Introduction to Human Nutrition

Measuring Food Intake 245

same pot this may be the only practical approach
because it does not disrupt the normal pattern of food
intake. Unlike the indirect measures of food intake,
direct measures provide suffi cient information on
food consumption to convert the food intake into
energy and nutrient intakes.
Irrespective of the method used, the process of
obtaining food intake information and converting
this to energy and nutrient data is the same. The
procedure for measuring food and nutrient intake
involves fi ve steps (Figure 10.1).

1 obtaining a report of all the foods consumed by
each individual
2 identifying these foods in suffi cient detail to choose
an appropriate item in the food tables
3 quantifying the portion sizes
4 measuring or estimating the frequency with which
each food is eaten
5 calculation of nutrient intake from food tables.

To convert the information on food intake into
nutrient intake, the nutrient content of each food
eaten is calculated from food tables as:

Portion size (g) × Frequency ×

Nutrient content per g

and summed for all foods eaten by each individual

during the study period.

Direct measurement of food intake can be divided

into two basic approaches:

1 reports of foods consumed on specifi ed days: menu

records, weighed records, estimated records, and 24

hour recalls

2 reports of food intake over a period in the past,

which are used to construct typical food patterns:

food frequency questionnaires and diet histories.

Records are usually limited to fairly short periods,

usually not longer than 7 consecutive days, while

recalls may relate to a single period of 24 hours or

occasionally 48 hours. Diet histories and food fre-

quency questionnaires relate to longer periods and

their purpose is to obtain an assessment of habitual

intake over the period in question and not a detailed

day-to-day recall of what was eaten during that time.

When records are kept portions may be either weighed

Step 1

Basic procedure Type of dietary assessment

Report RECORD RECALL HISTORY FFQ

Step 2 Identify food Subject’s choice

from questionnaire

Step 3 Quantify Weighed/ Estimated

estimated

Average portion

or small/medium/large

Step 4 Frequency As reported Subject's

estimate

Subject’s choice

from questionnaire

Step 5 Calculate intake Food code

x Portion weight

x Nutrient content/g

Researcher’s choice

from food tables

Food code
x Portion weight
x Frequency
x Nutrient content/g
Figure 10.1 The fi ve basic steps in a dietary assessment and the variations according to different methods. FFQ, food frequency
questionnaire.