Methods of Dietary Intake and Food Habits Examination
Methods of Examination of Dietary Intake and Food Habits (Nutritional Monitoring)
Background:
– Food consumption can be assessed at individual, household, or national levels through the use of surveys.
– The resulting data may be expressed in terms of nutrients and/or types of food.
– The method selected for dietary assessment in research depends on the purpose of the assessment, the available funding, and the burden it is appropriate to impose on the respondents and the study.
Commonly used methods include:
– A single 24-hour recall
– Multiple 24-hour recalls or multiple diet records
– Food frequency questionnaires
– Brief dietary screening tools
– Dietary history since early life
Recall Records:
– Based on a 24-hour or 3-day dietary record, including one weekend day (Saturday or Sunday).
– The patient should write everything they ate and drank for 3 days without changing their food habits.
– They should record portion sizes accurately and keep an activity record of the exercise they did every day, including the time spent on each activity.
– Risks of the analysis:
o Motivation of the patient to stay honest
o Inability to give correct data due to unawareness of cooking methods or products.
o Computer errors according to the composition of food and nutrients.
– Single 24-hour recall:
o A trained interviewer asks the subject to recall all food and drinks taken in the previous 24 hours.
o It is quick, easy, and depends on short-term memory but may not be truly representative of the person’s usual intake.
o Method of choice if:
The purpose of the study is simply to describe the average intake of a group → Because it provides a mathematically accurate group mean.
Note: It does not provide a good estimate of an individual’s usual intake for any individual member of the group.
One wants to examine whether two groups have similar mean intakes.
E.g., the baseline levels of an intervention and a control group.
o Multiple 24-hour recalls or multiple days of diet records:
Use for evaluation of a single person.
Generally, at least three days of diet data are required for the most stable nutrient, percent of calories from fat.
Micronutrients such as vitamin C and vitamin A require many more days.
Except for very large, well-funded studies, anything larger than three days is not generally feasible.
Disadvantages:
Respondents may choose not to consume certain foods during the recording period.
Respondents tend to forget to record their food intake as the day progresses.
Food Frequency Questionnaires (Semi-Quantitative):
– Dietary pattern assessment tool used in large epidemiologic studies of diet and health.
– The subject is given a list of around 100 food items to indicate his or her intake (frequency and quantity) per day, per week, and per month.
– Inexpensive, more representative, and easy to use.
– Limitations:
o Long questionnaire.
o Errors with estimating serving size.
o Needs updating with new commercial food products to keep pace with changing dietary habits.
– Most nutrition research is interested in the usual intake of the individual:
o Consequently, single 24-hour recalls are not appropriate.
o Thus, many researchers have turned to food frequency questionnaires as the most appropriate method.
Dietary History:
– It is an accurate method for assessing nutritional status.
– The information should be collected by a trained interviewer.
– Details about usual intake, types, amount, frequency, and timing need to be obtained.
– Cross-checking to verify data is important.
Food Diary:
– Food intake (types and amounts) should be recorded by the subject at the time of consumption.
– The length of the collection period ranges between 1-7 days.
– Reliable but difficult to maintain.
Dietary Screening Tools:
– For some research or public health purposes, a full-length questionnaire is not practical.
– Therefore, screening tools have been developed, usually to assess just one or two nutrients or food groups.
– They generally do not include portion size but just ask about frequency.
Household Surveys:
– The main objective is to collect data on the quantities of food items consumed by random families from the population.
– They provide detailed data on food consumed in the household as well as away from home (i.e., any food and beverages, meals and snacks eaten outside the home by members of the family).
– The information on household food consumption is obtained by weighing and measuring food items to be used before preparing each meal. The amount of food should be divided by each family member.
– Information on food consumed away from home is obtained by interviewing each member of the household.
– The food consumption data obtained from this type of survey represents an estimate of the quantities actually eaten.
– This is normally carried out for 2, 5, and 7 consecutive days.
National Food Supply:
– The most used method that assesses the food available nationally for consumption.
– It is based on food balance sheets (which are published annually by the Food and Agriculture Organization – FAO).
– It is based on an estimated value of the population number and doesn’t provide information about the distribution or extent to which the food intake of individuals varies within the population.
– The results are frequently used to compare the available food supply between countries and to monitor trends over time within an individual country.
Total Diet Studies – TDSs:
– They’re sometimes called the market basket study.
– They are specifically designed to establish (by chemical analysis) the dietary intake of food contaminants by a person consuming a typical diet from a particular region or country.
– From this information, dietary intakes of the selected group can be estimated.
– This is because exposure assessment may be different from one country to another due to differences in food consumption habits or food contamination.
o For example, the dietary exposure to aluminum, chromium, copper, selenium, and zinc can be regularly checked to see if there are any health risks from the levels found.
– For this type of study, food items that comprise part of the average diet of the selected group of interest are purchased from shops representative of the town/country.