Dietary assessment

Question 1

Objectives of dietary assessment To characterise the diet of an individual

Answer 1

# Therapeutic
# Research

Question 2

Objectives of dietary assessment To characterise the diet of a population

Answer 2

# Sociological
# Public Health 
# Research

Question 3

Components required to measure food and nutrient intakes

[5]

Answer 3

# A report of all food consumed by an individual
# Identification of foods such that an appropriate item can be chosen from a standard food table
# Quantification of the portion size of each food item
# Determination of the frequency of consumption
# Calculation of nutrient intake, (portion size (g) x frequency x Nutrient content per gram.)

Question 4

Food composition tables

[3]

Answer 4

Average macro and micronutrient content of foods

UK - McCance and Widdowson’s The Composition of Foods integrated dataset

USDA reference database

Question 5

Computer database programmes [4]

Answer 5

Based on Food Composition Tables
# COMPEAT
# Foodbase
# Whisp etc
# Dietplan

Question 6

Limitations of Food Composition databases and computer programmes [4]

Answer 6

Seasonal variation in the nutrient content of foodstuffs

Batch to batch variation in the composition of processed foods (depends on the origin of the food ingredients)

Lack of information on specific foods (especially important for minority ethnic groups)

Incomplete nutrient analysis for all foods.

Question 7

Tools for assessing diet in the individual [2types & examples]

Answer 7

Prospective :
# Food diaries
# Weighed food diaries
# Estimated food records

Retrospective
# Food frequency questionnaires
# 24 hr recall methods

Question 8

assessment tool selection depend on

Answer 8

assessment purpose:
# Measuring food consumption
# Measuring nutrient intake
# Characterising eating habits

Question 9

Consideration of which method [4]

Answer 9

Importance of diet to study
Focus on one or many foods/nutrients
Variability within the study population
Resources available

Question 10

Prospective tools

Answer 10

Tools to capture dietary intake data over a defined future period

Variation in degrees of accuracy:
# Estimated food intake
# Food Diary
# Weighed food Diary

Question 11

7 Day weighed food diaries

Answer 11

Gold Standard

Volunteer records all that they eat over a 7 day period
They couple each recording to a measurement of the weight of the food consumed

Question 12

7 Day weighed food diaries strength & weakness

Answer 12

Strength:
# Highly accurate
# Quantitative- Faithful recording of portion size

Weakness:
# High responder burden
- Selectively representative
- Requires literacy

Reactivity

• The more you invade someone’s dietary habits the more they amend them
• Used as a weight loss tool
• Not necessarily representative of usual diet

Question 13

an example of the use of food diaries

Answer 13

NDNS

NDNS is the best available survey of the dietary intake of the population
# Optimum measure of food consumption by the individual
# Provide data on diet, nutritional status, and general health of the population

Question 14

24 hour recall

Answer 14

Respondent prompted to remember all foods consumed over previous 24 hours

Question 15

24 hour recall Strengths

Answer 15

# Literacy not required
# Low respondent burden= Representative cohort
# Adaptable to multi-cultural populations
# Recall does not influence behaviour

Question 16

24 hour recall Weaknesses

Answer 16

Recall bias - Selective bias =Under-reporting of energy

Assumes a very regimented diet = Multiple recalls required

Training/ Time /Cost

Portion size estimation

Question 17

The Food Frequency questionnaire

Answer 17

Composite food list - Lacks detail
# 100 000 commonly eaten foods 
# FFQ: 10-150 questions

Requires literacy and cognitively demanding

Measurement error can be high = Subjective recall

Question 18

Factors to consider in the design of a dietary questionnaire

Answer 18

Maximally Informative Minimally invasive

Target population
Fit for purpose - Socio-cultural differences in dietary habits
Questionnaire validation

Question 19

FFQ structure

Answer 19

Composite food list - Generated through surveys and focus groups

Corresponding multiple response grid in which respondents can estimate frequency of foods eaten over past year.

Participant estimates portion size

Question 20

food frequency questionnaires Strengths

Answer 20

Minimally invasive: completed in 20-25 minutes by the volunteer

Well suited to large studies

Can capture a lot of data

Low Cost

External validity - validated questionnaires can be used to compare data across cohorts

Question 21

food frequency questionnaires weakness

Answer 21

# Volunteers subjectively estimate portion size
 # Tendency amongst volunteers to over report “healthy foods” and under-report “un-healthy foods”
# Newly developed FFQs require validation against other food intake methods
# Reliant upon accuracy of food composition tables and portion size measures
# Poorly indicative of changing dietary habits across the life-course in the individual

Question 22

Where is an FFQ appropriate

Answer 22

# Prospective epidemiological studies
# Case control studies
# Observational studies 
# Interventions aimed at changing overall dietary behaviours

Question 23

Using the data

Answer 23

Data output- Converting categorical into continuous data

Portions per day- Worked example

Enhancing the data- Food composition tables- Micronutrients

Question 24

Worked example

Answer 24

Composite scores for food (100g)
Estimated portion size of a serving
Calculate mean contribution to daily diet for beef

Question 25

Handling the weaknesses of an FFQ

Answer 25

Adjusting to percentage energy per day
+ ameliorates the problem of over-reporting
- Values become relative as opposed to absolute
- decreases contribution of low energy foods
- increases contribution of high energy foods
+ adjustments can be made to account for macro/micronutrients

Adjusting to percentage of total portions per day
+ ameliorates the problem of over-reporting
- Values become relative as opposed to absolute.
- portions per day can be a vague measurement unit
- does not lend itself to the assessment of macro/micronutrients

Question 26

FFQ/ 24 hr recall validation

Answer 26

Usually against some other instrument:
# These aren’t usually designed to look at long-term diet
# Food diary
# Biomarkers