No 6

Dietary assessment

Purpose of dietary assessment

• 1-To estimate population prevalence of particular foods or food components

• 2-To study time trends in consumption patterns

• 3-To compare intakes of groups

• 4- To study the relationships between intake and health outcomes

• 5-It is used by nutritionists to design nutritional care plans

• 6-To evaluate the effectiveness of therapeutic and educational interventions

• Measurement of nutrient intake is probably the most widely used indirect indicator of nutritional status

It is used routinely in

1. National nutrition monitoring surveys.

2. epidemiologic studies

3. Nutrition studies of free-living participants(those living outside a controlled setting).

4. Various federal and state health.

5. Nutrition program evaluations.

the uninitiated, measurement of nutrient intake may appear to be straightforward and fairly easy. However, estimating an individual’s usual dietary and nutrient intake is difficult.

The task is complicated by

1. Weaknesses of data-gathering techniques

2. Human behavior

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3. The natural tendency of an individual’s nutrient intake to vary considerably from day to day

4. The limitations of nutrient composition tables and databases

• Despite these weaknesses, nutrient intake data are valuable in assessing nutritional status when used in conjunction with anthropometric, biochemical, and clinical data.

• In some instances, data on the kinds and amounts of food eaten by groups or individuals are important because they allow the estimation of nutrient intake. However, conversion of dietary intake data to nutrient intake data requires information on the nutrient content of foods. This is provided by food composition tables and nutrient databases, which are subject to certain limitations and potential sources of error.

• REASONS FOR MEASURING DIET

Assessing dietary status includes considering the types and amounts of foods consumed and the intake of the nutrients and other components contained in foods.

• When food consumption data are combined with information on the nutrient composition of food, the intake of particular nutrients and other food components can be estimated.

Why measure diet?

o To improve human healtho Nutritional problems are at the root of the leading causes of death,

particularly in developed nations. Food and nutrient intake data are critical for investigating

o The relationships between diet and these diseaseso Identifying groups at risk for nutrient deficiency or excesso Formulating food and nutrition policies for disease reduction and

health promotion.

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In general, however, there are four major uses of dietary intake data:

a- Assessing and monitoring food and nutrient intake.

b- Formulating and evaluating government health and agricultural policy.

c- Conducting epidemiologic research.

d- Using the data for commercial purposes.

• Planning national and international food and nutrition programs depends on estimates of per capita (per person) food, energy, and nutrient consumption. Although per capita consumption cannot easily be measured directly, estimates of food disappearance (or availability) are frequently used indirect indicators of consumption.

• Food consumption data are used in formulating public and private agricultural policies for the production, distribution, and consumption of food.

• Repeated surveys estimating food disappearance, such overall patterns of food consumption over time. Among these are changes in the American diet since the early 1900s in sources of energy, composition of foods, consumption of specific food groups, and eating patterns (such as snacking and eating away from home), all of which can have profound health, social, and economic implications

Dietary assessment is used in

• Determining the extent of malnutrition in a population

• Developing nutrition intervention and consumer education programs

• Constructing food guides

• Devising low-cost food plans.

• Providing a basis for food and nutrition legislation.

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Comparisons of dietary practices and nutritional intake with the distribution of disease have demonstrated important links between diet and disease and have shown how dietary changes can modulate disease risk and enhance health.

APPROACHES TO MEASURING DIET

• Various methods for collecting food consumption data are available. It is important to note, however, that no single best method exists, and diet measurement will always be accompanied by some degree of error.

• Selecting the appropriate measurement method, correctly applying it, and using proper data analysis techniques can make the difference between data showing a diet-disease relationship and data showing no relationship where one may actually exist

Choosing the appropriate method for measuring diet depends on such considerations as

• the research design

• Characteristics of the study participants.

• Available resources.

Research Design Considerations

Let’s consider four types of research designs:

a- correlational

b- survey, or cross-sectional

c- case-control

d- longitudinal, or cohort.

Correlational studies compare the level of some factor (e.g., saturated fat intake) with the Level of another factor (e.g., coronary heart disease mortality ) in the same population

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They are useful only for generating hypotheses regarding associations between suspected risk factors and disease outcome and are incapable of testing hypotheses to determine whether a cause-and-effect relationship exists between two variables. It is important to keep in mind that correlation is not necessarily causation. The data used in Correlational studies often are only a rough estimate of dietary intake derived from food disappearance studies and are not based on actual dietary intake measurements.

Using such data, early researchers into the causes of coronary heart disease (CHD) showed that saturated fat consumption is positively correlated with risk of (CHD). This association led to more definitive studies that demonstrated a cause and effect relationship between high saturated fat intake and increased risk of CHD.

Analysis of the data collected from the sample allows conclusions to be drawn about the health and dietary habits of the population from which the sample has been taken. Examples of surveys include the National Health and Nutrition Examination Survey, the National Health Interview Survey (NHANES), the Behavioral Risk Factor Surveillance System. and the Diet and Health Knowledge Survey.

The goal is to collect information on the current diet or dietary habits in the immediate past. The 24-hours recall is the most common method used in surveys, although rod records (or food diaries) and food frequency questionnaires are sometimes used.

• Case-control studies compare levels of past exposure to some factor of interest (e.g., some nutrient or dietary component) in two groups of study participants cases and controls) to determine how the past exposure elates to a currently existing disease. Cases are those people who are diagnosed with a disease being studied (e.g.. coronary heart disease, cancer, or osteoporosis).controls do not have the disease but share certain characteristics with the cases.

• The investigators then look retrospectively (backward in time) to assess each group’s less of exposure to the factor of interest to determine if the disease

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was preceded by the exposure. Thus, case- control studies require methods that measure dietary intake in the recent past (e.g., the year before diagnosis) or in the distant past (e.g., 10 years ago or in childhood). Methods that focus on current behavior, such as the 24-hour recall and food records, are not suitable.

• The only good choices for case control studies are food frequency questionnaires and diet history, which assess diet in the past. Numerous case-control studies have compared fruit and vegetable intake with risk of cancer at various sites. Past intake of fruits and vegetables among persons diagnosed with cancer (cases) has been compared with that of persons apparently free of cancer (controls).

• In these studies, increased fruit and vegetable consumption is consistently linked with reduced risk of cancer of the lung and stomach.

• Longitudinal, or cohort, studies compare future exposure to various factors in a group or cohort of study participants in an attempt to determine how exposure to the factors relates to diseases that may develop. These are also known as prospective studies.

• Thus, longitudinal studies require methods that measure current diet or dietary habits in the immediate past. such as 24-hour recalls, food records, and food frequency questionnaires.

• Sometimes the goal of dietary assessment is to quickly screen a group of people for probable dietary risk. In these instances, a brief questionnaire identifying people with a high intake of fat, cholesterol, or sodium or a low intake of dietary fiber, fruits, or vegetables can be administered. Two such instruments - the fat screener, developed by researchers at the National Cancer Institute, and the MEDFICTS questionnaire

• The food frequency questionnaire and the 24-hour recall are also suitable for this purpose. Time and budgetary constraints are major factors influencing the choice of a dietary measurement method. Analyzing the nutrient content of foods recorded in 24-hour recalls and food records can be labor intensive and costly. These methods also require research stall time in checking them

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over and reviewing them with study participants for completeness and accuracy.

• Self-administered food frequency questionnaires, on the other hand, can save considerable time and expense. They can be mailed to study participants, who can complete them on their own and then mail them back to the researchers for data entry and processing. Some food frequency questionnaires are designed to be optically scanned, thus resulting in further saving of staff time and expense.

Characteristics of Study Participants

• Factors influencing the selection of a dietary measurement technique include literacy, memory, commitment, age, ability to communicate, and culture of the participants. If some study participants are likely to be unable to read and/or write, the best methods are the 24-hour recall and the food frequency questionnaire administered by a member of the research team. The food record or self-administered food frequency questionnaire is not recommended.

• The 24 hour recall and food frequency questionnaire require the ability to remember past eating habits. Food records and self administered food frequency questionnaires require the training and active participation of the study participants. The level of effort required can also lead participants to change their dietary patterns during the recording period. Consequently, there is concern about response rates, the comparability of recording skills among participants, and the quality of dietary intake results.

• The ability to communicate may be limited in study participants who are very young, elderly, developmentally disabled, victims of stroke or Alzheimer’s disease, or deceased.

• In these instances, dietary intake data may have to be collected from another person familiar with the study participant. such as a parent. spouse. child, or sibling. This other person is known as a surrogate source.

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• A food inventory method can be done by older persons living at home. Direct observation of eating habits of persons in institutional care facilities can also be done. The eating habits of children has been assessed using the 24-hour recall, food records, and food frequency questionnaires.

• Assessing the diets of younger children may require information from surrogates or use of the “consensus recall method,” in which the child and both parents give combined responses on a 24—hour recall. This approach has been shown to give more accelerate information than a recall from either parent alone .

• Assessing the diets of ethnic populations requires modification of existing methods. If participants are interested, it is preferable that these be done by persons of the same ethnic or cultural background. so that dietary information can be gathered more effectively.

• Nutrient analyses of ethnic foods and dishes will likely require changes in food composition databases. Food frequency questionnaires will have to be modified to include food common to the ethnic group being studied.

Available Resources

• Some methods for measuring diet are more expensive and labor intensive to administer than others. Before a study begins, the budget must be carefully considered, so that the costs entailed will match the available resources.

• The 24—hour recall, for example. must be administered by a trained interviewer. If the food record is used, study participants should be trained to properly record their diets. Considerable labor is required to enter data from 24—hour recalls and food records into a computer for analysis

• Food frequency questionnaires can be self— administered, and responses can be marked on a form. which is then optically scanned. Data can then be downloaded into a computer for analysis. thus saving considerable time, effort, and expense.

• Food records and 24—hour recall Is tend to be more feasible methods to use in research with smaller numbers of participants. Food frequency

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questionnaires. on the other hand, are often preferred by researchers studying large numbers of people

TECHNIQUES IN MEASURING DIET

• Measurement of dietary intake usually is conducted for one of three purposes: to compare average nutrient intakes of different groups, to rank individuals within a group, and to estimate an individual ‘s usual intake.

• Dietary measurement techniques can be categorized as daily food consumption methods (food record and 24—hour recall) and recalled ‘usual” or average food consumption methods (diet history and food frequency questionnaire).

• These techniques has e also been categorized as meal—based (food record and 24—hour recall) and List—based (food frequency questionnaire ).

24-Hour Recall

• In the dietary recall method, a trained interviewer asks the respondent to recall in detail all the food and drink consumed during a period of time in the recent past.

• The interviewer then records this information for later coding and analysis. (In coding. a number is assigned to each kind of food, allowing it to be identified easily for computer analysis.) In most instances, the time period is the previous 24 hours. Thus, the method is most commonly known as the 24—hour recall.

• Occasionally. however, the time period is the previous 48 hours, the past 7 days, or. in rare instances, even the preceding month. However. memories of intake may fade rather quickly beyond the most recent day or two, so that loss in accuracy may exceed gain in representativeness.

• In addition to recording responses. The interviewer helps the respondent remember all that was consumed during the period in question and assists the respondent in estimating portion sizes of foods consumed. A common technique of the 24—hour recall is to begin by asking what the respondent

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first ate or drank on last awakening. The recall proceeds from the morning of the present day to the current moment.

• The interviewer then begins at the point exactly 24 hours in the past and works forward to the time of awakening. Some researchers ask respondents to recall their diet from midnight to midnight of the previous day. Asking the respondent about his or her activities during the day and inquiring how they might has e been associated with eating or drinking can help in recalling food intake.

• An inquiry about the previous evening's activities, for example. will stimulate the respondents memory and may help him or her recall the snack eaten while watching a favorite ides television program. After the interview, the recall is checked or omissions and/or mistakes. A respondent nay has e to be contacted later by telephone or nail to clarify an entry or to obtain information such as brand names

• preparation methods, and serving sizes .The recall can then be analyzed rising a computerized diet analysis program. Most programs allow research staff to enter the name of the food into the computer and then select the appropriate method of preparation, serving size, and number of servings from a list of choices displayed on the computer screen.

• In some instances, however, each food may have to be coded using a unique number of food code that identifies each food. For the food “green beans,’’ there may be separate code numbers for cooked frozen credo beans, canned green beans, cooked fresh green beans, and so on.

• This code then is entered into the analysis software (to identify the food) along with the serving size and number of servings to calculate the nutrients of that food.

Strengths and Limitations of the 24-Hour Recall

• Strengths

• Inexpensive

• Requires less than 20 minutes to administer

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• Easy to administer

Can provide detailed information on types of food consumed

• Low respondent burden Probability sampling possible

• Can be used to estimate nutrient intake of groups

• Does not alter usual diet

• Useful in clinical settings

• More objective than dietary history

Multiple recalls can be used to estimate intake of individuals

• Limitations

• One recall is seldom representative of a person’s usual intake

• Underreporting/overreporting occurs

• Relies on memory

• Omissions of dressings, sauces, and beverages can lead to low estimates of energy’ intake

• May be a tendency to overreport intake at low levels and overreport intake at high levels of consumption

• Data entry can be very labor intensive

Food Record, or Diary

• In this method, the respondent records, at the time of consumption, the identity and amounts of all foods and beverages consumed for a period of time, usually ranging from I to 7 days.

Food and beverage consumption can be quantified by estimating portion sizes, using household measures, or weighing the food or beverage on scales. In many instances, household measures such as cups. tablespoons,

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and teaspoons or measurements made with a ruler are used to quantify portion size.

• Certain items, such as eggs, apples, or 12-oz cans of soft drinks. may be thought of as Units and simply counted. This method is sometimes referred to as the estimated food record because portion size are estimated ,or household measures are used. When food is weighed, the record may be referred to as a weighed food record .

Comparison of the Estimated Food Record and the Weighed Food Record

Estimated Food Record

Amounts of food and leftovers are measured in household measures (cups. tablespoons. teaspoons) or estimated using such measures as coffee cups, bowls, glasses, and dippers

• The researchers then quantify these measures by volume and weight

• Considered less accurate than the weighed food record

• Considered an acceptable method for collecting group intake data .

• Puts less burden on the respondent than the weighed food record and thus cooperation rates are likely to be higher, especially over long recording periods .

• As effective in ranking subjects into thirds and fifths as weighed records

Weighed Food Record

• Food and leftovers are weighed using scales or computerized techniques supplied by researchers .

• Considered more accurate than the estimated food record

• Preferred by some researchers for gathering data on individuals

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• Requires a greater degree of subject cooperation than the estimated food record and thus is likely to have a greater impact on eating habits than the estimated food record

• Cost of scales may be prohibitive in some instances

Strengths and Limitations of the Food Record

• Strengths Does not depend on memory Can provide detailed intake data Can provide data about eating habits multiple—day data more representative of usual intake Reasonably valid up to 5 days

• Limitations Requires high degree of cooperation Response burden can result in low response rates when used in large national surveysSubject must be literate Takes more time to obtain data Act of recording may alter diet Analysis is labor intensive and expensive

Food Frequency Questionnaires

• Food frequency questionnaires assess energy and/or nutrient intake by determining how frequently a person consumes a limited number of foods that are major sources of nutrients or of a particular dietary component in question.

• The questionnaires consist of a list of approximately 150 or fewer individual foods or food groups that are important contributors to the population’s intake of energy and nutrients. Respondents indicate how many times a day, week, month, or year that they usually consume the foods . In some food frequency questionnaires, a choice of portion size is not given.

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• These generally use “standard” portion sues (the amounts customarily eaten per serving for various age/sex groups) drawn from large- population data. It simply asks how many times a year. month, week, or day a person eats dark bread or ice cream.

• This is sometimes referred to as a simple, or non-quantitative food frequency questionnaire format. The semi- quantitative food frequency questionnaire, gives respondents an idea of portion size. It asks how many times a year, month, week, or day a person eats a slice of dark bread or a cup serving of ice cream.

• Food frequency questionnaires known as “screeners’’ have been developed to assess intake of calcium, dietary fiber, fruits and vegetables. and percent energy from eat. Screeners are particularly useful in situations that do not require assessment of the total diet or quantitative accuracy in dietary estimates and in situations in which financial resources are limited .

• They are commonly used in epidemiologic research investigating the relationship between diet and such conditions as cancer and cardiovascular disease but are not considered substitutes for more definitive approaches to measuring diet.

• one were shown to have potential for estimating median intake of fruits and vegetables but were less useful for accurately ranking the intakes of individuals

• A questionnaire developed to quickly estimate how frequently foods high in total fat, saturated fatty acids. and cholesterol. It is called the MEDEICTS Dietary Assessment Questionnaire (Meats, Eggs Dairy, Fried foods, In baked goods, Convenience foods, Table fats, Snacks) and is recommended by the National Cholesterol Education Program as a simple approach to assess a person's intake of total kit, saturated fat, and dietary cholesterol

• MEDFICTS focuses on foods that are major contributors of total fat, saturated fat, and cholesterol commonly eaten by North Americans. Within each of the questionnaires eight categories. foods are placed into either a

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high—fat. high—cholesterol group (Group I ) or a low-fat, low-cholesterol group (Group 2).

• Group I foods are major contributors of dietary fat and cholesterol, and to the right of these groups is a series of boxes with numbers representing points under each box. Group 2 foods are minor contributors of fat and cholesterol.

• Studies suggest that the MEDFICTS does a good job of estimating intake of total fat, saturated fat, and cholesterol, compared with intake estimates based on multiple food records. Numerous food frequency questionnaires have been developed and tested.

Strengths and Limitations of Food Frequency Questionnaires

Strengths Can be self-administeredMachine readable Modest demand on respondents Relatively inexpensive for large sample sizes

May be more representative of usual intake than a few days of diet records Considered by some as the method of choice for research on diet disease relationships

• Limitations May not represent usual foods or portion sizes chosen by respondents Intake data can be compromised when multiple foods are grouped within single listings Depend on ability of subject to describe diet

Willett Questionnaire

• Beginning in 1979, a team of Harvard University nutritionists and epidemiologists headed by Walter C. Willett developed a series of self—administered semi- quantitative food frequency questionnaires to conduct

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epidemiologic research on the relationships between nutrient and food intake and risk of’ chronic disease.

• Over the years, their original 61 —item questionnaire was modified several times. A more recently developed 131 item questionnaire was designed to classify individuals according to levels of average daily intake of nutrients and certain foods and food components during the past year.

• It is self- administered and machine readable, thus making it convenient for use in large epidemiologic studies. Foods included in the questionnaire are those that are major sources of the nutrients, foods, and food components of interest to the researchers. Open-ended questions are also included to identify specific brands of margarine, ready-to eat cereals, cooking oils.

• vitamin/mineral supplements. and other foods eaten at least once per week. For each item on the questionnaire, respondents are given nine choices ranging from less than once per month to six or more times per day .

• Nutrient values are calculated by multiplying nutrient content of each item by frequency of use.

• The Willett questionnaire has been designed to be self-administered by nurses and other health professionals in such epidemiologic studies as the Nurses’ Health Study and the Health Professionals Follow-up Study with populations of more than 120,000 female nurses and nearly 50.000 male health professionals respectively.

• However, the similar food frequency questionnaire has been used successfully in a group of socioeconomically diverse group of older women living in Iowa. Researchers at Harvard University Medical School and Brigham and Women’s Hospital in Boston have adapted the Willett food frequency questionnaire for assessing the diets of children and adolescents ages 9 to I 8.

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Block Questionnaire

• The Block Dietary Questionnaire is a self-administered, scannable quantitative food frequency questionnaire developed by Gladys Block and based on an earlier food frequency questionnaire known as the Block Health Habits and History Questionnaire (HHHQ). which was developed by Block and coworkers at the National Cancer Institute in l992.

• The HHHQ was designed to collect data on diet and well—established risk factors for cancer and total mortality, and it has proven useful in assessing total dietary intake.2t ‘ Block revised the HHHQ in 1995 and 1998, and the most recent version is known as the Block Dietary Questionnaire, or the “Block98.”

• The Block Dietary Questionnaire was developed using data from the 24—hour recalls of a statistically representative sample of more than 20.000 American adults who participated in the third National Health and Nutrition Examination Survey (NHANES Ill), conducted from 1988 to I 994.

• The 4312 different food codes recorded in these 24-hour recalls were grouped into more than 200 conceptually similar food items based on several criteria, including similarity in nutrient content per usual serving (for example, 29 different codes for green beans were consolidated into one food item labeled “green beans”).

• The decision to include an item on the food list was based on whether it was a major contributor of energy and nutrients, the frequency of its consumption by the population. and the typical serving size. Foods included in the 109-item food list are those contributing more than 90% of the nation’s total energy and nutrient intake.

Diet History Questionnaire

• The Diet History Questionnaire (DHQ) is a self-administered, scannable food frequency questionnaire developed by staff at the U.S. National Cancer Institute’s Risk Factor Monitoring and Methods Branch. It contains 124 food items and include both portion size and dietary supplement questions.

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• The DHQ is based on research that led to the development of the Block Health Habits and History Questionnaire (H HHQ): however, HHHQ in three ways. First, the design of the DHQ incorporates results from cognitive testing on more than 75 people, 50 to 70 years of age, of varying income, occupation. and ethnicity.

• This testing addressed commonly encountered problems in food frequency questionnaires related to comprehension, order of food items, intake of seasonal foods, intake averages from multiple food items, and format.

• Second. the list of foods and portion size in the questionnaire were updated to reflect recent changes in the dietary habits of many Americans, including the increased use of low—fat foods and changes in the types of fats used in food preparation. Third. the DHQ uses an improved method to convert information about frequency of food intake and port ion sizes into daily nutrient intake estimates.

Diet History

Diet history is used to assess an individual’s usual dietary intake over an extended period of time, such as the past month or year. Traditionally , the diet history approach has been associated with the method of assessing a respondent’s usual diet developed by B. S. Burke during the l940s

• Burke’s original method involved four steps: (I) collect general information about the respondent’s health habits, (2) question the respondent about his or her usual eating pattern. (3) perform a cross-check on the data given in step 2, and (4) have the respondent complete a 3-day food record.

• A trained nutritionist begins the interview by asking questions about the number of meals eaten per day appetite: food dislikes: presence or absence of nausea and vomiting: use of nutritional supplements: cigarette smoking: habits related to sleep, rest, work, and exercise: and so on.

This allows the interviewer to become acquainted with the respondent in ways that may be helpful in obtaining further information. This is followed by a 24—hour recall, in which the interviewer also inquires about the respondents usual

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pattern of eating during and between meals, beginning with the first food or drink of the day.

• The interviewer records the respondent’s description of his or her usual food intake, including types of food eaten, serving sizes. frequency and timing. and significant seasonal variations.

Strengths and Limitations of the Diet History Method

• Strengths Assesses usual nutrient intake Can detect seasonal changes Data on all nutrients can he obtained Can correlate well with biochemical measures

• Limitations Lengthy interview process Requires highly trained interviewersDifficult and expensive to code May tend to overestimate nutrient intake

Duplicate Food Collections

• Collection of food consumption data generally is not an end in itself but, rather, it means of eventually arriving at an estimate of nutrient intake.

• The limitations of using food consumption data to arrive at nutrient intake are the incompleteness of food composition tables, mistakes in coding and entering data, and nutrient losses during food storage and preparation that may not be accounted for in food composition tables

• A more direct method of calculating nutrient intake that avoids these particular problems is duplicate food collections

Strengths and Limitations of the Duplicate Food Collection Method

• Strengths Can provide more accurate measurements of actual nutrient intake than calculations based on food composition tables.

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• Limitations Expense and effort of preparing more food Effort and time to collect duplicate samples May underestimate usual intake

Food Accounts

• Food accounts are used to measure dietary intake within households and institutions where congregate feeding is practiced, such as penal institutions, nursing homes , military bases, and boarding schools.

• The method accounts for all food on hand in the home or institution at the beginning of the survey period, all that is purchased or grown throughout the period, and all that remains by the end of the survey.

• Inventories establish amounts of food on hand at the beginning and ending of the survey period, and invoices or other accounting methods provide records of food purchased or obtained from a farm or garden.

ESTIMATING PORTION SIZE

• A variety of approaches can be used to help participants estimate portion sizes. Among the simplest and least costly are “food models” composed of various geometric shapes cut out of poster board.

• Circles of various diameters can be used to help estimate the diameter of round foods, such as apples, oranges. tomato slices, hamburger patties. hamburger buns, and cookies.

• Square and rectangular pieces are used in estimating the length and width of bread, cake, some cuts of meat, and cheese. Pie—shaped pieces of various radii can be used in estimating portion sizes of pie , round cake, watermelon, and pizza.

• Two dimensional food models have been shown to be as effective as three—dimensional models for estimating portion size In nutritional research. In addition, glasses. bowls, and cups of various sizes; household spoons: measuring spoons: and measuring cups can be used as aids in helping respondents estimate portion size .

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