Task:
In this assignment, you will critically review this research paper:
Armah SM, Boy E, Chen D, Candal P & Reddy MB. (2015) Regular
Consumption of a High-Phytate Diet Reduces the Inhibitory Effect of
Phytate on Nonheme-Iron Absorption in Women with Suboptimal Iron
Stores. J. Nutr (epub ahead of print)
Prepare for the assignment by reading the section in a good textbook on iron and assessment or iron status.
1. Prepare an introductory section that outlines iron uptake, assessment of iron status and the factors that need to
be considered when selecting the most appropriate method for measuring these.
2. Prepare a detailed, critical, scientific review of the paper you have selected, including comment on items such as
the research approaches adopted, methodology (as far as you are able to), any relevant ethical issues, numbers of
samples/participants etc as appropriate, the quality of the results, the significance and justification of the conclusions
that were reached and whether or not the paper appears to have provided a significant advance in the area.
You will be using your own judgment in commenting on the paper, and you may feel uncertain about evaluating some aspects,
but please be as analytical and critical about assessing the paper as you can. Note that a critical appraisal does not
necessarily mean a negative commentary – you may give a very positive critical appraisal if you think the research appears
to have been very well executed with regard to sample/participant numbers and quality of results.
You might qualify a negative comment, for example that the participant numbers were very low, with comment about the
difficulty of getting volunteers for the type of study involved. Note that all your comments, positive or negative, should
be justified with discussion and reference to other studies where appropriate. For example, it is not sufficient to just
comment ‘I do not think the research in this paper is well done’.
You need to explain in detail why you are making the comment, for example because the researchers have used very few
subjects, and do not appear to have taken due care in selection of participants etc.
3. Write a conclusion and recommendations for further research.
4. As well as the introduction, critical review and conclusion, briefly comment about topical issues associated with
the research in the paper and literature you have reviewed on iron nutrition. This might include recent news items,
general significance to the public, medical significance or other topical issues as appropriate to the area.
Tips:
1. Clearly indicate which paper you are critically evaluating.
2. Provide a reference list (particularly for the introduction section)
3. You will need to appreciate the biomarkers and factors affecting them used to assess iron status but do not become too
immersed in this area, think about the how you can assess how robust the tests are.
4. Use the allocation of the marks to guide how much you write and the depth required.
ASSIGNMENT 1 MARKING SCHEME
Introduction
Content, suitable coverage of background 30
Critical review
Content, clear explanation and justification of conclusions about the paper 40
Conclusions and recommendations for further research 20
Topical issues
Identification and discussion of appropriate topical issues 10
TOTAL 100
The Journa l of Nutrit ion
Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions
Regular Consumption of a High-Phytate Diet
Reduces the Inhibitory Effect of Phytate on
Nonheme-Iron Absorption in Women with
Suboptimal Iron Stores
1,2
S e t h M A r m ah ,
3
Erick Boy,
4
Dan Chen,
3
Pri sci l a Candal,
3
and Manju B Reddy
3
*
3
Department of Food Science and Human Nutr ition, Iowa State U ni versity, Ames, IA ; a nd
4
Har vestPlus/ In ternati ona l Food Policy
Resea rch Insti tute, Wa shington, DC
Abstract
Background: High-phytate (HP) consumption is a concern in developing countries because of the high prevalence of iron
deficiency in these countries.
Objective: We investigated whether habitual consumption of an HP diet reduces the inhibitory effect of phytate on
nonheme-iron absorption.
Methods:Thirty-two nonanemic females, 18–35 y of age, with normal body mass index but with suboptimal iron stores
(serum ferritin, #30mg/L), were matched for serum ferritin concentration and randomly assigned to HP and low-phytate
(LP) groups, in a parallel design study. Each subject consumed HP or LP foods with at least 2 of their daily meals for 8
wk,
resulting in a change in phytate intake (from 718 to 1190 mg/d in the HP group and 623 to 385 mg/d in the LP group). The
serum iron response over 4 h after a test meal containing 350 mg of phytate was measured at baseline and
postintervention. Ferritin, transferrin receptor, and hepcidin concentrations were measured at baseline and 8 wk.
Results: Twenty-eight subjects completed the study (n = 14 per group). The serum iron response to the test meal
increased in the HP group at postintervention, resulting in a 41% increase in the area under the curve (AUC; P < 0.0001).
However, no effect was observed in the LP group (21% decrease in AUC; P = 0.76). The postintervention serum iron
response was lower ( P < 0.0001) in the LP group than in the HP group after controlling for the baseline serum iron
response and hepcidin concentration, reflecting in a 64% lower AUC.
Conclusions:We found that habitual consumption of an HP diet can reduce the negative effect of phytate on nonheme-iron
absorption among young women with suboptimal iron stores. Future studies are needed to explore possible
mechanisms. This trial was registered at clinicaltrials.gov as NCT02370940. J Nutr doi: 10.3945/jn.114.209957.
Keywords: iron bioavailability, phytate, serum iron curve, hepcidin, iron status
Introduction
Numerous studies have been conducted to investigate the effects
of dietary factors on iron absorption (1–7). These dietary factors
include meat, calcium, ascorbic acid, tea/polyphenols, phytic
acid, and nonheme iron. These, along with an individual s iron
status, are well-recognized determinants of nonheme-iron
absorption based on single-meal absorption studies (8, 9).
However, studies have suggested that the effects of dietary
factors may be dampened when nonheme-iron absorption is
measured from the whole/complete diet. In one study, Cook
et al. (10) demonstrated that the effects of these dietary factors
on iron absorption are exaggerated in single-meal studies. They
reported that modifying the usual diet of subjects to include high
amounts of meat and other enhancers resulted in only a small
increase in nonheme-iron absorption from this diet, whereas an
exaggerated increase was observed in the corresponding single
meal. Similarly, an inhibitory diet, limited in meat and ascorbic
acid and generous in phytic acid, calcium, and polyphenols,
consumed over a 2-wk period resulted in a relatively lower
reduction in iron absorption compared with what was observed
in the corresponding single meal. In other studies, the effects of
meat and ascorbic acid on nonheme-iron absorption from a
complete diet were shown to be marginal, compared with the
reported enhancing effects in single meals (1, 4). This is
corroborated by other studies that have shown that regular
inclusion of enhancers or inhibitors of iron absorption in the diet
does not affect iron status (11–13).
1
Suported by the Interna tional Food Policy Research Institute/H arvestPlus.
2
Author disclosure s: SM Arm ah, E Boy, D Chen, P Candal, and MB Reddy, no
conflicts of interest.
* To whom correspondenc e should be addressed. E-mail: mbreddy@ iastate.edu.
ã 2015 America n Society for Nutrition .
Manusc ript received January 12, 2015. Initia l review completed Febr uary 20, 2015. Revision accepted May 15, 2015. 1of5
doi: 10.3945/jn.1 14.209957.
The Journal of Nutrition. First published ahead of print June 3, 2015 as doi: 10.3945/jn.114.209957.
Copyright (C) 2015 by the American Society for Nutrition
at PURDUE UNIVERSITY on June 18, 2015 jn.nutrition.org Downloaded from
The dampened effects of dietary factors in long-term studies
may be caused by the interaction of other meal components or
effects of residual components from the previous meals. Various
studies, including both human and animal studies, have inves-tigated the latter and resulted in conflicting outcomes (14–
16). In
this study (NCT02370940), we focused on the inhibitory effect
of long-term consumption of phytate on nonheme-iron absorp-tion. Unlike a previous study by Brune et al. (14), which
involved
both males and females with a wider range of ferritin concen-trations, we focused on female subjects with suboptimal iron
stores (serum ferritin concentration, # 30 mg/L), representing
developing countries where high-phytate (HP)
5
consumption is
thought to compromise iron status. We investigated whether
regular consumption of phytate dampens its negative effect on
nonheme-iron absorption, as assessed by the serum iron curve.
The serum iron curve method was validated by Conway et al.
(17) by showing a strong positive correlation with erythrocyte
incorporation of isotopic iron. We hypothesized that fractional
nonheme-iron absorption from an HP test meal will increase in
subjects consuming an HP diet and decrease or not change
among those consuming a low-phytate (LP) diet for 8 wk.
Methods
Subjects.Female subjects, 18–35 y old, were recruited for this study by
sending mass e-mails to all female students at Iowa State University in
the spring of 2013. A total of 113 students responded; however, only
97 participat e d i n the initial screening (Figure 1) . Be fore screening,
participants were required to read and sign an informed consent
document, and all procedures and potential risks and benefits were
explained to them. Potential subjects were required to go through 3
different stages of screening. At the first screening, they completed health
and medical history questionnaires and their height and weight were
measured for BMI assessment. Subjects who were eligible came back for
a ferritin eligibility assessment (#30mg/L) and then for a pregnancy test.
We determined that 14 subjects were needed in each group to determine
a change in the AUC for serum iron by one-third as statistically
significant with 80% power and at an a-level of 0.05 (17). To be included
in the study, subjects must be female, 18–35 y of age, with serum ferritin
concentrations of #30m g/L, and BMI within the normal range (18.5–
24.9 kg/m
2
). Additionally, subjects must be nonsmoking, nonlactating,
nonpregnant, and not taking any drug that interferes with iron absorption
and should not have any gastrointestinal disease/condition that can
affect absorption. Of the 97 individuals who participated in the initial
screening, 65 did not meet these criteria (Figure 1). Thus, a total of 32
subjects were enrolled in the study. Subjects who were anemic (hemo-globin, <120 g/L) were referred to their personal
physician and were
not included in the study. Subjects were instructed not to use dietary
supplements during the study period. The 32 subjects were first matched
for serum ferritin concentration and then randomly assigned to either
the HP or the LP group ( n = 16 per group). The assignment of subjects
was performed by a person who was not involved in the study, using a
computer-based random-number generator (Microsoft Excel 2010,
RAND command; M icrosoft Corp.). From each pair, the subject with
the higher random number was assigned to the HP group and the one
with the low number was assigned to the LP group.
Study protocol. After recruitments, subjects were asked to keep a 3-d
weighed dietary record (2 weekdays and a weekend) before reporting to
the Nutrition and Wellness Research Center (NWRC) at Iowa State
University for baseline absorption measurements. Iron absorption from
an HP test meal, to which 10 mg of iron as iron (II) sulfate has been
added, was measured using the serum iron curve (17). The test meal
contained 350 mg of phytate and was composed of 1 small corn tortilla
(27.2 g ), 100 g o f b la ck be ans (drained from can) , 5 0 g of cooked
white rice, 30 g of salsa, and 120 g of orange juice. Subjects were asked
to fast overnight before coming to the NWRC for the first absorption
measurement. An indwelling catheter was used by a nurse practitioner to
collect multiple venous blood samples. An initial baseline blood sample
was collected before the test meal administration. After consuming the
test meal, blood samples were collected every 30 min for 4 h. After the
first absorption measurement, subjects participated in an 8-wk dietary
intervention in which each subject consumed either HP or LP diets.
Postintervention iron absorption from the same test meal that was
administered at baseline was measured for each subject after the 8-wk
dietary modification.
All foods needed for the dietary modification were supplied to
subjects. Their first 2-wk food supply was given on the day they came for
the baseline multiple blood draw. Subjects reported to the NWRC every
2 wk to pick up food. The HP group received whole grain ready-to-eat
cereals, whole wheat pasta/spaghetti, tortillas, bagels, bread and dinner
rolls, corn tortillas, brown rice, canned black beans, edamame, and tofu
and was encouraged to consume generous amounts of nuts and other
legume products high in phytate. The LP group received similar foods
made from refined wheat and white rice, eggs, and cheese and was
instructed to avoid HP foods. The phytate concentration of the food
provided for the HP group ranged from 210 mg/100 g to 1500 mg/100 g
with a mean of 590 mg/100 g, and those for the LP group ranged from
0 mg/100 g to 420 mg/100 g with a mean of 90 mg/100 g. At weeks 4
(data not shown) and 7 of the study, the subjects were asked again to
keep 3-d dietary records. All dietary records were for 3 nonconsecutive
days (2 weekdays and a weekend). Subjects were provided with weighing
scales and were required to weigh and record all foods consumed during
these days. Dietary data were analyzed using the Nutrition Data System
for Research (University of Minnesota).
Four subjects dropped out during the study (one got an internship
and could not continue with the study, one got sick but not related to the
treatment, one did not want to follow the dietary modification and opted
to quit, and the last one had difficulty with the multiple blood draws and
decided to quit), leaving 28 who completed the study (14 in each group).
To assess compliance, subjects were required to write down daily all of
the foods they consumed from what they were provided. They were
required to incorporate the foods they were provided in at least 2 of their
daily meals. Also, at the end of the study, they were asked to provide
information on how frequently they consumed specified HP foods listed
in an FFQ. The FFQ was designed to contain a list of selected HP foods,
belonging to the following categories: nuts and their products, whole
FIGURE 1 Subject selection. HP, high phytate; LP, low phytate.
5
Ab breviations used: CRP, C-reactiv e protein; HP, high phyta te; LP, low phyta te;
NWRC; Nutrition and Wellness Resea rch Cent er.
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grain cereals and their products, and legumes and legume pr oducts.
Compliance was estimated as the pe rcentage o f d ays i n w hich they include d
the foods they were pr ov ide d in at least 2 o f their daily meals. There were no
re strict ions on the amount to be included in the me als. On the FFQ, subjects
were required t o se le ct the f requenc y of consum ption of each list ed food.
These f requencie s were tallied to estimate the number of times they
consumed e ach liste d HP food over the 8-wk period as a measure of
compliance to the study pr otoc ol. The study p rotocol was approved by the
Institutional Revie w Board at Iowa State University (no. 12-470).
Blood sample analysis. Before administering the test meal, 2 separate
fasting blood samples were collected, one for the measurement of plasma
hepcidin and the other for measurement of initial (T0) serum iron, serum
C-reactive protein (CRP), serum transferrin receptor, and serum ferritin
concentrations. Multiple blood samples collected after the test meal was
consumed were analyzed for serum iron by a certified laboratory (Quest
Diagnostics, Inc.), and results were used to construct a serum iron curve
for each subject. Blood samples were centrifuged and serum or plasma
was divided into microcentrifuge tubes and frozen until they were
analyzed. Aprotinin (Fisher Scientific) was added to the hepcidin samples
and they were frozen at 280 C. Samples for measurement of CRP,
transferrin receptor, and ferritin were stored at 220C until the end of
the study. Serum CRP, plasma hepcidin (hepcidin-25), serum ferritin, and
serum transferrin receptor were measured using ELISA. Kits for the
measurements were obtained from American Laboratory Products
Company (ALPCO Diagnostics) for CRP, Peninsula Laboratories for
hepcidin-25, and Ramco Laboratories, Inc., for ferritin and transferrin
receptor. The intra- and interassay CVs for the different assays were
6.6% and 8.9% for serum transferrin receptor, 6.9% and 11.4% for
serum CRP, 9.3% and 8.1% for plasma hepcidin, and 10.6% and 6.9%
for serum ferritin.
Statistical analysis.Data were analyzed using the GraphPad Prism 6
(GraphPad Software, Inc.) and R Statistical Software, version 3.1.2 (R
Foundation for Statistical Computing) (18). For all variables, analyses
included all 28 subjects who completed the study (14 per group). The
serum iron response to the test meal was our primary outcome. We
estimated total body iron using the equation by Cook et al. (19). Means
(95% CIs) were reported for body iron, weight, height, and BMI and
the geometric means (95% CIs) for serum ferritin, serum transferrin
receptor, nutrients intake, serum CRP, and AUC. Comparisons between
groups (baseline or postintervention measurements) were performed using
independent t tests and paired t tests were used to compare baseline and
postintervention values within each group. F tests for nonlinear regression
models with second-order polynomials, controlling for subject effects,
were used to compare the serum iron curves within groups (baseline and
final) and also to compare the postintervention serum iron curves between
the 2 groups controlling for the baseline serum iron response and plasma
hepcidin concentration. ANCOVA was used to determine the effect of
dietary intervention on iron status biomarkers using respective baseline
values as covariates after testing for homogeneity of regression slopes. The
significant level was set at 0.05.
Results
Of the 28 subjects who completed the study, 22 were white, 3 were
Asian, 2 were black, and 1 was Latino. Their ages ranged from 18
to 33 y. The means (95% CIs) for height, weight, and BMI of all 28
subje cts at bas eline w er e 167 c m (164, 170), 62 kg (60, 64) , and
22. 3 kg/m
2
(21.7, 22.9), r es pect iv ely. Ta b l e 1 compares the
bas eline and pos tinte rv e nt ion dietar y int ak e s of s ubjec ts by group.
Fat int ake t ended to decr eas e in t he L P g roup ( P = 0.06). Phytate
intake incr ea s ed b y 6 6% in t he HP g roup and de cr ease d by 38% in
the LP group ( P < 0.01). This was corroborated by the compliance
re su lt s f ro m the FFQ, whic h i ndic at ed that the H P group
consumed HP foods much more frequently (a mean of 271 times
over the 8-wk period) than the LP group who rarely consumed any
HP foods (a mean of 27 t imes ove r the int er ve ntion per iod).
TABLE 1 Nutrients intake of women who consumed HP or LP diets for 8 wk
1
HP ( n = 14) LP ( n = 14) P
2
Baseline Final Baseline Final Baseline Final
Fat, g 1000 kcal
21
d
21
36 (33, 39) 36 (33, 40) 35 (32, 40) 31 (28, 36) 0.92 0.06
Protein, g 1000 kcal
21
d
2 1
36 (31, 42) 37 (33,41) 38 (34, 43) 39 (35, 42) 0.47 0.49
Vitamin C, mg/d 89 (61, 128) 76 (49, 117) 61 (35, 106) 52 (33, 83) 0.24 0.22
Calcium, mg/d 783 (638, 960) 806 (684, 949) 729 (531, 999) 840 (677, 1040) 0.68 0.75
Iron , m g/d 13.2 (10.1, 17.2) 14.1 (11.7, 17.0 ) 13.4 (11.2, 16.0) 14. 1 (12.2, 16.3) 0.92 0.99
Phyt ate, mg/d 718 (548, 941) 1190 (1030, 1380)* 623 (482, 804) 385 (324, 457)* 0.42 , 0.001
1
Values are geometric means (95% CIs). *Different from baseline, P # 0.01. HP, high phytate; LP, low phytate.
2
Values refer to comparison between HP and LP groups.
TABLE 2 Iron status, inflammatory markers, and AUC for serum iron (unadjusted) in women who
consumed HP or LP diets for 8 wk
1
HP ( n = 14) LP (n = 14) P
2
Baseline Final Baseline Final Baseline Final
Ser um ferritin, μg/L 17.4 (16.4, 18.5) 18.7 (17.5, 20.0) 20.7 (18.2, 23.4) 18.6 (16.8, 20.6) 0.41 0.97
Ser um transferrin recep tor, μg/mL 5.0 (4.6, 5.4) 4.7 (4.4, 5.1) 5.5 (4.9, 6.1) 5.5 (5.2, 5.8) 0.67 0.29
Bod y iron, mg /kg body weight 3.0 (2.0, 4.1) 3.5 (2.3, 4.7) 3.3 (1.3, 5.3) 2.9 (1.5, 4.4) 0.79 0.56
Plasma hepcidin, μg/L 1.5 (1.2, 1.9) 1.6 (1.3, 2.0) 3.6 (3.0, 4.3) 3.8 (3.4, 4.3) 0.04 0.02
Ser um CRP, m g/L 0.53 (0.43, 0.64) 0.67 (0.55, 0.82) 1.13 (0.88, 1.44) 1.46 (1.19, 1.80) 0.10 0.07
AUC for seru m iron,
3
μmol L
21
h
21
640 (556, 724) 905 (805, 1020) * 337 (288, 393) 267 (229, 312) , 0.0001 , 0.0001
1
Values are geometric means (95% CIs); means (95% CIs) for body iron. *Different from baseline,P # 0.05. CRP, C-reactive
protein; HP,
high phytate; LP, low phytate.
2
Values refer to comparison between HP and LP groups using t test.
3
P values are based on F test for nonlinear regression models of the serum iron curves.
High-phytate diet and nonheme-iron absorption 3 of 5
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Compliance, as estimated by the percentage of days in which
subjects incorporated foods provided to them in their daily meals,
w as 87% in t he L P gr oup and 96% in the HP group. Base d o n t he
results, we estimate that the HP diet provided approximately an
e xtr a 470 mg/d of phytate. N one of the nut rie nt intakes diff er ed
be twe en the 2 gr oups, at bot h bas eline and pos tinte rv e ntion,
e xce pt for post inte rvent io n phytate int ake , whi ch was 68% lower
in the LP group (P < 0 .0001) .
Serum ferritin, transferrin receptor, CRP, and body iron did
not differ between the HP and LP groups at both baseline and
postintervention ( P > 0.05). Plasma hepcidin concentration was
higher in the LP group than in the HP group by 2.1 mg/L at
baseline and 2.2mg/L at postintervention ( P < 0.05;Table 2).
Serum ferritin, serum transferrin receptor, plasma hepcidin, and
serum CRP concentrations as well as body iron did not change
within groups (P > 0.05). Figure 2 shows the serum iron curves
for the HP and LP groups at baseline and postintervention. In the
HP group, the AUC increased by 41% compared to baseline ( P <
0.0001) and in the LP group, there was no significant change
( P = 0.76). Baseline iron absorption, as assessed by the serum
iron curve, was significantly lower ( P < 0.0001) in the LP group
than in the HP group even though subjects were randomly
assigned to the groups. At postintervention, absorption was
higher in the HP group than in the LP group after controlling for
the baseline serum iron response and hepcidin concentration
( P < 0.0001), resulting in a 64% lower AUC in the LP group
( Table 3). As shown in Table 3, the dietary intervention did not
show any significant effect on any of the iron status biomarkers
( P > 0.05).
Discussion
Phytate isknown as one of the major inhibit ors of nonhem e- iron
abs orption (20). H igher inosit ol phosphate s s uch a s inosi tol
he xaphos ph at e a nd inosit ol pent aphos phate , in part icular, a r e
known to bind to ir on and m ak e i t unavailable for abs orpt io n ( 21).
H allber g et a l. (22) have r epor ted a dos e- depende nt inhibit ion of
s odium phytate on ir on absor ption fr om me al s cons ume d t oge th er
w ith radiolabele d whe at rolls . A key r eas on f or the c oncer ns about
phytate is that it i s a m aj or c omponent of staple foods in m any
de ve loping count ri e s wher e i ron defici en cy ane mia pr eval ence is
high ( 23). Inte re st ingly, s tudie s that have me as ure d nonhem e-i ron
absorption in complete diets suggested that the effect of dietary
fact ors m ay be dam pened whe n the whole die t is cons ider ed (10).
Part icularly for phytate, data are s car ce on i ts ef fe ct on nonhem e-iron absorption measured from the whole diet.
Brune et al. (14)
compared the effect of bran on iron absorption between a
veget ar ia n g r oup and a nonveget ar ia n c ontr ol gr ou p and found no
s ignific ant diff er en c e be twe en the 2 g roups . H owever, the me an
daily phytate intake among the vegetarian group was 323 mg/d,
which is well below what has been reported for many countries.
For example, median phytate intake in the United Kingdom was
es ti m ated to be 809 mg/d (24). In m os t developing c ountri es , daily
phytate int ake value s a re even highe r (25) . Mor eo ver, their s tudy
included both males and females with a wider serum ferritin
concentration range. In this study, we i nv estigated whether
habitual HP diet consumption reduces the inhibitory effect of
phytate on nonheme-iron absorption among female subjects
with serum ferritin concentrations of # 30mg/L.
Generally, daily nutrient intakes were lower than recommen-dations (26). However, this observation is not unexpected
among college female students. For example, mean daily iron
intakes at baseline for subjects in our study (13.2 and 13.4 mg)
were similar to the intakes among college female students 18–28 y
of age reported in our previous study (13).
Baseline phytate intakes were 718 and 623 mg/d for the HP
and LP groups, respectively, which are comparable with the
reported mean intake of 750 mg/d for US adults (27).
The results of this study indicate no effect of intervention on
the biomarkers of iron status (serum ferritin, serum transferrin
receptor, and body iron) because none of them changed signifi-cantly after the 8-wk dietary modification. These results
are
similar to the observation by Hunt and Roughead (15), who found
t hat 10- wk di et ar y i nt er ve nt io n w it h a high or l ow bi oavail abil it y
diet did not affect blood indices of iron status. Based on our
previous studies, we found that long-term consumption of soy
protein rich in phytate reduced ferritin concentration in postmen-opausal women with high iron status (28) but consuming
soy
foods s howed no sig nificant ef f ect in pre m enopausa l w ome n
with low iron status (13). These studies suggest that the effect of
phytate depends on baseline iron status of subjects. Hence, our
results may apply to only populations with suboptimal iron stores
and cannot be generalized to all populations. Also, because mean
hepcidin concentration was higher in the LP group than in the HP
group, and based on its inverse relation with iron absorption, it
was not surprising to see that baseline absorption was lower in the
LP group than in the HP group.
FIGURE 2 Iron bioavailability from an HP test meal in young women
who had consumed an LP or HP diet for 8 wk. Values are means 6
SEMs, n = 14. The serum iron response for curves with different letters
are significantly different (P , 0.0001) based on F test comparisons of
nonlinear regression models. HP, high phytate; LP, low phytate.
TABLE 3 Adjusted postintervention means of iron status,
inflammatory markers, and AUC for women who consumed HP or
LP diets for 8 wk
1
HP ( n = 14) LP ( n = 14) P
2
Serum ferritin, μ g/L 19.6 (15.8, 24.2) 17. 8 (14.4, 22.0) 0.52
Serum transferrin receptor, μg/mL 4.8 (3.9, 5.8) 5.4 (4.5, 6.6 ) 0.33
Body iron,
3
mg/kg body weight 3.6 (2.4, 4.8) 2.9 (1.7, 4.1 ) 0.40
Plasma hepc idin, μg/L 2.1 (1.4, 3.0) 3.0 (2.0, 4.4 ) 0.20
Serum CRP, m g/L 0.87 (0.57, 1.33) 1.1 2 (0.74, 1.72) 0.39
AUC for serum iron,
4
μmol L
21
h
21
815 (527, 1260) 296 (192, 459) , 0.0001
1
Values are postintervention geometric means (95% CIs) after adjusting for the
respective baseline values. For each variable, the P value was based on ANCOVA with
baseline values as covariates. CRP, C-reactive protein; HP, high phytate; LP, low
phytate.
2
Values are for treatment effect.
3
Values are means (95% CIs).
4
Values were adjusted for both baseline AUC and baseline hepcidin concentration.
P value is based on F test for nonlinear regression models of the serum iron curves.
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Hepcidin isknown as a key regulator of iron absorption. It
regulates iron absorption through ferroporti n, the main iron
exporter from intestinal cells and macrophages. Hepcidin binds
to ferroportin and prevents the export of iron, resulting in the
internal izati on of the ferroportin and subsequent reduction in iron
absorpti on. Thus, higher hepcidin concentration l eads to lower
iron absorpti on and vice versa (29–32). After controlling for the
baseline values for hepcidin concentration and serum i ron response,
because they di ffered between the 2 groups at baseline, the serum
iron response was signi ficantly greater i n the HP group than in the
LP group at postintervention, suggesting that the inhibitory effect
of phytate on nonheme-iron absorption is dampened with habitual
HP di et consumpti on among females with suboptimal iron stores.
The effect of di etary intervention was not explained by any o f the
measured biomarkers of iron status. Future studies with longer
intervention peri ods and multiple m idpoint measurements of iron
status biomarkers and markers of oxidative stress, i nfecti on, and
inflammation are needed to understand the mechanism, taking into
account other possibl e factors such as genetic factors that influence
iron absorption and status.
We acknowledge the l imitations of t his s tudy. F irst, assessment of
compliance to the dietary intervention was based solely on records
ke pt by su bj e c ts be ca u se it wa s no t a c on t r ol l ed f e ed in g s tu dy.
A lt ho ug h s ub je ct s in bo t h gr ou ps w er e no t r e qu i re d to c on su me
specific amounts of HP or LP foods they were provided, phytate
intake was significantly higher in the HP group during t he inter-vention, as expected. We also recognize that there could
be large
variations in the amount of provided food intake, which has a
potenti al of influ encin g the outcome of the study. T his was i mpl e -men ted in part to create a c ondition similar to
a real-life scen ario
and to accommod ate i n dividu al di fferences i n food con su mption. In
conclusion , t he results of this study suggest that regular consumption
of an HP diet may red uce the inhibitory effect of phytate on iron
absorption among women with subop timal iron stores.
Acknowledg me nts
We ackno wledge the Nutrition Co ordinating Cen ter of the Univer-sity o f Mi nneso ta for p r o vid ing u s w i t h t h e
stu dent li cen ce versio n o f
the Nutrition Data System for Research software for dietary intake
analysis because the first author was then a P hD student. SMA, EB ,
and MBR were responsible fo r the ov erall r esearch design of the
study and modified the final paper; DC was responsible for the
laboratory analysis; PC was involved throug hout the study, especially
with subject recruitment, dietary in tervention, meal preparation, and
dietary data analysis. SMA conducted the research, performed
statistical analysis, and wrote the first draft of the paper. MBR
pro vided oversight o f the study and h ad primary resp onsibility for
the final content. All authors r ead and a pproved the final manuscript.
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