affect brain development.

If you eat fish that might be high in mercury, nutritionists recommend you stay away from all other seafood for up to a fortnight.

Ms Meerding says flake is a common shark species that’s often used in fish and chips.

She says kids who love this food may be exposed to high levels of mercury.

There are other risks from eating seafood.

There are other seafood risks, too.

Raw seafood may contain common bacteria known as Listeria, which may cause serious illness.

Ms Meerding says exposure to listeria is particularly dangerous during pregnancy.

“Listeria is a bacteria that can affect the unborn foetus quite severely and can lead to a premature miscarriage or it can lead to stillbirth. So we would recommend not having things like sushi or sashimi that are actually made from raw fish, if women are pregnant. There's a number of other foods that are recommended not to be eaten when they're pregnant for the same reason, like pre-prepared sandwiches or salads, or meats like hams and salamis.”

The NSW Food Authority advises pregnant women to avoid eating high-risk foods including raw seafood, soft and semi-soft cheeses, cold pressed meats and pre-prepared vegetables and salads.

Associate Professor at the Comparative Genomics Centre at James Cook University, Andreas Lopata explains one of the most common forms of seafood poisoning.

“One is called histamine, this is usually caused by bacteria, when you [don't] properly refrigerate the seafood, and it is also called scombroid poisoning. So this happens 90 per cent of the time with fish, not with shellfish or prawn.”

The only way to avoid excess histamine is to chill freshly caught fish properly, because you can't get rid of the toxin by cooking.

You may not even notice anything wrong with the fish.

The symptoms of this poisoning are similar to an allergic reaction, so it may be hard to diagnose as well.

Ciguatera illness is another fish poisoning which involves naturally generated toxins, usually in tropical areas.

“There are marine biotoxins - toxins from the marine environment, and they're usually caused or generated by algae. Subsequently seafood species eating this algae are often filter-feeders, such as molluscs, oysters, abalones. All of these guys can accumulate high rates of toxins.”

He says aside from testing seafood before it hits the shops, not much can be done to protect consumers from ciguatera.

“There is an increasing consumption of seafood, and the toxins we see, they are always around. It's not something we are doing really wrong, it's an environmental occurrence which happens over in the tropics, we know any time between April and October. So there we have these big algae blooms, and they generate these toxins. So what we have to do better, is better screening of seafood during this time of year.”

At least two per cent of the population have some type of seafood allergy.

According to Professor Lopata, the reactions from shellfish can be as severe as those from peanuts. However, there can be quite a few allergens at play.

“In crustaceans, molluscs there's a variety of up to seven allergens that we know. The seven different proteins can cause allergies, and there it gets really complex to have diagnostic tests to identify whether you are allergic to a particular seafood or you are not.”

These allergens are so specific; you may only be allergic to one particular type of prawn, but not others.

If seafood was labelled with more detail, it would be easier for consumers to avoid particular species.

While seafood is a healthy dietary choice with lots of benefits, it is not essential for wellbeing.

A vegetarian diet can be healthy too.

However seafood is still one of the best protein sources available.

Nutritionist Dr Rosemary Stanton says our seafood consumption needs to be responsible and we shouldn't choose fish based on their popularity or looks.

“I think that we've limited ourselves with fish quite a bit, and I think that we also need to look very closely at the sustainability of certain seafood. Wherever people live, there are different fish that are considered sustainable, and you can get lists of those. So I think we should be looking at that and remembering that all forms of seafood are healthy.”

She advocates eating a variety of fish.

“A bit of variety is good in every area of our diet. If you're going to eat only one vegetable, that would be silly, and yet you get people who, when they eat fish, only eat Atlantic Salmon. It is very good for you, but it's not the only one available.”

SBS' new three part series "What's the Catch?" airs Thursdays at 8.30PM on SBSONE.