Children's estimates of food portion size: the effect of timing of dietary interview on the accuracy of children's portion size estimates.
ABSTRACT For food intakes to be converted into nutrient intakes a measure or estimate of the amount of food consumed is required. A number of methods have been developed to assist subjects in providing an estimate of portion size. Children's ability to use perception, conceptualisation and memory skills to estimate food portion size has not been investigated systematically. The aim of the present study was to test the effect of the timing of a dietary interview on the accuracy of estimates of food portion sizes made by children, using food photographs, food models and an interactive portion size assessment system, developed for use with children and based on portion sizes of foods consumed by children. Children (n 108) aged 4-14 years were supplied with known quantities of foods and asked to estimate the portion size of each food using each of the three portion size assessment tools. Interviews took place (a) with the food in view, (b) just after the child had eaten the food or (c) 24 h after the child had eaten the food. There were no significant differences in children's ability to estimate food portion size (either as served or as eaten) with timing of interview. That is, children were as accurate in their estimates of portion size 24 h after consuming the food as when the food was in view. Under these conditions many children were able to estimate food portion size utilising perception, conceptualisation and memory skills.
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ABSTRACT: Food Photographs and standard portion sizes have been used with adults to assess portion size when recording dietary intake. The effectiveness of these methods may be reduced when memory/recall is required and children may have problems using these techniques. Adults (47) and children (37) were recruited from amongst university personnel, their children and children's friends to assess portion sizes of nine self-served amounts of selected food items using food photographs and standard descriptions of portion sizes. Portion sizes were estimated directly after self-serving and three - 4 days later. Substantial differences in the estimate of portion sizes were observed for most foods regardless of the method used or the age of the subjects, median difference range: -52-100%. For children there were greater errors using both methods than for adults. Significant differences were found between the two methods of estimating weight. The food atlas provided higher median estimated weights for the majority of the food items. There were very few differences in the estimation of portion sizes between the two testing periods. The findings would suggest that either an alternative method or a modification of the methods used here for estimating portion sizes in young subjects, for example standard food portion sizes for children of different ages such as those that are being developed by the Food Standards Agency, would be more appropriate.Journal of Human Nutrition and Dietetics 07/2003; 16(3):181-8. · 1.97 Impact Factor
- European Journal of Clinical Nutrition 04/1997; 51(3):199-200. · 2.76 Impact Factor
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ABSTRACT: The validity of the 24-hour recall, 3-day food record, and 5-day food frequency was assessed to decide on a dietary assessment method for the National Heart, Lung, and Blood Institute (NHLBI) Growth and Health Study. All subjects were assigned to one of three dietary assessment methods. Unobtrusive observers recorded types and amounts of foods eaten during lunch, and these were compared with the foods reported by the girls in the study. School lunchrooms in California and Ohio. 58 girls, aged 9 and 10 years. Reporting errors for dietary assessment methods. Descriptive statistics, matched pair t tests, and Spearman correlation coefficients. Comparison of the intakes of energy and selected macronutrients showed different ranges of, and median percentage absolute errors for, each dietary assessment method. Percentage absolute errors ranged between 20 and 33 for the 5-day food frequency method; 19 and 39 for the 24-hour recall; and 12 and 22 for the 3-day food record. The proportion of missing foods (ie, observed food items not reported) and phantom foods (ie, reported food items not observed) by each method were 46% and 40%, respectively, for the 5-day food frequency; 30% and 33%, respectively, for the 24-hour recall; and 25% and 10%, respectively, for the 3-day food record. Errors in food reporting and quantification can vary with the type of dietary methodology. Agreement between observed and reported intakes from 3-day food records made it the best overall choice. On this basis, it was selected as the method of assessment for the NHLBI Growth and Health Study.Journal of the American Dietetic Association 07/1994; 94(6):626-30. · 3.80 Impact Factor
Children’s estimates of food portion size: the effect of timing of dietary
interview on the accuracy of children’s portion size estimates
E. Foster1*, M. O’Keeffe2, J. N. S. Matthews2, J. C. Mathers1, M. Nelson3, K. L. Barton4, W. L. Wrieden4
and A. J. Adamson1
1Human Nutrition Research Centre, School of Clinical Medical Sciences, University of Newcastle, Room M1151, 1st Floor, William
Leech Building, Framlington Place, Newcastle upon Tyne, NE2 4HH, UK
2School of Mathematics and Statistics, Newcastle University, Newcastle upon Tyne, UK
3Department of Nutrition and Dietetics, Kings College London, London, UK
4Centre for Public Health Nutrition Research, University of Dundee, Dundee, UK
(Received 10 August 2006 – Revised 25 April 2007 – Accepted 30 April 2007)
For food intakes to be converted into nutrient intakes a measure or estimate of the amount of food consumed is required. A number of methods
have been developed to assist subjects in providing an estimate of portion size. Children’s ability to use perception, conceptualisation and memory
skills to estimate food portion size has not been investigated systematically. The aim of the present study was to test the effect of the timing of a
dietary interview on the accuracy of estimates of food portion sizes made by children, using food photographs, food models and an interactive
portion size assessment system, developed for use with children and based on portion sizes of foods consumed by children. Children (n 108)
aged 4–14 years were supplied with known quantities of foods and asked to estimate the portion size of each food using each of the three portion
size assessment tools. Interviews took place (a) with the food in view, (b) just after the child had eaten the food or (c) 24h after the child had eaten
the food. There were no significant differences in children’s ability to estimate food portion size (either as served or as eaten) with timing of inter-
view. That is, children were as accurate in their estimates of portion size 24h after consuming the food as when the food was in view. Under these
conditions many children were able to estimate food portion size utilising perception, conceptualisation and memory skills.
Portion size estimation: Children: Interview timing
Assessing nutrient intake at the individual level requires deter-
mination of portion size for each food consumed. Weighing all
foods consumed places a large burden on the subject and often
results in under-reporting of food intake1. Alternative methods
to weighing have been developed including those that rely on
subjects’ estimates of portion size. Tools are available to assist
the subject in this estimation such as food photographs, food
replicas and food models2–4. However, the application of
these tools in improving portion size estimation by children
has not been investigated systematically5.
In addition to the problems encountered with adults complet-
ing dietary assessment studies such as motivational issues, sub-
ject recording bias and subject selection bias, when children are
the subjects literacy, writing skills, limited food recognition
skills, memory constraints and concentration span are further
In subjects where memory is a concern the time delay
between the subject consuming the food and reporting the
consumption may be critical. However, there has been little
investigation into the effect on the accuracy of estimates of
the length of time between consuming a food and estimating
portion size. Indeed there has been limited research into the
effect of time delay on the accuracy of reporting of the type
of foods consumed. Smith et al.6investigated the ability of
adults to recall food items consumed with increasing time
intervals between consuming the food and reporting the con-
sumption. The length of time between consuming and report-
ing the foods investigated were much longer than would
usually be used in a dietary recall. Subjects were asked to
record their total dietary intake for either 2 or 4 weeks. The
subjects were then invited to return either at the end of the
recordingperiod or 2, 4 or 6 weeks after the end of therecording
period and were asked to recall all items consumed during
the recording period without the aid of the record. Not surpris-
ingly the authors reported a decrease in the number of positive
matches and an increase in the number of foods reported but
not recorded with increased time interval. Armstrong et al.7
asked adult subjects to keep a record of all food and drinks
consumed during a 24h period and to return after 1, 2, 4 or
8d to report orally the foods consumed during the recording
period. The time intervals tested by Armstrong et al.7are
more likely in dietary interviews than the periods of several
weeks tested by Smith et al.6. Again there was a decrease
in the accuracy of reporting with an increased time interval.
*Corresponding author: Dr Emma Foster, fax þ44 191 2225581, email Emma.Foster@ncl.ac.uk
Abbreviations: FIF, food in front; IPSAS, interactive portion size assessment system; JAE, just after eating.
British Journal of Nutrition (2008), 99, 185–190
q The Authors 2008
British Journal of Nutrition
Subjects correctly reported 92% of foods consumed 1d after
recording but this dropped with increasing time interval to
86% after 2d, 81% after 4d and 78% after 8d. Both omis-
sions and intrusions (foods reported as consumed which did
not appear on the record of intake) increased steadily as the
time interval between consuming and recalling the food
increased. Even 1d after recording, 75% of subjects omitted
at least one food from the recall and 23% of subjects reported
foods which were not recorded on the record of intake. This
level of error for adults reporting intake soon after consump-
tion suggests a short time interval would be essential to
obtain accurate reports of intake from children. Note, how-
ever, that this is not true validation since it relies on subjects’
initial records of the foods consumed and it is possible that
some of the intrusions were valid reports of foods which
were consumed but which the subject omitted to report in
the original record of intake. Furthermore, the accuracy of
reports in a ‘real-life’ recall of intake is likely to be lower
as the act of recording the intake may enhance the subsequent
recall of the foods consumed.
If food items can be forgotten in such a short period of time,
it is likely that retention of information on the portion sizes
consumed will be even poorer. A study which validated
9–10-year-old children’s estimates of food portion size
against observer assessment found estimates made during a
24h recall were more accurate than estimates made during a
the previous 3d8. The authors suggest this difference was due
to the short time interval between consuming and reporting
the food. Frobisher & Maxwell9examined the ability of
adults and children to estimate the portion sizes of foods
which they had served themselves either just after having
seen the food, or 3 to 4d after having seen the food. For
this study the food was not consumed. They did not find
any important differences in ability to estimate portion size
using food photographs4whether estimates were made just
after having seen the food or 3 to 4d later. As subjects esti-
mated the amount of food just after seeing it and were then
recalled 3 to 4d later to provide a portion size estimate for
that same food the authors noted that the subject may have
just been recalling their previous response rather than concep-
tualising the actual portion of food9.
The use of portion size assessment tools when used during a
24h recall interview or food diary interview relies on three
cognitive processes: perception,
memory. Perception (as related to portion size assessment)
can be defined as the ability to relate an amount of food
that is present in reality to an amount depicted in a portion
size assessment tool. Conceptualisation is a subject’s ability
to make a mental construct of an amount of food which is
not present in reality.
The aim of the present study was to assess the effect of timing
on perception, conceptualisation and memory on the ability of
children to estimate food portion size using three portion size
Ethical approval for the study was granted by the Newcastle
and North Tyneside Health Authority. Two primary schools
and one secondary school were recruited to take part in the
study. A recruitment letter detailing what the study involved
was sent to the parents of all children attending each school
and parental consent was sought for participation in the study.
Three portion size assessment tools were developed. These
were food photographs, food models and an interactive portion
size assessment software (IPSAS) package. All three tools
were developed for use with children and based on portion
sizes consumed by children. Full details of tool development
are given elsewhere10. Children were asked to quantify
foods using each of the portion size assessment tools.
The effect of perception, conceptualistion and memory on
children’s ability to estimate portion sizes using the three
tools was assessed using three interview types:
(1) ‘Food in front’ (FIF) interview. Children’s perception of
food portion size was tested by the FIF interview. For
this interview plates of food of known weights were pre-
pared and the children were asked to estimate the amount
of food in front of them using one of the three portion
size assessment tools.
(2) ‘Just after eating’ (JAE) interview. Children’s perception
and conceptualisation of food portion size was tested by
the JAE interview. For this interview children were
asked to eat foods of known weights and any leftovers
were weighed. Within 30min of consuming the food
the children were asked to estimate the amount of food
that they had been served and the amount they had left.
(3) ‘24h Recall’ interview. Children’s perception, conceptu-
alisation and memory of food portion size were tested by
the 24h recall interview. For this interview children were
asked to eat foods of known weights and any leftovers
were weighed. The following day the children were inter-
viewed and asked to estimate the amount of food that
they had been served and the amount they had left.
Children aged 4–16 years were included in the study, sub-
divided into four age groups; 4–6 years, 7–10 years, 11–14
years and 15–16 years.
In order for all children in the study to complete all inter-
view types with each of the three tools each child would
need to have been fed six times and interviewed nine times.
This was not deemed as likely to be acceptable for either
the children or the participating school. A randomised incom-
plete block design was used so that each child completed only
five interviews but all combinations of interview type and
tool were equally represented over the whole study and
administered in a randomised order.
The foods selected to be included in the study were foods
commonly consumed by children. The foods were selected
using information available on the food choices of children.
The principal data source was the National Diet and Nutrition
Survey: young people aged 4 to 18 years11. Foods of a var-
iety of appearances, consistencies and textures were selected
for inclusion in the study. They were foods commonly
consumed by all of the age groups included in the study,
excluding those which are generally presented in predefined
amounts (such as individual portion packs). They included
beverages and liquid foods (milk and orange squash),
uniform solid foods of undefined portion size (cheese),
mixed-texture foods (baked beans), foods served in distinct
pieces (chips) and single-item foods (fruit).
E. Foster et al. 186
British Journal of Nutrition
Twelve foods were selected for testing to be provided to the
children as three meals:
Breakfast: cornflakes, milk and sugar;
Lunch: sausage, baked beans, chips, ketchup and orange
Snack: apple and cheese sandwich (bread, margarine and
cheese, as slices).
The portion sizes presented in the tools were based on the
weights of foods consumed by children in the National Diet
and Nutrition survey which were calculated as described by
Barton et al.12. Four versions of each tool were developed
depicting portion sizes appropriate to children aged 4–6,
7–10, 11–14 and 15–16 years. Each tool presented portion
sizes for estimation of the amount of food served and left
over (for further details, see Foster et al.10). The children
were served a mixture of small, medium and large portions
based on the 25th, 50th and 75th centile, respectively, of
weight of food served according to data from the National
Diet and Nutrition survey11.
The data were analysed in two ways:
(1) The child’s estimate of the amount of food served was
compared with the actual weight of food served with no
account of leftovers.
(2) The child’s estimate of the amount of food they ate
(child’s estimate of the weight of food served – child’s
estimate of leftovers) was compared with the actual
weight of food consumed by the child.
A multilevel model was used, fitted in MLWin (Institute of
Education, University of London, London)13. The child was
fitted as a random effect and the effects of the tools and test
types were assessed using fixed effects.
The outcome variable was successively, (1) the ratio of the
amount of food estimated by the child to have been served to
the amount actually served, and (2) the ratio of the amount
estimated to have been eaten to the amount actually eaten.
The former was computed for twelve foods and the latter
for eight since it proved impractical to measure the amounts
left for the remaining four foods which were those served as
a snack. The distribution of ratios is generally skewed and
the analysis was therefore performed on the logarithms of
the ratios (base 10) and the results presented in terms of
ratios of geometric means.
The accuracy and precision of the children’s estimates of
portion size were assessed by plotting the geometric mean
of the ratio of the child’s estimate of the amount of food
served (or consumed) against the actual weight of the food
served (or consumed). The error bars depict the mean
plus and 2 2 standard deviations and give a measure of the
precision of the estimates. Accuracy is defined as the proxi-
mity of the mean of the children’s estimates of portion size
to the actual weight of the food served. Precision is defined
as the variability of individual estimates around the mean.
The purpose of this analysis was to assess the effect of time
of interview on the accuracy of estimates. For this reason the
data are presented by interview type and by age groups for all
foods included in the study. Data for differences by type of
assessment tool (food models, food photographs and IPSAS)
are not included in the present analysis and have been reported
A total of 108 children aged 4–14 years participated in the
study. The aim was to recruit thirty-six children in each of
the four age groups (4–6 years, 7–10 years, 11–14 years
and 15–16 years). This was achieved comfortably in all but
the oldest group (Table 1). Four children who were recruited
at age 6 years became age 7 years before completing the
study. The 15–16-year-old children proved difficult to recruit;
despite increasing the incentive offered to children taking part
(from a £10 voucher to £15) and recruiting a further school to
take part, the target number of children was not achieved. No
results are presented for estimates by children aged 15–16
Tables 2 and 3 show the accuracy of children’s estimates of
portion size for FIF, JAE and 24h recall interviews using all
three tools. The ratio is the geometric mean of the ratio of
the child’s estimate of the portion size of the food to the
actual portion size, therefore the closer the value is to 1 the
more accurate the estimates. There was a large variation in
the accuracy of estimates between types of food. Apples
were the most accurately estimated food, the portion size of
baked beans and tomato ketchup tended to be underestimated
and the portion size of sugar, margarine and cheese all tended
to be overestimated.
Table 2 shows the differences in portion size estimation
(‘as served’) by interview type and age. Although for indi-
vidual foods some P values are less than 0·05, the broad
picture is that there is little evidence that interview type
affects the reported ratio. That is, there is no evidence
that children’s ability to estimate portion size is significantly
different 24h after eating from just after eating a food or
indeed when the food is in view. Of the thirty-six obser-
vations, the FIF interview gave the most accurate mean
estimate of portion size nine times, the JAE interview
nine times and the 24h interview fourteen times. On four
occasions two or more interview types resulted in mean
estimates which were of equal accuracy. However, these
Table 1. Subject recruitment and interview completion
Consenting Interviews completed
Age group (years) Recruitment target (n) Approached (n)n% Included (n) Interviews intended (n)n%
Timing of children’s portion size estimates187
British Journal of Nutrition
differences were significant on six occasions where the FIF
interview was most accurate and two occasions where the
JAE interview and two where the 24h interview were the
Table 3 shows the results for the seven foods where it was
practical to assess leftovers. As with the analysis on the por-
tion sizes of foods served there is no clear evidence of differ-
ences between the interview types. The JAE interview gave
the most accurate mean estimate of portion size ten times
and the 24h interview ten times. On one occasion the two
interview types resulted in mean estimates that were of
equal accuracy. The JAE interview was significantly more
accurate than the 24h recall interview on three occasions.
Figs 1 and 2 show that the precision of estimates increases
with age as evidenced by the narrowing of the error bars as
age increases due to a reduced variability of estimates
around the mean. Accuracy also increases with age as the
mean ratio of estimated to actual weight of the food moves
closer to 1 as age increases (Figs 1 and 2). There is no clear
pattern for either accuracy or precision related to the timing
of the interview.
The accuracy of the different tools is described else-
where10. In brief, significant differences were found between
the accuracy of estimates using the three tools. Children of
all ages performed well using the IPSAS and food photo-
graphs. The accuracy and precision of estimates made
using the food models were poor. Estimates of the amount
of food served were more accurate than estimates of the
Dietary surveys often include an interview at some time after
the end of the recording period to clarify what foods were
consumed, attempt to uncover any omissions and to assess
the portion size of foods consumed. The present study set
out to examine the accuracy of children’s estimates of
portion size when foods were in front of them, compared
with JAE the food or 24h after eating the food. There was
no significant difference in children’s ability to estimate
food portion size (either as served or as eaten) with interview
type. That is children were as accurate in their estimates of
Table 2. Differences in portion size estimation by interview type and age (as served)
FoodAge group (years)FIF JAE 24h recallP
Tomato ketchup ketchup
FIF, food in front; JAE, just after eating.
*Ratio of the amount of food estimated by the child to have been served to the amount actually served.
E. Foster et al.188
British Journal of Nutrition
portion size 24h after consuming the food as when the food
was in front of them. Frobisher & Maxwell9also found no
significant difference between adults’ and children’s esti-
mates of portion size whether the estimate was made
just after having seen the food or 3–4d later. However, in
Frobisher & Maxwell’s study9, as both estimates were
made for the same portion of food the subjects may have
relied on their memory of their previous estimate rather
than their memory and re-conceptualisation of the size of
For the present study the children were required to attend a
number of interviews on separate days to provide estimates of
food portion sizes. They were therefore aware, after the first
test, that they would be questioned about the portion sizes
of the foods they were shown or that they consumed. This
and the novel way in which the food was presented
(participants were either asked to look at plates of foods or
provided with foods to consume in a separate room away
from their normal dining hall) is likely to have increased the
attention paid by the children to the food and therefore
improved memory. Covert observation and weighing of
foods consumed by children in their normal environment is
challenging but could give a better indication of the likely
error with increasing time delay of portion size estimation
of ‘normal’ diet.
The present study has established that, at least at a group
level, children are able to estimate food portion size
utilising perception, conceptualisation and memory skills
although ability varied both across and within each age
group. There was no evidence of any difference in mean
estimates using 24h recall when compared with FIF or
JAE interviews. An interval of 24h appears to be a short
enough interval between eating and estimating the portion
size of a food.
Further tests investigating time intervals of 1, 2, 3 and up to
7d after consumption with both adults and children, to provide
information on how long after eating the information on
portion sizes for that particular eating event are retained, are
Table 3. Differences in portion size estimation by interview type and
age (as eaten)
FoodAge group (years) JAE24h recallP
Baked beans 4–6
JAE, just after eating.
*Ratio of the amount estimated to have been eaten to the amount actually eaten.
Fig. 1. Accuracy of children’s estimates of food portion size by interview type and age (as served). FIF, food in front; JAE, just after eating. The line at 1.0
indicates where all the points would lie if estimates of portion size were completely accurate; ratios less than 1 indicate underestimation and those more than 1
indicate overestimation. Values are geometric means, with vertical bars representing ^2 standard deviations.
Timing of children’s portion size estimates189
British Journal of Nutrition
The authors gratefully acknowledge that the present research
was commissioned by the Food Standards Agency (project
number N08019). Special thanks to the Newcastle upon
Tyne schools, teachers, parents and children who participated
in the study.
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British Journal of Nutrition