Measuring Food Intake 253sheets of a 7 day weighed record used in a dietary
intake study in South Africa.
The strengths of the weighed record are that it pro-
vides the most accurate measurement of portion
sizes, as food is recorded as it is consumed, it does not
rely on memory, and it gives an indication of food
habits such as the number and times of meals and
snacks. Weighed records kept for 3 or more days and
including a weekend day are usually considered to
represent habitual intake.
Limitations are that weighed records are time-con-
suming and require a high level of motivation and
commitment from both the investigator/fi eldworkers
and respondents. Respondents may change their food
habits to simplify measuring and recording or may
not measure and record food items accurately.
Samples of respondents who keep weighed records
may not be representative of the population for three
reasons:
1 because of the high respondent burden, respon-
dents must be volunteers and thus random
sampling cannot be used
2 respondents are limited to those who are literate
and who are willing to participate
3 those who volunteer may have a specifi c interest in
food intake, e.g., being very health conscious, and
thus may not be representative of the population.
Metabolic studies carried out to determine absorp-
tion and retention of specifi c nutrients from mea-
surements of intake and excretion are a specialized
application of the weighed food intake record. In
metabolic studies all foods consumed by the respon-
dents are usually either preweighed or weighed by the
investigators at the time of consumption. The foods
consumed are usually also analyzed for the nutrient
constituents of interest or prepared from previously
analyzed ingredients.
Estimated records
This method of recording food intake is essentially
similar to weighed records except that the amounts of
food and beverages consumed are assessed by volume
rather than by weight, i.e., they are described in terms
of cups, teaspoons, or other commonly used house-
hold measures, dimensions, or units. Food photo-
graphs, models, or household utensils may be used to
assist quantifi cation. These descriptive terms have
then to be converted to weights by the investigator,
using appropriate conversion data when available, or
by obtaining the necessary information when not. For
example, the investigator can determine the volume of
the measures commonly used in a given household
and then convert these to weights by weighing food
portions of appropriate size or using information
about the density (g/ml) of different kinds of foods. A
record book for this kind of study is similar to that for
a weighed record study. In some situations a precoded
record form that lists the commonly eaten foods in
terms of typical portion sizes may be appropriate, but
an open record form is generally preferred.
Since there is no need for weighing scales to be
provided the record forms can be distributed by mail
rather than by interviewers. This is convenient if a
large number of respondents located over a large geo-
graphical area is involved. In this situation the follow-
up interview, after completion of the record, could
be conducted by telephone. In situations in which
respondents may not be familiar with measuring
foods, the investigator needs to train and provide
clear instructions to the respondents and to check
that respondents are performing measurements and
recording correctly during the record period.
The strengths and limitations of estimated records
are similar to those of the weighed record, but the
method has a lower respondent burden and thus a
higher degree of cooperation. Loss of accuracy may
occur during the conversion of household measures
to weights, especially if the investigator is not familiar
with the utensils used in the household.
Weighed records are used in countries where
kitchen scales are a common household item and
quantities in recipes are given by weight, e.g., the UK.
Estimated records are favored in countries where it is
customary for recipe books to give quantities by stan-
dard spoons and cups, e.g., the USA and Canada.
The dietary literature frequently uses the phrase “diet
record” without specifying how portions were quanti-
fi ed. In these instances, estimated records are most
likely to have been used.Recalled intake
Information on dietary intake over a specifi ed period
can also be obtained by asking individuals to recollect
the types and amounts of food they have eaten. This
approach therefore does not infl uence the type of
food actually consumed in the way that a food record
may do. However, it is open to misrepresentation of