3.1: Methods for measuring food con­sump­tion of indi­viduals

This chapter describes methods commonly used for measuring the food con­sump­tion of indi­viduals. Subsequent chapters discuss the factors associated with the reproducibility and validity of each of these methods (Chapters 5‑7) and the calcu­lation and, subse­quently, evaluation of nutrient intakes (Chapters 4 and 8b).

Two groups of methods are used to measure the food con­sump­tion of indi­viduals. The first group, known as quanti­tative daily con­sump­tion methods, consists of recalls or records designed to measure the quantity of the indi­vidual foods con­sumed over a one day period. By increasing the number of measurement days, quanti­tative esti­mates of the usual intakes of indi­viduals can be obtained, using the same methods. The number, selection, and spacing of the days depend on the food intake, the nutrients of inter­est, the day-to-day vari­a­tion in nutrient intake, and the level of precision required. Determination of the usual intake of indi­vid­uals is partic­ularly critical when relationships between diet and biological parameters or health or chronic disease are assessed. Estimates of usual intakes of indi­vid­uals in a group or popu­lation are also needed to estimate the prevalence of inadequate intakes.

The second group of methods includes the dietary history and the food fre­quency question­naire. Both obtain retrospective inform­ation on the patterns of food use during a longer, less precisely defined time period. Such methods can be used to assess the usual intake of foods or specific classes of foods. With modifi­cation , they can also provide data on usual nutrient intakes of indi­viduals.

Quantitative daily con­sump­tion methods such as 24h recalls and records, when adjusted appropriately statis­tically to assess usual intakes, provide less-biased esti­mates of dietary intake than those such as food fre­quency question­naires and dietary histories that are designed to generate data on usual intakes directly (National Cancer Institute, 2015).

The measurement of food con­sump­tion at the indi­vidual level is costly and time consuming. Hence, such studies should be planned with care (Thompson et al., 2015). Even with the advent of new technologies to measure dietary intakes (Section 3.2), challenges still remain. Consid­eration should be given to the cost-effective collection of additional data from the same indi­viduals at the same time; such additional inform­ation may significantly enhance the inter­pretation of the dietary data. At a minimum, socioeconomic and health-related inform­ation, simple anthropometric measures, possibly a physical activity question­naire, and biological samples for the determination of important biomarkers (Chapter 15) should be collected when time and resources permit (Buzzard and Sievert, 1994).

The accurate assess­ment of the food intake of infants is partic­ularly difficult, espe­cially when infants are receiving both breast milk and complementary foods (Piwoz et al., 1995). WHO (2023) has published guidelines that can be used to evaluate nutrient intakes of breastfed infants receiving complementary foods.

3.1.1 Twenty-four-hour recall method

In the 24h recall method, the respon­dent and, where necessary, their parents or caretakers are asked by the nutritionist, who has been trained in inter­viewing tech­niques, to recall the respon­dent's exact food intake during the previous 24h period or preceding day. Thus the method assesses the actual intake of indi­viduals. However, a single 24h recall is not sufficient to describe an indi­vidual's usual intake of food and nutrients; multiple 24h recalls on the same indi­vidual over several days are required to achieve this objective (Section 3.1.2). Nevertheless, multiple single-day recalls on dif­fer­ent indi­viduals can give a valid measure of the usual intake of a group or popu­lation (Section 3.3.1).

A multiple-pass inter­viewing tech­nique is recommended for the 24h recall methods. The USDA has devel­oped an automated multiple-pass method (AMPM) consisting of five steps to collect dietary data using the 24h recall method; these five steps are shown in Table 3.1. The AMPM is used by the US in the National Health and Nutrition Examin­ation Surveys (NHANES). Branded food products have now been added to the NHANES generic data­base to facilitate easier selection of foods con­sumed by the participants.

Table 3.1 USDA's Automated Multiple Pass Method. From (AMPM., 2013).

Design	AMPM Step	Memory Cues
Unstructured Respondents use their own strategy	Quick List ⇓ Collects recalled foods	Yesterday, midnight to midnight, day of week, activities, snacks and bever­ages, location
Structured Questions for specific types of foods	Forgotten Foods⇓ Probes for categories of forgotten foods	Seven question: Beverages, alcoholic bever­ages; sweets; savory snacks; fruits, veg­etables or cheese; breads or rolls; and one for anything else.
Structured Times and names of eating occasions	Time & Occasion⇓ Collects eating times and meal names	Breakfast, lunch, dinner, snack
Structured Standardized questions to collect details of each food Review foods for each eating occasion & intervals between each occasion	Detail Cycle⇓ Collect food details and amounts.	For breakfast you had a bagel & coffee Anything else? Did you have anything between your 7am breakfast and 10am snack?
Unstructured Respondents use their own strategy	Final Probe⇓ Anything else recalled	Situations where foods may have been easily forgotten: in the car, at meetings, when shopping, cooking, or cleaning up?

The first step in the AMPM is the Quick List where respon­dents list all food con­sumed in the previous 24h period. The second step, called Forgotten Foods, includes a series of questions that probes for categories of foods that are commonly forgotten. The third step, Time & Occasion, collects the time each food was eaten and the name of the eating occasion. The fourth step is the Detail Cycle which elicits descrip­tions of foods and amounts eaten, aided by the inter­active use of the USDA Food Model Booklet and measuring guide (USDA 2002+); see Chapter 5 for more details. The Detail Cycle also includes questions that review each eating occasion and each inter­val between eating occasions. The fifth step is a final review question, the Final Probe, which provides the respon­dent a final opportunity to recall any foods that had not been reported previously during the inter­view. The AMPM has been validated by comparing reported energy intake in young children with total energy expenditure assessed using the doubly labeled water method (Johnson et al., 1996) and in an observational study in which actual intakes of energy, protein, carbohydrate, and fat were compared with recalled intakes in men (Conway et al., 2004).

A modifi­cation of the multiple-pass 24h recall consisting of four passes — termed an interactive 24h recall — has been devel­oped to collect information on rural popu­lations in low- and middle-income coun­tries; details are given in the technical monograph by Gibson and Ferguson (2008).

In the first pass a complete list of all the foods and bever­ages con­sumed during the preceding day is obtained.

In the second pass, a detailed descrip­tion of each food and beverage con­sumed, including cooking methods and brand names (if possible) is collected. Standardized probe questions, specific for the popu­lation subgroup and setting, should be used to elicit specific details for each food item. For example, for milk products, probe questions should include the kind of dairy product, brand name (if appropriate), and percentage fat (as butterfat or milk fat). Further examples of probes that can be used to obtain detailed descrip­tions of specified foods are also provided in the monograph.

In the third pass, esti­mates of the amount of each food and beverage item con­sumed are obtained, generally in house­hold measures, and entered either on the data sheet Appendix 3.1 or a computer-based data-entry form. Care must be taken to record whether any fortified foods or bever­ages have been con­sumed. Graduated photo­graphs (Vossenaar et al., 2020), a set of measuring cups, spoons, and rulers, local house­hold utensils (calibrated for use), play dough, or food models of various types (Chapter 5) can be used to assist the respon­dent in assessing portion sizes of food items con­sumed (Gibson and Ferguson 2008; Lazarte et al., 2012). See guidelines on portion-size estimation methods by Vossenaar et al. (2020). Vossenaar et al. (2022) also provide technical guidance on how to collect, compile, and use portion size estimation method conversion factors in a 24h recall. Information on the amount of any mixed dishes con­sumed by the respon­dents, the amount of each ingredient in the mixed dishes, and the total amount of each cooked mixed dish prepared must also be collected at this time. These details are usually recorded on a separate data sheet or computer-based data-entry “recipe form". Vossenaar et al. (2023) have published guidance on the use of standard and non-standard recipes in quanti­tative 24h dietary recall surveys.

In the fourth pass, the recall is reviewed to ensure that all items, including the use of vitamin and mineral supplements, have been recorded correctly. Methods for coding the completed 24h recalls and potential sources of coding errors are discussed in Chapter 5.

Additional modifications that can be used in the interactive 24h recall are listed in Table 3.2 and are discussed in more detail in the technical monograph (Gibson and Ferguson 2008). Whenever possible, recall inter­views in rural settings in low and middle-income coun­tries should be conducted in the respon­dent's home, because the familiar environment encourages partic­ipation, improves the recall of foods con­sumed, and facilitates calibration of local house­hold utensils by the inter­viewer. For a review of potential measurement errors using self-reported 24h recalls in low-income coun­tries and strategies for their prevention, see Gibson et al. (2017). However, major challenges arise when assessing food con­sump­tion at the indi­vidual level in coun­tries or cultures where the majority of the food con­sumed is as shared plate eating. Strategies used to overcome some of these challenges are reviewed by (Burrows et al. 2019).

Table 3.2: Interactive 24-h recall modifications suggested for rural popu­lations in developing coun­tries to improve the recall of food items. From Gibson and Ferguson (2008).

Provide group training on portion size estimation before the actual recall.
Supply picture charts on the day before the recall for use as a checklist on the day the food is actually con­sumed, and for compar­ison with the recall to reduce memory lapses.
Provide bowls and plates for use on the recall days to help the respon­dents visualize the amount of food con­sumed.
Weigh the portion sizes of salted replicas of the actual foods con­sumed by the respon­dent.

A major advantage of a 24h recall is that the respon­dent burden is small so that compliance is generally high. In addition, the method is quick and relatively inexpensive, and can be used equally well with both literate and illiterate respon­dents. Nevertheless, any 24h inter­view protocol must be stan­dardized, pretested,and then piloted prior to use. Standardization is partic­ularly important in large-scale national surveys and for compar­isons across coun­tries(Slimani et al., 2000; Vossenaar et al., 2020). Adherence to the inter­view protocol and accuracy of food coding by the inter­viewers should be checked periodically during the survey, and the inter­viewers must be retrained if required to minimize inter­viewer bias (Chapter 5). Detailed sugges­tions on how to conduct the inter­view can be found in Hughes (1986) who stressed that leading questions and judgmental comments should be avoided. An indi­rect approach employing open-ended questions is recommended. This enables respon­dents to freely express their feelings so that answers are not biased. Piloting should be undertaken in an area near the study site, using respon­dents similar to those who will partic­ipate in the actual study.

When 24h recalls are used to characterize the average usual intake of a popu­lation group, the respon­dents should be representative of the popu­lation under study. In addition, the survey should be conducted in such a way that all days of the week are equally repre­sented. In this way, any day-of-the-week effects on food or nutrient intakes will be taken into account (Chapter 6). Seasonality must also be consid­ered as it affects food availability.

Guidelines on how to plan, design, and conduct large-scale 24h recall dietary surveys in low-and middle-income coun­tries have been devel­oped by the Intake Center for Dietary Assessment (Vossenaar et al., 2020; Deitchler et al., 2020), An outline of the main tasks that must be completed prior to the conduct of a large-scale 24h recall survey is presented in Figure 3.1. Intake.org also provide recommended specifications for dietary scales and procedures to test their accuracy and precision (Vossenaar et al., 2020).

Figure 3.1. PSEM: Portion size estimation method. FCDB: Food composition data­base. Guidelines on planning for a large-scale 24-hour recall dietary survey in low- and middle-income coun­tries. From: Vossenaar et al. (2020).

A 24h recall has been used in several national nutrition surveys in low‑, middle‑, and high-income coun­tries. Examples include the Cameroon (Engle-Stone et al., 2014), Nigeria (Maziya-Dixon et al., 2004), New Zealand (Hennigar et al., 2018). (MOH, 2011), and the US NHANES III survey (Hennigar et al., 2018). Intake.org has provided technical assistance to support national or large-scale dietary surveys in Ethiopia, Jordan, Kenya, Niger, Nigeria, Senegal, Viet Nam, and Zambia. The AMPR method, used in the US NHANES III, has been adapted for use by both the Canadian and Australian national health surveys.

The US National Cancer Institute have devel­oped an Automated Self-Administered 24h recall (ASA24) based on the US AMPR method which is suitable for large-scale epi­demio­logical studies (Subar et al., 2012). The ASA24 web-based system was tested for use with children and adults in Canada (Kirkpatrick et al., 2017). Overall partic­ipants were receptive to completing ASA24, although the ASA24 inter­face and the steps in completing the recalls were not necessarily intuitive, espe­cially for younger children and elderly adults. The inves­tigators emphasized the importance of piloting protocols using online tools and the potential need for tailored resources to support certain age groups.

In general, recall inter­views can be conducted on children aged > 12y (Deitchler et al., 2020), and on most adults, except for persons with poor memories (e.g., some elderly). Parents are typically relied upon as proxy reporters for capturing dietary intake for children under five years of age. Children aged from 5–12y should be inter­viewed along with their primary caretaker, usually the mother, an approach termed assisted reporting. It may be necessary to inter­view several people if the children are at school, day-care, or play in the homes of friends, to ensure that all foods eaten away from home are reported. Recipe data for school or day-care meals may be required to supplement the food intake data collected in the home. In a study of Canadian preschool children 2–5y in which parents used the online self-admin­istered 24h recall (ASA24), they were able to report the food and bever­ages that their child had con­sumed with reasonable accuracy but the accuracy of portion size esti­mates was low(Wallace et al., 2018).

In the end, the success of the 24h recall, irrespe­ctive of the method applied, depends on the respon­dent's memory, their ability to convey accurate esti­mates of portion sizes con­sumed, the degree of motivation of the respon­dent, and the persistence of the inter­viewer (Acheson et al., 1980).

3.1.2 Repeated 24h recalls

Twenty-four-hour recalls can be repeated to estimate the average food intake of indi­viduals over a longer time period (i.e., usual food intake). The number of 24h recalls required to estimate the usual nutrient intake of indi­viduals depends on the day-to-day vari­a­tion in food intake within one indi­vidual (i.e., within-person vari­a­tion ). In turn, this vari­a­tion is affected by the nutrient under study, the study popu­lation, and seasonal vari­a­tions in intake.

Repeated 24h recalls were recommended as part of a system for measuring food con­sump­tion patterns in the United States to account for within-person variability as early as 1981 (NRC, 1981). In the US NHANES 2011–2014, food intakes on two non-consecutive days were recorded, on the first day through using computer-assisted personal recall inter­views (CAPI), and on the second day via a computer-assisted systematic telephone inter­view (CATI), using the AMPR on both occasions (Amoutzopoulos et al., 2018). The second recall inter­views were not conducted on all respon­dents, but instead were repeated on a randomly selected sub­sample of the popu­lation. Tooze (2020) recommends that the repeated 24h recalls should be performed on non-consecutive days 3–10d apart, and when only a random sub­sample of the popu­lation is used, repeated on at least 50 indi­viduals per stratum. Moreover, when episod­ically con­sumed foods, food groups or nutrients are of partic­ular inter­est, then more replicates per person should be collected rather than increasing the sample size from which two replicates are obtained (Tooze, 2020).

Repeated 24h recalls assisted by inter­viewers were also used for the Dutch National Food Con­sump­tion Survey (DNFCS) (van Rossum et al. 2016)and the French Nutrition and Health Survey (Castetebon et al., 2009). Several research groups in the UK have incorporated new technologies to collect 24h recalls, including the two web-based methods, myfood24 (Carter et al., 2015) and INTAKE24 (Simpson et al., 2017); see Section 3.2.3 for more details.

3.1.3 Estimated food records

For the estimated food record, also referred to as a food diary by some researchers, the respon­dent is asked to record in house­hold measures, at the time of con­sump­tion, all foods and bever­ages eaten (including snacks), for a specified time period. Detailed descrip­tions of all foods and bever­ages (including brand names) and their method of preparation and cooking should also be recorded. For mixed dishes such as Spaghetti Bolognese, the amount of each raw ingredient used in the recipe, the final weight of the mixed dish, and the amount con­sumed by the respon­dent should be recorded, wherever possible. The inform­ation is recorded on a form similar to that shown in Appendix 3-1 , except that house­hold measures are used for food amounts. Usually, the respon­dent, parent, or caretaker completes the food record, although in low or middle-income coun­tries a local field inves­tigator may perform this task (Dufour et al., 1999). Reactivity, defined as a change in behavior due to awareness that behavior is being or will be measured, may be an issue with this method. The respon­dent has the opportunity to modify his or her “usual” diet, potentially in a more socially desirable manner or to simplify the recording task (Thompson et al., 2015) (Chapter 5).

Food portion sizes can be estimated by the respon­dent in a variety of ways. Standard house­hold measuring cups and spoons should be used if possible, supplemented by mea­sure­ments with a ruler (for meat and cake) and counts (for eggs and bread slices). Unfor­tu­nately, errors may arise because the respon­dent may fail to quantify portion sizes correctly. Additional errors may also arise during the conversion of volumes to weights (Chapter 5), although this latter step is usually completed by the inves­tigator. Details on how to convert portion sizes to weight equiv­alents are given in Gibson and Ferguson (2008) and Vossenaar et al. (2022).

The number of days included in an estimated record varies, depending on the study objective. When the objective is to obtain an average intake for a group, then only one day per person is required, provided all days of the week are equally repre­sented in the final sample. However, when esti­mates of usual intakes of each person are required, then the number, selection, and spacing of the days required per person depends on the factors described for the repeated 24h recall (Section 3.1.2). Weekend days should always be proportionately included in the dietary survey period for each person, to account for potential day-of-the-week effects on food and nutrient intakes. This problem is discussed in more detail in Chapter 6.

The European Prospective Investigation of Cancer (EPIC) study in Norfolk, U.K. collected food and nutrient intakes from 2117 men and women using a 7d estimated food diary. EPIC was a large multicenter prospective study aimed at investigating the relationship between nutrition and various life-style factors and the etiology of cancer and other chronic diseases. The study involved 23 regional centers located in ten coun­tries, and involved a total cohort of about 480,000 subjects. The respon­dents of the EPIC study in Norfolk were provided with a “diet diary” — a 45-page colored booklet in which they were asked to record the descrip­tion, preparation, and amounts of foods eaten over seven consecutive days. Food portion sizes were estimated by the respon­dents in terms of house­hold measures, with the help of 17 sets of color photographs of small, medium, and large portions of the dif­fer­ent foods. See Vossenaar et al. (2020) for guidance on the development of food photo­graphs for portion size estimation. Details on the EPIC study in Norfolk Details are given in (Bingham et al., 2001). The Danish National Survey of Diet and Physical Activity (4–75y) also used a seven-day estimated food diary with a paper format (Pedersen et al., 2015).

A four-day estimated food diary, recorded using a paper form, is used by the U.K. National Diet and Nutrition Survey rolling program. This is a continuous cross-sectional survey designed to collect detailed inform­ation on food and nutrient intakes and nutritional status for a range of ages and across the social strata in the UK. The field work for this rolling program began in 2008 and is on-going with about 1000 people surveyed per year (Ziauddeen et al., 2018).

3.1.4 Weighed food records

Weighed food records are more frequently used in the United Kingdom and Europe because weighing scales are often used for food preparation in these regions. In the earlier British National Diet and Nutrition Surveys of adults and children (Ashwell et al., 2006), seven-day weighed food records were used. However, when the rolling program was introduced in 2008, the seven-day weighed food records were replaced by a four-day estimated food diary due to concerns about respon­dent burden.

A weighed food record is the most precise method available for estimating usual food and nutrient intakes of indi­viduals. It is the preferred method when diet counseling or corre­la­tion of intakes with biological parameters are involved. In a weighed record, the subject, parent, or caretaker is instructed to weigh all foods and bever­ages con­sumed by the subject during a specified time period. Details of methods of food preparation, descrip­tion of foods, and brand names (if known) should also be recorded. For mixed dishes such as Spaghetti Bolognese, the weight of the portion con­sumed should be recorded, along with the weights and descrip­tion of all the raw ingredients, including flavors and spices used in the recipe, as well as the final total weight of the mixed dish. The method of recording is similar to that shown for a 24h recall (Table 3.1), with the weight of the food items being recorded under "Amount."

If occasional meals are eaten away from home, respon­dents are generally requested to record descrip­tions of the amounts of food eaten. The nutritionist can then buy and weigh a duplicate portion of each recorded food item, where possible, to assess the prob­able weight con­sumed. Alter­natively, if appropriate, the nutritionist can telephone a restaurant to obtain details of the portion sizes con­sumed.

As with the estimated record, the number, spacing, and selection of days necessary to characterize the usual nutrient intakes of an indi­vidual using the weighed record depend on the within-person vari­a­tion in food intake, which, in turn, depends on the nutrient of inter­est, the study popu­lation, and any seasonal vari­a­tion of intake. Again, week-end days should be proportionately included to account for any weekend effect on the nutrient intake. If a weighed food record method is to be used, respon­dents must be motivated, numerate, and literate. Reactivity may be an issue with this method, and inter­fere with the assessment of usual dietary intake. Respondents may change their usual eating pattern to simplify the weighing process or, alternatively, to impress the inves­tigator (Cameron and van Staveren, 1988; Thompson et al., 2015) (Chapter 7). In addition, respon­dent burden for a weighed food record is higher than for an estimated record or for a 24h recall, so indi­viduals may be less willing to cooperate. Reproducibility, however, is greater in the weighed record than in the estimated record method because the portion sizes are weighed, although significant underreporting (Chapter 5) may still occur.

3.1.5 Dietary history

The dietary history method (Burke, 1947) attempts to estimate the usual food intake and meal pattern of indi­viduals over a relatively long period of time — often a month. This inter­view method was originally designed to be carried out by a nutritionist trained in inter­viewing tech­niques. More recently, computerized versions have been devel­oped which provide stan­dardized methods for data collection and probing, and minimize potential inter­viewer bias in responses (Kohlmeier et al., 1997).

Initially, the dietary history had three components. The first component was an inter­view about the usual overall eating pattern of the subject, both at mealtimes and between meals. Such inform­ation included detailed descrip­tions of foods, their fre­quency of con­sump­tion, and usual portion sizes in common house­hold measures. “What do you usually eat for breakfast?” is a typical question that might have been included in the inter­view.

The second component served as a crosscheck and consisted of a question­naire on the fre­quency of con­sump­tion of specific food items. This part was used to verify and clarify the inform­ation on the kinds and amounts of foods given as the usual intake in the first component. Questions asked related to specific foods, such as: "Do you like or dislike milk." A 24h recall of actual intake may also have been included at this stage.

In the third component, subjects recorded their food intake at home for three days. Portion sizes at this stage were estimated using a variety of tech­niques, including stan­dard measuring cups and spoons, common utensils, commercial plastic food models, photo­graphs, or real foods. Today, the original dietary history method is seldom used in this three-part format, the third component being commonly omitted.

The time periods covered by the dietary history method vary. The maximum time period that can be used has not been definitely established. When shorter time frames (i.e., one month) are used, reproducibility and validity are apparently higher than for longer periods (see Chapter 7). Measurements of food intake over one-year periods are prob­ably unrealistic unless seasonal vari­a­tions in food intakes are taken into account.

Dutch inves­tigators used a three-part dietary history method covering one month to record usual food con­sump­tion on weekdays, Saturdays, and Sundays separately (van Staveren et al., 1985). This approach takes into account the potential effect of weekends on nutrient intake. The portion size of foods most frequently con­sumed in this study were weighed by a dietitian in the home. A weighted daily average intake was then calculated from the data, using the following formula:

\[((5 \times \text { Weekday })+\text { Saturday }+ \text { Sunday }) / 7\nonumber\]

A modified version of this dietary history method was adopted in the Survey in Europe on Nutrition in the Elderly: A Concerted Action (SENECA). This multicenter survey was designed to examine cross-cultural vari­a­tions in the nutrition, lifestyle, health, and perform­ance of elderly Europeans (Euronut - SENECA, 1991). The method involved the completion of a three-day estimated record, followed by an inter­view during which respon­dents were questioned about their usual dietary intake over the past month. Portions of the most commonly eaten foods were weighed by the inter­viewer (van Staveren et al., 1996).

The recording of a dietary history can be very labor intensive, with inter­views taking up to 2h per respon­dent (Slattery et al., 2000). Several inves­tigators have reported that the dietary history tends to overestimate nutrient intakes, when compared with results from weighed records. Nes et al.(1991), for example, used the dietary history devel­oped for the SENECA study and showed that the method generated consistently higher intakes of energy and nutrients than three-day weighed records. Livingstone and Robson (2000) reported similar findi­ngs in a study of children and adolescents, but claimed that the results obtained from the dietary history were more representative of habitual intake than those obtained from seven-day weighed records. In general, because dietary histories, unlike food fre­quency question­naires, do not limit the variability in the responses, they overcome many of the limitations of a food fre­quency question­naire. However, the absence of a stan­dardized format for the dietary history method limits compar­ison of its usefulness across studies (Thompson et al., 2015).

3.1.6 Food fre­quency question­naire

The food fre­quency question­naire, sometimes referred to as a diet history question­naire, aims to assess the usual fre­quency with which food items or food groups are con­sumed during a specified time period. It was originally designed to provide descriptive qualitative inform­ation about usual food-con­sump­tion patterns. With the addition of portion-size esti­mates and the introduction of improved computerized self-admin­istered question­naires, the method has become semi-quanti­tative, allowing the derivation of energy and selected nutrient intakes (Willett et al., 1985; Block et al., 1986).

In its simplest form, the question­naire consists of a list of foods and an associated set of frequency-of-use response categories ( Appendix 3-2 ). The list of foods may focus on specific groups of foods, partic­ular foods, or foods con­sumed periodically in association with special events or seasons. Alter­natively, the food list may be extensive to enable esti­mates of total food intake and dietary diversity to be made. The frequency-of-use response categories may be daily, weekly, monthly, or yearly, depending on the study objective.

Specific combinations of foods can be used as predictors for intakes of certain nutrients or non-nutrients, provided that the dietary components are concen­trated in a relatively small number of foods or specific food groups. Examples include the fre­quency of con­sump­tion of fresh fruits and fruit juices as predictors of vitamin C intake (Tsugane et al., 1998), green leafy veg­etables and carrots (O'Neill et al., 2001), or fruit and veg­etable intake as predictors of carotenoid intakes (Whitton et al., 2017), whole grain cereals, legumes, nuts, fruits, and veg­etables as predictors of dietary fiber intakes (Merchant et al., 2003), and dairy products as predictors of calcium intakes (Barr et al., 2001; Horiuchi et al., 2019). The method can also be used to assess the intake of fats and cholesterol (Feunekes et al., 1993; Eng and Moy, 2011; Riordan et al., 2018), artificial sweeteners (Dewinter et al., 2016), certain contaminants present in specific foods (MacIntosh et al., 1997; Filippini et al., 2018), alcohol (Bazal et al., 2019), and condiments (Leyvraz et al., 2018).

The food fre­quency question­naires should feature simple, well-defined foods and food categories. Open-ended questions should be avoided as preformatted lists of food categories act as a memory prompt. The method may use a stan­dardized inter­view, a self-admin­istered machine-readable printed question­naire, or a computer-admin­istered question­naire. Most question­naires usually list 80 to 120 indi­vidual items and take from 15–30minutes to complete (see abbreviated example given in Appendix 3.2). Hence, the food fre­quency question­naire imposes less burden on respon­dents than most of the other dietary assess­ment methods. The results are easy to collect and process and are generally taken to represent usual intakes over an extended period of time, and hence are not affected by day-to-day variability. As food fre­quency question­naires are designed to provide retrospective inform­ation about diet, they are often used in retrospective case-control studies (Schink et al., 2019). However, their validity and feasibility for estimating food intakes in the remote past has not always been clearly established (van Staveren et al., 1986; Dwyer and Coleman, 1997; Ambrosini et al., 2003; Barrett et al., 2019).

WHO has issued guidelines on a Healthy Diet (WHO, 2020). A (Healthy Eating Index) (HEI‑2015) has been devel­oped by the USDA, that measures alignment of US diets with the 2015‑2020 Dietary Guidelines for Americans. The HEI‑2015 has 13 dietary components in total, of which nine are “adequacy” components (those recommended for inclusion in a healthy diet) and four “moderation” components that should be con­sumed sparingly. These dietary components are listed in Table 3.3. This table also shows the scoring stan­dard for each of the dietary components. The scores for each of the 13 com­ponents derived from the indi­vidual's intake, are added to give an HEI Index score (maximum = 100) for the indi­vidual.

Table 3.3 HEI–2015 Components & Scoring Standards. From HEI (2020).
¹Intakes between the minimum and maximum standards are scored proportionately.
²Includes 100% fruit juice.
³Includes all forms except juice.
⁴Includes legumes (beans and peas). ⁵Includes all milk products, such as fluid milk, yogurt, and cheese, and fortified soy bever­ages.
⁶Includes legumes (beans and peas).
^6,7Includes seafood, nuts, seeds, soy products (other than bever­ages), and legumes (beans and peas).
⁸Ratio of poly- and monounsaturated fatty acids (PUFAs and MUFAs) to saturated fatty acids (SFAs).

HEI–2015^1 Components & Scoring Standards
Component	Max. points	Standard for max. score (per 1,000 kcal)	Standard for min. score (0)
Adequacy
Total Fruits^2	5	≥ 0.8 cup equiv.	No Fruit
Whole Fruits^3	5	≥ 0.4 cup equiv.	No Whole Fruit
Total Vegetables^4	5	≥ 1.1 cup equiv.	No Vegetables
Greens and Beans^4	5	≥ 0.2 cup equiv.	No Dark Green Veg. or Legumes
Whole Grains	10	≥ 1.5 oz equiv.	No Whole Grains
Dairy^5	10	≥ 1.3 cup equiv.	No Dairy
Total Protein Foods^6	5	≥ 2.5 oz equiv.	No Protein Foods
Seafood and Plant Proteins^6^,7	5	≥ 0.8 oz equiv.	No Seafood or Plant Proteins
Fatty Acids^8	10	(PUFAs + MUFAs) /SFAs ≥ 2.5	(PUFAs + MUFAs) /SFAs ≤ 1.2
Moderation
Refined Grains	10	≤ 1.8 oz equiv.	≥ 4.3 oz equiv.
Sodium	10	≤ 1.1 gram	≥ 2.0 grams
Added Sugars	10	≤ 6.5% of energy	≥ 26% of energy
Saturated Fats	10	≤ 8% of energy	≥ 16% of energy

Kant et al. (2000) used food fre­quency inform­ation to calculate a “Recommended Food Score” (RFS) to evaluate the con­sump­tion of foods consid­ered to be consistent with the U.S dietary guidelines existing at that time. In a prospective study of diet quality and mortality in women from the United States, they showed that the RFS was inversely associated with all‑cause mortality. Since that time, the RFS has been used in Australia as a diet quality index for preschoolers (Burrows et al., 2014), and in Korea to investigate links with physical perform­ance among the elderly (Jeong et al., 2019), and depression, anxiety, and quality of life (Lee et al., 2019).

Many recent users of food fre­quency question­naires have quantified portion sizes of food items of inter­est, often using photo­graphs (Nelson et al., 1994; Amougou et al., 2016). Portion sizes can be ranked as small, medium, and large, preferably based on age and sex-specific portion size data generated from country-specific national nutrition surveys (Willet et al., 1985; Block et al., 1986; Bohlscheid-Thomas et al., 1997). Note that inclusion of inform­ation on portion sizes produces semi-quanti­tative food fre­quency data (Appendix 3-3 ). This can be converted to data on energy and nutrient intakes by multiplying the fractional portion size of each food con­sumed per day by its energy and nutrient content, obtained from appropriate food composition data. The results are then summed to obtain an estimate of an indi­vidual's total daily energy and nutrient intake.

Block et al. (1986) derived a food list for a food fre­quency question­naire with portion sizes from the NHANES II results. Food items selected were based on the fre­quency of con­sump­tion of certain specific food items and which contributed significantly to the total popu­lation intake of energy and each of 17 nutrients. Serving sizes were estimated from observed portion size distri­butions in the NHANES II data. Medium serving sizes for each food were specified in the food fre­quency question­naire, and the respon­dent indi­cated whether his or her usual serving size was small, medium, or large, as shown in Appendix 3.3. A specialized food composition data­base was devel­oped for use with this food fre­quency question­naire. A very similar approach has been used to design semiquanti­tative multi-ethnic food fre­quency question­naires (Deurenberg-Yap et al., 2000; Beukers et al., 2015).

An improvement to the Block food fre­quency question­naire termed the Diet History Question­naire (DHQ) has been devel­oped. The DHQ consists of 124 food items, portion sizes, and dietary supplement questions and takes one hour to complete. Results of a comparative validity study showed that the perform­ance of the DHQ is better than that of the food fre­quency question­naires of both Block and Willett(Subar et al., 2001).

The semi-quanti­tative food fre­quency question­naire has become a widely used tool in dietary assess­ment. Country-specific semiquanti­tative food fre­quency question­naires containing between 130 and 300 food items were used in the EPIC study to estimate indi­vidual usual food intakes (Margetts and Pietinen, 1997). In the EPIC study in Norfolk, U.K. (Bingham et al., 2001) respon­dents (n = 23,003) estimated how frequently foods were eaten over the past year, from nine possible frequency-of-use response categories from a list of 130 foods. Reduced versions containing only 60 food items that require only 17 min to admin­ister by an inter­viewer are available; even the full 98‑item Block question­naire requires only 30‑35 min of inter­viewer time (Block et al., 1990). In some coun­tries, a semi-quanti­tative food fre­quency question­naire has been used in national nutrition surveys (e.g., 1995 Australia National Dietary Survey) (Williams, 2005).

More recently in Australia, an on-line suite of validated semi-quanti­tative food fre­quency question­naires, the Australian Eating Surveys (AES) have been devel­oped. The AES is a 120‑item food fre­quency question­naire with fifteen supplementary questions, including food and sedentary behaviors and supplements, with the aim of capturing the usual dietary intakes of children, adolescents, and adults over the previous six months. The AES takes only 15‑20 min to complete on-line and can generate a personalized dietary feedback in real time as an incentive to encourage partic­ipation and enhance the response rate (Collins et al., 2014).

In many low-income coun­tries no national food con­sump­tion surveys have been conducted so the key inform­ation needed to develop a food fre­quency question­naire is often not available. Such inform­ation includes a listing of foods commonly con­sumed in the study popu­lation, details on the way the foods are typically prepared or con­sumed, and the usual range of portion sizes con­sumed. In response to this need, Hotz and Abdelrahman (2019) have devel­oped some simple methods to obtain food listing and portion size distri­bution esti­mates for use in semi-quanti­tative food fre­quency question­naires.

Table 3.4 Ref = reference quintile. Multivariate model: age at baseline, total calorie intake, smoking history, cancer (yes/no) hypertension diagnosis (yes/no), use of antidepressants, elevated cholesterol, physical activity level, body mass index, cardiovascular disease, multivitamin use, intake of alcohol, total calorie intake, profession, missing indicator for SCF, and number of dietary assess­ments during1986–2002. From Yuan et al. (2019).

Odds Ratios (95% CIs) for poor Subjective Cognitive Function (SCF), compared with good function, associated with total veg­etable, fruit, and fruit juice intakes
Quintile of intake (n = 27,842 men)	Q1	Q2	Q3	Q4	Q5
Total veg­etable intake Median, servings/d	1.7	2.5	3.2	4.1	5.7
Odds Ratio 95% Confidence Interval	Ref	0.92 (0.79, 1.08)	0.85 (0.73, 0.99)	0.71 (0.60, 0.83)	0.62 (0.52, 0.74)
Total fruit intake Median, servings/d	0.5	1.1	1.5	2.0	3.1
Odds Ratio 95% Confidence Interval	Ref	1.00 (0.85, 1.18)	0.96 (0.81, 1.13)	0.81 (0.68, 0.96)	0.79 (0.66, 0.94)
Total fruit juice intake Median, servings/d	0.1	0.4	0.7	1.0	1.5
Odds Ratio 95% Confidence Interval	Ref	0.78 (0.67, 0.91)	0.81 (0.70, 0.94)	0.66 (0.57, 0.77)	0.65 (0.55, 0.76)

Food fre­quency question­naires are often used by epidemiologists studying associations between dietary habits and disease. For example Yuan et al. (2019) in their study of the relationship between long-term intake of veg­etables and fruits and subjective cognitive function in US men, used this approach (Table 3.4). See also: (Willett, 1994; Harris et al., 2018; Zhong et al., 2019). In such studies, the food fre­quency question­naires must be semi-quanti­tative, with the ability to rank subjects on the basis of their intakes, so that subjects with low intakes can be separated from those with high intakes. This permits the calcu­lation of the odds ratio or relative risk of disease in relation to intake of certain foods, food groups, or nutrients (Masson et al., 2003).

Box 3.1 summarizes the five methods discussed above that can be used to assess the food con­sump­tion of indi­viduals and their uses and limitations. For a more detailed review of the strengths and weaknesses of each of these methods for use in low- and middle-income coun­tries, see (FAO, 2018).

Box 3.1 Uses and limitations of methods used to assess the food consumption of individuals.

24h recall. Subject or caretaker recalls food intake of previous 24h in an inter­view. Quantities estimated in house­hold measures using food models as memory aids or to assist in quantifying portion sizes. Nutrient intakes calculated using food composition data.

• Uses and Limitations Useful for assessing average usual intakes of a large popu­lation, provided that the sample is truly representative and that the days of the week are adequately repre­sented. Used for inter­national compar­isons of relationships of nutrient intakes to health and susceptibility to chronic disease. Inexpensive, easy, quick, with low respon­dent burden so that compliance is high. Large coverage possible; can be used with illiterate indi­viduals. Element of surprise so less likely to modify eating pattern. Single 24h recalls likely to omit foods con­sumed infrequently. Relies on memory and hence unsatisfactory for the elderly and young children. Multiple replicate 24h recalls can be used to estimate the usual intakes of indi­viduals.

Estimated food record. Record of all food and bever­ages “as eaten” (including snacks), over periods from one to seven days. Quantities estimated in house­hold measures. Nutrient intakes calculated using food composition data.

• Uses and Limitations Used to assess actual or usual intakes of indi­viduals, depending on number of measurement days. Data on usual intakes used for diet counseling and statis­tical analysis involving corre­la­tion and regression. Accuracy depends on the conscientiousness of subject and ability to estimate quantities. Reactivity may be an issue. Longer time frames result in a higher respon­dent burden and lower cooperation. Subjects must be literate unless a trained researcher conducts the estimated food record in the home.

Weighed food record. All food con­sumed over a defined period is weighed by the subject, caretaker, or assistant. Food samples may be saved indi­vidually, or as a composite, for nutrient analysis. Alter­natively, nutrient intakes calculated using food composition data.

• Uses and Limitations Used to assess actual or usual intakes of indi­viduals, depending on the number of measurement days. Accurate but time consuming. Setting must permit weighing. Subjects may change their usual eating pattern to simplify weighing or to impress inves­tigator — termed — reactivity. Requires motivated, and willing partic­ipants. Expensive. For illiterate participants, weighed food records can be conducted by a trained research assistant in the home.

Dietary history. Interview method consisting of a 24h recall of actual intake, plus inform­ation on overall usual eating pattern, followed by a food fre­quency question­naire to verify and clarify initial data. Usual portion sizes recorded in house­hold measures. Nutrient intakes calculated using food composition data.

• Uses and Limitations. Used to describe usual food or nutrient intakes over a relatively long time period, which can be used to estimate prevalence of inadequate intakes. Such inform­ation is used for national food policy development, for food fortification planning, and to identify food patterns associated with inadequate intakes. Labor-intensive, time-consuming, and results depend on skill of inter­viewer. The absence of a stan­dardized format limits compar­ison of its usefulness across studies.

Food fre­quency question­naire. Uses comprehensive or specific food item list to record intakes over a given period (day, week, month, year). Record is obtained by inter­view or self-admin­istered question­naire. Questionnaire can be semi-quanti­tative when subjects asked to quantify usual portion sizes of food items, with or without the use of food models.

• Uses and Limitations Designed to obtain qualitative, descriptive data on usual intakes of foods, classes of foods, or nutrients (if semi-quanti­tative) over a long time period. Useful in epidemio­logical studies for ranking subjects into broad categories of low, medium, and high intakes of specific foods, food components, or nutrients, for compar­ison with the prevalence or mortality statistics of a specific disease. Can also identify food patterns associated with inadequate intakes of specific nutrients. Method is rapid, with low respon­dent burden and high response rate, but accuracy is lower than for other methods.