Critical Reviews in Food Science and Nutrition, 45:497–510 (2005)
Copyright C ?
?Taylor and Francis Inc.
Alginate as a Source of Dietary Fiber
I. A. BROWNLEE, A. ALLEN, and J. P. PEARSON
Cell & Molecular Biosciences, University of Newcastle-upon-Tyne, NE2 4HH, UK
P. W. DETTMAR, M. E. HAVLER, and M. R. ATHERTON
Reckitt Benckiser Healthcare (UK) Ltd, Dansom Lane, Hull, HU8 7DS, UK
FMC Biopolymer a.s., Postboks 494, 3002 Drammen, Brakeroya, Norway
Alginate, an algal polysaccharide, is widely used in the food industry as a stabilizer, or as a thickening or emulsifying agent.
As an indigestible polysaccharide, alginate may also be viewed as a source of dietary fiber. Previous work has suggested that
dietary fibres may protect against the onset and continuation of a number of cardiovascular and gastrointestinal diseases.
This article aims to examine what is currently understood about the fiber-like activities of alginate, particularly its effects on
intestinal absorption and the colon, and therefore aims to gauge the potential use of alginate as a dietary supplement for the
maintenance of normal health, or the alleviation of certain cardiovascular or gastrointestinal diseases.
colonic health, colonic microflora, glycaemic response, mucus
Alginate is a polyuronic saccharide that is isolated from the
cell walls of a number of brown seaweed species around the
world, and it is produced as an extracellular matrix by certain
bacteria (Stokke et al., 2000). Alginates have a number of large-
scale industrial [e.g., as an ingredient in shoe polish and as an
important factor in the dye industry and industrial separation of
milk whey (Yamamoto et al., 1992; Jensen, 1993)] and medical
uses [such as for cell microencapsulation (Uludag et al., 2000),
for making dental impressions (Ertesvag and Valla, 1998) and
as the active ingredient in absorbent dressings (Ingram et al.,
and seaweed products in human nutrition (Jensen, 1993). While
large quantities of seaweed are eaten in South East Asia, the
inclusion of algal phycocolloids (i.e., alginate, carrageenan and
agar) as thickeners and stabilizing or emulsifying agents is the
main use in the Western world (Moe et al., 1995; Ertesvag and
Address correspondence to I. A. Brownlee, School of Molecular Bio-
sciences, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, NE2
4HH, UK. E-mail: email@example.com
Alginate is the most widely produced algal polysaccharide,
with 27,000 tons produced every year compared to 15,500 tons
per year of carrageenan and 11,000 of agar (Jensen, 1993). In
driven, and usually range between 0.5–1.5%. Propylene gly-
col alginates (PGA—used as stabilizers in low pH applications)
have a wider variety of uses than alginates, but are used at much
lower levels in these applications. Table 1 shows a number of
common uses for alginate in the food industry.
Alginates consist of 1→4 linked α-L-guluronic acid (G) and
β-D-mannuronic acid (M) pyranose residues in an unbranched
chain. These residues can combine to form G-rich (G blocks)
or MG areas (MG blocks), as well as M-rich areas (M blocks),
especially predominant in bacterial alginates. G blocks are be-
lieved to be important to alginate structure as a function of their
Ca++/H+binding capability, which allows alginates to form
gels in the presence of Ca++or H+ions. MG blocks allow
polysaccharide chain flexibility. Therefore, MG areas will re-
duce alginate solution viscosity (Smidsrod and Draget, 1996).
Alginate biochemical and biophysical properties are, therefore,
details of alginate structure are available elsewhere (Moe et al.,
Intake of dietary fiber (regarded in this article as dietary
material that escapes digestion and/or absorption before reach-
ing the colon) is generally accepted as being beneficial to both
I. A. BROWNLEE ET AL.
Common uses of alginate in food products
% of total alginate
food applicationsApplication of alginateNotes on application
Premium beer foam stabilizer
PGA useage allows better head retention, and protects against foam-negative contaminants
Use in reformation of food materials (e.g. onion rings, pimento pieces in olives). Endows food product
with thermostability and desired consistency.
PGA is acid stable and resists loss of viscosity. Has unique suspension and foaming properties. Wide
range of applications including:
• Soft drinks
• Milk drinks
• Ice cream
Provides bakery creams with freeze/thaw stability and reduced syneresis.
Improves shelf life and mositure retention in bread and cake mixes.
Allows cold solubility in instant flan preparations.
Commonly used as gelling, thickening, and stabilizing agents in jams, marmalades, and fruit sauces.
Alginate-pectin gels are heat reversible and give a higher gel strength than either individual component.
Allows correct viscosity of ice cream, while avoiding crystallisation and shrinkage. Also secures heat
shock resistance and allows homogenous melting without whey separation. Used in combination with
other stabilizers for further effects (e.g., increased thickening and slow melting with guar/ locust bean
Desserts (e.g., mousses, instant puddings, ripple syrups)
Emulsions and sauces (e.g., low-fat mayonnaise, tomato ketchup, salad dressings, low fat spreads)
Extruded foods (e.g., noodles and pasta)
Further uses of PGA18.9
Ice cream 3.8
Compiled by FMC biopolymer. All applications use alginate, unless otherwise stated. PGA = propylene glycol alginates.
cardiovascular and colonic health, although a number of epi-
demiological studies have suggested that source and type of di-
etary fiber may be more important modulators of colonic health
and disease (Bonithon-Kopp et al., 2000; Goodlad, 2001; Levi
et al., 2001; Terry et al., 2001). Dietary fibers are known to have
much more closely associated with health benefits than others.
Reduction of Intestinal Absorption Rates and
Viscous dietary fiber (classified chemically as “soluble” di-
etary fiber (Englyst et al., 1994)) intake has been previously
shown in a number of clinical studies to lower the rate of small
intestinal absorption of metabolizable nutrients, thereby reduc-
this reduces the level of insulin response necessary. As a result
of this decreased absorption rate, the likelihood of cardiovascu-
2002; Willett et al., 2002). Previous studies have also suggested
that viscous fiber intake alleviates the symptoms in sufferers
of cardiovascular disease and type II diabetes (Simpson et al.,
1981; Jenkins et al., 2002).
Reduction of Colonic Luminal Toxicity
and Heaton, 1999) and increased stool bulk and water content
(Blackwood et al., 2000; Munro, 2001). Dietary fibers have also
1998; Karakaya and Kavas, 1999). All of these physiological
transit time and increased mutagen binding) lead to a reduction
in colonic mucosal exposure to the wide range of potentially
damaging agents of bacterial, dietary, and endogenous origin
that may occur within the colon.
Alteration of Colonic Microflora
Between 1013and 1014bacteria reside in the human colon
(Roberton, 1993; Topping and Clifton, 2001). The microfloral
content of the colon will be modulated by dietary fiber type oc-
curring within the lumen. The identity of all the normal colonic
microflora is not yet established. Although attempts are cur-
rently being studied to determine the diversity within this com-
plex microbiota, classical microbiological methods, and there-
fore established views on the colonic microflora, may be some-
what inaccurate (Blaut et al., 2002). Anaerobic bacterial degra-
dation of material entering the colon leads to the production of
short-chain fatty acids (SCFA), which may be taken up and me-
tabolized by the host. Recently much work has focused on the
effects of SCFA on colonic well-being, with SCFA (especially
butyrate) often touted as potential preventative and/or curative
agents in inflammatory bowel diseases and colorectal cancer.
So far, only a handful of clinical studies have shown any
direct beneficial effects of SCFA (administered in enemas) in
colitis (Harig et al., 1989; Breuer et al., 1991; Scheppach et al.,
ALGINATE AS A SOURCE OF DIETARY FIBER
1992; Scheppach et al., 1996; Scheppach et al., 1997). Numer-
ous previous studies have shown that fermentable dietary fiber
intake is beneficial to colonic health both in animal models and
clinical trials (Kanamori et al., 2001; Videla et al., 2001; Bamba
et al., 2002; Bielecka et al., 2002; Guigoz et al., 2002; Losada
and Olleros, 2002). These health benefits are, however, not nec-
essarily due to SCFA production.
Direct Action on Colonic Mucosa
Relatively few studies have focused on the effects of dietary
tential of the colonic mucosa as a barrier will reduce the chance
of colonic infection and disease. Dietary fiber intake has been
previously demonstrated to decrease paracellular permeability
(Mariadson et al., 1999) and directly increase the number of
colonic crypts (McCullough et al., 1998) (i.e., increase colonic
surface area). Dietary fiber has also been implicated in modu-
lating the colonic mucus barrier—the first line of defence that
the colonic mucosa has to luminal aggression (Brownlee et al.,
ithelium is increased when a very high fiber diet (37%) is fed to
have since suggested that colonic mucus secretion (measured
indirectly as levels of luminal mucin/luminal and intraepithelial
mucin is not just dependent on amount, but also on the type
of dietary fiber present in the colonic lumen (Satchithanandam
et al., 1996; Barcelo et al., 2000).
Although alginate consumption is increasing in the Western
world, relatively few studies have been completed as to its po-
tential health benefits as a dietary fiber. This article aims to first
review the evidence for the efficacy of alginate as a dietary fiber
under the four subheadings given above, and then demonstrate
novel data from our laboratories for the effects of alginate on
colonic health and protection. Where possible, these physiolog-
ical effects have been compared to those of other dietary fiber
REVIEW OF ALGINATE AS A DIETARY FIBER
Reduction of Intestinal Absorption Rates and
As alginates are viscous dietary fibers, they would be ex-
work as to the fiber-type physiological effects of alginates have
focused in this area.
Effects on Digestion Rates
A number of previous studies have reported that alginates
may reduce the activity of certain digestive enzymes within the
upper GI tract. In vitro determination of protease activity un-
der physiological conditions has suggested that low concentra-
tions (<0.1%) of alginate reduce pepsin activity by up to 80%
on trypsin activity (Hart J.L., Brownlee I.A., Dettmar, P.W. and
Pearson J.P., unpublished work). These results are supported by
the effects of higher concentrations of alginate on reducing pro-
teolytic degradation of casein upon incubation in pepsin and/or
pancreatic enzyme solutions (Manchon and Desaintblanquat,
1986; El Kossori et al., 2000). In comparison to other fibers
in these in vitro studies, the inclusion of 33 mg of alginate in
a solution containing 330 mg casein reduced peptic/tryptic di-
gestion of the casein by similar levels (% inhibition as mean
unreleased casein N ± SD, 54.1 ± 1.3) as analogous quantities
(52.3 ± 4.5). Locust bean gum (47.2 ± 2.3) gave a significantly
prickly pear fruits (62.0 ± 2.5) gave significantly better protec-
tion against proteolysis than the above single fiber sources (El
Kossori et al., 2000). Increased levels of alginate (i.e., 66 mg
and 82.5 mg) added to casein solution did not lead to better
efit in reducing the heightened glycaemic index of mixed (i.e.,
in the Western world by reducing glycaemic load from amino
acids. Previous work has reported that, although powdered sea-
et al., 1997). This suggests that seaweeds may contain a specific
inhibitor of amylase that may increase a reduction in glycaemic
Effects on Blood Cholesterol Levels
A meta-analysis of 67 controlled trials suggested that pectin
had the greatest effect in lowering total cholesterol levels per
gram of 4 common viscous fiber sources (reduction in choles-
terol of 70 µM/L plasma/g fiber, compared to 37 µM/L/g oat
effects appeared to be almost entirely due to a reduction in LDL
cholesterol, rather than HDL cholesterol (Brown et al., 1999).
This style of analysis does not account for variations in the
study populations used, and currently no single study has ad-
equately compared the cholesterol-lowering effects of dietary
fiber types to each other within the same population. Also, rel-
atively few studies have considered the effects of alginates in
Alginate (7.5 g/d, M/G 1.5) supplementation of a low fiber
diet has previously been shown to more than double (140%
increase) mean fatty acid excretion in the digesta of a small
cohort (n = 6) of human ileostomy patients (Sandberg et al.,
1994). It must be noted, however, that 4 of the 6 subjects had
only a 50% or less increase in fatty acid excretion, while the
much higher fatty acid release in the other 2 patients may have
accounted for this apparently large rise.
I. A. BROWNLEE ET AL.
Animal model studies have also demonstrated that the pres-
fats and reduces plasma cholesterol under zero cholesterol (Seal
and Mathers, 1996; Seal and Mathers, 2001), low fat (Ito and
Escrig and Sanchez-Muniz, 2000). These effects are likely to be
due to the increased levels of faecal bile and cholesterol excre-
tion that have previously been reported (Kimura et al., 1996;
Seal and Mathers, 2001); they could be of benefit in reducing
blood cholesterol levels in the general population.
hypocholesteraemic effects (mean reduction in plasma choles-
terol from fiber-free controls of 8.5% and 20.5%, respectively)
to those of the algal polysaccharide funoran (7.3% and 20.9%),
but less than those of carrageenan (14.6% and 29.9%) (Ito and
Tsuchiya, 1972; Jimenez-Escrig and Sanchez-Muniz, 2000) in
rats fed 1% dietary cholesterol. All of these fiber types had a
much larger effect than agar (3% in diet gave a reduction of
only 1.8% in total plasma cholesterol). Within this study, it
was also shown that low Mralginates do not appear to have
these hypocholesteraemic effects. In rat diets with higher total
cholesterol and fat content, Na-alginate inclusion had similar
effects on total cholesterol reduction to a range of other algal
polysaccharides (sulphated glucuronoxylohamnan, porphyran,
and furonan), and it reduced blood cholesterol more than fu-
coidan and agar (Ren et al., 1994; Jimenez-Escrig and Sanchez-
Muniz, 2000). Feeding a cholesterol-free diet containing 5% or
10% Na-alginate or guar gum to rats caused a similar drop in
plasma cholesterol levels over a 21 d period (Seal and Mathers,
In contrast, Jimenez-Escrig and Sanchez-Muniz (2000) re-
ported data from two studies (Kiriyama et al., 1969; Nishide
et al., 1993), where the inclusion of alginic acid in diets had
greatly reduced or had no effects in lowering blood cholesterol
compared to Na and Ca salts of alginate.
Increased G block content will lead to an increased gel form-
ing capacity of the alginate, which would be expected to re-
uptake into the bloodstream have previously been suggested
to increase with a lower M/G (Suzuki et al., 1993b), but this
was believed to be due to the effects of the high viscosity al-
ginate on depression of appetite (i.e., lower levels of ingested
cholesterol), rather than effects on intestinal absorption and/or
increased cholesterol excretion.
Effect on Blood Glucose Levels
to test meals containing similar levels of digestible carbohy-
drates, fats, and proteins was given to a cohort of diabetes Type
II patients. This low level of dietary alginate caused a reduc-
tion in blood peak glucose and plasma insulin rise (by 31% and
(Torsdottir et al., 1991). Similar results of blunting postprandial
plasma glucose and insulin elevation have also been reported
upon feeding a low dose of alginate (1.5 g Na-alginate within
a liquid drink) to non-diabetic, healthy human subjects (Wolf
et al., 2002). Recent studies where higher doses of alginates
have been fed to rats (Kimura et al., 1996) and pigs (Vaugelade
et al., 2000 as algal non-starch polysaccharide have also shown
In comparison to other fiber types in an ileal-cannulated
dog model, an alginate-containing diet (3% alginate by weight)
reduced plasma glucose elevation more than diets of similar
composition containing either oat and soy fiber (50:50 mix,
total fiber by weight of 3%) or a diet containing higher levels
(6.8% by weight) of soy fiber (Murray et al., 1999). Within the
study of Wolf et al. (2002), the 1.5 g alginate drink reduced both
peak postprandial glucose and total glucose uptake over 3 h
(32.8 ± SE 3.4 mg/dL and 1429 ± 276 mg/dL, respectively).
This is significantly more than an analogous drink containing
1.2 g of gum arabic and 0.3 g of guar gum (40.4 ± 3.3 mg/dL
and 1717 ± 433 mg/dL, respectively) in the same population
of 30 healthy adults.
CONCLUSIONS ON INTESTINAL UPTAKE/SYSTEMIC
EFFECTS OF ALGINATE
These effects of alginates on glucose/cholesterol uptake
would suggest that the inclusion of alginate in the diet may
reduce the likelihood of the onset of diabetes Type II (especially
in high risk populations) and/or obesity, and possibly cardiovas-
cular disease, as well as reduce systemic risk factors in patients
with these diseases. Furthermore, animal studies have shown
that alginate inclusion in the diet may reduce hypertension in
a high fat, high sodium diet (Ren et al., 1994; Jimenez-Escrig
and Sanchez-Muniz, 2000). The level of reduction of plasma
glucose/cholesterol seen with alginates appears to approximate
those seen with other types of viscous algal polysaccharides in
animal models. This effect of alginate in lowering plasma glu-
cose/cholesterol has been attributed to its reduction in intestinal
absorption and its prolongation of gastric emptying (also result-
energy uptake rates can be envisaged due to the inhibitory effect
of alginate on gastrointestinal proteases.
Neither inhibition of proteolytic activity or a reduction in
number of studies carried out. Although an increased level of
et al., 1994), no data as to its effects on lowering total plasma
cholesterol are available in humans. No direct comparison be-
tween glycaemic responses in the presence of alginate or other
fiber types is possible past those made in Wolf et al., (2002) due
to the massive variety of test meals and/or diets used in this type
ALGINATE AS A SOURCE OF DIETARY FIBER
Previously, it has been suggested that alginate may be much
more palatable than similar levels of other viscous fibers due to
its unique gelation properties (Wolf et al., 2002). Unlike many
other polysaccharide gums, which give a slimy and unpleas-
ant mouth feel, alginate can be given at relatively low viscos-
ity in liquid form. Once the alginate comes into contact with
acid in the stomach, it will become a gel, leading to prolonged
gastric emptying and a considerably slower rate of intestinal
absorption than would be seen under the initial viscosity of
the ingested alginate. This factor would suggest that alginate
may be clinically more useful in reducing blood cholesterol and
further tests are necessary to evaluate alginates role in combat-
ing and/or preventing such conditions as obesity and Type II
As with other viscous fibers, the inclusion of high levels of
alginate in the diet have been linked to a reduced bioavailability
of certain beneficial dietary components, including β-carotene
(Riedl et al., 1999), and minerals, such as calcium (Bosscher
et al., 2001), iron, chromium, and cobalt (Harmuth-Hoene and
Schlenz, 1980). This reduced nutrient and mineral absorption
might suggest that the inclusion of high levels of alginate in the
diet of the elderly, pregnant women, and infants may outweigh
any potential health benefits.
Reduction of Colonic Luminal Toxicity
Bulking of Colonic Contents
Any method by which dietary constituents can reduce the
has previously been shown to increase stool wet and dry weight,
but not decrease whole gut transit time (Anderson et al., 1991).
Similar bulking of luminal products have also been reported in
pigs fed a diet containing 5% alginate (Hoebler et al., 2000),
and this effect was reported to be higher in the colon than other
seaweed dietary fibres (i.e., cellulose, xylan, or carrageenan)
of the same concentration. Stool bulking will act to effectively
Adsorption of Toxins Found within the Colon
Alginates have been reported to adsorb a range of poten-
tial food and chemical mutagens, thereby not only lowering
colonic exposure to these agents, but also to the rest of the body
(Nishiyama et al., 1991; Nishiyama et al., 1992; Maruyama and
Yamamoto, 1993; Ikegami et al., 1994; Sugiyama et al., 1999;
Aozasa et al., 2001). The data pertaining to these effects will,
therefore, be looked at more closely.
In vitro experimentation allows measurement of the levels
of specific toxins, mutagens, or carcinogens bound to fibres in
solution. In pH 7.6 aqueous buffer, 5mg/mL alginic acid ad-
sorbed dioxin isomers (toxins found in food and water) better
than a wide range of other fiber types (i.e., glucomannan, gum
karaya, lignin, chitin, cellulose, mannan, and xylan), but not as
well as others (i.e., locust bean gum and pectin) at the same
concentration (Aozasa et al., 2001). Further in vitro work has
times as much of the heterocyclic amine food mutagens Trp-P-
1 and Glu-P-1 as defatted corn fiber (Nishiyama et al., 1991).
Alginic acid showed similar adsorption characteristics for these
of alginates was brought about by binding the amine mutagens
via their carboxylic groups (Nishiyama et al., 1992). Sodium
alginate showed extremely low binding levels (<0.5%) for the
agar (Maruyama and Yamamoto, 1993).
Within animal studies, a basal chow containing 5% sodium
alginate reduced accumulation of toxic pentachlorobenzenes
(given as single bolus in food) in rats by similar levels as guar
gum and λ-carrageenan over a 7 d period (Ikegami et al., 1994).
The same level of dietary alginate reduced D-galactosamine
induced liver injury in rats, although this effect was modest
by comparison other fiber types (e.g., cellulose, glucomannan,
chitin, chitosan, and hemicellulose) (Sugiyama et al., 1999).
One of the factors believed to be important in colorec-
tal carcinogenesis is luminal bile acid content (Owen, 1997;
Ochsenkuhn et al., 1999; Debruyne et al., 2001). The increased
initially be seen as a protective factor (Kimura et al., 1996; Seal
and Mathers, 2001). However, earlier work has suggested that
the inclusion of 5% alginate in rat diet gave rise to an increased
biliary output (Ikegami et al., 1984). This would imply that,
although alginate may act to increase whole body cholesterol
to the colon.
aging to the colon than primary bile acids. Therefore, increased
binding of secondary bile acids may help prevent mucosal dam-
age occurring in the colon. Table 2 shows cited values for bile
acid binding by various dietary fibers, including alginate. Algi-
nate binds a similar level of primary bile acids (i.e., total cholate
and chenodeoxycholate binding capacity) and secondary bile
acids (i.e., deoxycholate) as other algal polysaccharides (Wang
et al., 2001), but significantly lower levels of secondary bile
acids than another polyuronate, pectin (Camire et al., 1993).
CONCLUSIONS ON REDUCTION OF COLONIC
LUMINAL TOXICITY BY ALGINATES
Alginates, much like other fiber types that are not fully fer-
mented in the colon, increase stool wet and dry weight. They
bind bile acids more strongly than cellulose, but this effect is
only modest compared to that of pectin. A number of studies
have suggested that alginates could bind up a wide range of
other damaging agents from the GI lumen, thereby lowering
colonic and systemic exposure to these moieties. These studies
I. A. BROWNLEE ET AL.
Bile acid binding properties of a range of dietary fibers
Binding of bile acid (µmol/g)
(Wang et al., 2001)
9 (Vahouny et al., 1980)∗
0(Camire et al., 1993)
LV = low viscosity, HV = high viscosity.∗These studies used bile acids conjugated to taurine rather than basic salts. All tests were carried out at approximately
neutral pH for various lengths of time (10 min for Camire et al. (1993), 1 h for Vahouny et al. (1980) and 2 h for Wang et al. (2001)).
also suggest that these effects are not exclusive to alginates, as
other fiber types have similar effects.
Although alginate has the potential to reduce the exposure
of the colonic lumen to certain damaging agents, it is unsure
whether this effect will reduce disease risk within the normal
Alteration of Colonic Microflora
Previous studies have reported the bacterial degradation of,
and short-chain fatty acid production from, alginates (Suzuki
et al., 1993a; Michel et al., 1996; Kuda et al., 1998). However,
relatively few models have considered the effects of alginate in-
clusion on the bacterial microflora, and the potential effects of
this on the host, or how alginate structure may effect its degra-
dation. This will be briefly reviewed below.
Upon incubation in human faecal microflora, alginate degra-
dation does not show signs of SCFA and gas production until
after 6 h (Michel et al., 1996). Although over 80% of alginate
was degraded in 24 h incubation with faecal inoculum, levels of
SCFA release were significantly lower than this (Michel et al.,
1996). This could suggest that alginates are increasing the num-
bers of aerobes in the inoculum, therefore reducing the levels
of measured SCFA released (due to the aerobic metabolism of
alginate/SCFA), or that SCFA are not being produced as a by-
to alter the total aerobe/anaerobe balance in faecal inoculum
(Michel et al., 1999). In other faecal inoculum studies, the fer-
mentability of faecal alginate is suggested as being much lower
than the values quoted by Michel et al., (1996), as only 50%
of alginate had disappeared after 24 h (Bobin-Dubigeon et al.,
1997). Alginates appear to have a slightly lower fermentability
in vivo in rats, as 64% of alginate is recovered in faeces upon
initial feeding with alginate. However, over continuous feed-
ing (for 4 wk), it was found that alginate fermentability had
increased, with only 39% of the alginate being recovered in the
faeces (Suzuki et al., 1993a). The faecal alginate that was re-
covered after 4 wk was much more fragmented than after the
initial feeding, with measured Mrs of 44,000 and 110,000, re-
spectively (Suzuki et al., 1993a). This, therefore, suggests that
alginate feeding over time will result in an increase in the num-
ber of bacteria in the colonic microflora that have the necessary
enzymes to cleave alginates.
Two previous studies have cited the production of various
SCFA from sodium alginate by human faecal microflora innoc-
ulates (Michel et al., 1996; Kuda et al., 1998). These are shown
below in Table 3.
degradation (Table 3). Variations in the level of production of
other SCFA are likely to be due to variations in the colonic
microflora of the faecal donors, which are known to alter SCFA
patterns (Topping and Clifton, 2001), but may also be due to
variations in the starting materials.
metabolism, very little work has been done. In comparison to
unaltered alginates, oligosaccharides produced by enzymatic or
acid hydrolysis (Mr1,000–5,000) have been shown to produce
higher volumes of gas and total SCFA concentrations upon in-
cubation in human faecal inocula (Michel et al., 1996; Michel
et al., 1999), suggesting that alginate chain length is important
in its fermentability. There is, however, no data available to sug-
gest that natural alginates of different Mrwill have different
In the experimental set-up of Michel et al. (1996), man-
nuronate was slowly fermented, suggesting that human-derived
microflora do not metabolize this sugar well. In the rat model of
smaller molecular weight fragments of alginate recovered from
faeces), the M:G ratio of recovered alginate fell. This suggests
human faecal inocula
Cited production of SCFA derived from fermentation of alginates by
Total production of SCFA in 24 h (mM)
Study Acetate Propionate Butyrate LactateOther
Michel et al. (1996)
Kuda et al. (1998)
ALGINATE AS A SOURCE OF DIETARY FIBER
that, although mannuronic acid is not initially well fermented
by the endogenous colonic microflora, the continued feeding of
alginate will lead to a microbiota that is more capable of its fer-
mentation. Caution must be taken in making this assumption,
as colonic bacteria derived from two species (man and rat) are
Further fermentation studies on alginate investigated which
human faecal bacterial strains, from a total of 435 tested,
were able to metabolize alginates. Only 3 Bacteroides strains
were found to do so. Among 21 strains of authentic human
intestinal bacteria, only Bacteroides ovatus could thrive on
tostreptococcus productus and Pseudomonas aeruginosa were
depressed (Fujii et al., 1992). This further suggests that algi-
nates can alter the colonic microflora, depending on the time
and levels of alginate exposure.
One study has been carried out as to the in vivo effects of
alginate consumption (10 g/d over a 2 wk feeding period vs.
alginate-free control diet) on human faecal bacteria. This study
suggested that faecal bifidobacteria levels increased, while the
numbers of some potentially pathogenic bacteria (i.e., Enter-
ing alginate consumption. Faecal levels of sulphide, ammonia,
and bacterially derived phenolic toxins were also significantly
reduced. Levels of acetate and propionate production had also
been significantly increased over the alginate consumption pe-
riod (Terada et al., 1995). This work once again demonstrates
that alginates may alter the microflora of the human colon, but
uniquely, this study suggests that this alteration may be benefi-
formed by putrefaction are reduced.
CONCLUSIONS ON ALGINATES’ EFFECTS ON THE
From the above evidence, it seems indubitable that alginates
have an effect on the colonic microflora, in terms of populations
Whether these effects are truly beneficial to the host, as with the
lowering levels of putrefaction by the colonic microflora. Once
the benficial and detrimental effects of the colonic microfloral
populations and their metabolites on the host are more clearly
Direct Effects on Colonic Mucosa
As alginates are hydrocolloids that escape full bacterial fer-
tent and bulk, as has been previously demonstrated (Anderson
croflora (Terada et al., 1995) by increasing bifidobacterial num-
bers and reducing bacterial toxin levels in the colonic lumen.
These factors may be extrapolated to benefits for colonic health
and colonic mucosal integrity, but the direct effects of alginate
on the colonic mucosa has rarely been tested.
Although reduction of luminal aggression is of benefit to
colonic health, a strengthening of colonic mucosal barrier func-
The primary factor in protection of the colonic mucosa is the
colonic mucus barrier that lines the entire colon. Colonic mucus
layer thickness and integrity (Pullan et al., 1994; Strugala et al.,
2001), factors vital to colonic mucus barrier function, may be
reduced in colonic disease.
A previous study, where low levels (25 µg in 1 mL saline)
of sodium alginate were directly instilled into a vascularly per-
fused rat colon for 30 min, showed that the presence of alginate
in the colon increased total colonic mucin output by approxi-
mately 140% (Barcelo et al., 2000) compared to saline (control)
solutions. Cellulose, pectin, and arabic gum did not cause a
significant increase in total colonic mucin output vs. controls.
Within the same model, Ulvan (25 µg/mL), a sulphated algal
polysaccharide, elevated mucin output (by 190%), as did the
isotonic SCFA solutions 5 mM butyrate (130%) and 100 mM
acetate (160%), or the sugars glucuronic (210%) and galactur-
onic (110%) acids (25 µg/mL).
Although this work suggests that total mucin production by
the colon is elevated by the presence of alginate, it did not di-
rectly measure the colonic mucus barrier (instead measuring
goblet cell numbers and luminal mucin content); therefore, it
was unable to give any information as to the its thickness and
protective function. We, therefore, decided to test the effects of
dietary alginate on colonic mucus barrier dynamics and to fur-
ther compare these to the effects of other dietary fibers, so that
alginate efficacy as a dietary fiber could be evaluated.
As the colonic mucus layer is altered in colonic mucosal dis-
that the colonic mucus barrier represents a “window” of colonic
health. Histological techniques will lead to underestimation of
in vivo mucus layer thickness (Strugala et al., 2003), because
tissue handling and use of dehydrating fixatives will damage the
mucus layer and only allow a snapshot of mucus integrity. It
is, therefore, necessary to study the effects of dietary fibers, or
other colonic luminal agents, using a suitable in vivo method.
dietary fibers as an additional index of colonic mucosal health.
MEASURING THE EFFECTS OF ALGINATES AND
OTHER DIETARY FIBRES ON COLONIC MUCUS
BARRIER DYNAMICS AND MUCOSAL BLOOD
All experimental procedures carried out were approved by
I. A. BROWNLEE ET AL.
Fibers types used in dietary feeding study
Diet Total fibre content1
Control (Wheat bran)
Pectin (from apple)
1Total fiber content and the ratio of soluble:insoluble fiber were determined
by a previously described chemical method (Englyst et al., 1994). n/a = not
applicable. All diets were produced by adding fiber to the same basal diet
(23.2% rice starch, 20% Ca-caseinate, 32.5% sucrose, 5% soya oil and 5% vi-
rice starch. There was no significant difference in the weight of feed eaten by
the rats within each dietary group (p > .05 by one-way ANOVA).
Animals and Diets
Groups of 10 male Wistar rats were housed in individual
cages at 24 d-old and fed one of the 6 diets shown in Table 4.
All diets, except the fiber-deficient, were produced to contain
c. 15% dietary fibre (SDS, UK). As wheat bran is the fiber
normally included in rodent diets, this diet was selected as a
positive control. To produce both alginate diets (1% and 5%),
a feed containing c.15% alginate (Mr c. 400 kDa, M:G ratio
0.45, supplied by FMC Biopolymer, Norway) was mixed with
the control (wheat bran) diet to give two diets that contained
1% and 5% alginate, but that still had a total fiber content of
around 15%. Diets were all produced from the same basal diet
5% soya oil, and 5% vitamin/mineral mix), so that there was no
variation of dietary constituents (except fiber) between groups.
The fiber-deficient diet contained extra rice starch instead of
Feeding took place over an 8-wk period. During this time,
rats were kept in a 12 h light-dark cycle at constant tempera-
ture and humidity and allowed free access to food and water.
Rodent health and food/water intake were measured throughout
this feeding period. At the end of the feeding period, rats were
fasted overnight (15 h) in order to empty the colon of luminal
contents before being anaesthetized.
Measurement of Mucus Layer Dynamics
The surgical procedure used here is described elsewhere
(Holm and Flemstrom, 1990; Sababi et al., 1995; Atuma et al.,
2001; Strugala et al., 2003). Briefly, rats were anaesthetized by
administration of 0.26 mL/g body weight Inactin (Thiobutabar-
bital sodium, Sigma, UK) intraperitoneally. Body temperature,
breathing rate, and blood pressure were monitored and con-
trolled throughout the procedure. Laparotomy was performed,
and the colon was opened by microelectrocautery c.1 cm dis-
tal to the caecum. The colon was carefully placed over a spe-
cial viewing chamber, lit from above and below. The chamber
was filled with 0.9% saline solution, and the mucosa was left
to equilibrate for 30 min. The mucosa was then observed via
trinocular microscope (Olmypus, SZ-CTV).
fluid. The carbon particles sank and demarcated the luminal
surface of the mucus barrier. Mucus thickness was measured by
a micromanipulator (Mitutoyo, Japan) from the luminal surface
of the mucus to the mucosal surface.
Measurements were made every 10 min in triplicate at con-
stant sites on the mucosa. First, the maximal mucus thickness
was assessed by measurement of the mucus layer over 60 min.
measurements continued as the mucus layer replenishment oc-
curred. If the mucus barrier reached its maximal thickness level
over 3 consecutive readings, partial removal was repeated and
replenishment rate once again assessed. Mucus thickness mea-
surements were taken over a total time (excluding equilibration
period) of 6 h.
Measurement of Mucosal Blood Content (Colonic IHB)
Throughout the mucus thickness measurement period, mu-
Camedia, C-3030) every 30 min and also after the initial partial
removal of the mucus layer by suction.
Measurement of mucosal blood content was completed by
densitometric analysis of these images, using the methods of
Ishiguro et al., (2001). Briefly, this method allows for the mea-
surement of mucosal redness caused by hemoglobin, and it ex-
presses this as a unitless index of haemoglobin, or colonic IHB
(Ishiguro et al., 2001). This measurement is dependent on the
redness:greenness ratio of the image.
Effect of Alginate on Maximal Mucus Thickness
below in Table 5 and Figure 1. Of the 6 diets tested, 1% alginate
gave the highest mean maximal mucus thickness (p < 0.01);
was approximately 25% thinner than the 1% alginate diet, but
Effect of Alginate on Mucus Layer Replenishment
The 1% alginate diet gave a significantly higher mucus re-
the wheat bran control (p < 0.0001, assessed using a, paired t-
test of the data presented in Figure 2). 5 percent alginate also
ALGINATE AS A SOURCE OF DIETARY FIBER
Effect of diet on indices of colonic health
Mean index of colonic mucosal health ± SEM
Maximal mucus Mucus replenishment
thickness (µm) rate (µm/h)Diet Colonic IHB
Control (Wheat bran)
660 ± 37b
429 ± 19e
763 ± 56a
555 ± 13c
476 ± 25d
440 ± 16e
133 ± 26b
54 ± 14e
170 ± 75a
114 ± 26c
80 ± 16d
35 ± 5f
6.80 ± 0.118c
5.84 ± 0.098a
6.04 ± 0.070b
7.09 ± 0.164c
9.23 ± 0.203d
Values in same column that share superscripts are not significantly different (p
maximal thickness for the entire dietary group (n = 10 rats) as assessed every
10 min over the first hour. Mucus replenishment rate is the mean (±SEM) total
IHB (±SEM) over the entire time course for each dietary group.
each other (see Table 5) with the order 1% alginate > control >
5% alginate > pectin > fibre-deficient > cellulose.
Effect of Alginate on Colonic IHB
The mean colonic IHB did not change over time for each
by one-way, unpaired t-test with Welch’s correction. Rats fed
on the 1% alginate diet showed a less reddened colonic mucosa
than all other dietary groups. Rats fed 5% alginate also had a
Results are displayed in Table 5.
ness. Error bars show SEM.
Effect of dietary fiber type on mean maximal colonic mucus thick-
Error bars show SEM.
Effect of dietary fiber type on colonic mucus layer replenishment.
CONCLUSIONS ON DIRECT EFFECTS OF ALGINATE
ON COLONIC MUCOSA
Inclusion of low levels (i.e., 1%) of alginate within the diet
benefit all indices of colonic mucosal health tested here. Inclu-
sion of higher levels of alginate (i.e., 5%), however, only reduce
mucosal reddening (compared to wheat bran controls), while
also appearing to reduce the benefits to the dynamics of the
colonic mucus barrier (i.e., maximal barrier thickness and mu-
cus replenishment rate) seen after feeding 1% alginate. Due to
its effects on the colonic mucus barrier, inclusion of low lev-
els of alginate (i.e., 1% or less) in the diet may be beneficial
in alleviating the histopathological symptoms seen in ulcerative
colitis (i.e., a thinner, discontinuous mucus layer). Five percent
dietary alginate, due to its reduction in mucus barrier potential
and compared to 1% alginate, may eventually cause increased
mucosal damage by luminal contents. Therefore, a low level of
alginate inclusion in the diet seems appropriate for colonic pro-
tection. It must be noted that, compared to the effects of pectin,
cellulose, or fibre-deficient diets, 5% alginate was beneficial to
colonic health and protection.
The mode of action of alginate in reducing mucosal redden-
ing is not fully understood. By reducing wound-healing time
(Del Buono et al., 2001; Dunne et al., 2002), alginates would
also be expected to reduce mucosal bleeding and/or inflamma-
and Kaeffer, 1997; Son et al., 2001; Peddie et al., 2002). This
I. A. BROWNLEE ET AL.
would be expected to reduce the likelihood of intestinal infec-
tion, resulting in reduced intramucosal damage and, therefore,
Allen, A., Dettmar, P.W., and Pearson, J.P., unpublished work)
by in vitro rheological studies. It is, therefore, likely that they
will have a similar synergism with colonic mucins. Putatively,
this could be expected to increase the rate of colonic mucus re-
moval by shear in vivo. An increased “mechanical challenge”
on the colon by dietary fiber has previously been suggested as
a factor in increasing the number of mucus producing goblet
cells in the colon (Enss et al., 1994), and a similar effect may
be brought about here. This increase in goblet cell numbers
would be expected to result in a thicker in vivo maximal mucus
layer, which was secreted faster. However, in our study, gob-
let cell numbers were not assessed, so this mode of action is
Further research in this field will focus on the effects of algi-
nate structure on its alteration of colonic mucus barrier dynam-
ics. Lower levels of alginate inclusion will be tested. It is also
fiber deficient diets, thus allowing an in vivo test of alginate’s
potential as a simple dietary fiber supplement in fibre deficient
mentable in the bowel. Similar results have been demonstrated
using this methodology for diets containing ispaghula husk as
a source of dietary fiber (Brownlee et al., 2002), and previous
work has suggested an increase in colon mucus production and
goblet cell numbers may be caused by another water soluble,
seaweed derived fiber, Ulvan (Barcelo et al., 2000).
Further Benefits of Alginates to the Gastrointestinal Tract
Outside of the effects beneficial to health previously dis-
cussed, alginate intakes has been suggested to have further
benefits to the gastrointestinal tract. The effects are discussed
Recent studies have suggested that certain alginates may en-
hance repair of mucosal damage in the GI tract in vivo and
in vitro. Male Sprague Dawley rats fed an 8 mg dose of an
M-rich alginate prior to gastric lesion by indomethacin (20 mg/
macroscopic damage seen in untreated individuals (Del Buono
et al., 2001). This level of damage reduction was similar to
rats administered 50 µg/kg of the known cytoprotective agent,
epidermal growth factor (EGF). A G-rich alginate did not re-
duce levels of gastric damage. The same M-rich alginate caused
cell migration (similar to EGF) in esophageal and gastric cell
lines, whereas the G-rich alginate did not (Dunne et al., 2002).
A modified alginate containing almost exclusively M-blocks
(>95%) did not cause cell migration within this study, sug-
gesting a necessity for both M and G-blocks to have this
Hemostatic wound dressings containing alginates as the ac-
tive component are commonly used for skin lesions. Their effi-
cacy on reducing bleeding and aiding wound healing have also
of calcium alginate leads to formation of a gel over the wound.
Exchange of calcium ions from the alginate gel with sodium
from the plasma is believed to stimulate platelet activation and
clotting at the wound site, thereby aiding hemostasis (Matthew
wound healing (Ingram et al., 1998).
In a study on oral mucosa wound healing in dogs, alginate
containing gauze significantly increased haemostasis within a 2
mm deep surgical wound (Matthew et al., 1994), although his-
tological analysis suggested no benefits to wound healing with
alginate at the time points tested (1, 4, 12, and 24 wk). Alginate
containing dressings did not cause an reduction in hemmorhage
in the rectal tissues of post-operative haemorrhoidectomy pa-
tients (Ingram et al., 1998).
The effect of alginates on wound healing of intestinal mu-
cosa has not yet been ascertained. Any mucosal protection that
alginate may provide in the stomach (Del Buono et al., 2001)
will not necessarily be mirrored by similar effects throughout
the GI tract.
Alginates have previously been shown to stimulate inter-
leukin and TNF-α production by isolated human monocytes
(Otterlei et al., 1991) in vitro. The presence of the membrane-
bound CD14 receptor on macrophages has been shown to be
necessary for this stimulatory actions of alginates, and it is the
same mechanism by which bacterial lipopolysaccharides are
sensed (Espevik et al., 1993). Intraperitoneal injection of al-
ginates caused an increased immune response in fish (Peddie
timulatory activities appear to be heightened with increased
mannuronate content of the alginate (Otterlei et al., 1993). β-
glucans have also been shown to stimulate immune responses
(Roubroeks et al., 2000; Son et al., 2001).
sized proteins was three times higher than that of non-alginate
ginate compared to larvae fed the same feed without alginate
(Conceicao et al., 2001). Pigs fed high mannuronate alginate
non-alginate-fed animals (Gaserod and Dessen, 2003). Both of
these factors would suggest that the alginate-fed animals were
generally more healthy than animals fed the same feed without
alginate. In the study outlined by Gaserod and Dessen (2003),
the oxidative burst of isolated phagocytes from the alginate-fed
ALGINATE AS A SOURCE OF DIETARY FIBER
feeding), as was the level of circulating monocytes and lym-
phocytes (after 6 wk feeding). Therefore, the alginate-fed pigs
appeared to have a greater number of immune cells that were
could become detrimental with higher levels of alginate intake.
However, this is unlikely in human nutrition terms, as alginate
is not used at high levels within food and drinks.
Recent reviews have suggested a number of dietary fibers
Schley and Field, 2002). This action is attributed to either the
alteration they cause in the colonic microflora, or the alteration
in SCFA production by the microflora. A direct effect of fiber
on immunostimulation cannot necessarily be discounted, as low
levels of fibers will be sampled by gut-associated lymphoid tis-
sues and presented to the immune system. Other fibers may also
have direct stimulatory effects on immune cells that are similar
to the effect of alginate on isolated macrophages, as reported by
Otterlei et al. (1991).
CONCLUSIONS ON FURTHER BENEFITS OF
ALGINATES TO THE GASTROINTESTINAL TRACT
studied in this area. Further studies need to be done to test the
efficacy of alginate in wound healing throughout the GI tract
and to compare the effects of alginates on GI wound healing
to other types of dietary fibers (i.e., are these effects specific to
alginates, or merely a function of large polysaccharides/viscous
polysaccharides have previously been used in topical wound
dresings (Koide, 1998; Lloyd et al., 1998); therefore, they also
have the potential to aid GI wound healing.
Evidence exists, both from in vitro and in vivo models, that
alginates with high M-content cause stimulation of the immune
system. Whether this will occur through dietary intake of algi-
nate is currently unclear.
The potential GI wound-healing and immunostimulatory ca-
pabilities of alginate have initially been studied due to non-food
uses of alginate (as an anti-reflux therapy and to encapsulate
of living cells for implantation, respectively). These properties
of other types of dietary fiber are, therefore, not as well char-
acterized as those of alginate. This makes comparison of algi-
nate to other fiber in these contexts very difficult, but also high-
lights areas that require future study in the field of dietary fiber
Evidence suggests that the intake of dietary alginates re-
sults in a number of potentially beneficial physiological ef-
fects, such as reduced intestinal absorption, increased satiety,
reduced damaging potential of GI luminal contents, modulation
of colonic microflora, and elevation of colonic barrier function.
Alginates have all these properties, whereas other fiber types
have previously been reported to have some but not all of these
effects. Similar effects have also been noted for other dietary
fibers. A direct comparison of the physiological effects of algi-
nate to those of other dietary fibers is not always possible, since
relatively few studies have considered the potential of alginate
as a dietary fiber. Further studies on the dietary fiber properties
are necessary to allow this.
Due to the gelation of alginate in the presence of acid or cal-
cium, it may, unlike other hydrocolloids, be taken in relatively
large and initially low viscosity doses without the reported poor
palatability of other viscous fibers (Murray et al., 1999; Wolf
et al., 2002). Because of this, the administered dosages of al-
ginate that can have the relevant, physiological effects on the
reduction of glycaemic response, alteration of the colonic mi-
croflora, and reduction of mucosal aggression by the luminal
contents, as well as increase colonic mucosal barrier function
and colonic health, should be possible. Furthermore, alginates
have a number of novel mechanisms of gastrointestinal protec-
tion for dietary fibers, such as mucosal wound healing and im-
munostimulation from their ingestion. These unique actions for
dietary polysaccharides may give alginates gastrointestinal and
systemic health properties not associated with any other dietary
fiber, furthering their uses as a functional food component.
A wide range of alginates, with varying structural proper-
ties that govern their physiological actions are available world-
wide. Once the effects of these structural properties on physi-
ological parameters are fully elucidated, it may be possible to
produce functional alginates for intestinal and cardiovascular
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