Direct observation

Direct observation of dietary intake is often undertaken as a means of validating a dietary assessment method by providing an objective measure of dietary intake. Eating behaviours, including items and amounts of foods consumed, received or given away, or spilt, can all be noted [1]. However, it is not a feasible method for obtaining habitual dietary data at either a group or an individual level. Dietary dimensions assessed by direct observation are summarised in table D.15.1.

Table D.15.1 Dietary dimensions assessed by direct observation.

Dietary dimension Possible to assess?
Energy and nutrient intake of a total diet Yes
Intake of specific nutrients or food Yes
Infrequently consumed foods Yes
Dietary pattern Yes
Habitual diet No
Within-individual comparison Yes
Between-individual comparison Yes
Meal composition Yes
Frequency of eating/meal occasions Yes
Eating environment Yes
Adult report of diet at younger age Yes

Observation of diet should be carried out in a systematic way, employing standardised methodology across observers and observation periods. Researchers directly observe participants and note down their eating behaviours during a defined time period (e.g. during school lunch) [1].

The observation period

Observation typically takes place over a relatively short period, for example, a one hour lunch break. However, some studies have reported much longer observation periods, such as 12 hours of continuous monitoring, with participants being followed throughout this time [2].

The recording form

In structured settings such as school canteens and hospitals, it may be possible to know in advance the foods to be served and the standard portion sizes. In these instances, the recording form must list the foods served with space for the observer to note the serving size provided and the percentage of that serving that is actually consumed [5]. It is often necessary to account for the amount of food dropped or shared, especially among children. In more free-living scenarios, the recording form must be more flexible in order to capture the wide variety of possible intakes, including spaces for [5]:

  1. Brand names
  2. Ingredients
  3. Preparation practices
  4. Condiments
  5. Portion size
  6. Percent of portion consumed/remaining at the end of the meal

Portion sizes can be obtained by weighing plate waste, visual estimation, or use of Likert-scale ratings. For example, Baglio et al. [1] used the following ratings:

  1. All (100%)
  2. Most (75%)
  3. Half (50%)
  4. Little bit (25%)
  5. Taste (10%)
  6. None (0%)

Minimising the impact of observation on normal behaviour

It is important that the observation takes place with minimal intrusion on the participant(s) so as to reduce the effect of reactivity bias. Strategies may include:

  1. In controlled settings, observers may be able to take covert positions
  2. Using a pre-test period can mean that participants lose interest in the presence of the observer, reducing reactivity [4]
  3. In some settings, such as school dining halls, children are accustomed to being observed and may not perceive the presence of a researcher as unusual

Quality control

It is crucial that observers undergo extensive training and that quality control procedures are in place to ensure accurate and consistent recording and data processing, especially if portion sizes are to be recorded. It is important that observers record intake in the same way, as inconsistencies in weights/volumes can be difficult to reconcile. Such training can include [5]:

  1. Discussion of the observation protocol.
  2. Practice in laboratory and field settings.
  3. Regular feedback and opportunities to discuss difficulties.
  4. Regular testing to assess inter-observer reliability.
  5. Data processing by multiple researchers.

It is essential that inter-rater reliability is assessed and clearly reported in research outputs. If it is not, it remains unclear whether differences between individuals represent true variation or depend upon who was conducting the observation [1]. Figure D.15.1 presents an example of calculating inter-rater reliability.

Figure D.15.1 Example of calculation of inter-rater reliability for a single participant.

Inter-rater reliability calculation:
Number of items = 11
Number of items with agreement within ¼ serving = 7
Percent agreement = (7 ÷ 11) * 100 = 63.6%

Direct observation can be used in the following situations:

  1. Observation of school meals to validate recalls in children [1, 4]. In one study, children were observed in school and in their home over a year to establish familiarity without collecting data. The following year, 3-day observations from 40 children were collected.
  2. Occasionally in studies fieldworkers visit homes and observe mealtimes and record dietary intake.
  3. Evaluation of nutrition education interventions [3]

Estimates of nutrient intakes follow a common procedure with weighed food diaries and food-frequency questionnaires. The following steps to estimate nutrient intakes are undertaken:

  1. Disaggregate records of mixed meals quantitatively to individual foods and ingredients (if a food composition table has a mixed meal which is comparable to that in the recall output, disaggregation is not necessary)
  2. Convert portion size to gram amounts or amounts in a standard unit (e.g. ml for liquids) of each dietary consumption
  3. Match all foods and ingredients with items in a food composition table
  4. Calculate nutrient intakes from each food, by multiplying the amount of each item consumed and nutrients contents per amount of each item
  5. Calculate nutrient intakes per day by summing the daily intakes of the nutrient from all items for each individual
  6. These calculations can be specific to intake periods, for example, at breakfast or different settings in a day

It's worth noting that inference of dietary intake is not always needed. For example, a research question could be: “How many children in a school select fried products and sugar-sweetened products in a buffet-style school lunch?”. Direct observations in a school dinner hall could provide the answer to this question without any estimation or additional inferential steps.

Key characteristics of direct observation are summarised in Table D.15.2.


  1. Observation provides an objective assessment of dietary intake
  2. Minimises errors associated with recall and social desirability biases
  3. Provides accurate information on the social and physical context of dietary intake
  4. Useful for populations unable to record their own intakes


  1. Observer inattention and imprecise recording will lead to errors [5]
  2. Extensive training required for observers
  3. It can be intensive for researchers and therefore expensive
  4. It can practically only be done in settings such as canteens and school dining halls and it is limited to specific times that individuals can be observed
  5. Observation may alter individuals’ usual eating patterns
  6. It can be perceived as invasive
  7. The ability to generalise from the observation period to habitual dietary consumption is likely to be limited unless multiple assessments are conducted separately over time
  8. The burden could be greater than an individual anticipated at the time of providing consent

Table D.15.2 Characteristics of direct observation.

Characteristic Comment
Number of participants Small
Cost of development Low
Cost of use High
Participant burden Low
Researcher burden of data collection High
Researcher burden of coding and data analysis High
Risk of reactivity bias Yes
Risk of recall bias No
Risk of social desirability bias Minimised
Risk of observer bias Yes
Participant literacy required No
Suitable for use in free living No
Requires individual portion size estimation Yes

Direct observation can be implemented for anyone as long there are no ethical restrictions. Considerations relating to the use of direct observation for assessing diet are summarised in Table D.15.3.

The target can be a population as a whole, rather than each individual in that population. For example, as mentioned above, if a research question is about the proportion of children who select fried or sugar-sweetened products in a school lunch, the output can be produced without any estimation of individuals’ diet.

Table D.15.3 Diet assessment by direct observation in different populations.

Population Comment
Pregnancy Suitable
Infancy and lactation Suitable
Toddlers and young children Records of foods shared/dropped more likely to be required
Adolescents Records of foods shared/dropped more likely to be required
Adults Suitable
Older Adults Suitable
Ethnic groups Suitable

Informed consent needs to be obtained as usual by providing detailed but succinct information on the direct observation method. The burden could be greater than what individuals anticipate at the time of providing consent. Thus, individuals should be informed with an emphasis about their freedom to request termination of direct observations.

  • This method requires many field workers trained in the collection of dietary data. The number of field workers required depends on the number of people being observed in one session.
  • Practice sessions should always be carried out to ensure that intra-observer reliability is acceptable.
  • The data obtained requires processing in a similar way to dietary data obtained from diaries or recalls.

A method-specific instrument library is being developed for this section. In the meantime, please refer to the overall instrument library page by clicking here to open it in a new page.

  1. Baglio ML, Baxter SD, Guinn CH, Thompson WO, Shaffer NM, Frye FH. Assessment of interobserver reliability in nutrition studies that use direct observation of school meals. J Am Diet Assoc. 2004;104(9):1385-92.
  2. Baranowski T, Dworkin R, Henske JC, Clearman DR, Dunn JK, Nader PR, et al. The accuracy of children's self-reports of diet: Family Health Project. J Am Diet Assoc. 1986;86(10):1381-5.
  3. Coates TJ, Jeffery RW, Slinkard LA. Heart healthy eating and exercise: introducing and maintaining changes in health behaviors. Am J Public Health. 1981;71(1):15-23.
  4. Davidson FR, Hayek LA, Altschul AM. Towards accurate assessment of children's food consumption. Ecol Food Nutr. 1986;18(4):309-17.
  5. Simons-Morton BG, Baranowski T. Observation in assessment of children's dietary practices. J Sch Health. 1991;61(5):204-7.