• What is assessed?
• How is the measurement conducted?
• When is this method used?
• How are estimates of diet derived?
• Strength and limitations
• Populations
• Further considerations
• Resources required
• Instrument library
• Development of new tool/method
• References

Weighed food diaries (diet diaries or food records) are prospective dietary assessment methods, providing descriptions of the foods consumed and eating occasions [1]. These methods provide excellent estimates for energy, nutrients, foods and food groups. The outcomes measured by weighed food diaries are described in Table D.8.1. Recommendations are based upon multiple days of food diary entries rather than a single day in order to account for daily variation in diet.

Table D.8.1 Dietary outcomes assessed by weighed food diaries over multiple days.

*  possible when repeated measures were collected over time.

Measurements of weighed food diaries involve respondents or investigators weighing every item of food and drink consumed at the time of consumption. The following are also recorded as much as possible:

1. Water
2. Dietary supplements
3. Alcohol
4. Ingredients
5. Eating occasions and other relevant information

Timeframe

1. Several days of recording are necessary because of daily variations in what people eat [2].
2. The more days of recording, the less bias there is toward certain days of the week (i.e. weekday/weekend variation).
3. The more days of recording, the greater the likelihood of capturing information on foods sporadically consumed. This characteristic is in common with 24-h recall.
4. The more days of recording, the less accurate the reporting may be towards the end of the recording period due to study fatigue.
5. Researchers may also request a respondent to do the assessment repeatedly to account for seasonal differences in consumption, e.g. using 2-day food diaries (weekend and weekday) four times over a year.

Procedure

1. Instructions and record sheets or booklets are provided, together with a set of weighing scales for the food and drink.
2. For each food item consumed, the respondent records the description of the food, its brand, the weight served, and any leftovers.
3. For composite foods which could not be readily split into components, such as a fruit pie or meat casserole, the respondent should provide recipe details.
4. For recording the foods eaten away from home, the respondent is asked to record the details as much as possible. Pocket booklets probing information on portion size, price, place of purchase, and any leftovers can be used.
5. A short questionnaire can also be included to aid interpretation of the record and to capture details of core foods regularly eaten (e.g. type of milk), and to inquire about non-food items such as dietary supplements.
6. The respondent may keep packages and labels as parts of records.
7. Recording may also be maintained by using electronic devices, including an audio device and a digital camera.

1. Recording exact portion sizes, such as in the study of dietary behaviours
2. Providing excellent estimates of energy, nutrient, food and food group intake, this method is useful for study of diet-disease associations
3. To develop or calibrate diet history or food frequency questionnaires methods [3]
4. Population-level survey. Traditionally, the United Kingdom implemented weighted food diaries in the National Diet and Nutrition Survey [4, 5], but updated to estimated food diaries and multiple-day 24-hour recalls later.

Estimates of diet can only be derived following extensive data entry. One person may consume more than 50 items per day, and the number of food items in a population-based study can easily become thousands. Data entry should consider the following issues:

1. Hand-written records may be unreadable and may include spelling mistakes. Ideally, these should be confirmed by contacting the respondent.
2. For a group-level assessment, entry names need to be harmonised, often by using food codes. For example, coca-cola and fizzy drinks (of no specific brand) may be kept as they are and also coded into a food code of ‘soft drinks’ and brand.
3. Ideally, food codes should be comprehensive to capture every dietary item consumed in a given population, including brand names and sub-types. Text entry for further details is needed.
4. Quantity needs to be entered in a standardised manner, including raw information, information with specific units (gram or volumes), and any uncertainty.

Each dietary entry may include the following attributes:

1. Temporal factors: date; day of the week; and time
2. Item: food name; food code; food group (text + code); recipe if any (text + code); homemade or purchased (text + code); and brand
3. Quantity: amount in grams; amount in volume
4. Setting: occasion (e.g. consumed as breakfast); location; with whom; watching TV (yes/no); sitting at a table (yes/no)

Outcomes can vary depending on aims, level of detail of information, and the number of days recorded. Outcomes extracted from diaries may be averaged across multiple days of measurement to estimate a ‘typical’ daily consumption.

Example of dietary estimates from weighed food diaries include:

1. Temporal information on dietary consumption: e.g. dietary consumption in different contexts (e.g. breakfast, weekend).
2. Frequency: e.g. how often takeaways are consumed per week; how often breakfast is skipped by using 1-week diaries (but not by 2-day diaries).
3. Items can be specific foods (e.g. fried chicken purchased outside) or food groups (e.g. total chicken).
4. Dietary components such as nutrients, phytochemicals, and toxins, can be estimated, as far as a food-composition table is available and linked to food items entered from diaries.
5. Levels can be assessed for the overall diet or specific dietary items (e.g. daily iron intakes from an overall diet, meat, and supplements, separately).

Key characteristics are described in Table D.8.2.

Strengths

1. Does not rely on individual memory and recall as the food/drink are recorded at the point of consumption
2. Provides weighed portion sizes and therefore does not rely on portion size estimation
3. Provides detailed descriptions of the foods consumed and all eating occasions 

Limitations

1. The weighed food diary imposes the biggest respondent burden among all methods, and individuals must be motivated and compliant
2. The individual must be sufficiently numerate and literate
3. Weighing and recording food eaten away from home can be difficult
4. Foods eaten less than once or twice a week may not be captured
5. The individual may alter his/her diet to make it easier to record, or to conceal poor eating habits (reactivity bias)
6. It is time-consuming and labour-intensive, and therefore costly, for researchers to conduct data entry and standardisation of data
7. Dietary data input and translation into nutrient data is complex
8. Thoroughness and errors are likely to be differential, depending on whether or not the individual prepared meals by themselves

Table D.8.2 Characteristics of weighed food diaries.

Considerations relating to the use of weighed food diaries for assessing diet in specific populations are described in Table D.8.3.

Table D.8.3 Diet assessment by weighed food diaries in different populations.

1. Instructions must be provided on food recording, ideally face-to-face or alternatively via phone call; a practice session is conceivable.
2. Once complete, trained fieldworkers can go through the record with the individual to probe for the level of detail required to code dietary intake. Feedback can be given to fieldworkers on the quality of their coding and probing.
3. Phone calls or mobile phone messages can be sent to respondents during the period of food recoding to maintain compliance and motivation.
4. Dietary feedback can be provided to respondents about their diet after the completion of diary coding.
5. Individuals should be instructed to keep food labels of any unusual foods and ready meals consumed to help coders identify or clarify items.
6. If a respondent consumes meals with family members or peers, their understanding and cooperation should be sought.
7. Diaries should be formatted to allow sufficient space to record the entire dietary intake.
8. It is useful to supply a separate instruction book so this can be referred to when the diary is being completed.
9. A pocket notebook is also useful to record consumption away from home, weighing food eaten away from home can also be problematic.
10. The maximum cumulative weight of a scale (e.g. 2.5 kg) can be a problem where a heavy plate is used; plastic plates can be suggested to use in these circumstances.
11. A shared meal makes it challenging to complete weighed food records accurately. When studying one participant in a family in a single household, investigators may have to communicate all the family members proactively.
12. Food could be photographed by study participants to help interpretation.

1. Weighed food diary in record sheet or pocket booklet form for when away from home
2. Weighing scales
3. Additional questionnaire to aid interpretation
4. Trained research assistants to instruct individuals on undertaking a weighed food diary
5. Clear written instructions on completion and return of the tool
6. Trained diet coders
7. Nutrient database and analysis program

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 in a new page.

Weighed food diaries are known as a resource-intensive method. Thus, they may not be adopted readily in an epidemiological study with a large sample size. However, food diaries, whether estimated or weighed, are realistic and conceivable to implement in a subset of a study population, although this still requires expert knowledge on data entry and further processing. Food diary data in a subset should then be combined with the dietary data of an entire study population deriving from another dietary assessment (e.g. multiple 24-h recalls, food frequency questionnaires). Unique statistical approaches are required to accurately merge multiple dietary datasets obtained from different methods [9].

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2. Lanigan JA, Wells JC, Lawson MS, Cole TJ, Lucas A. Number of days needed to assess energy and nutrient intake in infants and young children between 6 months and 2 years of age. Eur J Clin Nutr. 2004;58(5):745-50
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5. Henderson L GJ, Irving K, Swan G. The National Diet and Nutrition Survey: adults aged 19 to 64 years, Vol. 2: energy, protein, carbohydrate, fat and alcohol intake. . London: 2002.
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8. Livingstone MB, Prentice AM, Strain JJ, Coward WA, Black AE, Barker ME, et al. Accuracy of weighed dietary records in studies of diet and health. BMJ. 1990;300(6726):708-12.
9. Souverein OW, Dekkers AL, Geelen A, Haubrock J, de Vries JH, Ocke MC, et al. Comparing four methods to estimate usual intake distributions. Eur J Clin Nutr. 2011;65 Suppl 1:S92-101.