Weighed food diaries

Weighed food diaries (diet diaries or food records) are prospective dietary assessment methods, providing descriptions of the foods consumed and eating occasions. These methods provide excellent estimates for energy, nutrients, foods and food groups. The outcomes measured by weighed food diaries are described in Table D.2.5. Recommendations are based upon multiple days of food diary entries rather than a single day in order to account for daily variation in diet.

An example of a weighed food diary is displayed in Figure D.2.3. Measurement involves 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:

• Water
• Dietary supplements
• Alcohol
• Ingredients
• Eating occasions and other relevant information

Timeframe

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

Procedure

• Instructions and record sheets or booklets are provided, together with a set of weighing scales for the food and drink
• For each food item consumed, the respondent records the description of the food, its brand, the weight served, and leftovers
• For composite foods which could not be readily split such as a fruit pie or meat casserole, the respondent provides recipe details
• 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
• A short questionnaire can also be included to aid interpretation of the record and to record details of core foods regularly eaten e.g. type of milk, and to inquire about non-food items such as dietary supplements
• The respondent may keep packages and labels as parts of records
• Recording may also be maintained either by using an electronic device including an audio device and a digital camera [1]

Figure D.2.3 Example of weighed food diary.
Source: MRC Epidemiology Unit.

• Recording exact portion sizes such as in study of dietary behaviours
• Providing excellent estimates of energy, nutrient, food and food group intake and thus useful for study of diet-disease associations
• To develop or calibrate diet history or food frequency questionnaires methods
• Traditionally used in the United Kingdom for the assessment of dietary intakes in national surveys [3, 4]

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

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

Each dietary entry may include the following attributes:

• Temporal factors: date; day of a week; and time
• Item: food name; food code; food group (text+ code); and recipe if any (text + code); home-made or purchased (text + code); brand
• Quantity: amount in gram; amount in volume
• Setting: occasion (e.g. consumed as breakfast); location; with whom; watching TV (yes/no); sitting table (yes/no)

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

Example of dietary estimates from weighed food diaries include:

• Temporal information on dietary consumption: e.g. dietary consumption in different contexts (e.g. breakfast, weekend)
• 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)
• Items can be specific foods (e.g. fried chicken purchased outside) or food groups (e.g. total chicken)
• 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.
• Levels can be from an overall diet or specific dietary items (e.g. iron intakes per day from an overall diet, meat, and supplements, separately)

Key characteristics are described in Table D.2.6.

Strengths

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

Limitations

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

Considerations relating to the use of weighed food diaries for assessing diet in specific populations are described in Table D.2.7.

• Instructions must be provided on food recording, ideally face-to-face or alternatively via phone call; a practice session is conceivable
• 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
• Phone calls or mobile phone messages can be sent to respondents during the period of food recoding to maintain compliance and motivation
• Dietary feedback can be provided to respondents about their diet after the completion of diary coding
• Individuals should be instructed to keep food labels of any unusual foods and ready meals consumed to help coders identify or clarify items
• If a respondent consumes meals with family members or peers, their understanding and cooperation should be sought
• Diaries should be formatted to allow sufficient space to record the entire dietary intake
• It is useful to supply a separate instruction book so this can be referred to when the diary is being completed
• A pocket notebook is also useful to record consumption away from home, weighing food eaten away from home can also be problematic
• 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
• Food could be photographed by study participants to help interpretation

• Weighed food diary in record sheet or pocket booklet form for when away from home
• Weighing scales
• Additional questionnaire to aid interpretation
• Trained research assistants to instruct individuals on undertaking a weighed food diary
• Clear written instructions on completion and return of the tool
• Trained diet coders
• 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, this could not be adopted readily in a common epidemiological study with a large sample size. Thus, food diaries (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 are then to be combined with 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 validly merge multiple dietary datasets from multiple methods [9].