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Phytic acid added to white-wheat bread inhibits fractional apparent
magnesium absorption in humans
1–3
Torsten Bohn, Lena Davidsson, Thomas Walczyk, and Richard F Hurrell
ABSTRACT
Background:Phyticacidhasbeenreportedtoimpairtheabsorption
of minerals and trace elements such as calcium, zinc, and iron in
humans. However, limited information is available on the effect of
phytic acid on magnesium absorption.
Objective:Theobjectivewas to evaluate the effect of phytic acid on
fractional apparent magnesium absorption in humans.
Design: Two stable-isotope studies were performed with 8–9
healthy adults per study. Test meals were based on 200 g phytic
acid–freewheatbread;testmealswithandwithoutadded phytic acid
were served on days 1 and 3 according to a crossover design. Phytic
acid was added in amounts similar to those naturally present in
whole-meal(1.49 mmol) and in brownbread (0.75 mmol). Each test
meal was labeled with 0.7 mmol
25
Mg or 1.1 mmol
26
Mg. The total
magnesium content was standardized to 3.6 mmol in all test meals.
Apparent magnesium absorption was based on fecal monitoring.
Results: The addition of phytic acid lowered fractional apparent
magnesium absorption from 32.5 앐6.9% (no added phytic acid) to
13.0 앐6.9% (1.49 mmol added phytic acid; P쏝0.0005) and from
32.2 앐12.0% (no added phytic acid) to 24.0 앐12.9% (0.75 mmol
addedphyticacid;P쏝0.01).Theinhibitingeffectof phytic acid was
dose dependent (P쏝0.005).
Conclusion:Theresultsshowthatfractionalmagnesiumabsorption
from white-wheat bread is significantly impaired by the addition of
phyticacid, in a dose-dependent manner, at amountssimilartothose
naturally present in whole-meal and brown bread. Am J Clin
Nutr 2004;79:418–23.
KEY WORDS Magnesium absorption, phytic acid, wheat
bread, stable isotopes, fecal monitoring
INTRODUCTION
Phytic acid, myo-inositol hexakisphosphate, is widely distrib-
uted in nature because it is the major storage form of phosphorus
in cereals, legumes, and oil seeds (1). It is typically found in the
outer (aleuron) layers of cereal grains and in the endosperm of
legumesand oil seeds. For example,cereal products such as bran
andwhole-mealbreadarerich in phytic acid (2). The daily intake
of phytic acid has been estimated to be 앒200–800 mg in indus-
trialized countries and 앒2 g in developing countries (3).
Although an inhibiting effect of phytic acid on mineral and
trace element absorption has been reported for iron, zinc, cal-
cium,and manganese (4–10), information on the effectof phytic
acid on magnesium absorption is limited. Negative magnesium
balances were reported to correlate with dietary phytic acid in-
take, on the basis of observations in 2 human subjects (11), and
magnesium absorption was shown to be significantly impaired
when phytic acid was added to white-wheat bread (12). In addi-
tion, chemical balance studies have indicated significantly in-
creased magnesium absorption after dephytinization of bran
muffins (13). However, the dose-dependent effect of phytic acid
on magnesium absorption has not been evaluated with the use of
isotopic techniques in humans.
The aim of the present study was to evaluate the effect of
phytic acid on magnesium absorption in adult humans. Test
meals were based on phytic acid free–white-wheat bread; phytic
acid was added to simulate the native content of phytic acid in
whole-meal and brown-wheat bread. Fractional apparent mag-
nesiumabsorptionwasevaluatedwitha stable-isotope technique
based on extrinsic labeling of the meals and fecal monitoring of
the excreted labels.
SUBJECTS AND METHODS
Subjects
Twenty (10 women and 10 men) apparently healthy free-
living adults were recruited. Exclusion criteria included preg-
nancy and lactation. No medication, except for oral contracep-
tives, was allowed during the study. Intake of mineral and
vitamin supplements was not permitted 2 wk before the start of
and during the study. All subjects were informed about the aims
and the procedures of the study orally and in writing, and written
informed consent was obtained from all participants. The partic-
ipants were instructed not to change their dietary habits or life-
style during the study. The study protocol was reviewed and
approvedbythe Ethical Committee at the SwissFederalInstitute
of Technology, Zurich.
Isotopic labels
Highly enriched
25
MgO (1.04 앐0.01%
24
Mg, 98.73 앐0.01%
25
Mg,and0.23앐0.01%
26
Mg)and
26
MgO(0.39앐0.01%
24
Mg,
1
FromtheLaboratoryforHumanNutrition,InstituteofFoodScienceand
Nutrition, Swiss Federal Institute of Technology, Zurich.
2
Supported by the Swiss Federal Institute of Technology (grant
41-2701.5).
3
Reprints not available. Address correspondence to L Davidsson, Labo-
ratory for Human Nutrition, Institute for Food Science and Nutrition,
Seestrasse 72, PO Box 474, 8803 Ru¨schlikon, Switzerland. E-mail:
lena.davidsson@ilw.agrl.ethz.ch.
Received May 15, 2003.
Accepted for publication August 4, 2003.
418 Am J Clin Nutr 2004;79:418–23. Printed in USA. © 2004 American Society for Clinical Nutrition
0.11 앐0.01%
25
Mg, and 99.50 앐0.01%
26
Mg) labels were
purchased from Chemotrade (Du¨sseldorf, Germany). The en-
riched
25
Mglabel(28 mmol as
25
MgO)and
26
Mglabel(43 mmol
as
26
MgO) were dissolved in 10 mL of 4 mol HCl/L and diluted
to 100 mL with water. Solid NaHCO
3
(Merck, Darmstadt, Ger-
many) was added to adjust the solution to a pH of 6. Concentra-
tions of the
25
Mg and
26
Mg isotope labels in solution were de-
termined by isotope dilution mass spectrometry against a
commercialmagnesiumstandardofnaturalisotopic composition
(Titrisol;Merck).Unlessotherwisespecified,all chemicals were
of analytic grade, and acids were further purified by surface
distillation. Only 18 M⍀water (Milli Q Water System; Milli-
pore, Zurich, Switzerland) was used for the laboratory analyses
and test meal preparation.
Test meals
All test meals were based on 200 g phytic acid–free white-
wheat bread. Bread rolls were prepared by mixing 1 kg white-
wheat flour (Migros, Zurich, Switzerland) with water (600 g),
salt (10 g), sugar (32 g), and dry yeast (15 g). The dough was left
to ferment for5hatroom temperature. The bread rolls were
baked for 15 min at 200 °C. Individual servings were weighed
andstoredfrozen(Ҁ25 °C)untilserved.Themagnesiumcontent
of all test meals was standardized by adding a solution of MgCl
2
(Merck) to the white-wheat bread before serving. Phytic acid in
its dodecasodium form (Sigma, Buchs, Switzerland) was dis-
solved in water (73.5 mmol/L), and aliquots of phytic acid and
stable-isotope labels in solution were pipetted onto the wheat
bread 1 h before administration. The rare earth elements ytter-
bium and europium (in chloride form; Aldrich, Buchs, Switzer-
land) were added to 600 mL water, which was served as a drink
with the labeled bread.
Study design
A fecal sample was collected to determine baseline magne-
sium isotope ratios before intake of the labeled test meals. Bril-
liant blue (100 mg; Warner Jenkinson Europe, King⬘s Lynn,
UnitedKingdom),adyeusedasafecalmarker,was administered
in a gelatin capsule on the day before intake of the first labeled
test meal to indicate the start of the fecal pooling. After the
subjects fasted overnight, a venous blood sample (10 mL) was
drawn into a heparin-treated glass tube (Evacuated Tube Sys-
tems, Plymouth, United Kingdom) for the measurement of
plasma magnesium concentrations. Plasma was separated by
centrifugation(Omnifuge2.0RS; Heraeus, Zurich, Switzerland)
at 20 °Cand앒500҂g(5 min) and storedin acid-washed plastic
vials at Ҁ25 °C until analyzed.
Eachsubjectactedashisorherowncontrol.Twotestmeals(A
andB)wererandomlyallocatedtobeserved in each study on day
1orday3(Table1). Test meal A consisted of 200 g wheat bread
prepared from 150 g flour, to which phytic acid and
25
Mg were
added. Test meal B (no added phytic acid) consisted of 200 g
wheat bread labeled with
26
Mg (Table 1). Because of the lower
analytic precision in the measurement of
26
Mg/
24
Mg than in that
of
25
Mg/
24
Mg, a higher dose of
26
Mg was administered. Water
(600 mL) was served as a drink. Test meals were divided into 2
identical portions and served at breakfast (0730–0830) and
lunch (1200–1300) on the same day. No food or drink was
allowedbetween the intake of the 2 labeledtest meals and for3 h
after intake of the second labeled test meal served at lunchtime
(days 1 and 3). Standardized dinners (frozen pizza and white-
wheat crisp bread) and drinking water (2 L) were provided on
days 1 and 3. No additional food or drink was allowed on days 1
and 3. Diet was unrestricted at all other times.
Preweighed polypropylene containers (Semadeni, Oster-
mundingen,Switzerland)wereprovidedforstoolcollection.The
subjectscollectedallstoolsseparately,starting immediately after
intake of the first labeled test meal on day 1. On day 8, a second
brilliant blue capsule was administered. Fecal collections were
continued until excretion of the second brilliant blue marker.
Stool samples were stored frozen (Ҁ25 °C) until processed.
Preparation of fecal pools and mineralization
Each individual stool sample was freeze-dried (Modulyo; Ed-
wards,NorthBergen,NJ)andgroundtoapowderinamortar.All
stool samples, beginning with the first fecal sample dyed by the
firstbrilliant blue marker until,but not including, thestools dyed
by the second marker, were included in the fecal pool. After
undergoing a drying step in a drying chamber (Binder, Tuttlin-
gen,Germany)at20hat65 °Ctostandardizehumidity,followed
bycoolingatroomtemperature(4h),allindividualstoolsamples
were weighed and milled (mill with 1-mm pores, ZM1; Retsch,
Haan, Germany), starting with the first (most enriched) samples.
Milled fecal material was transferred back into its original con-
TABLE 1
Total magnesium content, added stable-isotope labels, added phytic acid, and molar ratio of phytic acid to magnesium in different test meals
1
Study 1 (n҃9) Study 2 (n҃8)
Test meal A Test meal B Test meal A Test meal B
Magnesium (mmol) 3.63 앐0.04
2
3.64 앐0.05 3.63 앐0.04 3.65 앐0.03
Stable-isotope label (mmol)
25
Mg 0.65 앐0.02 —0.65 앐0.02 —
26
Mg —1.12 앐0.01 —1.12 앐0.01
Phytic acid (mmol) 1.488 앐0.022 ND 0.746 앐0.002 ND
Phytic acid:magnesium (molar ratio) 0.41 ND 0.21 ND
Fecal marker (nmol)
Ytterbium 31.38 앐0.58 —31.38 앐0.58 —
Europium —33.17 앐0.26 —33.17 앐0.26
1
Test meals A and B were based on 200 g phytic acid–free white-wheat bread and 600 mL water served as a drink. Both meals, in each study, were served
as 2 identical portions at breakfast and lunch on days 1 and 3. ND, not detectable; the limit of detection was 쏝0.5
mol/100 g.
2
x앐SD.
PHYTIC ACID INHIBITS MAGNESIUM ABSORPTION 419
tainer, dried again for 20 h at 65 °C, cooled for4hatroom
temperature,andreweighed.Allmilledstoolsamplesincludedin
a single pool were combined in a 2-L polyethylene container
(Semadeni) and mixed for 90 min with a rotator (UG 70/20;
Micro Motor, Basel, Switzerland). Aliquots of freeze-dried
pooledstoolsamples (1.0–1.6g),freeze-dried wheat bread (0.25
g), and plasma (1 g), were mineralized in a microwave digestion
system (MLS 1200; MLS GmbH, Leutkirch, Germany) in a
mixture of 14 mol HNO
3
/L and 8.8 mol H
2
O
2
/L (Merck). All
samples were mineralized in duplicate.
Separation of magnesium
Magnesiumwasseparated from the mineralized stool samples
by cation-exchange chromatography with a strongly acidic ion-
exchange resin (AG 50W X-8, 200–400 mesh; Bio-Rad, Her-
cules, CA). Aliquots containing 앒30
mol Mg were evaporated
todryness,redissolvedin1mL of 0.7 mol HCl/L, and transferred
onto the top of a column (1-cm inner diameter; Bio-Rad) filled
with the ion-exchange resin to a height of 7 cm. The column was
rinsed with 56 mL of 0.7 mol HCl/L, followed by 24 mL of 0.9
mol HCl/L to elute sodium and potassium. Magnesium was
elutedwith12mLof1.4 mol HCl/L.Thesolutionwasevaporated
todrynessandredissolvedin 50
Lwater.Magnesiumrecovery,
evaluated with a diluted magnesium standard solution (Titrisol;
Merck), was found to be 94.8 앐1.8% (n҃10). Resins were
regenerated with 30 mL of 6 mol HCl/L and replaced after the
fifth run. Only acid-washed polytetrafluoroethylene and poly-
ethylene laboratory ware were used during sample processing.
Aliquotsofthe
26
Mgisotopelabelwereprocessedin parallel with
eachbatch for blank monitoring,from ion-exchange chromatog-
raphy onward. Sample contamination due to natural magnesium
was 10.8 앐7.0 nmol (n҃9) for combined sample preparation
and filament loading, which was 쏝0.4‰of the amount of mag-
nesium separated.
Isotopic analysis by thermal ionization mass spectrometry
About 20 nmol Mg, separated from fecal samples, was loaded
onto the metal surface of the evaporation filament of a double-
rhenium filament ion source. Magnesium was coated with 5–10
g silica gel 100, 0.8
mol boric acid, and 30 nmol Al as AlCl
3
(all chemicals were from Merck). Compounds were loaded in
aqueous solution and dried electrothermally at 0.8 A after each
step.Finally,theevaporation filament was heated to dull red heat
(1.6 A) for 30 s. The ionization filament remained unloaded.
Isotope ratios were determined with a single-focusing magnetic
sectorfieldinstrument(MAT262;FinniganMAT,Bremen,Ger-
many) equipped with a Faraday cup multicollector device for
simultaneous ion-beam detection. The evaporation filament was
heated to 1230 °C according to a standardized procedure. The
ionization filament was heated gradually to 1250–1350 °C until
a stable Mg
ѿ
ion beam of 1–2҂10
Ҁ11
A was obtained. Each
measurementconsisted of 30consecutive isotope ratio measure-
ments. Repeatability (5 independent analyses) was 앐0.2% (rel-
ative SD) for the
24
Mg/
25
Mg isotope ratio and 앐0.4% for the
24
Mg/
26
Mg isotope ratio. A standard reference material (stan-
dard reference material 980; National Institute of Standards and
Technology, Gaithersburg, MD) was analyzed in parallel. The
results (0.12631 앐0.00029 for the
25
Mg/
24
Mg isotope ratio and
0.13876앐0.00059 for the
26
Mg/
24
Mgisotope ratio) agreed with
isotope ratios from the International Union of Pure and Applied
Chemistry: 0.12663 앐0.00013 and 0.13932 앐0.00026, respec-
tively (14).
Magnesium analysis by atomic absorption spectroscopy
Quantitative magnesium analysis of the mineralized and di-
lutedsamplesofplasma,bread,andfecalmaterial was performed
by flame atomic absorption spectroscopy (SpectrAA 400; Var-
ian, Mulgrave, Australia). Plasma samples were measured by
external calibration with the use of a commercial magnesium
standard (Titrisol; Merck). All other samples were measured by
aninternal calibration technique (standardaddition)to minimize
matrix effects. In addition, all measured solutions contained
La(NO
3
)
3
at 5000 mg La/L to suppress precipitation of magne-
sium salts. Certified reference materials—Seronorm Trace Ele-
ments Serum (Nycomed, Oslo) and wheat flour 1567a (National
BureauofStandards,Gaithersburg,MD)—wereanalyzedinpar-
allel. Ytterbium and europium were measured by electrothermal
atomic absorption spectroscopy by external calibration with the
use of a standard solution containing ytterbium and europium
(Titrisol; Merck). Mineralized fecal samples were diluted with 1
molHCl/L, and aliquots (10
L)were injected into pyrolytically
coated graphite tubes. Heating procedures and absorption wave-
lengths were used according to the manufacturer (15).
Phytic acid analysis
Samples of bread rolls were freeze-dried and ground in a
mortar.Phyticacid was extracted from a1-galiquotwith 0.5 mol
HCl/L. The extract was purified by anion-exchange chromatog-
raphy, evaporated to dryness, and redissolved in water before
analysis with the use of reversed-phase HPLC (16).
Calculations
Molaramounts and ratiosof the
25
Mgand
26
Mgisotope labels
in the samples were calculated on the basis of double-isotope
dilution principles (17, 18). Fractional apparent magnesium ab-
sorption was calculated on the basis of the dose (
mol) of the
stable isotope label of magnesium administered (D
o
) and the
amount of the label excreted in feces (F
o
).
AA(%) ⫽(Do⫺Fo/Do)⫻100 (1)
The recovery of the rare earth elements ytterbium and europium
was used to evaluate the completeness of the stool collections.
Statistics
Calculations were made by using commercial software:
EXCEL 97 (Microsoft, Chicago) and SPSS 10.0 (SPSS Inc,
Chicago).Results are presented as arithmetic means 앐SDs.The
normal distribution of magnesium absorption data was verified
with the use of the Kolmogorov-Smirnoff test. Homogeneity
between groups was tested by Levene’s test. Paired Student’st
test (two-tailed) was used to compare magnesium absorption
fromthe 2 different test meals within eachstudy. The dose effect
of phytic acid on magnesium absorption was evaluated with the
use of an unpaired Student’sttest based on absorption ratios
(with/without added phytic acid). In addition, a linear mixed
model was used to evaluate the dose effect of phytic acid on
magnesiumabsorption.Thismodelincludedmagnesiumabsorp-
tion as the dependent factor and meal (with or without added
phytic acid) and study (1.49 or 0.75 mmol added phytic acid) as
420 BOHN ET AL
fixed factors. Subject, as a random factor, was nested within
study. Pvalues 쏝0.05 were considered statistically significant.
RESULTS
Subjects and test meals
The ages and body mass indexes (in kg/m
2
) of the subjects
were 27 앐12 y and 22.1 앐3.8, respectively, in study 1 (n҃9)
and 24 앐2 y and 21.7 앐1.0 in study 2 (n҃8). Mean plasma
magnesium concentrations were 0.77 (range: 0.67–0.85)
mmol/L and 0.84 (range: 0.77–0.90) mmol/L in studies 1 and 2,
respectively. Two subjects had slightly lower magnesium con-
centrations (0.67 and 0.73 mmol/L) than the reported normal
range (0.75–0.96 mmol/L) (19).
Thenativecontentofphyticacidinthewheatbread was below
thedetection limit (쏝0.5
mol/100g; n҃3). The nativecontent
of magnesium in the wheat bread was 0.96 앐0.03 mmol/100 g
(n҃3). The magnesium and phytic acid contents of the labeled
test meals are presented in Table 1.
Magnesium absorption
Addition of 1.49 mmol phytic acid to 200 g phytic acid–free
bread inhibited apparent magnesium absorption significantly:
32.5앐6.9%(testmealA)comparedwith13.0앐6.9%(testmeal
B) (P쏝0.0005, Figure 1). One subject was excluded from the
evaluation because of a low recovery of ytterbium (쏝85%). The
exclusion criteria were based on the estimated relatively high
combined uncertainty of the recovery of rare earth elements in
fecal material and on previous studies that used rare earth ele-
ments as fecal markers (20, 21). For all other subjects, mean
ytterbium recovery was 99.5% (range: 86.4–107.1%) and mean
europiumrecoverywas 101.7% (range: 89.5–116.3%). Addition
of 0.75 mmol phytic acid to 200 g bread inhibited magnesium
absorption significantly: 32.2 앐12.0% (test meal A) compared
with 24.0 앐12.9% (test meal B) (P쏝0.01; Figure 2). Two
subjects were excluded from the evaluation because of low yt-
terbium recovery. For all other subjects, mean ytterbium recov-
ery was 105.4% (range: 97.5–115.6%) and europium recovery
was96.9%(range:90.2–120.6%).The inhibitory effect of phytic
acid on magnesium absorption was dose dependent (P쏝0.005,
unpaired Student’sttest). On the basis of a linear mixed model,
a statistically significant effect of meal (with or without added
phyticacid; P쏝0.001) on magnesium absorptionwas observed,
but no significant effect of study was observed (1.49 or 0.75
mmol added phytic acid). The study-by-meal interaction was
statistically significant (P쏝0.005), which indicated that mag-
nesiumabsorptionwas significantly influenced by the amountof
phytic acid added to the meal.
The mean loss of fecal material during stool pool preparation,
determined by weighing the pools before and after milling, was
1.9앐1.1%.The measured isotopic enrichment of the stoolpools
was 5.2 앐1.9% (
24
Mg/
25
Mg) and 8.4 앐2.7% (
24
Mg/
26
Mg) on
the basis of differences in the measured isotope ratios of fecal
pools and natural isotope ratios of a standard (Titrisol; Merck)
divided by the measured isotope ratio of the standard.
DISCUSSION
Mean fractional apparent magnesium absorption was 앒60%
lower when phytic acid was added to phytic acid–free white-
wheat bread at an amount similar to that in whole-meal wheat
bread (1.49 mmol/200 g) and 앒25% lower when added at an
amount similar to that in brown bread (0.75 mmol/200 g). The
inhibiting effect of phytic acid was dose dependent (P쏝0.005).
Although this is the first time that the inhibition of magnesium
absorption by phytic acid was observed with single meals, such
an effect was indicated by chemical balance studies in humans
that evaluated phytic acid added to white bread (12) and dephy-
tinized bran (13). In these earlier studies, a somewhat more lim-
ited inhibitory effect of phytic acid on fractional apparent mag-
nesium absorption was found at molar ratios of phytic acid to
magnesium that were similar to those used in the present study,
ie, absorption of 13% and 38% at molar ratios of 0.2 and 0.4,
FIGURE1.Apparentfractional magnesium absorptionfrom200gwhite-
wheat bread with 1.49 mmol added phytic acid (test meal A) compared with
that from 200 g white-wheat bread with no added phytic acid (test meal B) in
9 subjects. Individual data are represented by triangles. The mean value is
indicated by the solid, horizontal line.
FIGURE2.Apparentfractional magnesium absorptionfrom200gwhite-
wheat bread with 0.75 mmol added phytic acid (test meal A) compared with
that from 200 g white-wheat bread with no added phytic acid (test meal B) in
8 subjects. Individual data are represented by triangles. The mean value is
indicated by the solid, horizontal line.
PHYTIC ACID INHIBITS MAGNESIUM ABSORPTION 421
respectively.However,itisimportantto stressthatthemagnitude
oftheinhibitoryeffect might have been influenced by the control
diets, which were not completely free of phytic acid, or by ad-
aptation to decreased dietary magnesium bioavailability.
Aswithiron,zinc,andcalcium,itisassumedthatmagnesium–
phytic acid or protein-magnesium–phytic acid complexes are
formed in the intestine, which are insoluble at a pH 쏜6 (22–24)
and thus are not absorbable. However, the stability of the mag-
nesium–phytic acid complex is weaker than phytic acid com-
plexes with iron, copper, and zinc (25, 26). It is also important to
stress that endogenous losses of magnesium represent a signifi-
cant fraction of total magnesium losses and that phytic acid can
be expected to form complexes with both food magnesium and
endogenous magnesium in the gastrointestinal tract. However,
on the basis of rat studies, it is not certain whether the reabsorp-
tion of endogenous magnesium is inhibited by phytic acid (27,
28).
In the present study, all test meals were based on phytic acid–
free wheat bread and differed only by whether phytic acid was
added.Wechosenottodephytinizewhole-mealandbrownbread
soastoavoidpotentialdifferencesbetweentestmealsbecauseof
differences in ingredients, food-preparation methods, or both.
The phytic acid content and molar ratios of phytic acid to mag-
nesiuminthetest meals were similar to those reported forwhole-
meal and brown bread. In whole-meal bread, the phytic acid
contentisreportedtobeintherange0.7–1.6mmol/100g,andthe
molar ratio is between 0.2 and 0.5; in brown bread, the corre-
sponding values are 쏝0.1–0.4 mmol/100 g, and the molar ratio
is쏝0.1–0.3 (2). The additionof phytic acid would seem a useful
approachtosimulatenativephytic acid because phytic acid com-
plexes are largely soluble at a pH of 2–3, as in the stomach, and
mineral binding is weak (23, 24). Thus, under these conditions,
an exchange of minerals bound to phytic acid can be expected to
occur. This approach was used previously in human studies, for
example, to evaluate the effect of phytic acid on iron absorption
(29). The magnitude of the inhibitory effect of added phytic acid
on iron absorption in the study by Hallberg et al (29) was similar
to that reported for native phytic acid by Hurrell et al (30).
Our data indicate that fractional magnesium absorption from
whole-mealandbrown bread is significantly inhibited compared
withthatfromphyticacid–free white-wheat bread. However, the
absolute amounts of magnesium absorbed from whole-meal and
brown bread can be expected to be higher than those from white
bread because of the 2–3-fold higher magnesium content (31),
unless other components in whole-meal and brown bread (such
as dietary fiber, minerals, and trace elements) influence magne-
sium absorption or modify to a great extent the effect of phytic
acid on magnesium absorption.
In conclusion, the results of the present study indicate that
fractional magnesium absorption from white-wheat bread is sig-
nificantly inhibited by phytic acid, in a dose-dependent manner,
when it is added at amounts similar to those naturally present in
whole-meal and brown bread.
Allauthorscontributed tothestudydesign. TBwasresponsiblefor thedata
collectionanddataanalysis.TWwaspartlyresponsibleforthedataanalysis.
The manuscript was prepared by TB and LD and revised by TW and RFH.
None of the authors reported any conflict of interest.
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