Dietary assessment methods

Bingham, S.A. et ah, Comparison of dietary assessment methods in nutritional epidemiology — weighed records v 24-h recalls, food frequency questionnaires and estimated diet records, Br. J. Nutr., 72, 619, 1994. 

Retrospective dietary-assessment methods are simpler and less expensive than prospective and duplicate-diet methods, and therefore are used more often as the basis of dietary expostrre assessments. Food-fiequency studies take the form of participants identifying their typical fish consrrmption (e.g., How many times per week/month do you usually eat fish AT). Diet histories involve recollection of specific meals over a specific time (e.g. 24-hr or 1-week periods). In the studies mentioned above, Sherlock et al. (1982) and Haxton et al. (1979) used retrospective assessment of typical consumption to preselect subjects. In a recent study of MeHg exposure among pregnant women in New Jersey (Stem et al. 2000), participants were asked to identify their typical consumption frequency and typical portion size of 17 species of fish and... 

Dietary assessment methods, total diet studies, and the duplicate portion method are evaluated with regard to their adequacy for obtaining iodine intake data. The advantages and shortcomings of catalytic spectrophoto-metric methods, nuclear analytical methods, spectromet-ric, electrochemical, and other techniques, which are used for the determination of iodine in foodsmffs and related materials, are reviewed. 

The main purpose of iodine assay in foodstuffs is to obtain data on intake by an individual or a population. Commonly used approaches to evaluate intake of various diet components, such as nutrients, vitamins, minerals and trace elements, contaminants, and so on, involve dietary assessment methods, total diet studies, and the duplicate portion method. In general, their ease of execution and the validity of the results obtained differs for all diet components, and this particularly applies to iodine. The use of biomarkers to assess iodine intake, specifically iodine excretion in urine, is also mentioned. 

The dietary assessment methods are based on taking a dietary history, such as diet recall (usually 24-h recall, but sometimes for longer periods), diet history (an interview about typical or usual food intake), and food frequency and/or amount questionnaires (food frequency questionnaire, FFQ and/or food amount questionnaire, FAQ, respectively). More details about these methods are discussed by Margetts and Nelson (1997). Intake of iodine from the data obtained is calculated using various national or international food composition databases, such as INFOODS (Scrimshaw, 1997 Schlotke and MoUer, 2000 Braithwaite et al., 2006). There are currently over 150 food composition tables in use around... 

The accuracy of the total diet study depends on two fundamental data components (i) the quantity of each prepared food consumed by individuals, usually obtained in a separate study by the dietary assessment method and (ii) the background concentration of analytes of interest in the foods as ready for consumption. In order not to overestimate dietary intakes, the analytical methods used to measure analytes of interest should have appropriately low detection limits. 

Previous studies investigating dietary intake of micronutrients have reported that the dupficate portion technique offers the most accurate estimation. A study comparing dietary assessment methods to measure selenium intake concluded that diet record assessment was not adequate for predicting selenium intakes of individuals, and that duplicate diet analysis remains the recommended measure for research purposes (Duffield and Thomson, 1999). Furthermore, Koutras et al. (1970) state that if iodine intake is to be measured, the best method is the dupficate portion technique. However, the dupficate portion technique is labor intensive and requires a significant amount of subject commitment therefore, its use is usually restricted to small groups and data are usually collected over a short period of time. 

Table 45.3 Dally Iodine Intake in vegans using different dietary assessment methods (mean vaiues standard deviation) ...

Study Location Dietary assessment method (days) subjects (M F) Male Female... 

An increase in precision may be achieved by increasing the number of subjects, although more involved dietary assessment methods, such as the duplicate portion technique, are labor intensive and require a significant amount of subject commitment therefore, their use is usually restricted to small groups and data are collected over a short period of time (Petersen and Barraj, 1996). However, short time periods will miss any seasonal differences in the iodine content of foods that may occur. Seasonal variations were minimized in the Waldmann study, as 7-day FFQs were completed in both the autumn and spring seasons. 

Bingham, S.A., GUI, C., Welch, A. et al. (1997). Validation of dietary assessment methods in the UK arm of EPIC using weighed records, and 24-hour urinary nitrogen and potassium and serum vitamin C and carotenoids as biomarkers. International Journal of Epidemiology, 26, S137-S151. 

The principal and most accurate method for estimating sodium intake is to measure sodium excretion rates in individuals who are asked to collect one or more complete 24-h urinary outputs. To measure absolute amounts a marker for completeness of collections is required. Measurement of intake from dietary assessment methods alone is considered unreliable. Until recently, however, there was no way of establishing how much of the 24-h sodium... 

BINGHAM s (1987) The dietary assessment of individuals methods, accuracy, new techniques and recommendations. NutrnAbsr Rev. 57 705-41. 

Associations between breast cancer and total and specific fruit and vegetable group intakes were examined using standardized exposure definitions (Smith-Warner and others 2001). Data sources were eight prospective studies that had at least 200 incident breast cancer cases, included assessment of usual dietary intake, and had completed a validation study of the diet assessment method or a closely related instrument. 

As the authors recognized, however, their methods are open to numerous criticisms. For example, as they state "Retrospective dietary assessments made at a single interview, even when this is conducted by an experienced dietician, are open to criticism since they rely heavily upon the memory of the subject interviewed, the estimates of quantity made by the dietician, and the subsequent expression of those quantities in mass units. The opportunity for error is clearly increased when the interview is conducted through an interpreter" (28). 

A Comparison of Dietary Exposure and Risk Assessment Methods in US and U... 

This brief review has shown that there are some differences in the way dietary risk assessment is practiced between the US and the EU. Many of the differences have to do in the types of input data that are available, or in some of the methods used to collect the data. Regarding the food consun tion data, the US surveys use a dietary recall method, whereas the UK approach is a diary method that weighs and measures the amount of food consumed. In the US, data are collected for two non-consecutive days, whereas in the UK surveys, data are collected for either 4 or 7 consecutive days. The US survey is conducted as an integrated whole and includes all segments of the population. In contrast, the UK surveys are conducted for specific population groups. Finally, the US survey collects data at the household level, whereas the UK survey targets demographic characteristics, based upon census information. 

Nelson M. Methods and validity of dietary assessment. In Garrow JS, lames WPT, Ralph A, eds. Human nutrition and dietetics. Edinburgh Churchill Livingstone, 2000 311-31. 

It has been suggested that conventional dietary assessment techniques, in conjunction with food tables, do not provide realistic estimates of micronutrient intakes and that accurate data on dietary intake of such nutrients can only be obtained by direct chemical analysis of foods or diets (Abdulla et aL, 1989 Bro et aL, 1990). There are three different methods of collecting data for direct chemical analysis (duplicate portion technique, aliquot samphng technique and equivalent composite technique) however, the most precise method of direct chemical analysis is the duplicate portion technique, as it directly measures actual nutrient intake (West and van Staveren, 1997). 

FFQs, as a direct semi-quantitative method of dietary assessment, are often easier to handle and can result in higher subject compliance, compared to weighed food records and the duplicate portion technique. However, the use of FFQs, as used in the study performed by Waldmann et al. (2003), may result in more sources of error in the estimation of iodine intake compared to other dietary assessment techniques, due to the choice of food portion... 

Although the duplicate portion technique may be considered the best method for the assessment of trace element intake, it is not always practical to determine iodine intake using this method of dietary assessment. 

Iodine intake can be measured as urinary iodine excretion in a casual urine sample or, preferably, in a 24-h urinary sample. Iodine excretion in a casual urine sample can be expressed as a concentration, as p,g I/g Cr, or as estimated 24-h urinary iodine (p,g/day) if p,g I/g Cr is multiplied by daily expected Cr excretion for the actual age and gender group. However, none of these measures can be used to determine an individual s habitual iodine intake. Iodine intake can also be assessed using dietary intake methods, but like urinary measurements, to determine the habitual iodine intake in an individual, 24-h recalls should be repeated several times or dietary records should be kept for several days (the number of days needed to determine the habitual iodine intake is not known, but is probably more... 

Alternative methods of dietary assessment, such as food frequency questionnaires (FFQs) and 24-h recalls, are less burdensome for participants, but are associated with other limitations such as difficulty with estimating portion sizes and memory bias. If used to determine iodine intakes, FFQs should be validated against another method of dietary assessment (e.g., diet record) with different limitations to determine their accuracy or long-term measures of... 

In most studies, phytoestrogen intake has been estimated by direct methods that evaluate food intake either by recall (food-frequency questionnaires -FFQs) or by record (food diary), and subsequently by composition databases based on information of this kind. Food-frequency questionnaires are widely administered to subjects involved in epidemiological studies. Their validity and reproducibility is considered sufficient when statistically correlated to data obtained from dietary records (a properly-completed and comprehensive food diary) and from analysis of blood and urine samples (Kirk et ah, 1999 Huang et al, 2000 Yamamoto et al, 2001 Verkasalo et al, 2001). FFQs can be repeated several times a year and may be administered to large populations. Such an approach provides an easy and low-cost method of assessing the... 

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