Measuring Food Intake 257naires, which are defi ned in Box 10.3. The type of
food frequency questionnaire used depends on the
purpose of the study, the target population, and the
required level of accuracy of food portion
estimation.
The period of recall depends on the study objec-
tives. In the past, most food frequency questionnaires
used the preceding year or 6 months as the reference
period. Theoretically, this should eliminate the effects
of season. In practice, however, respondents tend to
answer according to what is in season or available at
the time of the study. For example, intake of oranges
was found to be higher when interviews were carried
out during the citrus season than at other times of the
year. Information may be more reliable when recall
period is shorter. Recent recommendations are that
recall periods should not be longer than 1 month. If
annual intakes are required, the food frequency ques-
tionnaire must be repeated in different seasons. It is
very important that the respondent understands what
the recall period is and that only this period should
be considered when giving frequencies of intake.
The frequency of consumption is usually indicated
by options such as:
● more than once a day
● daily
● 3–4 times per week
● 1–2 times per week
● 1–2 times per month
● occasionally
● never.This type of response format requires only that the
appropriate columns be marked and is most suitable
for self-administered questionnaires. When appropri-
ately designed, such questionnaires can be optically
scanned, which saves time on data entry and checking
procedures (Figure 10.5).
Closed response options, however, treat the fre-
quency of consumption as a categorical variable and
assume that frequency of consumption is constant
throughout the recall period. The choice of categories
may bias the results: too few categories may underes-
timate frequencies whereas too many may overesti-
mate frequencies. Respondents may have diffi culty in
matching their food intake to the available categories.
For example, when food is purchased on a monthly
basis food items such as fresh fruit and vegetables may
be consumed every day while the stocks last, but, once
used up, will not be consumed until purchased in the
following month.
An alternative method for recording responses is to
provide columns headed as the number of times per
day, per week and per month, seldom, and never.
From this, the average frequency of consumption and
the amount of food consumed per day can be calcu-
lated. Table 10.3 shows an extract from such a food
frequency questionnaire. The advantage of this
response format is that it allows the respondent to
describe the frequency of consumption in detail.
Responses such as consumption of a food twice a
day for 6 days of the week can be recorded. The
disadvantages are that clear instructions must be
given, making this method more appropriate for
interviewer-administered questionnaires than self-
administered questionnaires, and the interview
takes longer and requires more writing and calcula-
tions than the closed format, making more room for
errors.
Most food frequency questionnaires obtain infor-
mation only on the frequency of consumption of a
food over a given period and not on the context in
which the foods were eaten, i.e., on meal patterns.
Meal-based food frequency questionnaires have been
used on the basis that it may be easier for respondents
to provide the information in the context of meals.Box 10.3Food frequency questionnaire (FFQ) (simple/nonquantitative):
respondents report usual consumption of foods and beverages
from a set list of items for a specifi c period. Portion sizes are not
determined.
Semiquantitative food frequency questionnaire: a FFQ which
includes estimation of portion sizes as small, medium, or large. A
reference portion (usually medium) may be provided as a guide.
Quantitative food frequency questionnaire: more precise esti-
mates of portion sizes are given by reference to portion size mea-
surement aids (PSMAs) such as food models and photographs of
known weight, household measures, or by direct weighing.
List-based food frequency questionnaire: food items are listed
according to groups or categories of similar foods or foods usually
eaten together.
Meal-based food frequency questionnaire: foods are asked
about according to meals or the time of day at which they are
consumed.
Culture-sensitive food frequency questionnaire: a FFQ that
takes account of the food values, beliefs, and behaviors of a
specifi c population or cultural group.