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Keywords:

  • children;
  • dietary assessment;
  • food photographs;
  • portion size

Abstract

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

Novel methods of assessing dietary intake are required to reduce the participant burden in dietary surveys, improve participation rates and thereby improve the representativeness of the sample and minimise the impact of measuring dietary intake on a subject's food intake during the recording period. One method of reducing the burden placed on participants in recording dietary intake is to replace weighing of foods with estimation of portion size using tools such as food photographs. The interactive portion size assessment system (IPSAS) is an interactive portion size assessment system for use in assessing portion sizes of foods consumed by children aged 18 months to 16 years. The system is computer-based and is designed to be administered during an interview for a food diary or 24-h recall. The portion sizes depicted are age-specific and based on the weights of foods served to children during the UK National Diet and Nutrition Surveys. The system displays digital images of food used to estimate the amount of each food served to the child and the amount of any food left over. Foods are categorised within the system using a three-tier structure. Twenty-seven food group icons are used with two further drop-down menus to select first the food group, then the food category and, finally, the actual food product. Each food is linked to UK food composition codes and all photographs are linked to the weight of the food depicted. Nutritional output is via a companion database. The present study describes the development of the IPSAS and the structure of the system.


Introduction

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

Accurate information on the dietary intake of children is essential to inform and monitor nutrition-related health policy and for the evaluation of interventions. However, obtaining information on food intake presents many challenges. The common problems encountered include under-reporting (Black, 1996; Goris et al., 2000), subject selection bias and recording bias (Livingstone et al., 1990). Traditional ‘Gold Standard’ dietary assessment methods, such as weighed food intakes, are costly and can be impractical, with high levels of participant burden resulting in a poor response and low completion rates. Subconscious and/or intentional changes to diet to facilitate recording are also common (Berg et al., 1998).

One method of overcoming some of these challenges is to reduce participant burden by using portion size assessment tools to obtain an estimate of the amount of food consumed. Portions size estimation tools have been developed using one or a combination of two- or three-dimensional drawings (Steyn et al., 2006), food models (Steyn et al., 2006; Foster et al., 2008a), digital images of foods and food receptacles (Baranowski et al., 2002; Vereecken et al., 2005; Subar et al., 2010), and digital graphics of shapes and mounds (Baranowski et al., 2002; Subar et al., 2010).

Estimation of portion size, rather than weighing portions, is associated with a loss of precision as a result of over- and under-estimation. Printed food photographs, however, have been shown to increase the accuracy of portion size estimation (Lucas et al., 1995; Robinson et al., 1997) and to result in an increased accuracy of reported nutrient intakes (Nelson et al., 1996) compared to unaided estimates.

The reduced burden may also improve participation rates and improve the quality of the data collected; participants are less likely to make changes to their dietary intake to facilitate recording (Howat et al., 1994).

In the UK, the Photographic Atlas of Food Portion Sizes (Nelson et al., 1997) has been developed for use with adults; however, no similar tool existed for use with children. Frobisher & Maxwell (2003) and Foster et al. (2006) found that errors in portion size estimation made by children using the adult food photographs (Nelson et al., 1997) were much greater than those observed when adults used the photographs. It was concluded that the tool was unsuitable for use with children.

Formative research

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

In 2003, a pilot study was conducted to develop and test portion size assessment tools for use with children aged 4–16 years. This study has been reported previously (Foster et al., 2008a,b) and is only described briefly here. Three age-specific portion size assessment tools were developed: food photographs, food models and an interactive portion size assessment system (IPSAS). First, the effect of perception, conceptualisation and memory on childrens' (= 108) ability to estimate the portion size of 12 foods using the portion size assessment tools was assessed. This was carried out using three test types:

  • Food in front. The child estimated the amount of food with the food in view (i.e. to test perception)
  • Just after eating. The child estimated the amount of food immediately after having consumed the food (i.e. to test perception and conceptualisation)
  • 24-h recall. The child estimated the amount of food the following day (i.e. to test perception, conceptualisation and memory)

There were no significant differences in the childrens' ability to estimate portion size with timing of interview (Foster et al., 2008b). Therefore, the main focus of the pilot study was on the 24-h recall interview because this is the situation in which the tools would most likely be used.

These tools were further tested in a feeding study of children (= 201) aged 4–16 years. Children were provided with known quantities of 22 foods that were consumed in school and all leftovers were recorded. The amount of food served and left over was then estimated by the children the following day using one of the tools. The children were fed the same food on several occasions so that estimates of portion size were made for each food using each tool seperately. This resulted in a total of 9843 estimates of portion size. Two of the tools showed potential for estimating portion sizes of foods consumed by children aged 4–16 years (Foster et al., 2008a), one of which was IPSAS. The present study describes the further development of IPSAS into a comprehensive portion size assessment system for use during a 24-h recall or food diary interview for children of preschool (1.5–4 years), primary school (4–11 years) and secondary school (11–16 years) age.

Selecting which foods to include

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

Portion size photographs were developed for estimation of amount served and amount left over. This decision was made because children often leave a proportion of the foods that they are served and therefore, in many instances, asking for an estimate of amount consumed would require a child (or their parent) to conceptualise an amount of food they had never actually seen (because they would see the amount served and the amount left over but not the amount consumed) (Foster et al., 2008a). The range of food photographs for portion size estimation developed for the feeding study was extended to include the top 100 foods based on frequency of consumption, weight of food consumed and contribution to energy intake of foods consumed by children in the most recent National Diet and Nutrition Surveys (NDNS) (a total 2055 images of 104 foods) (Gregory, 1995; Gregory & Lowe, 2000).

The digital images for estimation of portion size were presented in two formats:

  • Seven portions for estimation of amount served and seven portions for estimation of amount left over for foods that are not usually served in predetermined amounts (e.g. beans) (Fig. 1 shows the screen for selection of the amount served; the screenshot includes six of the seven portions provided, the additional image is displayed by scrolling).
  • Guide photographs for foods that are usually served in predetermined amounts, such as crisps, where a range of commonly consumed portion sizes are displayed in one photograph (Fig. 2.
image

Figure 1. Example screenshot of portion size photographs for estimation of the amount served.

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image

Figure 2. Example screenshot of guide photograph for portion size estimation.

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For the seven portions for estimation of amount served, weights from the fifth to the 95th centile of weight served during the NDNS (Gregory, 1995; Gregory & Lowe, 2000) were calculated as equal increments on a log scale for each age group. Seven weights from the fifth centile to the smallest presentable portion were used for estimation of the amount of any food left over. The portion sizes are presented on a log scale because it is well established that sensory systems respond in a logarithmic fashion to objects in the external world (MacMillan & Creelman, 1991). The just noticeable difference (JND) is defined as the minimum difference between two stimuli that leads to a change in experience. Weber's law asserts that, as the magnitude of a stimulus increases, the JND becomes larger, usually in proportion to the stimulus magnitude. Thus, applying this to portion size perception the difference between 5 g of baked beans and 10 g of baked beans is more noticeable than the difference between 105 g and 110 g.

In addition to the food images for portion size estimation, the original IPSAS system was expanded from 22 foods to include a total of 1301 food types (this includes different variants and cooking methods of the same food type). Foods are located using a three-tier categorisation system. The portion size of 1072 (82%) of these foods can be estimated using digital images of the actual food or a substitute food that is similar in terms of morphology and density (e.g. mashed potato may be used for mashed swede). For a small proportion (18%) of infrequently consumed foods, there is no suitable photograph. For these foods, a description of the portion size is collected using household measures, brand and pack information, or comparison with a standard sized object.

Overview of the system

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

The system is designed to be an interviewer-led tool for use during a 24-h dietary recall or an interview after completion of an estimated weight food diary. The interviewer enters the time, date and eating occasion; finds and inputs the correct foods; and can probe for further information on foods. The interviewer explains the task of portion size estimation to the participant and asks them to select from the range of portions displayed on the screen. The workflow through the system is shown in Fig. 3.

image

Figure 3. Overview of work flow through the interactive portion size assessment system (IPSAS).

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The 1301 food types within IPSAS are organised into 27 categories. The categories are displayed as food images and moving the cursor over each icon displays the full category title. These link to a series of two drop-down boxes to select food type (Figs 4 and 5).

image

Figure 4. Screenshot showing 27 main food categories for selection of food type.

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image

Figure 5. Screenshot showing drop-down menus for selection of food type.

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Selection of the food type automatically links to the appropriate portion size images. For foods that are not in predetermined amounts, thumbnail images of the seven served portions are displayed on the left of the screen. The interviewer clicks through the thumbnails changing the main image and the subject selects the portion size that they were served (Fig. 1). The range of images presented for leftovers is from the selected served portion through to the smallest presentable portion. The served portion selected is displayed in the top right-hand corner to aid estimation of amount left over.

When a food or drink is presented as a guide photograph, the subject is asked to select the item that looks most like the size of the item they ate and to indicate how many they had and whether any part of an item was not consumed. If a food or drink is not present in the system, a free text description box for the amount served and left over is used.

The IPSAS records the subjects' personal details, the date and time of the eating occasion, and the food eaten linked to McCance and Widdowson food composition codes, (Holland et al., 1988, 1989, 1992a,b, 1993; Chan et al., 1992, 1994, 1995), as well as portion size served and left over. The data output from IPSAS can be uploaded into a custom designed companion database in access (Microsoft Corp., Redmond, WA, USA). Foods for which a description of the food type or amount has been recorded require manual coding by the nutritionist/researcher. A form within the database displays entries where food codes and/or weights are required. Once these are entered, nutritional analysis can be generated by meal, day and total intake.

Validation

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

During the pilot study, an absolute validation of estimates made by children aged 4–16 years using IPSAS was conducted against known weights of foods served and left over in a feeding study (described in detail above). Mean ratios of estimated : actual weight served were 1.05 (a 5% over-estimate) for 4–6-year-olds, 0.94 (a 6% under-estimate) for 7–10-year-olds, 0.91 for 11–14-year-olds and 0.92 or 15–16-year-olds. Mean ratios of estimated:actual weight consumed were 1.36 for 4–6-year-olds, 1.17 for 7–10-year-olds, 1.17 for 11–14-year-olds and 0.94 for 15–16-year-olds, indicating a tendency for the younger children to under-report the amount of food left over.

After expansion to cover the top 100 foods, IPSAS was validated in a relative validation against weighed intakes to determine how the tool performed in a real-life setting. Children aged 18 months to 16 years were recruited and interviews were performed with both the parents and, for children of school age, also with the child.

Estimates of food portion sizes using IPSAS were validated against 4-day weighed intakes (WI), kept by the parent, along with in-school/nursery observations by the research team. Interviews were conducted the day after completion of the WI with parents and separately with the child (for children aged 4–16 years). Interviews were completed for 84 preschool children (18 months to 4 years), 90 primary school children (4–11 years) and 88 secondary school children (11–16 years). The ratio of an individual's mean daily weight of food consumed based on the estimated food diary using IPSAS (estimated) to the mean daily weight of food reported in the concurrent WI diary (actual) was calculated (accuracy). The ratio of estimated:actual mean daily energy intake was also calculated. The method of Bland and Altman was used to calculate the limits of agreement (within which 95% of estimates lie) of the method (precision).

Parents of preschool children estimated their children's intakes with good accuracy and reasonable precision using IPSAS. The weight of food consumed was over-estimated by 2% on average, whereas energy intake was under-estimated by 3%. The limits of agreement ranged from an under-estimate of 41% of energy intake to an over-estimate of 60%.

Parents of primary school children were slightly more accurate and precise in their estimates of intake using IPSAS than the children themselves. The weight of food consumed was over-estimated by 5% on average by the children compared to 2% by their parents. The mean ratio of estimated : actual energy intake for children was 1.01 indicating an over-estimate of 1% of energy intake on average, whereas, for parents, the ratio was 0.96, indicating an under-estimate of energy intake of 4% on average. Parents were more precise than their children as indicated by the limits of agreement, which ranged from an under-estimate of 33% of energy intake to an over-estimate of 37% for parents, indicating good precision. For children, the limits of agreement were substantially wider, ranging from an under-estimate of 41% to an over-estimate of 72%.

There was very little difference in the accuracy and precision of estimates made using IPSAS by secondary school children (age 11 years and over) compared to their parents (Table 1). The weight of food consumed was over-estimated by 2% on average by the children compared to 1% by their parents. The mean ratio of estimated : actual energy intake for children (age 11–16 years) was 0.95 and the limits of agreement ranged from an under-estimate of 37% of energy intake to an over-estimate of 43%. Parents also under-estimated energy intake by 5% on average using IPSAS but with slightly lower precision than their children, as indicated by the wider limits of agreement, which ranged from an under-estimate of 40% of energy intake to an over-estimate of 49%.

Table 1. Accuracy and precision of estimates made using the interactive portion size assessment system (IPSAS)
Age groupRespondentRatio n MeanLimits of agreement
Estimated : ActualLowerUpper
PreschoolParentWeight of food841.020.631.63
Energy840.970.591.60
PrimaryChildWeight of food901.050.631.77
Energy901.010.591.72
ParentWeight of food841.020.661.59
Energy840.960.671.37
SecondaryChildWeight of food881.020.661.57
Energy880.950.631.43
ParentWeight of food861.010.661.57
Energy860.950.601.49

Use of the interactive portion size assessment system in dietary assessment

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

The IPSAS is designed for use by a nutritionist or dietician as an aid to portion size estimation during a 24-h recall interview or an interview for an estimated weight food diary. Although much of the data collected using the system are coded automatically, there is a ‘food not listed’ option where free text can be entered and, for some foods, the amount is collected using a description/household measures and therefore an understanding of food coding systems and assessment of portion size is required.

The IPSAS is suitable for use in assessing dietary intake of children aged 18 months to 16 years. For children aged 10 years or younger, it is advised that the tool be used with the parent. For children aged 11 years or older, the interview may be conducted with the child themselves.

Conclusions

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

The IPSAS is practical, easy to use and provides a viable and valid alternative to the weighed food diary in this age group. The IPSAS has the potential to make participation in dietary assessment studies less onerous, thereby increasing participation and completion rates and so the representativeness of the sample and data collected. It is recognised that portion size estimation does result in some loss of accuracy and precision in measures of amount consumed compared to the weighing of foods; however, this is offset by a reduced respondent burden and, thus, a reduced impact on the respondent's habitual diet.

The IPSAS system is an accurate and automated data collection and analysis system that is less resource intensive than traditional methods, especially in the data coding and analysis phases. The automated nutritional output means that both time and the resources needed to code and data entry are significantly reduced compared to traditional methods. Therefore, the costs of large scale studies of dietary intake are considerably reduced.

Acknowledgments

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

The authors gratefully acknowledge the commissioning of this research by the Food Standards Agency (project number N08027). We especially thank the Newcastle schools, parents and children who participated in the study.

Conflicts of interest, sources of funding and authorship

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References

The authors declare that there are no conflicts of interest.

The Food Standards Agency (project number N08027) funded the present study.

EF was the principal investigator who conceptualised and designed all studies and also wrote the first draft of this paper. AH and ES participated in running focus groups, system design, dietary data collection and analysis. AJA was co-investigator and guided study design and development. All authors reviewed and extensively edited multiple drafts of this paper and approved the final version submitted for publication.

  1. [Correction added on 27 January 2014, after print publication and first online publication: The publication year for Foster et al. in the citation details has been updated to 2014.]

References

  1. Top of page
  2. Abstract
  3. Introduction
  4. Formative research
  5. Selecting which foods to include
  6. Overview of the system
  7. Validation
  8. Use of the interactive portion size assessment system in dietary assessment
  9. Conclusions
  10. Acknowledgments
  11. Conflicts of interest, sources of funding and authorship
  12. References
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