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The potential health benefits of seaweed and seaweed
extract
BROWNLEE, Iain, FAIRCLOUGH, Andrew, HALL, Anna and PAXMAN, Jenny
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BROWNLEE, Iain, FAIRCLOUGH, Andrew, HALL, Anna and PAXMAN, Jenny
(2012). The potential health benefits of seaweed and seaweed extract. In: POMIN,
Vitor H., (ed.) Seaweed : ecology, nutrient composition and medicinal uses. Marine
Biology : Earth Sciences in the 21st Century . Hauppauge, New York, Nova Science
Publishers , 119-136.
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THE POTENTIAL HEALTH BENEFITS OF SEAWEED
AND SEAWEED EXTRACTS
I. A. Brownlee, A. C.Fairclough,
A. C. Hall, and J. R. Paxman
Centre for Food Innovation, Sheffield Hallam University,
Howard St, Sheffield, S1 1WB
ABSTRACT
Edible seaweeds have historically been consumed by coastal populations across the
globe. Today, seaweed is still part of the habitual diet in many Asian countries. Seaweed
consumption also appears to be growing in popularity in Western cultures, due both to
the influx of Asian cuisine as well as notional health benefits associated with
consumption. Isolates of seaweeds (particularly viscous polysaccharides) are used in an
increasing number of food applications in order to improve product acceptability and
extend shelf-life.
Epidemiological evidence suggests regular seaweed consumption may protect
against a range of diseases of modernity. The addition of seaweed and seaweed isolates to
foods has already shown potential to enhance satiety and reduce the postprandial
absorption rates of glucose and lipids in acute human feeding studies, highlighting their
potential use in the development of anti-obesity foods. As seaweeds and seaweed isolates
have the potential to both benefit health and improve food acceptability, seaweeds and
seaweed isolates offer exciting potential as ingredients in the development of new food
products.
This review will outline the evidence from human and experimental studies that
suggests consumption of seaweeds and seaweed isolates may impact on health (both
positively and negatively). Finally, this review will highlight current gaps in knowledge
in this area and what future strategies should be adopted for maximising seaweed's
potential food uses.
1. INTRODUCTION
Biologically, seaweeds are classified as macroalgae, with subclassification as brown
(Phaeophyta), red (Rhodophyta) or green algae (Chlorophyta). Some examples of these
edible algae are outlined in Table 1. The nutritional properties of these seaweeds are
discussed earlier in this edition and reviewed elsewhere [1,2]. In 1994/95 over 2,000,000
tonnes (dry weight) of seaweed was harvested [3]. Much of this may be consumed as whole
seaweed products, while a large proportion is also used in the production of over 85,000
tonnes of viscous polysaccharides for various food and industrial applications [4].
Historically, seaweed is a readily available food source that has been consumed by
coastal communities likely since the dawn of time [15,16]. Seaweed is consumed habitually
2
in many countries in South-East Asia [17]. However, as a wholefood it is not considered a
habitual component of the Western diet [2]. In the West, seaweed isolates (e.g. alginate from
brown algae and agar or carrageenan from red algae) are typically used industrially [18].
Seaweed consumption has gained a measure of acceptance in some Westernised cultures such
as Hawaii, California and Brazil, where there are large Japanese communities who have had a
tangible influence on the local dietary practices [19,20]. Low consumer awareness regarding
potential health benefits and a lack of previous experience of seaweed challenges its use in
the daily diet [21].
Table 1. Examples of edible algae
Subclassificaton
Genus
Common Name
Brown algae (Phaeophyta)
Alaria
Kelp/ bladderlocks
Himanthalia/ Bifurcaria
Sea spaghetti, fucales
Laminaria
Kelp/ kombu/ kumbu/ sea tangle
Saccharina
Sugar wrack
Undaria
wakame
Ascophyllum
Egg wrack
Fucus
Bladder wrack, rockweed
Sargassum
Mojaban/Indian brown seaweed
Hizikia
Hijiki
Sargassum
Sea holly
Dictyotales
Eisenia
Arame
Red algae (Rhodophyta)
Rhodymenia/ Palmaria
Dulse
Porphyra
Nori/ haidai/ kim/ gim
Chondrus
Irish moss/ carrigeen
Mastocarpus/ Gigartina
Stackhouse, Guiry
Gracilaria
Asparagopsis
Limu Kohu
Grateloupia
Green algae (Chlorophyta)
Ulvaria/ Enteromorpha
Laver/sea lettuce/ sea grass/nori
Adapted from [2,5,6]. Further details from [7-14].
2. SEAWEED AS A WHOLE FOOD
Consumption of seaweed in Europe and North America is minimal at present [22]. While
instruments within Japan and Korea have been developed to assess dietary intake of seaweed
[23,24], consumption is so infrequent in most Western cultures that it is not considered within
nationwide dietary intake assessment surveys. In the USA and Canada seaweed is cultivated
in onshore tanks and the market for it is growing. In Ireland there is a renewed interest in
seaweed that once formed part of the traditional diet. Recipe books promoting the use of 'sea
vegetables' or 'marine vegetables' [25] in home cooking are becoming more popular. As
consumer health and nutrition become more influential in the food industry, the use of
seaweed as an ingredient is on the rise [25], and product development involving salads and
wraps appears to be slowly evolving.
3
The rich mineral and trace element content of seaweed compared to terrestrial plant foods
can however, impact negatively on its sensory characteristics [2]. As an ingredient of
composite foods, it has been shown to be acceptable to consumers when baked into breads
(Ascophyllum nodosum up to 5% w/w; Hall et al., 2010; Mahadevan and Fairclough, personal
communication) and added to pasta (Wakame - Undaria pinnatafida - up to 10% w/w;[26]).
Further from these applications, seaweed has been added to low fat meat products where it
contributes to water retention and gel formation [27]. Collectively, these results suggest that
seaweed may be successfully included as an ingredient in a number of food applications. As
dried seaweed is high in dietary fibre, along with a range of other potentially bioactive
components, this addition has the potential to enhance the nutritional quality of a product.
Habitual consumption of seaweed may offer a nutritionally rich addition to the diet.
However, micronutrient intakes in excess of the RNI could be of concern to nutritionists,
particularly where bioavailability is high.
3. WHOLE SEAWEED USE IN FOODS
Whole seaweeds have been incorporated into a range of foods including meat, and bakery
products. Fairclough and Williams (personal communication) have recently successfully
incorporated Ascophyllum nodosum into sausages. This usage has also previously been
reported with Laminaria japonica (sea tangle) powder [28]. Previous authors have included
Himanthalia elongate (sea spaghetti), Undaria pinnatifida (Wakame) and Porphyra
umbilicalis (Nori) in frankfurter type products (gel/emulsion meat systems [29] and H.
elongate in frankfurters [27,30,31]. More recently, U. pinnatifida and H. elongate have been
incorporated into beef patties and restructured poultry steaks, respectively [32,33]. Recent
work has also resulted in the production of an acceptable wholemeal bread enriched with
Ascophyllum nodosum [34]. Locally, our research group has also added Ascophyllum
nodosum to pizza bases, cheese and frozen meat products. Prabhasankar and colleagues have
incorporated Sargassum marginatum (Indian brown seaweed) and U. pinnatifida into pasta
[26,35]. The previously published literature described above reports mixed success in terms
of acceptability of whole seaweed-enriched food products. There may also be issues involved
in the large-scale processing of whole seaweed-enriched foods.
4. ANTIMICROBIAL PROPERTIES OF WHOLE SEAWEEDS
The incorporation of seaweed into foods has also been shown to have a preservative
effect, particularly with regards to Gram-negative bacteria (Gupta et al., 2010), reducing the
need to add salt. The antimicrobial properties of seaweed extracts have been well documented
over the years [36-39]. However, there would appear to be a lack of published information
regarding the antimicrobial properties and preservative effects when seaweed as a 'whole
food' is incorporated into a food matrix. Previous studies would suggest that the overall
antimicrobial capacity of seaweeds appears to be linked to their antioxidant content [40].
Several studies have been undertaken at Sheffield Hallam University where seaweed
(Ascophyllum nodosum, Seagreens®) as a dried whole-food has been incorporated into
various products for example processed meat products and bread products.
4
Figure 1. Changes in Total Viable Count (TVC ∎) and coliform -life in frozen
processed meat products containing seaweed (dashed line). Control product (no seaweed added) is
shown by continuous line.
Figure 2. Changes in the population of lactic acid bacteria (LAB) in meat products containing
Seagreens® (Ascophyllum nodosum). The dashed line represents the seaweed-enriched product, while
the control product is denoted by a continuous line.
Figure 1 shows that the 3% w/w dried seaweed added to this processed meat product
results in an overall 0.3 log10 cfu/g reduction in the total viable count over the two month trial
period; however, when looking at specific populations of micro-organisms, this antimicrobial
activity is particularly effective against Gram negative micro-organisms such as coliforms
(showing a 0.7 log10 reduction cfu per gram of product) which is to be expected since Gram
negative micro-organisms have a thinner cell wall than Gram positive micro-organisms
making them more susceptible to antimicrobial agents. However, there is a significant
reduction in the Gram positive lactic acid bacteria (LAB) population over shelf-life (0.5 log10
- see Figure 2). Other data suggest similar reductions in yeast and mould populations (data not
shown).
Interestingly when a methanolic extract of the seaweed is used in a typical antimicrobial
susceptibility test then the trend is also mirrored with Gram positive organisms, on the whole,
showing more susceptibility to the antimicrobial agent(s) contained within the seaweed;
5
especially Bacillus cereus and Staphylococcus aureus, which show the greatest sensitivity to
the extracted agent (see Table 2). Listeria monocytogenes also shows a noticeable
susceptibility to the extract although to a lesser extent than the organisms named above.
Table 2. Antimicrobial effects of a methanolic extract
from Seagreens® (Ascophyllum nodosum)
Micro-organism
Sensitivity
Bacillus cereus (NCTC 7464)
+++
Staphylococcus aureus (NCTC 12981)
+++
Listeria monocytogenes (NCTC 7973)
++
Bacillus subtilis (NCTC 10400)
+
Listeria innocua (NCTC 11288)
-
Enterococcus faecalis (NCTC 775)
-
E. coli (NCTC 12241)
±
E. coli 0157 * (NCTC 12900)
±
Pseudomonas fluorescens
-
Salmonella typhimurium (NCTC 12023)
+
+++ - - zone of clearance 2.5 - 7.5 mm, + -
- - no discernible zone of clearance, ± - indeterminate zone of clearance.
Figure 3. Mould growth at nine days post-production in wholemeal breads containing differing amounts
of Seagreens®. Photograph A - control loaf with standard salt content. Photograph B - loaf containing a
50:50 mix of added salt and Seagreens®. Photograph C - loaf with Seagreens® instead of added salt.
When Seagreens® is incorporated into bakery products especially wholemeal bread as a
replacement for salt (as sodium chloride) there is a suppression of mould growth for up to 9
days in preservative-free bread when compared to preservative-free control bread containing
5 g of salt (as sodium chloride) and no Seagreens®. Similar results have been recorded in all
the other bread varieties baked at Sheffield Hallam University; with the exception of white
bread where no significant suppression has been seen and mould growth occurs after 3 to 4
days. Figure 3 shows wholemeal breads containing different amounts of Seagreens® at 9
days.
6
5. COMPONENTS OF SEAWEEDS
As previously stated, the use of seaweeds in Western diets is predominantly limited to
use in food additives or extracts [41]. In line with other natural foods like fruits, vegetables
and grains, there has been marked interest within the scientific community to assess which
fractions of seaweeds may be linked to the historically observed health benefits. For the
purpose of this review, these factors are considered under two relatively crude banners:
seaweed phytochemicals and seaweed polysaccharides. Seaweed proteins have also
previously been assessed for their nutritional value [42-47] but will not be discussed within
this chapter. As with other foods that have historically been consumed whole (e.g. fruits,
vegetables and grain products), it must also be noted that isolation of such bioactive
components may allow the development of food products and/or supplements with potential
health benefits. This should not however preclude a drive to increase population-wide
consumption of the original whole foods.
5.1. Seaweed Polysaccharides
Each seaweed subclassification differs in the type of dietary fibres they contain. Brown
seaweeds for example contain the dietary fibres alginates, fucans and laminarans; red
seaweeds contain galactans, agar and carageenans; whereas green seaweeds contain soluble
ulvans and other insoluble fractions such as cellulose.As with plant polysaccharides, non-
starch entities play a vital role in seaweed structure both at a microscopic and macroscopic
level. The varying roles of these polysaccharides within the macroalgae structure should be
considered when comparing these different types of polysaccharides.
In alginates, the presence and arrangement of carboxyl groups on spans of 3 or more
guluronic acid residues can act to interact with hydrogen ions and divalent cations
(particularly calcium) to cause gelation [48]. This allows gelation in specific formulations at
room temperature. The presence and position of sulphate ester groups in carrageenans and
other seaweed polysaccharides also appears to affect their gelation and ability to interact with
other factors in composite foods [49,50]. The physicochemical variations in these
polysaccharides allow for a wide variety of applications within the food industry.
Polysaccharides of different viscosities that react differently under various conditions of
temperature, pH and food chemistry are important tools in the arsenal of food formulators in
order produce products with increased acceptability.
Seaweed polysaccharides are extensively used as thickening agents in sweet and savoury
sauces and condiments [51-53]. A number of applications of seaweed polysaccharides are
also utilised in order to stabilise food products against degradation, staling and heating or
cooling/freezing. These applications also act to improve the consumer acceptability of such
products, as well as extending the shelf-life. A further novel applications of seaweed
polysaccharides in food manufacture are discussed elsewhere [54].
Seaweed polysaccharides are generally water-soluble and very hydrophilic. Their action
as stabilizers within food oil-water emulsions is suggested to be a result of their ability to
7
precipitate/adsorb onto oil droplets and sterically stabilize emulsions against flocculation and
coalescence [55,56].
Previous studies have also suggested that seaweed polysaccharides may be used at fat
replacers in a range of food applications. Where this is carried out, seaweed polysaccharides
and other hydrocolloid thickening agents can be used to reduce or replace added fats within
foods in order to produce an end-product with reduced total fat content, while still allowing
for a product with improved moisture retention and consistency. This role is crucial in the
development of low-fat products with high consumer acceptability. This use of seaweed
polysaccharides has been shown to facilitate the production of low fat versions of meat-based,
starch-based, fat-based and fruit/vegetable-based products [51,52,57-59].
High viscosity polysaccharides are likely to have detrimental effects both in terms of the
manufacturing process and product acceptability. As with other types of viscous
polysaccharides, low viscosity fractions of the indigestible carbohydrate material from
seaweeds could be used to develop food products with higher fibre content.
5.2. Seaweed Phytochemicals
Seaweeds also contain a range of unique phytochemicals not present in terrestrial plants.
As such, edible seaweeds may be the only relevant dietary source of some of these factors. A
wide range of studies have described the high antioxidant capacity of a range of edible
seaweeds [18,60-62]. This capacity is endowed by the presence of sulphated polysaccharides
[63], polyphenolic compounds [64] and antioxidant enzymes [65]. Oxidative stress may play
a key role in the development of cancers and cardiovascular disease [66]. Phytochemical-rich
foods should clearly form part of a healthy balanced diet. However, the human body has a
number of physiological, biochemical and enzymatic processes by which it can combat
oxidative stress outside of dietary intake. The routes by which the wide variety of phenolic
compounds enter the circulation is not well characterised, nor is the bioavailability and half-
life/distribution of such factors in the human body. Previous intervention studies where
dietary antioxidant intake has increased have not evidenced a parallel change in the total
antioxidant capacity of the body [67,68]. While this casts doubt on the benefit of increasing
polyphenolic consumption from the perspective of reducing oxidative stress, it must be noted
that such compounds may have other physiological effects.
Previous studies in animal models and cell culture have suggested that seaweed
phytochemicals have the potential to inhibit the progression of carcinoma formation [69,70].
In vitro studies have also suggested a potential for phenolic compounds from seaweeds to
inhibit the action of digestive enzymes [71,72]. Such an action would be considered to have
the potential to affect macronutrient uptake and act as a therapeutic agent to help combat
metabolic diseases. Further from these findings, a recent study has suggested that a
polyphenol-rich extract of Ecklonia stolonifera improved glycaemic control in a non-insulin
dependent diabetic mouse model [73]. A similar effect was also noted in a chemically-
induced diabetic mouse model [74]. Anti-inflammatory properties of a phlorotannin-rich
extract from Ecklonia cava have also been demonstrated in vitro [75].
The above experimental evidence highlights some interesting ways in which these
phytochemical compounds isolated from seaweed could benefit health. Certainly there has
been great interest from the pharmaceutical industry in the high-throughput analysis of
8
macroalgal compounds for the development of novel drugs [76-78]. The new, more stringent
regulations on novel food ingredients within the EU is likely make the inclusion of specific
seaweed phytochemicals as bioactives more problematic than whole seaweed or seaweed
polysaccharides, both of which have been used historically within this context. This should
not act as a barrier to research that characterises the physiological effects of this range of
interesting compounds and potential therapeutic agents, however.
6. SEAWEEDS AND HEALTH
Previous studies on seaweed consumption in humans have centred in the areas of the
world where reasonable amounts of seaweeds are habitually consumed (particularly South-
East Asia). The evidence detailed below outlines a variety of potential benefits to health, with
much of the research in whole seaweeds either focussed around their impact on metabolic
disease (associated with increased phytochemical and fibre intake) or breast cancer (linked to
increased iodine consumption). Both of these topics are reviewed in detail elsewhere [79,80].
6.1. Experimental Studies
Numerous researchers have studied the health benefits of seaweed incorporation in the
diets of rats, particularly with reference to their effects on blood lipid profiles. Wong et al.
(1999) examined the lipid changing effects of 4 types of seaweed (1 red, 1 green and 2 brown
at 5% dry weight of feed) compared to a control group (cellulose) in 60 male Sprague Dawley
rats. Comparisons were made between serum total cholesterol, HDL cholesterol, LDL
cholesterol, triglycerides and hepatic cholesterol. The results suggested that the red algae
Hypnea charoides had the greatest hypocholesterolaemic effect; however no significant
reductions in cholesterol were seen between any of the seaweeds. On the contrary,
Colpomenia sinuosa (a brown algae) induced a significant (p<0.05) increase in total serum
cholesterol [81].
Carvalho et al. (2009) showed that the total cholesterol levels of rats fed a
hypercholesterolaemic diet increased significantly (p<0.05) when supplemented with
cellulose as opposed to the green seaweed Ulva fasciata (24% dry weight seaweed meal). The
seaweed containing diet was able to keep the total cholesterol at levels similar to baseline,
leading the authors to suggest the incorporation of seaweed into the diet might be important in
the reduction of total cholesterol [41].
Bocanegra et al. (2009) conducted a study in groups of ten rats that were fed a diet
containing a cholesterol raising agent with either a cellulose-wheat starch mix, Nori algae or
Konbu algae (7% weight as freeze-dried material). Rats fed the Nori and cholesterol-raising
diet had lower postprandial cholesterolaemia, and a more positive lipid profile with regards to
HDL and LDL lipid fractions (p<0.05) when compared to the comparable Konbu diet [82].
These studies, among othersof similar design, hint towards the variability of the
biological effects of different varieties of edible seaweeds. They also highlight the potential
for cardiovascular health benefits in certain cases. As with most animal-based dietary
9
interventions, the amounts of seaweed incorporated in the diet are extremely high and do not
bear resemblance to the amounts eaten within the human diet.
6.2. Epidemiological Studies
The lack of a dietary intake assessment tool alongside the likely exceedingly low intake
of seaweeds at a population level means that observational data linking seaweed intake to
reduced disease risk have only been collected in South East Asian populations. The most
recent, accessible data are summarised in Table 4.
Such data should be interpreted with caution, firstly as they do not necessarily represent a
causal relationship between seaweed intake and health outcomes, but rather an association
between the two factors. Also, different species of edible seaweeds appear to have different
effects on disease risk. In a Korean case-controlled study, increasing frequency of Porphyra
species consumption was associated with reduced risk of breast cancer, whereas Undaria
pinnatifida consumption did not [15]. These results highlight the wide variability in the
bioactive content of seaweed species. Even within a specific type of seaweed, previous
research has suggested there are significant seasonal variations in nutritional content [83-85],
which is likely to impact the biological effects of edible components. As outlined in the
section below on the negative impact of seaweed intake, certain population groups may be at
risk from global or national guidelines based on high seaweed consumption.
However, these data suggest that achievable daily intakes of seaweed (equating to
approximately 30 g of fresh seaweed [15,24,86] or 2 g of dry seaweed [15] a day) appear to
reduce disease risk compared to the lowest (close to zero intake) percentiles of seaweed
consumption. Such data are also routinely extrapolated to represent lifelong patterns that
reduce a disease risk and are therefore a rational basis on which to develop prudent lifestyle
choices across the whole life-course.
6.3. Intervention Studies
Relatively few human intervention studies have assessed the impact on seaweed
consumption on risk factors for future disease. One previous study [91] has assessed the
impact of seaweed consumption over a number of weeks on markers of cardiovascular
disease risk. The physiological effects of seaweed supplementation were investigated in terms
of effect on a number of markers of health, including blood glucose levels and blood lipid
profiles in males and females with type II diabetes mellitus and a BMI of <35kg/m2. Dried
brown seaweeds (sea tangle and sea mustard) incorporated into a pill were consumed 3 times
a day for 4 weeks as a food supplement. Total daily consumption of seaweed was 48g. After
random assignment to either the control group or the seaweed supplementation group, and the
completion of the trial, fasting blood glucose levels (p<0.01) and 2 hour postprandial glucose
levels (p<0.05) were significantly lower in the seaweed supplemented group. However, while
serum concentrations of triglycerides decreased, and HDL cholesterol levels significantly
increased (p<0.05), levels of total and LDL cholesterol were not affected by seaweed
supplementation. Nutrient intake (% energy from macronutrients) was identical over the 4
10
weeks, but the study had a relatively small sample size (n= 20), and while there was a control
group (n=11), the study did not have a cross over design.
Table 4. Summary of recent observational studies relating to dietary
seaweed intake and health
Disease/health
concern
Study design
Odds ratio (95% CI) of
highest seaweed to lowest
Reference
Serum total
cholesterol
Retrospective study in the Japanese
population with data from 1980 and
1990 for > 7000 people. Data were
adjusted for age, BMI and total
energy intake.
Not reported. No
significant effect of
seaweed consumption
[87]
Type II
diabetes and
prediabetes
3,405 Korean individuals, aged 20 -
65 y. Retrospective study. Adjusted
for diet and lifestyle.
0.66 (0.43-0.99) for
men and 0.80 (0.51-
1.24) for women
[24]
Osteoporosis
214 Japanese elderly participants.
Prospective study assessing
calcaneus stiffness changes over 5
years. No adjustment of data.
0.22 (0.07-67) in all
individuals
[88]
Obesity
3760 Japanese women aged 18-20 y.
Cross-sectional study assessing 3
different eating patterns.
0.57 (0.37-0.87) for
BMI >25.0a
[89]
Cardiovascular
disease
mortality
40547 Japanese men and women
aged 40-79 y. Prospective study over
seven years of follow-up. Not
adjusted.
0.73 (0.59 -0.90)a
[90]
Allergic
rhinosinusitis
1002 pregnant Japanese women.
Cross-sectional study. Data adjusted
for lifestyle and risk factors.
0.51 (0.300.87)
[86]
Breast cancer
occurrence
South Korean case-control study.
362 cases (30-65y) with controls
matched for age and menopausal
status. Data adjusted for
multivitamin supplement use,
number of children, breastfeeding,
dietary factors, education, exercise,
oral contraceptive use.
0.48 (0.27-0.86)
[15]
aSeaweed was included as part of a healthy/traditional Japanese eating pattern (i.e. high intakes of
vegetables, mushrooms, seaweeds, potatoes, fish and shellfish, soy products, processed fish, fruit
and salted vegetables) and was not assessed independently.
The amount of seaweed consumed within this intervention was very high compared to the
amounts consumed in the observational studies above that appeared to have a biological
effect. As such, they may not be sustainable within the diet of individuals on a long-term
basis if such an amount were not consumed in pill-form. Nonetheless, these findings warrant
the development of further participant-based interventions involving long-term seaweed
consumption and cardiovascular health.
In a study with twelve healthy female volunteers of healthy BMI, inclusion of 3 g of Nori
(in capsules) 15 minutes before eating significantly blunted the postprandial glycaemic rise
11
elicited from consumption of a white bread meal (containing 50 g of starch) [92]. These
results were not duplicated in a recent study where the impact of inclusion of Ascophyllum
nodosum as an integral ingredient within bread, consumed within a composite meal, was
compared to a standard seaweed-free meal [93].
Daily supplementation with seaweed (20 g of Laminaria japonica diluted in water or a
beverage) was administered in combination with diet, exercise and behavioural therapy to
female, Korean college students (19-24y) over 8 weeks. Pre-post test analysis showed there
were significant improvements, consistent with recommendations for weight management,
across a range of anthropometric measures. However, the lack of a control group prohibits the
authors from attributing such effects to any particular aspect of the intervention. There were
no significant changes in blood lipids during this time [94].
Dietary supplementation with seaweed (5 g of Alaria esculenta in capsule form)
consumption (Alaria esculenta (L.)) did not signficantly affect serum oestradiol
concentrations in a recent randomised, placebo-ontrolled crossover trial in fifteen healthy,
postmenopausal females [95] . However, it was noted in this study that there was a signficant
inverse correlation between seaweed dosage (expressed in terms of mg/kg body weight) and
serum oestrodiol concentrations. The same intervention also elicited a significant increase in
circulating levels of thyroid-stimulating hormone [96]. It was calculated that c.75mg/kg of
body weight of seaweed would need to be ingested to have this oestodiol lowering effect,
which would equate to approximately 4 - 5 g/day of dry seaweed consumption for females
weighing between 55 and 75 kg. These preliminary results highlight the potential for seaweed
as an important dietary factor in the prevention of breast cancer.
There is a growing body of evidence on the acute benefits of alginate consumption to
health-related parameters. Alginates are widely researched due to their unusual gelling
properties and relatively low viscosity, meaning that higher amounts can be incorporated in
foods or beverages than other types of seaweed polysaccharide. Relevant food products could
be used to deliver other types of seaweed polysaccharide in such studies. An example of this
is the work of Panlasigui et al. (2004) in which carrageenan in a powdered form was
incorporated into 4 food products common in the Philippines: a yeast bread, a corn pudding,
fish balls and a gruel like product [97]. Following a two-week intervention with these
products, participants had significant improvements to plasma concentrations of total and
HDL cholesterol compared to the control group (no intervention).
Hoad et al. (2004) investigated the gastric emptying rates of a strong gelling (high-G) and
a weaker gelling (low-G) alginate meal compared to a guar-based meal and a control (without
added fibre). In vitro characterisation of the gelling properties of both alginate meals showed
n to be associated with feelings of
fullness and a reduction in hunger in the strong-gelling alginate condition[98]. The authors
purport that acid-gelling agents, such as alginates, may be useful for those aiming to adhere to
a weight-reducing diet.
To that end, Paxman and colleagues (2008) demonstrated the capacity for a strong-
gelling alginate formulation to restrict free-living energy intake compared to a commercially
available control formulation. The 7% (134.8 kcal) reduction in reported daily energy intake
was consistent with published guidelines for weight management [99]. Similar significant
findings were reported previously in overweight and obese women [100]. Such effects may be
explained by the potential for seaweed isolates, particularly alginate to enhance satiety [101].
12
The potentially satiating effects of seaweed isolates are by no means unaminously
reported in the literature, however. Findings from a well-controlled intervention show an
alginate and guar-based breakfast bar had no effect on energy and macronutrient intake when
incorporated into the habitual diet over 5 days [102]. The breakfast bar was consumed daily
for 5 days and food intake recorded on 3 randomly selected days, however the authors purport
that poor intragastric gelation of the fibres may explain the lack of a treatment effect.
Similarly, acute ad libitum food intake was reportedly unaltered after a meal replacer
containing alginate (0.4% and 0.8%) compared to a meal replacer alone [103], though hunger
was significantly reduced for several hours following the treatment.
Numerous authors have reported beneficial effects of seaweed isolates on postprandial
glycaemia. 5.0 g of sodium alginate, added to food significantly attenuated the postprandial
glycaemic response in type 2 diabetics by 31% compared to the control meal [104]. Wolf et
al. (2002) incoporated 1.5 g of sodium alginate into a 100 g liquid glucose-based preload
along with an acid-soluble calcium source to produce an acid-induced viscosity complex. The
authors reported a non-significant fall in peak glycaemia and a significant reduction in
incremental change from baseline AUC in healthy, non-diabetic adults following ingestion of
the acid-induced viscosity complex compared to a soluble fibre-based control [105]. Williams
and colleagues (2004) investigated the glycaemic response to a novel induced viscosity fibre
(IVF) "crispy bar" (including 5.5 g guar gum and 1.6 g sodium alginate) compared to an
alginate free bar in healthy adults. Postprandial glycaemia was significantly reduced at 15, 30,
45, and 120 minutes. The positive iAUC was significantly reduced by 33% following the IVF
Previous work suggested that the existing positive
correlation between AUC glycaemia and body fat percentage (control condition) could be
attenuated when an ionic gelling sodium alginate preload was ingested prior to a test lunch.
This finding suggests the enhanced postprandial glycaemic response at higher body fat
percentages could be normalised in response to alginate ingestion [107].
Effects on lipid uptake are less well-reported. In subjects with ileostomies, alginate added
to a meal increased the ileal output of fatty acids [108]. Similar to the previously reported
findings for postprandial glycaemia, Paxman and colleagues suggested that the existing
positive correlation between AUC cholesterolaemia and body fat percentage was also
eliminated by ingestion of an ionic gelling sodium alginate preload [107].
6.4. Potential Negative Effects of Seaweed or Seaweed Isolate Consumption
In Japan and Korea seaweed (often added to soup) is ingested by lactating mothers who
believe it to promote an adequate supply of breast milk. Iodine, found in high concentrations
in seaweed, is transmissible from mother to infant through breast milk and this local practice
has led to documented cases of neonatal iodine toxicity and consequent hypothroidism, with
its associated negative clinical consequences [109]. Toxic blue-green algae species can grow
on edible seaweed and have been noted in the literature to be the causative factor in a number
of food poisoning occurrences [110].
Components of seaweed bind to adsorb heavy metals [111], meaning that seaweed is
particularly prone to contamination from polluted water, and its consumption is a potential
route of toxic heavy metals entering the body. However, a recent Korean study assessed that
high seaweed consumption (8.5 g/day) would result in exposure of individuals to significantly
13
less than 10% of the toxic quantities of arsenic, mercury, lead and cadmium [112]. Associated
with this is the action of alginates and other seaweed polysaccharides in binding divalent
cations. This has led to a concern over whether their inclusion in the diet could affect the
bioavailability of calcium, iron and some trace elements (reviewed in [113]). However, it
would be likely that these cations would be absorbed in the large intestine as dietary fibre
breaks down. There is no evidence that alginate inclusion in the diet drives micronutrient
deficiency in the toxicity studies previously carried out. Carrageenan intake has been linked
to breast cancer progression by in vitro studies, which have become somewhat magnified in
the safety literature [114].
SUMMARY
Seaweed is a foodstuff that has been historically consumed around the globe but is only
consumed in appreciable amounts in certain areas of the world today. Seaweed
polysaccharides have been used within the food industry in a wide number of important
applications aimed at improving the sensory properties and shelf-life of food products.
Previous research would suggest that incorporation of whole seaweeds and seaweed
polysaccharides into foods is generally acceptable to the consumer. Seaweed or seaweed-
isolate enrichment may not only benefit the nutritional value of a food product, but may also
benefit the product in terms of improving the shelf-life and in some cases actually improving
the sensorial properties.
While chemical analysis would suggest a number of nutritional benefits of seaweed
consumption, there is a need for a more evidence relating dietary intake to health. Acute
intervention studies would suggest alginate consumption could have long-term benefits to
parameters of cardiovascular health and in appetite regulation. As with whole seaweeds, there
is a need for long-term dietary intervention studies in this area. Design of intervention studies
is crucial to their success. As such, nutrition or health researchers should collaborate early on
with food technologists/food industry in order to design and develop suitably appealing
products with these ingredients.
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