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Dietary assessment in minority ethnic groups: a systematic review of instruments for portion-size estimation in the United Kingdom

Context: Dietary assessment in minority ethnic groups is critical for surveillance programs and for implementing effective interventions. A major challenge is the accurate estimation of portion sizes for traditional foods and dishes. Objective: The aim of this systematic review was to assess records published up to 2014 describing a portion-size estimation element (PSEE) applicable to the dietary assessment of UK-residing ethnic minorities. Data sources, selection, and extraction: Electronic databases, internet sites, and theses repositories were searched, generating 5683 titles, from which 57 eligible full-text records were reviewed. Data analysis: Forty-two publications about minority ethnic groups (n = 20) or autochthonous populations (n = 22) were included. The most common PSEEs (47%) were combination tools (eg, food models and portion-size lists), followed by portion-size lists in questionnaires/guides (19%) and image-based and volumetric tools (17% each). Only 17% of PSEEs had been validated against weighed data. Conclusions: When developing ethnic-specific dietary assessment tools, it is important to consider customary portion sizes by sex and age, traditional household utensil usage, and population literacy levels. Combining multiple PSEEs may increase accuracy, but such methods require validation.


INTRODUCTION
Dietary assessment in minority ethnic groups is critical for surveillance programs in countries with high proportions of settled and transitory groups as well as for implementing effective interventions in these populations. Multiethnic populations living in the same country may show wide variation in prevalence rates of noncommunicable diseases such as obesity and cardiovascular disease, and such variation may be associated with dietary practices more so than with genetic background. 1 The evaluation and improvement of health outcomes through health promotion interventions in these populations requires culturally appropriate dietary assessment techniques.
In the United Kingdom, foreign-born residents made up 13% (4.6 million) of the population in 2011, with Asian and Asian British accounting for 7.5% of all residents, followed by African, Caribbean, black, and black British, totaling 3.3%. 2 Of the ethnic minorities in the United Kingdom, those originating from the Indian subcontinent (India, Pakistan, and Bangladesh) have among the highest rates of cardiovascular and other noncommunicable diseases. 1 Investigating the experience of disease and dietary exposures in these groups may provide etiological clues. 3 Ethnic minority groups in countries such as the United Kingdom and the United States are immigrant groups that have settled over time, with successive generations becoming integrated into the host society. As a consequence, dietary acculturation is observed, 4 affecting dietary patterns. 5 Assessing individual diets in these groups is difficult because any tool must capture the complexity of the diet, which may be a combination of ethnic foods and those commonly consumed by the autochthonous (native) population. A further complexity is that the assessment of cultures in which food is consumed directly from a shared dish and with the hands (eg, Arab countries and some African countries) 6 may require resource-intensive techniques such as direct observation. Another well-recognized challenge in dietary assessment is the accurate estimation of portion sizes. 7 Traditional dietary assessment methods (eg, 24-hour recalls, food frequency questionnaires [FFQs], and unweighed food records) are subject to random error when estimating portion size. 8 Type of food eaten, sex and age of respondent, and the nature of the dietary assessment instrument used may also affect the validity of the data collected, especially if there is a need to recall amounts from memory. [9][10][11] Beyond generation and age factors, income, level of education, dietary laws, religion, and food beliefs are also influential. 6 A considerable number of studies reporting on PSEE performance and comparing the use of PSEE types in nonethnic populations have been conducted., and these are presented in a separate publication. 12 Some of this work highlighted the lack of reported quality measures for PSEEs, particularly for those used across sociodemographic groups. 8 Other studies looked at strategies to improve the recall of portion size during dietary assessment by both interviewers and respondents, [13][14][15] including the use of categorical size estimates (ie, large, medium, and small) in quantitative FFQs or the use of portion-size estimation aids (PSEAs) like food models, household utensils, photos, or diagrams in 24-hour recalls. 16 In some cases, the performance of these instruments depended heavily on the characteristics of the food, particularly the shape and texture. 17,18 Because of the popularity of amorphous foods in many ethnic cultures, ie, foods that take the shape of the container they are in, such as rice and noodle dishes, and the presence of traditional foods, the use of adequate PSEAs and other portion estimation tools is particularly important. While dietary assessment techniques in ethnic minority groups have been examined, 6,19 the portion-size estimation component has not been specifically addressed.
The present review explores the existing PSEEs applicable to UK ethnic minority groups to cover this gap. For the purpose of this work, a PSEE was defined as a component of the dietary instrument designed to help quantify the amount of food reported as consumed, including PSEAs (eg, photos, everyday reference objects, household utensils, food models), categorical size estimates, household utensil measures, unit food amounts (eg, 1 slice, 1 egg), standard units of measurement (grams, ounces, milliliters), and any other quantifying component. Although this review focused on the main UK minority ethnic groups, many of the studies identified explored multiethnic populations across North America, Africa, and the Indian continent, for which the same PSEEs may be applicable.

METHODS
A systematic review of the literature for records published between 1910 and 2014 was conducted between March and September 2014, using standard systematic review guidelines 20,21 (see the PRISMA 22 checklist in Appendix 1 in the Supporting Information online). This review was based on a larger systematic review of portion-size instruments for dietary assessment, 12 from which the subgroup of tools tested in minority ethnic groups in the United Kingdom was extracted. The study protocol is available by contacting the authors.
Studies were selected for review using population, intervention, comparison group, outcome, and study design (PICOS) criteria (Table 1). Two groups of records were selected: Group 1 (United Kingdom and related). Publications or other records reporting the development, application, or validation of a PSEE in a minority ethnic group in the United Kingdom (main minority groups, on the basis of census data 2 ) or in minority ethnic groups living outside the United Kingdom if they were of the same or related ethnicity as the UK groups (eg, African American, American Chinese, American South Asian, and Caribbean).
Group 2 (country of origin). Records reporting the development, application or validation of a PSEE in the country of origin of UK minority ethnic groups (eg, Jamaica, Sri Lanka, Nigeria).
Studies were excluded if they reported the use of a dietary assessment instrument without a portion-size measuring element (eg, nonquantitative FFQs) or if the PSEE was not described in full or was not applicable for dietary assessment in minority ethnic groups, particularly for ethnic foods. Studies using food guide pyramids were only included if they examined a sufficiently wide range of portion sizes across food groups and could assist with dietary assessment. Studies using instruments tested exclusively in minority ethnic groups not related to the main minority ethnic groups in the United Kingdom (eg, Native American Indian in the United States) were also excluded. In addition, titles with no accessible abstracts; editorials, commentaries, and opinion pieces; review papers with no relevant references; and papers in languages not covered by the research team were also excluded (ie, only papers in English, Spanish, French, Italian, Portuguese, Urdu, Punjabi, and Arab were included).
Searches were conducted across 21 medical, social, and economic databases (see Figure 1 for details). In addition, all titles from a published review on dietary assessment methods for minority ethnic group populations were also screened. 6 The title search was complemented by cross-referencing and by the authors' knowledge.
A search pathway containing keywords and combinations for the searches was designed and prepiloted (see Appendix 2 in the Supporting Information online). Searches were structured in blocks containing descriptors for PSEEs. The following block themes were used: portion size; tool; measures; assessment; quantity; dietary; electronic; foods; texture; and target population characteristics. Each block consisted of at least 3 descriptors. For instance, the block "portion" consisted of "portion OR serving OR helping"; the block "tool" consisted of "tool* OR utensil* OR appliance* OR guide* OR instrument*," and so on. In addition, for Group 1 records, keywords for the major minority ethnic groups in the United Kingdom were used, ie, "Ethnic OR Asian OR Indian OR Pakistani OR Bangladeshi OR Chinese OR Black OR Caribbean OR African OR Arab OR Polish OR Irish traveler OR Gypsy traveler." This was followed by a search of 19 different combinations of the above descriptor blocks, each containing the ethnic minority block. To reduce the number of ineligible hits in combinations producing more than 1000 hits, abstracts in which the words "portion" and "size" were not within 3 words of each other were excluded. For Group 2 records, the same search strategy was used, but the ethnic minority block was replaced by a country of origin block, ie,: "Asia* OR India* OR Pakistan* OR Bangladesh* OR China OR Chinese OR Caribbean OR Africa* OR Arab OR Poland OR Polish OR Romania* OR Ireland OR Irish OR Sri Lanka*." Title and abstract screening and data extraction were carried out by 3 investigators (A.A., E.A.R., and C.G.). A subsample of abstracts was screened in duplicate to assess consistency between reviewers. Disagreements were discussed within the team to reach consensus, and further information from authors was sought when necessary. When the same instrument appeared to be reported in different publications, this was verified and the instrument included only once. If a paper's abstract did not provide enough information to determine whether eligibility criteria were met, that paper was taken forward to full review.
Information was extracted on the instrument description (ie, name, origin, dimension); the instrument technique (indirect or direct measuring) and whether it was based on a portion reference scheme; the outcome measured and the intended population use/ setting; the efficacy of the tool; the relevance of the instrument to the population/target outcome; the instrument's validation and reliability status; the feasibility of the instrument (ie, low, medium, or high complexity); and the applicability of the instrument beyond the study population and context. Risk of bias in individual studies was examined by looking at study design, outcomes and analysis, and other strengths or limitations of the study, using adapted versions of published resources. 23,24 Analysis of risk of bias across studies was not applicable because this review is meant to inform decisions across a variety of settings. 23 Meta-analysis was not appropriate; rather, a narrative synthesis was conducted, and results were combined in tables and figures.

RESULTS
The search, identification, and screening process is shown in Figure 1. The searches identified 5683 record titles (approximately one-third were in the country of origin), from which 196 abstracts were screened. After removing noneligible abstracts, duplicates, and redundant instrument reporting, 57 records were retained for full review. From these, a total of 42 eligible records were retained for full analysis: 20 were aimed at a minority ethnic group in the United Kingdom or a related population outside the United Kingdom (Group 1), and 22 were related to autochthonous (native) populations in their country of origin, excluding the United Kingdom (Group 2).
Publication years ranged from 1984 to 2014, with an average of 2 publications per year. Group 1 records included 18 research articles, 1 internet site, and 1 doctoral dissertation (Table 2 2,3,10,25-50 ). Group 2 records included 17 research articles, 1 government publication, 1 doctoral dissertation, and 3 conference abstracts. For 2 of the abstracts, a follow-up full-length publication could be identified and was also included 51,52 (Table 3 11,17,18,27,35,49,79   Abbreviations  48 ). Dishes were photographed with the crockery most commonly associated with that dish, ie, rice, meat, vegetable, and bean curries on a plate, and dhal in a bowl. f The Beyond the Basics guide is the main tool in Canada for teaching about the exchange system approach to managing carbohydrate intake. This pictorial guide was developed from the Beyond the Basic tool and was subsequently applied for educating about the metabolic syndrome (P. Brauer, written communication, May 2016).   were used in women only (2 of which were used in pregnant women exclusively), 3 were used in secondary school or university students, and 1 was used in participants in a weight-loss trial. Eleven PSEEs (26%) were based on national survey samples. Nearly one-quarter of all PSEEs were tested in UK minority ethnic groups, while 17% were applied to US groups. Forty-eight percent of PSEEs were tested in native populations in their country of origin, excluding the United Kingdom. Figure 2 gives information on types of PSEEs and the dietary assessment instruments in which PSEEs were applied. The most common type of PSEE (47%) was a combination tool, ie, a tool that used more than one PSEE within the same dietary assessment instrument (eg, food atlases and household utensil measures as part of the same FFQ), followed by portion-size lists (in full units or fractions) and categorical size estimates (ie, small, medium, large) from questionnaires and guides. Image-based tools and volumetric tools followed in equal prevalence (Figure 2A). The most common dietary instruments were FFQs (36%), followed by 24-hour recalls, food records, and other instruments, including databases and other questionnaires. Only one In the same paper, the authors also report the development of an FFQ for Jamaicans living in Jamaica (see entries for Jamaica), as well as an FFQ for Jamaican and Caribbean immigrants living in the United Kingdom (see Table 2 under Sharma et al. 27 and Vyas et al. 35 ).
b Accuracy rate indicates the number of times a food's portion is estimated correctly, out of the total number of estimations, expressed as a percentage. eligible PSEE as part of a food guide pyramid was identified 28 ( Figure 2B). Dietary assessment was the most commonly reported main purpose for which the PSEE was used, followed by development and validation or comparison studies. About 40% of PSEEs were linked to published portion-size reference schemes, including US survey dataderived schemes, 45,46 the British Adult Dietary Survey, 48 the UK Food Standards Agency portion sizes, 73 and national dietary guidelines 49,67 (Tables 2 and 3, Tables S1-S4 in the Supporting Information online). Figure 3 gives information on study populations. The predominant population (around 50% of PSEEs) was the South Asian community, including both the immigrant and the native populations, followed by African, non-UK white European, Afro-Caribbean, Chinese, Cuban/Puerto Rican, mixed ethnicity, and Arab populations ( Figure 3A). Of the South Asian populations, the most common was Sri Lankan and the least common Bangladeshi, but proportions differed depending on whether participants were immigrants or

FGP 2%
Instrument PSEE was part of (n=42) "Lists" include lists of weights or volumes, such as those in household utensil measures or units; categorical size estimates, such as small, medium, or large; fractions of a reference portion (eg, "1/2 typical amount"); and text-based package information. "Pictures" include standalone photos, food atlases, diagrams, and drawing/picture guides. "Volumetric tools" include household utensils, food models, food replicas, non-food reference objects (eg, deck of cards), hands, packaging demarcations, measuring tapes, measuring jugs, and food scales. "Combination tools" are tools consisting of more than one PSEE applied within the same dietary assessment instrument. (B) Distribution by type of dietary assessment instrument into which the PSEE was integrated. "Food record" includes both weighed and estimated records. "Other" includes databases and no specific instrument. Abbreviations: 24h R, 24-hour recall; FFQ, food frequency questionnaires; FGP, food guide pyramids; Non-FFQ, questionnaires other than FFQs.
native residents ( Figure 3B). Studies of South Asians employed the widest range of PSEEs (from portion-size lists to food scales), while studies of non-UK white European immigrants employed a similar range of PSEEs. A narrower range of PSEEs was used in other groups ( Figure 3C).   Figure 4A). In total, 20 PSEEs had been validated (mostly in native populations) or calibrated against other estimating tools in comparison studies ( Figure 4B). Within these 20 PSEEs, those involving PSEE-based questionnaires were the most common. [25][26][27]31,32,[34][35][36]40,41 Only a few PSEEs had been validated or compared on their own, as opposed to being validated as part of a full dietary assessment instrument. These included household utensils, 33,51,66 previously validated by Edington et al., 81 and food atlas photos, 38 previously validated by Nelson et al., 10 but the validation had been done in native (rather than ethnic minority) populations. This also applied to other PSEEs, such as those used in the Oslo Immigrant Health Study questionnaire 41  The efficacy of a PSEE (defined as the degree to which the PSEE was capable of producing a portionsize estimate that was close to the real weight of the food) was difficult to determine, as only 7 (17%) of the PSEEs reported comparisons against recent weighed data. For these studies, accuracy rates (ie, the percentage of correct estimations, either as a perfect match or as a very close match, vs actual weight, relative to the total number of estimations) were frequently but not always high (>60%). However, the limited range of foods and the small sample size of participants in some of these studies may limit their application. 11,38,55 A UK study using food photos for 10 traditional South Asian dishes reported accurate estimates in 80% of the comparisons (defined as being between À6% and 17% of the correct weight) but used a sample of only 36 women. 39 A larger study with a food atlas tested in 169 South Africans reported 70% of 2959 estimations to be within 10% of the actual weight, but the degree of accuracy depended on the physical form of the food. 18 Similar results were reported for stand-alone photos, drawings, 84 and food models 11 tested in Sri Lankan children (n ¼ 80), but only 55% correct estimations (based on correct photo chosen) of 1028 comparisons were reported for a food atlas tested in Burkina Faso (n ¼ 257). 17 In Sri Lanka, an FFQ that included a set of 12 food photos showed only moderate correlation and agreement with 7-day weighed food records, depending on the nutrient, 52,65 but only 3 portion sizes and 4 foods were included. In India, the Pearson correlation coefficients between estimated and weighed portion sizes for 5 foods in preschool children using a questionnaire with portion fractions 55 were on average 0.88, but such correlation cannot guarantee agreement between the 2 methods. Moreover, the foods in that study were hardly consumed, and the PSEE had a limited range of options available (for further details, see Tables S2 and S4 in the Supporting Information online).corrections up to here are fine.
Pictorial guides, FFQ lists, package information, and some image-based PSEEs were the least complex tools, owing to reduced respondent burden and ease of administering; in addition, the data obtained could be processed automatically. However, they frequently involved complex development stages and trained staff. On the other hand, household utensils, scales, and some food models were cost-effective but less portable (as were some food atlases). The need for interpreters or translation of documentation into native languages increased the complexity further.
In general, studies that used FFQs had reasonable sample sizes and a wide range of ethnic    minority-specific primary data (eg, focus groups, interviews, visits to supermarkets) and employed methods of low burden to respondents; however, the PSEEs tended to be compared against other estimating methods rather than against weighed data. [25][26][27]31 Studies involving specific population groups, eg, immigrant pregnant women or small samples of native populations, used more labor-intensive, sensitive methodology, mostly food scales for weighed food records, which are considered the gold standard. 33,37,52 Several limitations were identified across most studies (Tables 2 and 3; Tables S3 and S4 in the Supporting Information online). Beyond the lack of absolute or relative measures of validity, reliability, or feasibility of some PSEEs 28,29,42,43,54,58,62,63,77,79 or the only partial validation of other PSEEs, 33,41,53,59,66,68,83 other limitations included the following: low sensitivity of the tool due to a small number of portion options or photos 11,17,25,26,29,32,40,43,52,55,65 ; grouping of mixed dishes and omission of food items in questionnaires 27,35,42 ; lack of breadth 28 ; requirement for high level of staff training or involvement 33,37,64,68 ; requirement for participants to be literate or skilled in operating equipment 33,37 or in performing numerical calculations 30 ; requirement for participants to possess specific technology 29 ; long time elapsed between dietary assessment with the new PSEE and the comparison method (which effectively means the 2 methods were comparing different things), or long time elapsed between test and re-test evaluations 26,38,40 ; and testing of PSEE in only one gender or age group. 17,25,[30][31][32][36][37][38]55,56,61,63,64,83,79 Other issues were validation conducted in nonminority ethnic group populations 30,41 ; low retention rates 41,43 ; study not powered to detect ethnic subgroup differences 29 or validity/reliability 38,55 ; and systematic measurement error. 31 In fact, all comparison studies suffered from this last type of error by not including a measure of actual weight. Language barriers were not an issue because, in most studies, interpreters or PSEE versions in native languages were available.

Group 1 publications
There were 20 eligible studies in UK immigrants or related populations describing 22 different PSEEs ( Table 2). Table S1 in the Supporting Information online provides further details, including the following: PSEE dimension; units of measure; technique used; link to portion-size reference scheme; purpose; outcome; and setting. The distribution of tool types was similar to that for the entire sample of studies, but with a lower proportion of combination tools and a higher proportion of 1-and 2-dimensional tools (Figure 2A). Moreover, as for the entire group of studies ( Figure 2B), FFQs were the most common dietary assessment instrument in which PSEEs were used, and dietary assessment as part of observational studies or interventions was the most commonly reported main purpose for which the PSEE was applied. The predominant study population was still the South Asian community (55% of PSEE), followed by non-UK white Europeans and other groups (18%) (Figure 3A and B). Instruments commonly used for the South Asian community included food scales, photos, and drawings, 38,42 a household utensil guide, 3 portion-size lists as part of an FFQ, 38,43 and other questionnaires. 41 In Indian and Pakistani groups, food models, scales, household utensils, 33 and combined PSEEs 35 were used ( Figure 3C).
Only one PSEE (5%) in Group 1 had been strictly validated against actual weights, and only 9 (45%) had been used in comparison studies ( Figure 4A, Table 5). On the other hand, 50% of the PSEEs had been piloted and/or tested for reproducibility (compared with 23% in Group 2 studies). Sixty-five percent of the PSEEs either contained a food scale component, whereby researchers or participants had used food scales solely or alongside other tools to weigh food, or had been previously validated in part or in whole, though not necessarily in the same population (vs 23% in Group 2).
Food frequency questionnaires containing lists of portion sizes had notable limitations, including underestimation of macronutrient and overestimation of micronutrient intake, 40 lack of sensitivity/precision for specific nutrients, eg, protein and cholesterol 32 or fats, 40 and low precision in certain population groups. 25 These FFQs typically contained stand-alone PSEEs of low sensitivity with 1 to 3 portion-size options as part of a list. On the other hand, an FFQ developed to measure fruit and vegetable intake in UK South Asian women and including a bespoke household utensil guide 3 showed good validity against biomarkers of dietary phytoestrogen intake in epidemiological studies. 85 Some food photos 29,38 showed good comparability with 24-hour recalls or food records, although in some cases the sample sizes were small and performance varied by ethnic group, sex, body mass index, and education level. 26 Food models used as stand-alone tools to assist in FFQs resulted in estimates comparable with other estimates for micronutrient intake but underestimated energy intake. 34 Combination tools were generally useful for dietary assessment of groups, to rank individuals across levels of intakes, 31,36 or to detect changes during health promotion interventions 30 but were not sensitive enough for individual assessment. Although combined PSEEs generally compared well against 24-hour recalls, systematic error and bias were an issue, resulting in misclassification of up to 10% of individuals in some studies. 31 In general, adding volumetric tools such as food models, everyday objects, and household utensils to semiquantitative FFQs or food records improved comparability with calibrated reference methods, [34][35][36]86 although effective validity could not be established. The same was found for household utensil measures combined with other tools as part of 24-hour recalls 3,86 and for food records used as reference methods 33,35,36 (details in Tables 2 and 5 and Table S2 in the Supporting Information online).

Group 2 publications
There were 22 eligible publications in native populations across a total of 9 countries, describing 20 different PSEEs (Table 3 and Table S4 in the Supporting Information online). The populations studied were African adults (from South Africa, Burkina Faso, Cameroon, Nigeria); Caribbean adults (Jamaican adults); Irish adults and children; Indian and Bangladeshi children; and Sri Lankan adults and children. Both rural and urban settings were proportionally represented. Seven of the PSEEs were tested in children only. The most common PSEEs were combination tools, most of which included household utensil measures, followed by other volumetric tools (Figure 2A).
Seven of the PSEEs were used in 24-hour recalls, while the rest were designed to develop or be used in FFQs or food records (except for 5 PSEEs that did not specify a dietary instrument). Only 4 PSEEs had been fully validated against actual weights and only 2 against weighed food records, but this represented a higher proportion than that seen for Group 1 studies ( Figure 4A). A comparison study 51,66 used food scales alongside other PSEAs but did not measure accuracy. Tests of agreement, sensitivity analyses, and other tests excluding reproducibility and piloting were reported for 27% of the PSEEs (compared with 15% in Group 1), while piloting/reproducibility was reported for only 23% of the PSEEs (compared with 50% for Group 1). Similar to findings for Group 1, 55% of the PSEEs in this group were based on previous research or field data (see Table 5 for examples).
Food texture had an impact on the performance of certain tools, but there was no consistent pattern. For example, in some studies, photos and diagrams worked better than volumetric tools for shaped food, while in other studies, the opposite was found. Likewise, the food atlas for South Africans from Venter et al. 18 produced a significantly higher percentage of correct responses for solid foods (77%) than for amorphous foods (63%) (P < 0.0001). However, in another study that compared the use of stand-alone vs combined PSEEs in Sri Lankan children, line diagrams worked better for foods with a defined shape (eg, fruit pieces), while photos were more accurate for amorphous foods (eg, curry dishes, cooked vegetable dishes). 56 Furthermore, Lanerolle et al. 11 showed that food models in 3 portion sizes correlated highly with actual weights, and Bland-Altman limits of agreement were relatively narrow between methods, but this applied mostly to the 6 amorphous foods tested (including noodles, rice, curries, pureed vegetables, and salad), since fish, papaya, and butter pieces tended to be overestimated and show greater variability.

DISCUSSION
Errors in portion-size estimation continue to be one of the main contributors to under-and overreporting during dietary assessment, and this applies to studies of minority ethnic groups as well. 6 Using extensive systematic searches, this review has identified and categorized 42 PSEEs applied to immigrant minority ethnic groups and to native individuals in the country of origin beyond the United Kingdom. Across all studies, combination tools were the most common (47% of PSEEs), followed by 1-, 2-, and 3-dimensional tools, which were found in similar proportions. Contrary to the trend seen in developed countries, 12,87,88 there was a low prevalence of computer-assisted methods applied to minority ethnic groups, which may be related to language, educational, and financial barriers. Close to 75% of all PSEEs were designed to assist with portion estimation in FFQs, 24-hour recalls, and food records (36% of all PSEEs were used in FFQs only), which illustrates the current challenges in portion-size estimation inherent to these methods. Findings across all studies are presented below, followed by highlights from Group 1 and Group 2 studies.

Findings across all studies
The main finding from this review, beyond the wide range of tools, was the lack of strictly validated tools (ie, those compared against actual weight or weighed food records), with only 17% (7 PSEEs) reporting such measures, confirming earlier work in nonethnic groups. 8 Attempts to calibrate a PSEE by comparing it with tools that produce other estimates were more common (31%), but systematic error from such comparisons cannot be excluded (a strong correlation does not mean the methods necessarily agree). Tests of agreement were reported for only 3 PSEEs. A larger proportion of the PSEEs (45%), especially combined PSEEs, included components that had been previously validated or calibrated. However, such components had sometimes been tested in a different population 41,54 or at a time long previous to the current application, 38,45 which would affect applicability to the group with which it was intended to be used. 19,89 The effectiveness of PSEEs per se was difficult to ascertain, because in many cases the portion-size evaluation component had been validated within the corresponding dietary assessment instrument (eg, FFQs, 24hour recalls). For the tools that were compared against weight information, accuracy rates were moderately high (>50%), but performance depended heavily on whether the food was of a defined shape or was amorphous. 11,18,56 Moreover, individual characteristics such as habitual choice of portion size 17 and education further influenced results. 17,18,66 In addition, several tools were tested only in children, women, elderly adults, or students, and thus their efficacy in other population groups is not yet established.
When reliability of PSEEs was tested, it tended to be moderate to high (with correlation coefficients ranging from 0.4 to 0.9), though not consistently. Beyond food scales and measuring jugs, 51 the best reproducibility was seen for food atlases, 18 a combined PSEE that included measuring tape and measuring cups, 57 and portion lists in FFQs 25 and other questionnaires. 30 Stand-alone food photos 51,66 and portion-size fraction lists 40 were less reproducible, perhaps because of the increased difficulty in conceptualizing volumes when using PSEEs that do not offer an absolute or relative measure for comparison against measuring utensils, photographic series, or volumetric tools. 10,13 Beyond the known difficulties in the perception, conceptualization, and memory stages associated with the accurate recall of amounts, 10 as well as the influence of food and subject characteristics, 17,90 the concept of a serving size may not exist in some cultures, especially those in which eating from a communal serving dish is a normal practice. 6 Tools able to assist in the estimation of communal servings are thus very relevant. Some of these instruments were identified in studies conducted in the country of origin and included food photos, 17,18,60 ; line drawings, 56 household utensil measures, 54 amount of food prepared/leftovers, 55 and combinations of these. 56,57 In an attempt to increase the accuracy of estimation, combination tools were applied to FFQs and other instruments that typically produce under or overestimates. Combining 1-, 2-and 3-dimensional components can account for variation between different types of foods and has the potential to increase the accuracy of portion-size estimation when these tools are applied across a range of foods. For these reasons, it has been recommended for individual dietary assessment. 6,13 While the potential effectiveness of combination tools was highlighted in several of the studies identified, 3,[34][35][36]53,56,86 in most cases comparisons were made against other estimating tools, and the validity of combined PSEEs was seldom demonstrated. 56 As previously suggested, 8,10,45 the number of portion options in questionnaire-based PSEEs, the number and size of photos in food atlases, and the type of tool (eg, 2-vs 3-dimensional) were all important factors affecting PSEE performance. For example, several of the PSEEs identified were based on the Block FFQ, 45 which incorporates 3 categorical size estimates presented as multiple-choice options to be compared against a reference "medium" portion size shown in ounces, size (eg, medium), household measures, or natural units, as derived from National Health and Nutrition Examination Survey (NHANES) II data. 36 The inclusion of the 3 portion-size options -compared with the inclusion of only the NHANES median portion sizeresulted in higher correlations for energy, fat, percent calories from fat, and vitamins A and C when compared with a 24-hour food record, but the descriptions of a reference medium portion are still prone to subjective interpretation. Specifically, the use of household measures may reflect measurement convenience and approximation rather than a behavioral truth, and measures may differ between ethnic groups and the native population. 6 One way to overcome this problem is to collect data on the capacity of usual household utensils and use this information in subsequent assessments 5 to produce ethnic-specific utensil guides 3 or to conduct individual assessment, using the number of people in the household and the proportion of food taken from the total amount prepared. 6 As for the number of photos in photographic series, the inclusion of 3 portion-size options in FFQs is likely to improve estimation relative to having no aid, 10 but this method may not be sufficiently sensitive in certain populations such as African Americans 26 and South Asians. 52 Nelson et al. 10 found that a series of 8 photos was associated with smaller errors of estimation when compared with a single photo. As a result, a series of photos was incorporated into their food atlas, although this increased the complexity of the atlas, making it impractical for large epidemiological studies. The application of food models alongside open-ended questions about portion size in FFQs may, in theory, increase sensitivity by allowing the questionnaire to add personal variability in food preferences and quantity to the age and sex components. 45 However, no studies in this review demonstrated validity in this context. The only study that attempted to calibrate food models as part of an FFQ 31 suffered from systematic error by including the models in the calibration of both the FFQ and the reference method.
User acceptability of the PSEE is important for continued application of the tool, but this was seldom reported. Food scales and measuring jugs were the least preferred tools in a study that compared a wide range of PSEAs in Irish adults, 51 who also rated household utensils as the easiest to use and the most likely to be used in the future, even though being the least precise. It is likely that PSEEs requiring numerical calculations, 51 volume conceptualization, 10,90,91 or prolonged time due to complexity or size (eg, food atlases) 51,52 may present barriers to implementation. In such cases, more culturally appropriate tools that allow for customary serving and eating practices may need to be considered.

Highlights from Group 1 studies
A large number of PSEEs applied to immigrant populations in the United Kingdom or to related groups elsewhere tended to be part of FFQs used in epidemiological studies. For such studies, complex development stages were sometimes reported, illustrating the challenges in developing any new tool that is culturally sensitive. For example, a UK study that developed an FFQ for South Asians included exhaustive data collected on recipes and more than 200 traditional foods and dishes (Kassam-Khamis et al. 38 ).
Many of the PSEEs used in related immigrant populations outside the United Kingdom were similar to those used in the United Kingdom (eg, those that included combinations of image-and list-based PSEEs), but they may need to be adapted for application in the United Kingdom, especially for portion sizes of commercial products. While the study populations may share a common country of origin, acculturation is likely, and the impact of host country food practices on the immigrant's diet may be significant. Still, some of the tools have good potential for adaptation, such as the Beyond the Basics pictorial guide for Canadian South Asians, 42 which, although not validated, is simple to use and has been applied in diabetes and metabolic syndrome education (P. Brauer, written communication, May 2016). Another such tool is the Oslo Immigrant Health Study questionnaire for Norwegian South Asians, 41 which includes questions on acculturation as well as a question on the proportion of staple foods to other foods included in the dish. Another potentially adaptable PSEE is the Chinese version of the Diet Habit Survey, 82 which quantifies usual amounts of spreads on bread with descriptors such as "lightly spread (can see the bread through it)" and "scrape (can barely see the spread)" 30 and allows the conversion of household utensil amounts and commercial drinks into volumetric units (S.L. Connor, written communication, February 2015). Some of these components may facilitate understanding in first-generation immigrants, even though they are subject to personal interpretation and may require numeracy skills. 41

Highlights from Group 2 studies
There was a relatively wide range of PSEEs identified in the countries of origin that may be applicable to immigrant populations elsewhere and that provide useful insight, especially into the feasibility and cultural acceptability of the PSEE. The PSEEs used in this group typically contained low-cost, culturally appropriate components such as local household utensils or everyday reference objects. Food photos and food models were also used frequently, especially in deprived areas. Results from studies in Sri Lankan children suggested that using a combination of PSEAs that includes lifesize representations of traditional foods is probably more suitable than using a single stand-alone tool in that population. Nevertheless, a wider range of food types needs to be explored with such tools, as performance depended heavily on food texture, and no consistent pattern was seen across studies (ie, some studies favored food picture-based PSEEs for foods with defined shape 18,56 and food models for amorphous food, 11 while others showed the opposite 56 ). Household utensils, on the other hand, were the least precise and least accurate in at least 2 studies, 51,56 as observed in some Group 1 studies. 5,32 While simple instruments may be nonintrusive, quick to complete, and suitable for low-literacy groups or those not speaking the language of the host country, limitations in the validity and reproducibility of such tools need to be considered. Specifically, several studies 53,61,66 compared PSEEs against estimates rather than actual weights, and some studies tested a limited number of foods, portion options, and individuals or used low-precision instruments. 11,17,52,55 Thorough methodology in the collection of traditional food lists and portion sizes is also essential to obtain good reliability and validity measures, especially when variability exists between and within geographical areas. 35,77 Finally, many Group 2 studies included information on typical serving sizes, traditional utensils, and foods commonly consumed from a shared dish, in addition to information on portion size, 17,54,72 all of which may be useful when adapting existing dietary instruments to minority ethnic group populations.

Comparison with previous work
In line with previous studies, 6,19 this review identified a large variety of methods for estimating usual portion size, particularly within FFQs (36% of all PSEEs). These PSEEs tended to be one-dimensional (eg, consisting of lists of average portion sizes) and were used with or without visual aids. 25,34,40. Visual aids were added with the aim of increasing specificity to capture the diets of the differing groups within each ethnicity without introducing differential bias for ranking individuals on the basis of food and nutrient intakes. 36 Regarding the low prevalence of computer-assisted methods, the present results agree with those reported by Ngo et al., 6 who found that 67% of 46 studies in European minority ethnic groups used noncomputerized visual aids, and 50% applied previously identified serving sizes in target ethnic groups. In the group of studies in countries of origin, household utensils and everyday objects were typically used. These can be easily bought in the community and are cheap and simple to apply, which may explain their widespread use in lowresource countries.
The lack of a consistent pattern with regard to the impact of food texture on PSEE performance also confirms previous findings, 15,17,51 suggesting that estimation accuracy may interact with other uncontrolled factors such as a participant's experience, level of attention, willingness to cooperate, or education. 17,51 A study in British adults in which photos were compared with weighed foods reported less accuracy in estimating French fries, mashed potatoes, and spaghetti than in estimating cornflakes, 92 while a study in Norwegian children 93 found that mashed potatoes and cornflakes, in addition to other shaped or amorphous foods, were the most accurately estimated foods. A third UK study using photos of single-portion foods also failed to find any consistent association between the texture of 17 foods and PSEE accuracy. 15 However, the methodologies in some of these studies differed from each other (eg, estimation of food 5 minutes after consumption vs the following day or later), and none of the studies focused on minority ethnic foods.
Regarding the accuracy of nutrient estimation, a previous review 19 suggested that mean intakes estimated from FFQs may be higher than intakes estimated using reference methods (eg, 24-hour recalls), but this depended on the reference method and, in particular, the PSEE used. 19 In the present review, intakes of nutrients and energy also differed from those estimated using reference methods, and some correlated well with the reference method, but only in certain ethnic subgroups. 25,34 Even in instruments adapted to be ethnic specific, misreporting was an issue 35 and was associated with higher rates of overweight, especially in women. 53 Overall, since many of the studies examining nutrient intakes used estimates as comparators, it is difficult to ascertain PSEE efficacy. Thus, the validity, sensitivity, and specificity of PSEEs still need to be considered, even if the PSEE was previously tested in an ethnic minority population.
The South Asian community was a commonly studied target group (examined in 20% of studies) in a previous review of European immigrants, 6 showing the greatest variety in terms of dietary assessment methods. Acculturation was measured in 87% of the studies, while only 2 (9%) of the studies in the present review reported measuring this aspect. 31,41 One study that measured acculturation, the Oslo Immigrant Health Study, 41 includes an index of dietary integration alongside questions on availability, cost, and quality of foods 94 and can thus be used as a cross-disciplinary tool to investigate how demographic and sociocultural factors may modify food habits in minority ethnic groups.

Strengths and limitations of this review
Previous reviews have highlighted the importance of accurate estimation of portion size for both population and individual assessment in ethnic minority groups, 6,19,89 yet the PSEE itself was not specifically addressed. The present review focused on UK ethnic minorities and related populations, and so the results may not be applicable to other groups such as Native Indian Americans and European minority ethnic groups, for which data are not yet available (eg, Polish). However, considerations related to the versatility, validity, and specificity of the instrument and to method development are likely to apply. A meta-analysis of the relative effectiveness of each instrument was not performed because measures of error were not reported in all the studies, but this would be worth exploring in the future. Three Irish studies were included because the Irish were identified as a UK minority group from census data. These studies, however, sometimes used UK portion reference schemes 68 and foods similar to those traditionally consumed in the United Kingdom. Therefore, information about the PSEEs from the Irish studies may not be relevant to certain ethnic minorities. In addition, more than 75% of the PSEEs described here were applied across various age and sex population groups, but some were tested only in women, children, or first-or second-generation migrants, thus preventing conclusions about their general application. The use of a controlled environment also may have influenced the results, 11,15,39,51 as participants might have been more aware of their portion size than in normal day-to-day situations. Finally, while portion size has been recognized as a growing contributor to variation in intakes in recent years, frequency of consumption continues to be the major cause of variation. 95,96 It is therefore important to ensure that errors associated with portion-size estimation do not mask true variability in portion size.

CONCLUSION
Accurate assessment of portion sizes and intake of ethnic diets requires certain considerations about the use of PSEEs, food lists, and food composition databases. 6 This review identified 5 main areas to consider when estimating portion size in minority ethnic groups ( Table 6). The PSEE needs to allow flexibility in the estimation of native, traditional recipes and to consider how food is eaten and served. Assessment may be improved by the use of combined PSEEs, especially for diets in which staple amorphous foods are common (eg, rice, couscous). However, the validity of any combined PSEE needs to be established beforehand, especially for the selective application of each component by food type, since using a combined PSEE across all foods could increase measurement error.
If household measures are used as a guide for volumes, the utensils employed for assessment need to be culturally appropriate, and the actual volume of each utensil may need to be measured. In low-literacy groups, it may be practical to investigate the ratio of staple food to vegetable/meat mixes using questionnaires, bespoke food models, or photos and to adapt the PSEE accordingly in future assessments. If a list of reference portion sizes is used, for example in an FFQ, the use of categorical size estimates or food models may improve results over using a single average portion. The reference portion sizes need to be representative of the ethnic group studied and account for sex and age differences. Studies in the country of origin provide invaluable information on ethnic recipes, foods, and serving sizes, but the foods typically consumed by related minority ethnic groups elsewhere may differ as a result of acculturation. Investigation in the host country may still be necessary, followed by validation against weighed data.
In summary, a variety of PSEEs have been reported in South Asian and other minority ethnic groups in the United Kingdom and in related groups elsewhere. Instruments suitable for use in low-literacy populations, such as household utensils, photos, and food models, are commonly used, but their efficacy has not always been demonstrated. For epidemiological studies, PSEA-assisted questionnaires save time and reduce participant burden but may have a limited number of portion-size options, require participant conceptualization skills, and involve complex developmental stages to be representative of the minority ethnic group diet. The use of computerized portion estimation tools warrants full investigation, as virtually no studies have explored these tools in minority ethnic groups, yet they may offer logistic advantages over traditional methods (eg, by having a wider reach). Validated instruments for groups with specific customary eating practices (eg, shared dishes, eating from hand) are particularly needed. Combined PSEEs show high potential for both group and individual assessment in ethnic minorities, but their validity needs to be more widely established. Table 6 Areas to consider when assessing portion size in minority ethnic groups

Area Considerations
Validity Whenever possible, choose a validated portion estimation instrument that has been compared against weighed data and tested for reliability in the population of interest. For new and existing tools, consider collecting information about customary portions by sex and age as well as by traditional household utensil measures via interviews or food records Specificity Consider using PSEEs that allow flexibility in estimating portions of traditional foods, including mixed recipes and ingredients/components. Examples may include bespoke tools, such as traditional food models, or a combination of instruments to be applied across a range of food types (eg, depending on food texture or shape, photos or food models may be used) Breadth For low-literacy groups, the ratio of staple food to vegetable/meat mixes may be a useful complementary measure obtainable with questionnaires, food models, or photos, in addition to food-specific portion size. When assessing changes in food habits in minority ethnic group populations, consider instruments that can measure food-related contextual factors and integration of the ethnic group into the country of residence Native population data Information on traditional foods, recipes, customary portions, and ways of serving may be found in studies conducted in the country of origin. This information may not always be representative of minority ethnic group diets (consider the generation and the degree of acculturation) Special considerations for FFQs Reference portion sizes need to be representative of the ethnic minority group studied and not taken from the general population because distributions may be skewed. The inclusion of FFQ options to indicate larger or smaller amounts from a reference portion, or the use of an open-ended question, may be more accurate than including a single reference portion. If open-ended questions about portion size are used, an accompanying aid such as photos or food models may increase accuracy of the tool Abbreviations: FFQ, food frequency questionnaire; PSEEs, portion-size estimation elements.
Author contributions. E.A.R. designed the study in collaboration with B.E. A.A. and E.A.R. performed the data searches and data extraction. C.G. contributed to the data searches and protocol development. E.A.R. conducted the data analysis and wrote the article. All authors contributed to the editing of the manuscript and share responsibility for the final content. All authors read and approved the final manuscript.
Funding/support. E.A.R. and C.G. were supported by the UK Medical Research Council, program U105960384. A.A. was employed by BE supported by the University of Chester QR grant 2013-SP2-3.
Declaration of interest. The authors have no relevant interests to declare.

Supporting Information
The following Supporting Information is available through the online version of this article at the publisher's website.
Appendix S1 PRISMA checklist Appendix S2 Search pathway Table S1 Description of 22 portion-size estimation elements (PSEE) identified across publications referring to major migrant groups in the UK or to related groups elsewhere Table S2 Effectiveness, validation and generalizability of 22 portion-size estimation elements (PSEE) identified across publications referring to major migrant groups in the UK or to related groups elsewhere Table S3 Quality evaluation of published sources reporting portion-size estimation elements (PSEE) applied to major migrant groups in the UK or to related groups elsewhere Table S4 Details of studies conducted in original countries relevant for UK ethnic minorities (20 portion-size estimation elements)