NUTRITION: Dietary Assessment Methodology Flashcards
Why measure dietary intake?
To monitor food and nutrient intake in individuals, groups and populations
To formulate the Government health, food, agricultural policies at a national level
To provide data for commercial purposes – guide product manufacture and development of new products: Product labelling / Food Standards Agency (FSA)
To conduct epidemiological research to investigate links between diet and diseases
what info does dietary intake provide?
- Amount and type of food consumed
- Intake of nutrients consumed
- Trends /changes in patterns of food consumption over time in populations (i.e. repeat National Food Surveys)
- Changes in sources of nutrients we consume, (i.e. from which foods do we get our energy, protein, fat) – effect on health
- Extent of malnutrition in individuals and populations
what are issues in dietary assessment? what can best understanding of these help you to do?
All methods have a degree of error – accuracy & validity of method should be confirmed, and the advantages, disadvantages, errors and limitations
Better understanding will allow you to:
• select an appropriate method to use
• aid evaluation of research papers
• draw conclusions about the results
Whose Diet Do We Want to Measure
- The Nation (Total Intake Statistics)
- Individuals
- Groups e.g. age specific, athletes
- Family/households
what 6 things will choice of method depend on?
- Purpose of the survey
- Sample size
- Age of subjects
- Time available
- Cognitive abilities/intelligence of subjects
- Financial constraints
what are the top 3 retrospective methods
- 24Hr recall
- Food Frequency Questionnaire (FFQ)
- Diet history
what is 24 hour recall
- Interview technique - subjects are asked to recall their food intake over last 24 (48) hours
- Food models, photographs (food atlas, Carbs & Cals), household portion sizes are used to help estimate intake
- Nutrient intakes are then calculated using food composition data (i.e. McCance & Widdowson book, software nutrient databases incorporating McCance & Widdowson food tables, Food Portion Sizes)
how should you carry out 24hr recall
Begin the interview by asking ‘what was the first thing that you ate or drank yesterday?’ & record it onto 24 hr recall sheet.
Avoid
• Leading questions, e.g. ‘What did you have for breakfast?’
• Closed questions, e.g. ‘Did you have breakfast yesterday?’
Next, ‘what was the next thing you had to eat or drink?’
Continue until a full day’s food and drinks are recorded.
Note times that meals and snacks are taken.
• Long gaps- memory?
• May need prompting
what are advantages of 24hour recall
- Inexpensive method
- Quick/easy to perform (20 mins approx)
- Low respondent burden – good response
- Can be used with most target groups
- Can provide info on type and variety of foods consumed by individuals and groups
- Can be used to estimate mean nutrient intake of groups (fairly accurate)
- Does not alter usual diet
- Hidden information
what are disadvantages of 24hour recall
- One day not representative – is it typical? Weekdays vs weekend days, holidays, seasonal influence?
- Relies heavily on memory: errors, omissions, cognitive ability (elderly, kids)
- Not easy to standardise method if more than one interviewer is involved (differences in interview techniques, language uses, subjective issues)
- Research shows subjects under-report and over-report energy intake
- Respondents may withhold information: memory, embarrassment, trying to please or impress interviewer (psychological reasons)
- Tendency to under-report binge eating, alcohol, unhealthy, and over-report foods seen as healthy
- Interviewer influence: non-judgemental!
- Multiple 24-hr recall to improve accuracy/mistakes in recording data on form/ diary
- Accuracy of food composition data itself (McCance and Widdowson)
- Input/analysis of data with software
what is the food frequency questionnaire
- Provides a detailed list of foods and food groups and determines how often these items are eaten over a specific period of time
- Numbers and types of food vary, depending on target population and survey needs
- May gather information on portion sizes, or may rely on standard food portion sizes to assess nutrient intake
- May be completed by interviewer or self- completed by subject
what are advantages of the FFQ
- Inexpensive?
- Good for describing food intake patterns
- Easy to perform
- Useful for large population studies – by post
- Adapted to suit particular populations/foods
- Allows easy analysis by computer
- Provides evidence of associations between diet and health
what are disadvantages of the FFQ
- High respondent burden - can affect response rates
- Expensive and time consuming
- Subject to bias – people may change or restrict their food intake during the recording period (see later)
- If eating out, you only get estimates: introduces inaccuracies
- Subjects must be highly motivated and literate so may not be suitable for all populations
Describe estimated records such as food diaries and food record charts
Simpler and less demanding than weighed records (WR)
Less precise than WR but less expensive
Subjects record an estimated weight, in terms of calibrated household measures, e.g. tablespoons; cupful
Alternative methods of estimating portions sizes include the use of photographs (Nelson, 1997), food models, pictures
what are the advantages of estimated records such as food diaries and food record charts
- Simpler and less demanding than weighed methods and more appropriate in some cases
- Higher rates of cooperation compared with the weighed method, especially over long periods (lower respondent burden)
- Quick and inexpensive compared with the weighed methods
- Does not rely on memory
- Less interference with food intake as scales are not used
