University of Nebraska - Lincoln
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Nutrition and Health Sciences -- Faculty
Nutrition and Health Sciences, Department of
Validity and Reliability of a Quantitative Food
Frequency Questionnaire Measuring n-3 Fatty
Acid Intakes in Cardiac Patients in the Midwest: A
Validation Pilot Study
Paula K. Ritter-Gooder
University of Nebraska-Lincoln, email@example.com
Nancy M. Lewis
University of Nebraska--Lincoln, firstname.lastname@example.org
Kimberly B. Heidal
East Carolina University, email@example.com
Kent M. Eskridge
University of Nebraska - Lincoln, firstname.lastname@example.org
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Ritter-Gooder, Paula K.; Lewis, Nancy M.; Heidal, Kimberly B.; and Eskridge, Kent M., "Validity and Reliability of a Quantitative
Food Frequency Questionnaire Measuring n-3 Fatty Acid Intakes in Cardiac Patients in the Midwest: A Validation Pilot Study"
(2006).Nutrition and Health Sciences -- Faculty Publications.Paper 15.
The purpose of this pilot study was to test the validity and re-
liability of a quantitative n-3 fatty acid food frequency ques-
tionnaire (FFQ) for later use with larger groups of individuals.
A convenience sample of heart patients provided dietary data
via three 24-hour food recalls and FFQs. Participants were
women (n = 17) and men (n = 11), 43 to 77 years of age. The as-
sociation of mean daily intake of n-3 fatty acids obtained us-
ing food recalls and the FFQ was assessed by Pearson correla-
tion. The reliability of the FFQ was assessed using coefficient
α. Correlation of n-3 fatty acid intake using the food recalls
and the FFQ was r = 0.42 (P < 0.05). The coefficient α for the
test-retest of the FFQ was .83. The top two foods, walnuts and
flaxseed, contributed 58% of the n-3 fatty acid intake, and the
third food, salmon, contributed 5%. This quantitative n-3 FFQ
is a valid instrument for use in place of food recalls for esti-
mating n-3 fatty acid intakes in heart patients and is a reliable
instrument to estimate n-3 fatty acid intakes from plant, ani-
mal, and seafood sources. The FFQ should be tested in a larger
population. Registered dietitians can use this FFQ to screen for
intakes, educate patients on food sources, and measure change
in intakes after nutrition intervention.
Numerous studies have emphasized the importance of
n-3 fatty acids in reducing the risk of cardiovascular dis-
ease. α-linolenic acid (ALA) (18:3n-3) is protective against
ischemic heart disease and can favorably change vascular
inflammation and endothelial dysfunction (1, 2). Both ALA
and the longer chain eicosapentaenoic acid (EPA) (20:5n-3)
and docosahexaenoic acid (DHA) (22:6n-3) have been shown
to be protective against cardiovascular risk (1–10). n-3 fatty
acids play an important role as structural membrane lipids,
particularly in nerve tissue and the retina, and are precur-
sors to eicosanoids. The reduced overall mortality observed
in cardiovascular patients is related to a reduction in myo-
cardial infarction and sudden death. Multiple mechanisms
are improved lipoprotein profile, including inhibition of tri-
glyceride synthesis, and diminished thrombogenicity. An
increased intake of EPA and DHA results in increased cir-
culatory levels of prostaglandins E3, which are anti-inflam-
matory, reducing incidence of cardiac arrythmias by pro-
moting vasodilation and preventing clot formation.
Dietary Reference Intakes for Adequate Intakes for ALA
were released by the National Academy of Sciences’ In-
stitute of Medicine in 2002 (11). The recommended Ade-
quate Intake for ALA is 1.6 g/day for men aged 14 years
to over 70 years and 1.1 g/day for women of the same age
group to maintain optimal health in both sexes. In 2005, the
American Dietetic Association issued The Disorders of Lipid
Metabolism Evidence Based Nutrition Practice Guidelines (12).
This evidence-based practice guideline recommends the in-
clusion of n-3 fatty acids from both plant and marine di-
etary sources in a cardioprotective diet.
Dietary intake surveys in the Midwest United States in-
dicate generally low n-3 fatty acid intakes (13). This is a re-
sult of infrequent fish consumption and lack of knowledge
of other food sources. n-3 fatty acids are concentrated in
fatty fish, flaxseed, walnuts, and certain oils, such as canola
oil and walnut oil. Smaller amounts of n-3 fatty acids oc-
cur in a wide range of other plant and animal foods. Past
surveys have used dietary recalls or frequency of fish con-
sumption to estimate intakes (3, 4). Measuring only fish fre-
quency in the diet limits total assessment of n-3 fatty ac-
ids because it does not include plant and animal sources
of ALA. The purpose of this pilot study was to assess the
validity and reliability of an n-3 fatty acid food frequency
Study Design and Population
Participants were recruited from a Midwest regional
heart clinic and had participated in a previous nutrition
study (14). Patients were invited by telephone 3 months
Published in Journal of the American Dietetic Association 106:8 (August 2006), pp. 1251–1255; doi:10.1016/j.jada.2006.05.005 Copy-
right © 2006 American Dietetic Association; published by Elsevier Inc. Used by permission.
Published online July 22, 2006.
Validity and Reliability of a Quantitative Food Frequency
Questionnaire Measuring n-3 Fatty Acid Intakes in Cardiac
Patients in the Midwest: A Validation Pilot Study
Paula K. Ritter-Gooder MS, RD,
Research assistant, Department of Nutrition and Health Sciences, University of Nebraska-Lincoln
Nancy M. Lewis PhD RD, FADA
Professor, Department of Nutrition and Health Sciences, University of Nebraska-Lincoln
Kimberly B. Heidal PhD, RD
Assistant professor, Department of Nutrition, East Carolina University, Greenville, NC
Kent M. Eskridge PhD
Professor, Department of Statistics, University of Nebraska-Lincoln
Corresponding author — Paula K. Ritter-Gooder, 312 RLH, University of Nebraska-Lincoln, Lincoln, NE 68583-0806
1252 P. K. RitteR-GoodeR et al. in Journal of the american Dietetic association 106 (2006)
after the first study ended to participate in this study. All
components of the study were approved by the Institu-
tional Review Board.
Dietary Intake Methods
Two methods of dietary intake assessment were used;
three 24-hour food recalls obtained by multiple-pass
method (15), and FFQ. For the three 24-hour food recalls,
a registered dietitian made an in-home visit and collected
one of the recalls. Visual aids, such as food models, house-
hold measuring utensils, and pictures illustrating por-
tion sizes, were used. Printed aids were left with the sub-
jects to use in estimating food portion size for the 24-hour
food recalls and FFQ that were collected later. Participants
provided two additional 24-hour food recalls, including a
weekend day. The registered dietitian collected these by
telephone. Portion-size estimates were clarified and com-
pleteness of food recalls was assured by query.
The 152-item FFQ was developed from foods that pro-
vided ≥10 mg n-3 fatty acid/medium serving using Food
Processor (Version 8.1, 2003, ESHA Research, Salem, OR).
ESHA Research uses US Department of Agriculture nutri-
ent data sets as its core (16). Small, medium, and large por-
tion sizes were defined for each food item, using the US
Department of Agriculture Food Guide Pyramid portion
guidelines (17). Frequency of consumption was categorized
as none, once a month, less than once a week, one to two
times a week, three to four times a week, five to six times
a week, daily, and more than once a day. After the food re-
call, and while the registered dietitian was on site, the par-
ticipant received instructions on how to complete the first
FFQ. Additional pictures and food models were used to
illustrate portion sizes for foods on the FFQ. For the sec-
ond administration of the FFQ, participants were provided
with a self-addressed envelope and instructed to complete
and return the FFQ again in 2 weeks.
Food Processor was used to analyze the food recalls and
to obtain total estimates of mean intake of ALA, DHA, and
EPA. On the FFQ, estimated intake of total n-3 fatty acids
was calculated for each food by multiplying the amount of
n-3 fatty acids for that food by the frequency selected (as
described above) by the selected serving size: small (0.5),
medium (1.0), and large (1.5). n-3 fatty acid intakes and es-
timates of n-3 fatty acids by food group were estimated
from the FFQ by the use of Microsoft Excel 2002 software
(Microsoft Corp, Seattle, WA).
Data were analyzed using Statistical Package for the So-
cial Sciences (version 11.0, 2002, SPSS, Inc, Chicago, IL).
Means and standard deviations for daily n-3 fatty acid in-
take were calculated for the food recalls and first adminis-
tration of FFQ. Pearson correlation was used to assess the
association between mean intakes as collected by 24-hour
food recalls and first administration of FFQ. The mean dif-
ference between the first administration of the FFQ and
24-hour food recalls and the standard error of difference
were estimated and tested with paired t test. The α coeffi-
cient was used to assess the reliability of the FFQ using the
first and second administrations of FFQ in the test–retest
approach (18). The α coefficient of the FFQ measures the
fraction of total variation that is a result of between-indi-
vidual variability. A value near 1.00 means low within-per-
Twenty-eight of 35 patients contacted agreed to par-
ticipate (80% response rate). Two thirds were female, 7%
were 43 to 50 years of age, 39% were 51 to 60 years of age,
and the remaining were between 62 and 77 years of age.
More than two thirds were married, over 60% had annual
incomes ≥$35,000, and all were white. Mean daily intake
of n-3 fatty acids by three 24-hour food recalls was 1.763
±1.949 g with a range of 0.210 to 8.150 g/day. Mean daily
intake of n-3 fatty acids as assessed by first administration
of FFQ was 2.468 ±1.927 g with a range of 0.340 to 7.638 g.
The difference between first administration FFQ and three
24-hour food recalls was 0.705 g, with 0.393 standard error,
and paired sample t test indicated no significant difference
between the two assessment methods (P > 0.05). Average
time to complete the FFQ was 20 minutes. Pearson correla-
tion between the food recalls and FFQ was 0.42 (P < 0.05).
ALA contributed 84% (1.48 g/day), EPA 5% (0.08 g/day),
and DHA 11% (0.20 g/day) of the total n-3 fatty acid in-
takes from three 24-hour food recalls.
The α coefficient for the total daily n-3 fatty acid intake
was .83. The α coefficient for food groupings ranged from
.93 for grains to .57 for vegetables.
Table 1 shows the rank order of foods providing n-3
fatty acids in the diets from FFQ. Participants obtained n-3
fatty acids from a wide variety of food sources. The top 28
foods (shown in Table 1) provided 90% of the n-3 fatty acid
intake. A total of 73 of 152 foods contributed 98% of the n-3
fatty acid intake. Overall, 113 of 152 items on the FFQ were
Cardiovascular risk is negatively associated with in-
creased intake of n-3 fatty acids (1–10). In addition, n-3
fatty acids may protect against cancer (19) and play a role
in reducing inflammation in rheumatoid arthritis (20, 21).
Because of these potential health benefits and the fact that
n-3 fatty acid intakes are low in certain groups, a reliable
and efficient method to estimate intake is needed. These
heart patients had higher intakes of n-3 fatty acids by three
24-hour food recalls than previously reported. Three Mid-
western populations had intakes of 1.060 ±0.300 g/day
(low-income pregnant women) (22), 0.887 ±0.121 g/day
(physically active adults) (23), and 0.620 ±0.710 g/day (vol-
unteers with hypercholesterolemia) (24). Involvement in
the earlier nutrition study may explain the higher intakes
A quantitative FFQ would be useful to
estimate intakes from fish, animal, and
plant sources to identify individuals
who need nutrition intervention.
Validity and Reliability of a quantitatiVe n-3 fatty acid ffq 1253
in the heart patients in our study. Several studies have uti-
lized a 62-item semi-quantitative FFQ including four fish
categories to assess n-3 fatty acid intake (6, 7). However,
the majority of previous studies have assessed n-3 fatty
acid intake from fish consumption alone (8, 9). A quantita-
tive FFQ would be useful to estimate intakes from fish, an-
imal, and plant sources to identify individuals who need
The correlation between the recalls and FFQ was 0.42.
This compares favorably with the results of other valida-
tion studies. Other researchers have obtained correlation
coefficients ranging from 0.40 to 0.70 for a variety of nu-
trients and among various population groups (25–27).
Lower correlations occur for nutrients such as vitamin A
(0.41), or vitamin E (0.19) because the amounts in food vary
Results of correlations between food recalls and FFQ
in this study were similar to those reported in a previous
study on the phytoestrogens, daidzein, and genistein con-
tained in soy products. The correlations of diet recall and
FFQ were 0.49 to 0.58 for diadzein and 0.45 to 0.54 for ge-
nistein (28). These dietary components are similar to the
n-3 fatty acids in that they are concentrated in a few foods.
Because n-3 fatty acids occur in highly variable amounts
among different foods, three 24-hour food recalls may not
be enough days to reflect usual intake (25–27). A range of
54 days for males and 71 days for females is required to get
within ±10% accuracy, with a 95% confidence level for esti-
mating fat intake, and vitamin A requires 40 days of food
recalls (29). Although multiple dietary records are believed
to provide the most accurate estimate of usual intakes, the
number of records needed is large and was not feasible for
this study. We chose three 24-hour food recalls to lower re-
Food recalls result in lower estimates of n-3 fatty acid in-
takes than the FFQ because of underreporting. When food
recalls are used, consumption may be underreported by
10% to 45%, and women are at a greater risk of underre-
porting than men (30, 31). Over two thirds of our subjects
Estimates of intake using FFQs are generally higher than
when food recalls are used. For example, pregnant wom-
en’s energy and nutrient intakes were 30% to 40% higher
with the FFQ than with food recalls (31). In our study, the
FFQ estimate of total n-3 fatty acid intake was 29% higher
than food recalls.
For test–retest reliability, results were comparable to
other studies. We administered the FFQ 2 weeks apart
to lessen measuring change in diet over time and main-
tain subject interest in the study. Our α coefficient of 0.83
was higher than 0.67 for vitamin E reported by Morris
and colleagues (32) when using FFQs in Chicago Health
and Aging Project participants. Erkkola and colleagues
(33) measured 0.62 for n-3 fatty acids in the Finnish pop-
ulation using FFQs. The closer the α coefficient is to 1.00,
the greater the internal consistency of items in the instru-
ment being assessed. This demonstrates that each partici-
pant was able to estimate and give the same information on
intake from one administration of the questionnaire to the
next administration 2 weeks later. For food groupings, the
α coefficients ranged from .93 for grains to .57 for vegeta-
bles between the two administrations of the FFQ. The vari-
ation in α coefficient among food groupings might be re-
lated to how frequently the same foods within that group
are consumed. For example, grain items, such as sliced
bread and breakfast cereal are relatively constant from one
day to the next, whereas for vegetables, the type of vegeta-
ble within that grouping varied from day to day. The test–
retest coefficients for fats/oils, fish, legumes, and nuts and
seeds were all ≥.81. These foods were major contributors to
n-3 fatty acid intake.
The top two n-3 fatty acid food sources were walnuts
and flaxseeds. Collectively these two foods provided 58%
of the n-3 fatty acids in the form of ALA (Table). The third
contributor to overall n-3 fatty acid intake was salmon,
which provided nearly 5% of the total daily intake or 0.123
g/day. In this population, beef and the n-3 egg each pro-
vided more n-3 fatty acids than tuna (1.32% and 1.16% of
intake vs 0.71%, respectively). Baked beans provided ap-
proximately the same amount of n-3 fatty acids as tuna.
Tuna was the next fish item ranked after salmon. Clearly,
Table 1. Rank order of food sources a of n-3 fatty acids in 28
male and female cardiac patients from a Midwest regional
n-3 Fatty Acid Intake
Rank Food % of Cumulative
order total %
Miracle Whip c?
a. Food frequency questionnaire.
1254 P. K. RitteR-GoodeR et al. in Journal of the american Dietetic association 106 (2006)
the heart patients were not consuming fish as their top di-
etary source of n-3 fatty acids. Without affecting reliability,
the FFQ may be improved by reducing the number of food
items it contains.
The limitations of this study are the small number of
subjects (n = 28), all of whom resided in the midwestern
United States, the small number of 24-hour food recalls
used (three recalls), and the short period between the test-
retest administration of the FFQ. Finally, the FFQ needs
to be validated in a population with a wider range of ages
and health conditions residing in different parts of the
• This FFQ can be used to estimate n-3 fatty acid intakes in
heart patients and requires additional testing before use
in research. The number of food items may be reduced
for use in future research and clinical settings.
• In these heart patients, the majority of n-3 fatty acid in-
take was provided by ALA from plant sources and a
smaller amount of long chain EPA and DHA was pro-
vided by fish. Therefore, when assessing n-3 fatty acid
intakes, registered dietitians need to use an assessment
tool that includes plant, animal, and fish sources.
• Use of the FFQ can contribute to evidence-based practice
by measuring outcomes of registered dietitian interven-
tion to increase dietary intake of n-3 fatty acids.
Acknowledgments — This article is a contribution of the Uni-
versity of Nebraska Agricultural Research Division, Lincoln,
NE 68583, Research Bulletin #14574. This research was sup-
ported in part through the Hatch Act.
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