Nutrition Research Methodologies – HNH24306
Week 1
Lecture 1 – Introduction to the course
Why are methods important:
- Chosen methods determine the strength of the results
- Better methods in proposal = easier to get through medical ethical review process = easier to get funding
- Better methods in research paper = better chance of publication
Not just for researchers:
- For policy makers: how strong is the evidence from observational and clinical studies?
- For health professionals: how convinced am I that treatment works?
- For marketeers: can I substantiate claims for my product?
- For grant providers: is my money well spent?
Different types and aims of interventions > different quality criteria for methods.
Chapter 1 NRM – Nature, Purpose and Implications of Research in Nutrition
Basal metabolic rate: the body’s ongoing demand under standardised resting conditions.
Nutritional demand: the ability to determine the requirements for energy and nutrients.
Nutritional state or status: the ability to determine the extent to which the demand has been met.
Lecture 2 – Assessment of dietary intake: Methods, quality and validation
1. Aims of dietary assessment
Purpose of dietary assessment is different:
- Research
o Experimental and clinical studies
o Surveillance and monitoring
o Epidemiological studies
- Patient care
o Dietary advice
Diet is complex to measure > some problems:
- Preparation methods
- New foods and their compositions
- Novel foods and supplements
- Age groups
- Characteristics
Hard to recall what you have eaten yesterday:
- Can you identify all ingredients?
- Do you know all amounts within 5 grams accuracy?
- Was the meal representative for your evening meal?
- Did you consume ingredients that would lead to socially desirable answering?
Assessment of dietary intake:
- By different dietary assessment methods
o To identify type of foods consumed
o To define the amounts
o Sometimes: times, location
- Using a food composition table or chemical analysis to convert this into intake of energy and nutrients
Essentials for each dietary assessment:
- Reference period
o E.g. previous month, today
- Portion sizes
o Weighing foods, household measures
- Food composition tables
o Local tables? Recent table?
o Specific components available?
2. Available methods
Dietary assessment: how? > self-reports or markers of exposure.
,Self-reports: different methods:
- 24-hour recall
- Food record or food diary
o Observation > food record but done by someone else
o Duplicate portion > don’t need a food composition table
- Dietary history method
- Food frequency questionnaire
* Written, oral, technology-based.
24-hour recall:
- Principle
o Recall of past 24-hours
o Interview
o Telephone/face-to-face
- Application
o Monitoring studies
o Easy for the respondent
o Comparison between cultures
- Disadvantages
o Day-to-day variation
o Response errors
Food record:
- Principle
o Record current intake
o Amount and time eaten
- Application
o Experiments
o Small studies
o Awareness of intake
- Disadvantages
o Change of intake when people are recorded
o Burdensome (weighing)
Dietary history method:
- Principle
o Interview
o Habitual intake
o Meal-based, much detail
- Different applications
o More or less extended
o Research or dietary advice
- Disadvantage
o Burdensome
o Experienced interviewers needed
Food frequency questionnaire:
- Principle
o Frequency of habitual consumption; few nutrients or comprehensive list
- Application
o Easy
o In large epidemiological trials
- Disadvantages
o Culturally-based
o Difficult to recall past intake
o No information on single foods
* Every country has its own FFQ > difficult to make comparisons between countries.
FFQ: screeners (only focus on one nutrient or food of interest):
, - Short questionnaires tailored for qualitative assessment of diet
o Fruits and vegetables, energy-% from fat, dietary patterns (e.g. Mediterranean Diet Adherence)
- Needed when very limited room for questions on diet
- Useful in situations that do not require assessment of total diet
- Estimates of intake are not as accurate as those from more detailed methods
Web-based > example FFQ = De Eetscore (Wageningen University)
- Estimate the Dutch Healthy Diet Index
- Assesses adherence to the Dutch dietary guidelines
- Implementation for use by dieticians, family doctors etc.
- Valid to identify risk groups
Technology-based instruments:
- Principle
o Often rest on self-reports as food records, 24-hour recalls, FFQ or screeners
o Novel technology may improve performance and save costs
- Types
o Web-based
o Mobile-phone (incl. camera)
o Scan- and sensor technology
§ Scan barcodes of purchased food items
§ Wear sensors that automatically record corporal movements related to eating activities
§ Advantage: memory-independent
- Several applications (e.g. adolescents or hospital)
Now, researchers use combinations of methods.
3. Choosing a method
Choosing a method > 6 steps:
1. What is the aim of the assessment?
2. What type of information do you need?
3. What is the target group?
4. What is the reference period?
5. Have the data to be comparable with former studies?
6. How much time/finances/experience are available?
What is the aim?
- Examples
o To assess the intake of the population to evaluate whether intake is adequate
o To assess the association between vegetables intake and cancer risk
o To give an individual advice on fat intake
Is the aim foods or nutrients?
- Dietary pattern
o Group or individual pattern, characteristics of a population with a specific pattern
o Average intake of a specific food or food group
Type of information needed?
- Nutrients
o Group means = mean intake of a group
§ Easiest type of information
o Group means and distribution = mean and variation in intake of a group
o Ranking or classification = people with lower and higher intakes
§ Relative assessment
§ Important for epidemiological studies
o Absolute individual intake
§ Most difficult type of information
Example 1: a researcher would like to know whether intake of calcium in this population is adequate > group
mean and distribution.
Example 2: a researcher would like to know what the relationship between chocolate consumption and risk of
myocardial infarction and stroke > ranking.
Example 3: a dietician would like to know whether intake and excretion of calcium of her patient is in balance >
absolute individual intake.
, Objective, required information and desired approach:
Step 1: aim = objective Step 2: type of information Approach
Mean intake population Group mean One day record / one 24-hour
recall
% < cut-off Group mean and distribution Repeated record / recall
> at least 2 days record needed
so you have the within person
variation: better idea of the
distribution
Association intake-health Ranking or classification FFQ / diet history (for usual
intake)
Intake individual Absolute intake Multiple records / recalls
What is the target group?
- Are there special subject characteristics to be considered?
o Memory problems, literacy, need of proxy
- Available dietary assessment methods of elderly
o Healthy elderly > 24-hour recalls, FFQ, food records, dietary history
o Disabled elderly > observed record, picture sort method, biological markers
§ Or a combination of methods
What is the reference period?
- Habitual or actual intake
o Aim of study
- Number of days: variability in intake in specific populations
- Memory: age groups
- FFQ and dietary history
o To assess usual intake = long term intake
o Retrospective
- 24-hour recall and food record
o To assess actual intake = recent/current intake
o To assess usual intake if repeated
o Recall: retrospective
o Food record: prospective
Variation in intake: number of days for record and recalls:
- One single day is not representative
- 2-day information provides within-person intake
- CoefficientVariationwithin (CWv) = (sd / mean) x 100%
- Number of days calculated from the formula:
- D0 = defined limitation (defined by researcher itself) > I want this much accuracy
o The higher the accuracy, the higher the days
- Example energy intake men: CVw = 33% > n = (1.96 x 33% / 20%)2 = 10 days
4. Errors in dietary assessment
Week 1
Lecture 1 – Introduction to the course
Why are methods important:
- Chosen methods determine the strength of the results
- Better methods in proposal = easier to get through medical ethical review process = easier to get funding
- Better methods in research paper = better chance of publication
Not just for researchers:
- For policy makers: how strong is the evidence from observational and clinical studies?
- For health professionals: how convinced am I that treatment works?
- For marketeers: can I substantiate claims for my product?
- For grant providers: is my money well spent?
Different types and aims of interventions > different quality criteria for methods.
Chapter 1 NRM – Nature, Purpose and Implications of Research in Nutrition
Basal metabolic rate: the body’s ongoing demand under standardised resting conditions.
Nutritional demand: the ability to determine the requirements for energy and nutrients.
Nutritional state or status: the ability to determine the extent to which the demand has been met.
Lecture 2 – Assessment of dietary intake: Methods, quality and validation
1. Aims of dietary assessment
Purpose of dietary assessment is different:
- Research
o Experimental and clinical studies
o Surveillance and monitoring
o Epidemiological studies
- Patient care
o Dietary advice
Diet is complex to measure > some problems:
- Preparation methods
- New foods and their compositions
- Novel foods and supplements
- Age groups
- Characteristics
Hard to recall what you have eaten yesterday:
- Can you identify all ingredients?
- Do you know all amounts within 5 grams accuracy?
- Was the meal representative for your evening meal?
- Did you consume ingredients that would lead to socially desirable answering?
Assessment of dietary intake:
- By different dietary assessment methods
o To identify type of foods consumed
o To define the amounts
o Sometimes: times, location
- Using a food composition table or chemical analysis to convert this into intake of energy and nutrients
Essentials for each dietary assessment:
- Reference period
o E.g. previous month, today
- Portion sizes
o Weighing foods, household measures
- Food composition tables
o Local tables? Recent table?
o Specific components available?
2. Available methods
Dietary assessment: how? > self-reports or markers of exposure.
,Self-reports: different methods:
- 24-hour recall
- Food record or food diary
o Observation > food record but done by someone else
o Duplicate portion > don’t need a food composition table
- Dietary history method
- Food frequency questionnaire
* Written, oral, technology-based.
24-hour recall:
- Principle
o Recall of past 24-hours
o Interview
o Telephone/face-to-face
- Application
o Monitoring studies
o Easy for the respondent
o Comparison between cultures
- Disadvantages
o Day-to-day variation
o Response errors
Food record:
- Principle
o Record current intake
o Amount and time eaten
- Application
o Experiments
o Small studies
o Awareness of intake
- Disadvantages
o Change of intake when people are recorded
o Burdensome (weighing)
Dietary history method:
- Principle
o Interview
o Habitual intake
o Meal-based, much detail
- Different applications
o More or less extended
o Research or dietary advice
- Disadvantage
o Burdensome
o Experienced interviewers needed
Food frequency questionnaire:
- Principle
o Frequency of habitual consumption; few nutrients or comprehensive list
- Application
o Easy
o In large epidemiological trials
- Disadvantages
o Culturally-based
o Difficult to recall past intake
o No information on single foods
* Every country has its own FFQ > difficult to make comparisons between countries.
FFQ: screeners (only focus on one nutrient or food of interest):
, - Short questionnaires tailored for qualitative assessment of diet
o Fruits and vegetables, energy-% from fat, dietary patterns (e.g. Mediterranean Diet Adherence)
- Needed when very limited room for questions on diet
- Useful in situations that do not require assessment of total diet
- Estimates of intake are not as accurate as those from more detailed methods
Web-based > example FFQ = De Eetscore (Wageningen University)
- Estimate the Dutch Healthy Diet Index
- Assesses adherence to the Dutch dietary guidelines
- Implementation for use by dieticians, family doctors etc.
- Valid to identify risk groups
Technology-based instruments:
- Principle
o Often rest on self-reports as food records, 24-hour recalls, FFQ or screeners
o Novel technology may improve performance and save costs
- Types
o Web-based
o Mobile-phone (incl. camera)
o Scan- and sensor technology
§ Scan barcodes of purchased food items
§ Wear sensors that automatically record corporal movements related to eating activities
§ Advantage: memory-independent
- Several applications (e.g. adolescents or hospital)
Now, researchers use combinations of methods.
3. Choosing a method
Choosing a method > 6 steps:
1. What is the aim of the assessment?
2. What type of information do you need?
3. What is the target group?
4. What is the reference period?
5. Have the data to be comparable with former studies?
6. How much time/finances/experience are available?
What is the aim?
- Examples
o To assess the intake of the population to evaluate whether intake is adequate
o To assess the association between vegetables intake and cancer risk
o To give an individual advice on fat intake
Is the aim foods or nutrients?
- Dietary pattern
o Group or individual pattern, characteristics of a population with a specific pattern
o Average intake of a specific food or food group
Type of information needed?
- Nutrients
o Group means = mean intake of a group
§ Easiest type of information
o Group means and distribution = mean and variation in intake of a group
o Ranking or classification = people with lower and higher intakes
§ Relative assessment
§ Important for epidemiological studies
o Absolute individual intake
§ Most difficult type of information
Example 1: a researcher would like to know whether intake of calcium in this population is adequate > group
mean and distribution.
Example 2: a researcher would like to know what the relationship between chocolate consumption and risk of
myocardial infarction and stroke > ranking.
Example 3: a dietician would like to know whether intake and excretion of calcium of her patient is in balance >
absolute individual intake.
, Objective, required information and desired approach:
Step 1: aim = objective Step 2: type of information Approach
Mean intake population Group mean One day record / one 24-hour
recall
% < cut-off Group mean and distribution Repeated record / recall
> at least 2 days record needed
so you have the within person
variation: better idea of the
distribution
Association intake-health Ranking or classification FFQ / diet history (for usual
intake)
Intake individual Absolute intake Multiple records / recalls
What is the target group?
- Are there special subject characteristics to be considered?
o Memory problems, literacy, need of proxy
- Available dietary assessment methods of elderly
o Healthy elderly > 24-hour recalls, FFQ, food records, dietary history
o Disabled elderly > observed record, picture sort method, biological markers
§ Or a combination of methods
What is the reference period?
- Habitual or actual intake
o Aim of study
- Number of days: variability in intake in specific populations
- Memory: age groups
- FFQ and dietary history
o To assess usual intake = long term intake
o Retrospective
- 24-hour recall and food record
o To assess actual intake = recent/current intake
o To assess usual intake if repeated
o Recall: retrospective
o Food record: prospective
Variation in intake: number of days for record and recalls:
- One single day is not representative
- 2-day information provides within-person intake
- CoefficientVariationwithin (CWv) = (sd / mean) x 100%
- Number of days calculated from the formula:
- D0 = defined limitation (defined by researcher itself) > I want this much accuracy
o The higher the accuracy, the higher the days
- Example energy intake men: CVw = 33% > n = (1.96 x 33% / 20%)2 = 10 days
4. Errors in dietary assessment
