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Seafood, nutrition and human health: A synopsis of the nutritional benefits of consuming seafood.

Authors:

Abstract

Seafood as a whole food is highly nutritious. Benefits to human health associated with the consumption of seafood are noted for multiple bodily organs and physiological functions. Seafood compares favourably with other protein sources as it offers superior macronutrients in the ideal form of lean proteins combined with healthy omega-3 long chain polyunsaturated fatty acids (n-3 LCPUFAs), and a wide array of highly bioavailable micronutrients. This exposition investigates the role of key nutrients present in seafood on human health. Particular focus is placed on marine sourced omega 3 fatty acids, protein, vitamins A, B12, D and E, iodine, selenium, calcium, zinc and iron. Centre of Excellence Science, Seafood & Health, Curtin Health Innovation Research Institute, Curtin University, Perth.
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Prepared by
Centre of Excellence Science Seafood &
Health (CESSH)
Curtin Health Innovation Research Institute
Curtin University of Technology
March 2011
Seafood, nutrition and
human health
A synopsis of the nutritional benefits of consuming seafood
CENT RE O F EX CE LL EN CE
S CIEN CE S EAFOO D HE ALT H
CESSH
Contributors
Professor Alexandra McManus
Director, Centre of Excellence Science Seafood & Health (CESSH)
Curtin Health Innovation Research Institute
Faculty of Health Sciences
Curtin University of Technology
Dr Wendy Newton
Post Doctoral Scientist
Centre of Excellence Science Seafood & Health (CESSH)
Preferred citation:
McManus A, Newton W. Seafood, nutrition and human health: A synopsis of the nutritional benefits of
consuming seafood. Centre of Excellence Science, Seafood & Health, Curtin Health Innovation Research
Institute, Curtin University of Technology, Perth. 2011.
Seafood, nutrition and human health
A synopsis of the nutritional benefits of consuming seafood
1.0 Abstract 1
2.0 Introduction 1
3.0 Nutrients found in seafood 1
3.1 Marine sourced omega 3 fatty acids 1
3.2 Protein 2
3.3 Vitamin D 2
3.4 Iodine 2
3.5 Selenium 3
3.6 Calcium 3
3.7 Vitamin B12 3
3.8 Vitamin A 3
3.9 Vitamin E 4
3.10 Zinc 4
3.11 Iron 4
4.0 Discussion 4
References 5
Table of contents
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1.0 Abstract
Seafood as a whole food is highly nutritious. Benefits to human health associated with the consumption of seafood are noted for
multiple bodily organs and physiological functions. Seafood compares favourably with other protein sources as it offers superior
macronutrients in the ideal form of lean proteins combined with healthy omega-3 long chain polyunsaturated fatty acids (n-3 LC-
PUFAs), and a wide array of highly bioavailable micronutrients.
This exposition investigates the role of key nutrients present in seafood on human health. Particular focus is placed on marine sourced
omega 3 fatty acids, protein, vitamins A, B12, D and E, iodine, selenium, calcium, zinc and iron.
2.0 Introduction
In the 1950’s it was noted that Eskimos native to Greenland had a low incidence of heart disease despite having a diet high in oil.
Furthermore, observational studies of Alaskan and Greenland Eskimo and Japanese populations revealed lower incidence and
morbidity associated with coronary heart disease (1). Consequently, there has been intense interest in the health benefits associated
with marine sourced omega-3 long chain polyunsaturated fatty acids (n-3 LC-PUFAs). Mounting evidence has shown that the
consumption of marine n-3 LC-PUFAs, fish, seafood or fish oils has been positively linked with cognitive development and a reduced
risk of chronic conditions including coronary heart disease, some cancers, diabetes, rheumatoid arthritis, dementia and Alzheimer’s
Disease (2).
While the health benefits of n-3 LC-PUFAs are now widely accepted, the benefits of fish or seafood consumption have largely been
obscured by the intense interest in n-3 LC-PUFA fortified foods and supplements. Food products fortified with n-3 LC-PUFAs abound
in the market place and the growth in the popularity of fish oil supplements has been extraordinary. Fish or seafood as whole foods
provide health benefits beyond those that can be attributed to n-3 LC-PUFAs alone. Furthermore, the superior bioavailability of
nutrients in seafood leads to the conclusion that seafood as a whole food is among the best dietary source of many nutrients (3).
This resource summarises the range of macro and micronutrients in seafood with a view to promoting the consumption of fish and
seafood as whole foods that are highly valuable to a balanced diet.
3.0 Nutrients found in seafood
3.1 Marine sourced omega 3 fatty acids
The there is mounting evidence of health benefits associated with ingestion of n-3 LC-PUFAs. These include brain and retinal
fetal development, cognitive development, mental health improvements (depression, schitzophrenia, dementia and attention
deficit hyperactivity disorder), lower risk of coronary heart disease and protection against heart arrhythmia, greater plaque
stability and anti-thombosis properties (4). Additionally, there is evidence of the role of n-3 LC-PUFAs in maintaining immune
function and reducing inflammation for the treatment of all forms of inflammatory arthritis (4). Marine sourced n-3 LC-PUFAs
are found in all seafood with the richest source being oily fish.
Marine sourced n-3 LC-PUFAs, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), are the important fatty acids
for which substantial scientific support for health benefit exists. EPA and DHA may be converted at a very low rate from plant
sources of a shorter chain omega-3 fatty acid, alpha-linoleic acid (ALA); recent reviews however conclude that supplementation
with ALA is not effective in raising blood DHA levels (5). Conversion rates of ALA to EPA and DHA are typically low and are
influenced by background dietary lipid profiles (6). Consumption of preformed EPA and DHA from marine food sources is the
most efficacious method to increase physiological status of EPA and DHA for the purpose of achieving the documented health
benefits associated with these n-3 LC-PUFAs.
Despite the commercial popularity of n-3 LC-PUFA fortified foods and supplements, recent research indicates bioavailability of
supplements varies dramatically (7). The shelf life of omega 3 fortified foods and supplements has been questioned in light of
their susceptibility to oxidation and further, the safety concerns about the peroxides and other products of oxidation (8) .
2
3.0 Nutrients found in seafood (contd.)
3.2 Protein
The importance of protein is now recognised as being more complex than long realised roles of maintenance of bodily
structures including muscles, bones, fingernails and hair. Protein, peptides and amino acid derivatives are important
components in bone health, regulation of body composition, glucose metabolism, satiety, cell signalling, gastrointestinal
health and bacterial flora (9).
Quality of protein has traditionally been assessed through the amino acid content, ratio of amino acids, source, susceptibility
hydrolysis during digestion and the influence of any processing carried out (10). Animal sourced dietary proteins tend to be
complete sources of protein in that they contain the full complement of essential amino acids. Fish protein tends to be high in
lysine, sulphur containing amino acids and threonine; these amino acids are limiting in cereal based diets and add significance
to the quality of fish and seafood protein sources.
Evidence suggests a link between high levels of red and processed meat consumption and bowel cancer (11). In contrast,
there is mounting evidence that consumption of seafood can be protective against some cancers (2). Further, consumption
of seafood protein has been associated with increased insulin sensitivity in diabetics (12-13), reduced inflammation (14)
and animal studies are consistently revealing that seafood protein results in lower blood pressure (15-18). Most commonly
consumed items of seafood are rich in complete protein.
3.3 Vitamin D
Vitamin D can be obtained from sunlight or dietary sources. Vitamin D is important in regulating calcium and phosphorous
in bone mineralization. Vitamin D also features in thyroid function, rennin and insulin production, immunity, skin condition,
muscle strength and has been linked to the prevention of some cancers (19-20). The roles of vitamin D in regulating bone
mineralization and adsorption of calcium inherently makes vitamin D important in the prevention of osteoporosis. As seafood
is a good source of calcium and vitamin D, research has found that increasing consumption of seafood in the diet significantly
improves bone mineral density in women(19).
Widespread awareness of the link between sun exposure and skin cancer in Australia and New Zealand has diminished vitamin
D obtained from the sun. Sunscreen and clothing act as a barrier preventing not only sun damage but also the synthesis of
vitamin D (20). Vitamin D deficiency and rickets (osteomalacia) are a current concern in paediatric health in Australia and
New Zealand (21). Additionally, at risk populations including dark-skinned individuals, the elderly, the infirm who have
limited mobility, and those who cover themselves due to adherence to religious beliefs, are especially susceptible to vitamin D
deficiency and may need an alternative source of this essential vitamin.
The food chain of marine animals concentrates vitamin D and makes seafood the best dietary source of vitamin D (22).
Although, seafood consumption can be beneficial in raising vitamin D levels, diet in isolation is unlikely to supply the
recommended daily requirement for vitamin D (23); some sunlight exposure is recommended. Standard 2.4.2 of the Australian
and New Zealand Food Standards Code specifies a minimal level of vitamin D to be contained in edible oils and spreads in an
effort to boost dietary vitamin D in the general populace (24). Prevention of vitamin D deficiency can be achieved with a diet
high in oily fish (20).
3.4 Iodine
Iodine deficiency disorders are diverse and include metal and physical disorders that can be debilitating (25). Iodine is vital
for the effective functioning of the thyroid gland and thyroid hormone production thereby having profound influence on
facilitating normal growth, metabolism, cell oxygen consumption and the development of the central nervous system.
Historically, iodine deficiency occurred in areas where the soil was low in iodine content and endemic goitre would be noted
in local populations. Until recently, the trade in fresh produce in modern times had overcome geographic soil limitations.
In contrast to the early 1990s where the iodine status of Australians was satisfactory, the iodine intake of the Australian
population was recently considered inadequate, prompting calls for iodine fortification of all edible salts (25). The primary
reason behind the decrease in iodine status over the last two decades has been the growth in popularity of chlorine based
cleaning products in dairies and their preferential use over iodine based products (25). October 2009 heralded a change to the
Australian and New Zealand Food Standards Code; Standard 2.1.1 now mandates that all salt used in bread making must be
iodized. Recent mandatory fortification of The NHMRC has recommended that ‘women who are pregnant, breastfeeding or
considering pregnancy take an iodine supplement of 150μg each day (26).
Iodine is found in most seafood, with shellfish containing the most abundant quantities. Further, fish and seafood have the
highest concentration of iodine relative to other foods commonly consumed in most diets (27). Seafood as a part of a healthy
diet will improve iodine status.
3
3.0 Nutrients found in seafood (contd.)
3.5 Selenium
Selenium plays an important role in the body. Selenium prevents cellular damage and is protective against oxidative stress (28).
Selenium also assists in regulating the function of the thyroid and supports healthy immune function. Selenium deficiency is
more likely to occur in areas such as New Zealand due to reduced selenium levels in the soil. Low soil levels of selenium results
in reduced selenium throughout the agricultural food chain.
Selenium is present in most finfish. Selenium in fish is highly bioavailable suggesting that fish is a superior source of dietary
selenium relative to other sources including yeast (29). Recent research comparing a diet that includes salmon and one that
includes salmon oil capsules, revealed that consumption of fish oil supplements deprived subjects of the dietary benefit of
selenium (30).
Further to the nutritional benefit of selenium consumption, there is a growing foundation of research suggesting that
selenium acts as a counteractive agent to mercury (28, 31-33). Studies have shown that when test organisms are exposed to
toxic levels of mercury, an equal dose of selenium can substantially reduce the detrimental effects. It is possible that concerns
of methylmercury accumulation in some fish populations may be moderated by selenium.
3.6 Calcium
Calcium is important for developing and maintaining bones and teeth as well as supporting the healthy functioning of
muscles, nerves and the heart. Skeletal calcium serves as a reservoir for the supply of calcium for other body functions such as
intracellular messaging(34) and as such after a long latency period, calcium deficiency results in osteoporosis (35). Adequate
dietary calcium is required throughout life to prevent low bone mineral density, increased risk of fragility fractures and
osteoporosis at a mature age (34).
Bony fish such as sardines and tinned salmon are very rich in calcium. Intakes of seafood greater than 250g per week, have
been associated with greater bone mineral density (19). Of note however, is that calcium adsorption is dependent on adequate
vitamin D and can be reduced by dietary interactions including dietary fibre and alcohol (34). It can be construed from
evidence that seafood can promote bone density when consumed within an otherwise healthy diet due to the susceptibility of
calcium to macro and micro nutrient interactions.
3.7 Vitamin B12
Vitamin B12 is important to DNA synthesis, red blood cell and neurological function. Deficiency of vitamin B12 can be
associated with megoblastic anaemia, neurological disorders, myelopathy, memory impairment, dementia, depression and
cerebrovascular disorders (36).
Most fish and shellfish contain vitamin B12. Clams, octopus, oysters, fish and fish roe are excellent sources of vitamin B12 (37).
Dietary intake of fish has been linked to significant improvements in plasma B12 status (36). Researchers have identified that
dietary vitamin B12 sourced from fish and a dairy product is more bioavailable than that from meat and eggs (36).
3.8 Vitamin A
Vitamin A plays an important role in supporting normal vision, reproduction, bone growth, immune functions and healthful
maintenance of the eye, respiratory and urinary tract linings, the skin and mucous membranes (38). Deficiency in vitamin A
is associated with increased infections from diarrhoea to respiratory infections. In developing countries supplementation can
prevent approximately a quarter of childhood deaths (38).
Most fish and shellfish contain Vitamin A though the best marine sources are oily fish. Animal sourced vitamin A is in the fat
soluble retinol that is converted to an active form such as retinal or retinoic acid; these are efficiently adsorbed and used by
the body (38). Plant sources of vitamin A are the water soluble pigment group of carotenoids. Carotenoids are less efficiently
adsorbed than preformed retinol (38)and are subject to a conversion factor when calculating retinol equivalents.
4
3.0 Nutrients found in seafood (contd.)
3.9 Vitamin E
Vitamin E is a highly efficacious antioxidant that is important to the skin, nervous system, heart and circulatory system.
Although deficiency in vitamin E is uncommon, the various forms of vitamin E are protective of vitamins A and C by preventing
their oxidation (38). Vitamin E is found in oils, nuts and green leafy vegetables (38); the highest marine source of vitamin E is
oily fish.
3.10 Zinc
While only small amounts of this essential trace element are required, zinc acts as a catalyst for over 100 specific enzymes
necessary for human metabolism (38). Zinc plays a role in optimal growth and development and functioning of the immune
system. Zinc deficiency may result in stunted growth, vulnerability to infection and pregnancy outcomes (38).
Widespread zinc deficiency is an issue affecting Australian arable land (39), and thus crops raised in Australia may not
continue to contribute significantly to human zinc requirements. Consequently, alternative sources such as zinc rich food
should be consumed so that optimal zinc levels are met and maintained. As zinc binds to protein, foods such as seafood, which
are sources of both zinc and protein, optimise bioavailability of dietary zinc (39). Oysters are known to be one of the richest
natural sources of zinc.
3.11 Iron
Iron plays a vital role in facilitating the transportation of oxygen throughout the body within the haemoglobin complex and is
associated with growth, healing and immune function. It is also critical for energy production within cells and DNA synthesis.
Research suggests that Australian women in particular may not be consuming adequate iron, and increasing the consumption
of iron rich seafood within a balanced diet can play an important role in addressing this imbalance (40). Heam iron, found in
seafood and animal sources is more readily bioavailable than non- heam sourced from plants.
4.0 Summary
The value of seafood within a healthy diet is clear from this overview of nutritional composition. Evidence on the health benefit of
marine sourced omega 3 fatty acids is mounting with the strongest evidence associated with DHA. Conversion of plant sourced omega
3 PUFAs is less effective in producing the health benefits. It is unlikely that the average consumer is aware of the differentiation in
function and education of the general public is required.
The importance of seafood as a whole food, in addition to n-3 LC-PUFA, cannot be underestimated. Seafood offers a range of nutrients
that are frequently under-represented in habitual diets, including iodine, calcium, vitamin D, zinc and iron.
5
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CENT RE O F EX CE LL EN CE
S CIEN CE S EAFOO D HE ALT H
CESSH
... Oysters contain high-quality proteins, omega-3 long-chain polyunsaturated fatty acids (n-3 PUFA) and bioavailable micronutrients (e. g., zinc and taurine) (McManus & Newton, 2011). However, the consumer preference of raw oysters has been associated with its taste profile, which is contributed by free amino acids (FAAs), 5 ′ -nucleotides, organic acids, inorganic ions, etc. (Liu et al., 2021). ...
... In this study, HHP-treated oysters caused minor changes in the fatty acid profiles compared to raw oysters, which is in agreement with the results reported in Hong Kong oyster, Pacific oyster and green-lipped mussel Perna canaliculus (Cruz-Romero, Kerry, & Kelly, 2008;Zhou, Balaban, Gupta, & Fletcher, 2014;Liu et al., 2021). Seafood can provide superior lipids containing high amounts of healthy n-3 PUFA and highly unsaturated phospholipids (McManus & Newton, 2011). The ratios of n-3 PUFA to n-6 PUFA are considered important to human health (Torstensen, Frøyland, Ørsnrud, & Lie, 2004). ...
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... In order to avoid low bone mineral density, reduce the risk of fragility fractures, and osteoporosis at a mature age, sufficient dietary calcium is required during life. Higher bone mineral density has been correlated with seafood intakes greater than 250g a week (McManus and Newton, 2011). It should be understood from the evidence that seafood, because of the sensitivity of calcium to macro and micro nutrient interactions, can improve bone density when eaten within an otherwise balanced diet. ...
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