What’s so healthy about seafood?
A guide for seafood marketers
Second edition

Questions and answers

Q1:      Is it true that seafood, especially shellfish, is high in cholesterol?

A1:      In the past, shellfish were excluded from low-cholesterol diets because they were believed to be high in cholesterol. New measuring techniques indicate that cholesterol levels of many shellfish are much lower than was previously thought. In fact molluscs — such as clams, oysters, scallops and mussels — were found to have a large amount of sterols, which have similar chemical structure to cholesterol.  These sterols appear to have a beneficial effect because they inhibit the absorption of cholesterol eaten at the same meal.

Cholesterol levels are not significant in most seafood products. Finfish are generally quite low in cholesterol; shellfish have low to moderate amounts. Cholesterol levels in crab and lobster are similar to that found in the dark meat of chicken. Because shellfish contain very little saturated fat, they are no longer excluded from typical low-cholesterol diets. Saturated fats may increase the ability of dietary cholesterol to increase blood cholesterol.

People with normal blood cholesterol (<5.0 mmol/L) can eat seafood daily if they wish. For people with higher cholesterol levels, seafood can be consumed a few times per week if saturated fat intakes are low.

Q2:      Which one is more nutritious —  fresh or sea water finfish?

A2:      When the essential fat content matters, there is little nutritional difference between fresh water finfish and sea water finfish if they both live in cold, southerly waters. However, given the differences between sea water and fresh water, sea water finfish have richer amounts of iodine, magnesium and sodium, which have multiple functions in the body.

Q3:      Which one has more omega-3 fatty acids — tropical or temperate finfish?

A3:      Omega-3 fats keep the blood flowing properly in humans, in the same way as they do in finfish when the fish swims in colder water. Therefore, finfish caught from southern locations or in spring season tend to have high omega-3 fatty acids. Tropical fish do not have much omega-3 fats in their fatty tissue, but they are still good sources of omega-3 fatty acids from their muscle tissue.

Q4:      Which one is better – farmed or wild caught finfish?

A4:      Generally farmed finfish (such as trout and salmon) have more total dietary fat  and the amount of omega-3 fat depends on the species and the oils used in fish feeds. For finfish caught in the wild, omega-3 fat levels vary according to species, the time of year, age and size. The best advice is to consume a wide variety of finfish and other seafood — both farmed and wild-caught.

Q5:      How much seafood do we need to eat to get enough omega-3 fats?

A5:      Currently Australia does not have recommendations for omega-3 fat intake. A report from the UK Department of Health recommends that the intake of marine omega-3 fatty acids should be at least 210 milligrams per day.  Just 60 grams of canned or smoked fish should achieve this amount.

Q6:      Can we get enough dietary omega-3 fats from plant food alone?

A6:      Certain plant foods — such as nuts, some vegetables and soy — contain omega-3 fats. But these fats are different from those provided by seafood.  Omega-3 fats from plants can be converted, to a limited extent, in the body to EPA and DHA — the type of omega-3 fats present in seafood. Therefore, we need to eat a very large amount of plant food to get health benefits similar to those we get from seafood.

Q7:      Which one is better — finfish or fish oil supplements?

A7:      Taking fish oil supplement may be much more convenient than eating finfish, but some health effects of finfish are not seen with fish oil. Generally speaking, fish contains more of the ‘long-chain’ fatty acid DHA. An excessive amount of omega-3 fats from fish oil may be harmful unless given under medical supervision. It can increase bleeding tendency or increase both ‘good’ and ‘bad’ cholesterol.

Q8:      Is cod liver oil the same as fish oils? Can we get omega-3 fats from cod liver oil instead of fish oils?

A8:      No, cod liver oil and fish oils are not the same. Cod liver oil is extracted from cod liver and is an excellent source of vitamins A and D. Fish oils are extracted from the flesh of fatty fish like salmon and herring, and are good sources of EPA and DHA. Fish oils contain very little vitamin A and D, but cod liver oil does contain EPA and DHA. However, if we try to obtain daily recommended intakes of EPA and DHA from cod liver oil, we would probably exceed the recommended daily intake of vitamins A and D.

Q9:      Which method is best to cook seafood?

A9:      Grilling, steaming, microwaving and baking are the best ways to cook seafood and maintain its health benefits. But if seafood is to be pan fried or deep fried, the cooking oil that is high in mono-unsaturated fats — such as olive or canola oil — is preferred because the oil is incorporated into the food.

Q10:    How do omega-3 fatty acids protect against heart disease?

A10:    Research suggests that omega-3 fatty acids from seafood protect against heart disease in a number of different ways:

• They inhibit the formation of blood clots (thrombi). This is important because most heart attacks result when blood clots get stuck in blood vessels leading to the heart or brain.
• They may prevent heartbeat abnormalities, thereby protecting against sudden cardiac arrest, a major cause of death from heart disease.
• They reduce triglycerides, a type of fat in the blood which, when raised, increases the risk of heart attacks.
• They can reduce blood pressure as a risk factor for heart disease.
• They may retard the growth of plaques that narrow arteries leading to the heart.

Q11:    Should pregnant women eat seafood?

A11:    For pregnant women, there are many benefits associated with eating seafood. Apart from the benefits supplied to the mother, many components in seafood are important for development of the foetus — such as protein and its amino acids, omega-3 fats, iodine and calcium.

However, all seafood contains mercury, which could have harmful effects if the intake is high. The amount of mercury in most seafood is very low, and since most people eat only moderate amounts of seafood the benefits of eating seafood far outweigh the risk posed by the small amounts of mercury. Regulations are also in place that set a limit on the amount of mercury that can be present in fish that is sold.

The amount of mercury in a fish depends on how long it lives and what it eats — so the big, long-living or predatory finfish tend to accumulate more mercury. Food Standards Australia New Zealand (FSANZ) has therefore recommended the number of serves of seafood that can be eaten safely, taking this factor into account — see table 4.

Notes

The FSANZ recommendations are based on knowledge of the Australian population and Australian diets and consumption, and may therefore differ from advice in other countries.

Some of the fish names in the above table have been amended from those in the FSANZ brochure in keeping with recommendations of the Australian Fish Names Committee. Comprehensive information on fish names is available from http://www.seafoodservices.com.au/fishnames/

* Blue grenadier (= hoki in New Zealand) or hake are the main species in fish fingers consumed locally.

More information is available from FSANZ on 02 6271 2222, e‑mail information@foodstandards.gov.au, or from www.foodstandards.gov.au — including a useful brochure, ‘Advice on fish consumption: mercury in fish’, at www.foodstandards.gov.au/_srcfiles/mercury_in_fish_brochure_lowres.pdf

Q12:    Should people with high blood pressure avoid eating seafood?

A12:    Although seafood may have a high salt content — and this can be a problem for people with high blood pressure — it is mainly related to the salt water when fish is packed in brine, which can be washed off.

Too much salt in the diet has been linked to high blood pressure. The extent to which sodium restriction lowers blood pressure is generally agreed to depend on age, initial blood pressure and degree of over-weight — it is greater with age, in people who are more overweight, and at higher blood pressures. Also, the beneficial effects of sodium restriction may not be seen for several weeks. Sodium restriction may not lower blood pressure further if blood pressure is within the normal range. The exact mechanism is unclear, but it is thought that the excess salt increases the blood volume, and also the contraction (and resistance to blood flow) of blood vessels.

Q13:    What is seafood allergy?

A13:    Seafood — particularly crustaceans, scaly finfish and molluscs — can be a cause of food allergy. Seafood allergens in sensitised individuals can cause adverse reactions to recur over a lifetime. Many reactions are mild and limited to localized hives or swelling. The most dangerous symptoms are breathing difficulties or hypotension (drop in blood pressure), either of which can be life-threatening. Anaphylaxis and death have been described in association with seafood allergy. Other symptoms include swelling of the face or throat, dizziness, difficulty in thinking, an intense sense of fear, tightness in the chest, vomiting or diarrhoea.

There are only a few studies which examine the actual allergens or substances involved in triggering reactions. Muscle proteins such as parvalbumin (in scaly fish) and tropomyosin (in crustaceans) appear to be important allergens. Seafood allergy usually involves only one group of foods — finfish, shellfish or crustaceans. People allergic to seafood from one group can usually tolerate those from another. In other words, allergy to one scaly fish often results in allergy to other scaly fish, but not necessarily to crustaceans. For those who are allergic to one or two proteins that may be present in multiple species, there is a risk of “cross-reactive” allergic responses to other animals as well.

Occasionally, intense cooking will partially or completely destroy the triggering allergen. This may explain why some people who are allergic to fresh fish are able to tolerate tinned salmon or tuna.

For seafood allergies, there is no effective prevention other than complete avoidance. Food labels need to be read carefully because highly processed foods may contain hidden fish or shellfish.

Q14:    What is ciguatera fish poisoning?

A14:    Ciguatera fish poisoning is probably more important than any other form of seafood poisoning. Its epidemiology is complex and it is impossible to predict outbreaks. Higher ocean temperatures may increase the incidence of ciguatera poisoning. This illness results from eating large reef fish that look, taste and smell normal but are affected with ciguatoxins, derived from algae that colonise coral beds. It first affects the coral-grazing fish and is then passed up through the food chain to the fish-eating fish (i.e., snapper, grouper, amberjack, barracuda) and finally to humans. The toxin is not destroyed by either cooking or freezing. If consumed in sufficient dose, it can cause diarrhoea, vomiting and abdominal pain, then abnormal sensation (such as burning, prickling and formication) and other neurological effects which may persist for weeks, months or years. Unfortunately, there is no way to identify whether the fish is contaminated. Therefore, always know what kind of fish you are eating and, during the hot season, avoid large predatory reef fish such as mackerel.

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