L3 - Dietary Assessment

What is dietary assessment?

A comprehensive process to evaluate food consumption at a national, household, and individual level

What is each level of dietary assessment needed for?

National - public health monitoring

Household - to assess food security and family habits

Individual - personal health or research

Why is dietary intake data collected in research and public health? (4)

• Assess dietary adequacy or gaps

• Monitor trends over time

• Evaluate impact of dietary interventions

• Explore links between diet and disease

Why is dietary intake data collected in a clinical and sports performance setting? (3)

• Support personalised dietary strategies

• Monitor adherence to dietary plans

• Inform medical or therapeutic decisions

Describe the individual-level methods for dietary assessment (2)

• Food records/diaries - weighted or estimated intake that is recorded prospectively (currently)

• Diet history - 24-hour recall or food frequency questionnaires, which are recalled retrospectively

Describe how food diaries are undertaken

• Require an individual to record everything consumed over a specified period (usually 5-7 days)

• The individual should stick to their normal diet

• Intake can either be weighed (weigh before and any leftovers) or estimated from household measures

• Visual estimates of portion size can also be used in more real-life settings

• Detail of food is needed, such as food varieties, thickness, preparation, size, shop bought or takeaway etc.

Why does misreporting occur in food diaries? (2)

• Burdensome - recording fatigue can lead to altered intake or misreporting, e.g., bored of weighing foods leads to changing the diet

• Hawthorne effect - observation prompts a behaviour change (social desirability bias) to stop or limit intake of foods they perceive as unhealthy. This is more common in females and is influenced by age and gender

Describe how food frequency questionnaires work

• Estimates habitual intake of foods or food groups

• Collects information on the frequency and quantity of consumption of specified items

• Provides an estimate of habitual intake over a period of months or years

What are the limitations of food frequency questionnaires? (3)

• Take a while to complete

• Not good for tracking each food portion

• Can consist of about 130 items and rely on memory for foods eaten seasonally

Give the strengths (2), weaknesses (3) and best use of food diaries

Strengths

• Real-time recording

• Sustainable for short term intake

Weaknesses

• High participant burden

• May alter eating behaviour

• Labour-intensive analysis

Best use

• Research studies

• Individual monitoring

Give the strengths (2), weaknesses (3) and best use for 24-hour recall

Strengths

• Easy to administer

• Suitable for short-term intake

Weaknesses

• Interviewer-dependent

• One recall isn’t accurate of overall general intake

• Labour-intensive analysis

Best use

• Population surveys

• Individual monitoring

Give the strengths (3), weaknesses (2) and best use of food frequency questionnaires

Strengths

• Captures habitual intake

• Low cost

• Adaptable to populations

Weaknesses

• Less accurate for absolute intake

• Fixed food list

Best use - large cohort studies

What are dietary reference values (DRVs)?

Population level estimates of energy and nutrient needs that are designed for groups, not individuals, and support public health strategies

Give the DRVs for free sugars, total fat, saturated fat, and trans fat

Free sugars - < 5% total dietary energy from 2 years old

Total fat - < 35% of total energy from 5 years old

Saturated fat - < 11% of total energy from age 5

Trans fat - < 2% of total energy from age 5

What do National Diet and Nutrition Surveys (NDNS) track?

Dietary shifts over time and comparison of averages to DRVs

How is data split in the NDNS and why is this a benefit?

• By years and by the age of the subjects

• Allows for comparison between years of the NDNS and between the ages of participants

What is the equation for estimating resting energy expenditure (REE)?

Males: REE = (10 x weight kg) + (6.25 x height cm) - (5 x age) + 5

Females: REE = (10 x weight kg) + (6.25 x height cm) - (5 x age) - 161

What is the equation for estimating total energy requirements?

Total energy requirements (kcal/day) = REE x physical activity levels x thermic effect of food

What are the different values for different physical activity levels?

Sedentary - 1.2

Lightly active - 1.4

Moderately active - 1.7

Very active - 2.2

What is the value used for thermic effect of food?

1.1

What are the strengths of predictive equations for energy expenditure? (2)

• Accessible and practical

• Predicts resting metabolic rate

What are the limitations of predictive equations for energy expenditure? (1)

Generalisations aren’t applicable for specific populations:

• Athletes - higher RMR and activity levels

• Pregnant women - no specific equation

• Clinical conditions - cancers, CoPD, burns or infections