Research into food portion sizes in children has traditionally examined the relationship between larger food portion sizes and voluntary energy intake in controlled feeding studies. Studies have shown that serving larger portions of a macaroni and cheese entrée to children aged 2–6 years typically leads to increased energy intake at that meal, with the increase becoming more pronounced as children transition through the pre-school period( Reference Fisher, Liu and Birch 1 – Reference Orlet Fisher, Rolls and Birch 3 ). Serving larger portions of snacks of varying energy densities (e.g. apple sauce, chocolate pudding) has also been associated with increased energy intake in children aged 2–5 years( Reference Looney and Raynor 4 ). No data of this kind appear to be available for older children or adolescents. More recently, observational data have been used to investigate associations between food portion sizes and energy intake in children using large food consumption data sets. An analysis of four US nationally representative surveys from 1977 to 2006 (n 31 337) found significantly higher energy intakes during meals at which larger portions of selected energy-dense foods (e.g. sugar-sweetened beverages, salty snacks, French fries) were consumed in both children and adolescents, with susceptibility to increased portion sizing more marked in adolescents( Reference Piernas and Popkin 5 ).
Traditionally, public health campaigns addressing food portion sizes have focused on a reduction in portion size, particularly for energy-dense foods, to reduce energy intake and to help tackle the obesity epidemic. However, the effect of reducing the portion size of such foods on dietary quality has not been addressed and there appear to be no available data on the relationship between food portion size and dietary quality for any population group. Such analysis is needed to identify foods for which larger portion sizes may be associated with positive dietary attributes, as well as the opposite. Findings will also be of use where strategies are being devised to target intakes of specific nutrients going forward.
Several aspects of dietary quality have been highlighted as areas of public health concern for Irish children and adolescents in recent years. Significant proportions of Irish children and adolescents fall short of the recommended intakes of dietary fibre( Reference Deasy, Walton and Hannon 6 , Reference Bannon, Walton and Hannon 7 ), Ca( Reference Hannon 8 , Reference Hayes, Walton and Hannon 9 ), Fe( Reference Hannon 8 , Reference Hayes, Walton and Hannon 9 ) and vitamin D( Reference Black, Walton and Flynn 10 ). Intakes of saturated fat as a percentage of total energy (%TE) have been shown to exceed recommendations in these groups( Reference Joyce, Wallace and McCarthy 11 ). O’Connor et al. showed there is a relationship between dietary energy density (DED) and dietary quality in Irish children and adolescents( Reference O’Connor, Walton and Flynn 12 ), while Joyce and Gibney described a relationship between added sugar intakes and micronutrient dilution in the same groups( Reference Joyce and Gibney 13 ). Na intakes in excess of the population-average target levels have also been reported in Irish children and adolescents( Reference Moloney, Hannon and Kiely 14 , Reference Hayes 15 ).
The aim of the current work was to investigate associations between food portion sizes and key indicators of dietary quality (energy-adjusted intakes of saturated fat, added sugars, dietary fibre, Na, Ca, Fe and vitamin D, and DED) in Irish children (5–12 years) and adolescents (13–17 years) on the days the foods were consumed.
Experimental methods
Survey methodologies
The analyses were conducted on data from the Irish National Children’s Food Survey (NCFS; 2003–2004) and National Teens’ Food Survey (NTFS; 2005–2006), which were carried out as part of a series of national food consumption surveys by the Irish Universities Nutrition Alliance, a formal association of the nutrition units at University College Cork, University College Dublin, the University of Ulster at Coleraine and Trinity College Dublin. The NCFS used a 7 d weighed food record to collect dietary intake data, with participating children (n 594) asked to weigh as many food items as possible throughout the recording period, with help from their parents. The NTFS used a 7 d semi-weighed food record to collect dietary intake data, with participating adolescents (n 441) asked to weigh portions of commonly consumed foods and beverages only, rather than all food items. Weighed data (either directly weighed on the digital scales provided or assigned a weight using manufacturer’s information) accounted for 87 % of all food items consumed on the NCFS and 46 % on the NTFS. The remainder of food items were assigned weights using a range of estimation tools (e.g. photographic food atlas( Reference Nelson, Atkinson and Meyer 16 ), household measures, food portion size reference books( 17 )). Recorded dietary intake data were converted to nutrient intake data using WISP© (Tinuviel Software, Anglesey, UK). WISP contains data from McCance and Widdowson’s The Composition of Foods, sixth( 18 ) and fifth( Reference Holland, Welch and Unwin 19 ) editions plus all nine supplemental volumes( Reference Holland, Unwin and Buss 20 – Reference Chan, Brown and Lee 28 ). The NCFS and NTFS were conducted according to the guidelines laid down in the Declaration of Helsinki. All procedures involving participants were approved by the St. James’ Hospital and Federated Dublin Voluntary Hospitals Joint Research Ethics Committee (NCFS) or the University College Cork Clinical Research Ethics Committee of the Cork Teaching Hospitals (NTFS). Written informed consent was provided by the participants, as well as their parents/guardians. Further detail on the survey methodologies is available at www.iuna.net.
Definition of food portion size
Food portion size was defined as the weight of food consumed per eating occasion, i.e. weight served minus leftovers, and was estimated once for each participant for each day a food was consumed. Where a particular food was consumed on more than one occasion on one day, the largest portion size was assigned for that day (on the basis that a larger portion weight is more likely to have an influence on dietary quality for that day). For some foods, the portion size is likely to represent the mean daily intake of that food (e.g. breakfast cereal is commonly consumed on one eating occasion per day), while for other foods, the portion size may be less than the mean daily intake (e.g. bread may be consumed on more than one eating occasion per day).
Selection of foods and dietary quality indicators for analysis
A selection of foods from all of the major food categories (i.e. starchy foods, fruit and vegetables, milk and dairy foods, meat and other protein foods, foods high in fat or sugar) was included to allow for a range of associations with dietary quality to be observed. Within food categories, specific foods were selected by the authors based on how frequently they were consumed by Irish children and adolescents. The dietary quality indicators selected were energy-adjusted intakes of saturated fat, added sugars, dietary fibre, Na, Ca, Fe and vitamin D, and DED. These were selected on the basis of their public health importance in the diets of Irish children and adolescents, as highlighted in previous analyses using data from the same cohorts( Reference Deasy, Walton and Hannon 6 – Reference Hayes 15 ).
Measurement of dietary energy density
DED is defined as the amount of available dietary energy per unit weight of food or beverage, and is expressed in kJ/g. In the current study, DED was calculated to include all foods and exclude all beverages, as recommended in the most recent systematic review on methods of calculation of DED( Reference Johnson, Wilks and Lindroos 29 ). There were five recording days on the NCFS on which beverages only were consumed (e.g. because the participant was sick); these days were excluded from the DED analysis.
Statistical analysis
Statistical analysis was conducted using the statistical software package SPSS© version 15·0 for Windows. Participants defined as energy under-reporters (32 % of children, 64 % of adolescents) using the method of Schofield (1985) were not excluded from the analysis( Reference Schofield 30 ). Some provision was made to minimise the effects of under-reporting by reporting energy-adjusted nutrient intakes as outcomes. For each food item examined, the portion size data were split by tertile (stratified by sex and age group where significant differences occurred between groups) to create relatively ‘small’, ‘medium’ and ‘large’ portion size groups. Mean values for each of the dietary quality indicators were compared across portion size tertiles for the days on which portions of a particular food were consumed. A one-way between-groups ANOVA was used to test for significant differences in means across tertiles where dietary quality indicators were normally distributed (P<0·05). Kruskal–Wallis tests were used where the data were not normally distributed (P<0·05). Normality was assessed using a Kolmogorov–Smirnov test. Following analysis, the Holm adjustment was manually applied to significant findings to reduce the possibility of Type 1 errors occurring.
Results
Table 1 describes the number of eating occasions of a food included for analysis as well as median portion weights within tertiles (g) for all foods consumed by both children (n 594) and adolescents (n 441). Important indicators of dietary quality in Irish children and adolescents were found to be associated with portion sizes of a range of foods on the days they were consumed. The following associations were noted in both children and adolescents (Tables 2 and 3).
Table 1 Number of eating occasions and median weights by portion size tertile (g) for foods consumed by nationally representative samples of children aged 5–12 years (n 594) and adolescents aged 13–17 years (n 441), Republic of Ireland
RTEBC, ready-to-eat breakfast cereals.
‘Tertile medians (g)’ reflect the median portion weights of the foods examined in each of the ‘small’, ‘medium’ and ‘large’ tertiles.
Table 2 Mean daily nutrient intakes (energy-adjusted) by tertile of food portion size on the days the food was consumed by a nationally representative sample of children aged 5–12 years (n 594), Republic of Ireland
%TE, percentage of total energy; DED, dietary energy density; RTEBC, ready-to-eat breakfast cereals.
T1, T2 and T3 describe mean intake values of the indicator being examined for each of the small (T1), medium (T2) and large (T3) portion size tertiles.
‘↑’ denotes a significant increase in values of the dietary quality indicator being examined with increasing portion size; ‘↓’ denotes a significant decrease in values of the indicator being examined with increasing portion size; ‘–’ denotes no discernible trend in values of the indicator across portion size tertiles, though significant differences may exist between pairs. Significance accepted at the level of P<0·05.
Table 3 Mean daily nutrient intakes (energy-adjusted) by tertile of food portion size on the days the food was consumed by a nationally representative sample of adolescents aged 13–17 years (n 441), Republic of Ireland
%TE, percentage of total energy; DED, dietary energy density; RTEBC, ready-to-eat breakfast cereals.
T1, T2 and T3 describe mean intake values of the indicator being examined for each of the small (T1), medium (T2) and large (T3) portion size tertiles.
‘↑’ denotes a significant increase in values of the dietary quality indicator being examined with increasing portion size; ‘↓’ denotes a significant decrease in values of the indicator being examined with increasing portion size; ‘–’ denotes no discernible trend in values of the indicator across portion size tertiles, though significant differences may exist between pairs. Significance accepted at the level of P<0.05.
Intakes of saturated fat were higher on the days larger portions of whole milk, cheese, butter and chocolate were consumed, and were lower on the days larger portions of white bread, boiled potatoes, fruit, sugary sweets and sugar-sweetened beverages were consumed. Intakes of added sugars were lower on the days larger portions of white bread, chips and whole milk were consumed. Intakes of dietary fibre were higher on the days larger portions of brown bread, boiled potatoes, chips, fruit, vegetables and baked beans were consumed, and were lower on the days larger portions of chocolate and sugar-sweetened beverages were consumed. DED was higher on the days larger portions of cheese, butter, chocolate and sugar-sweetened beverages were consumed, and was lower on the days larger portions of boiled potatoes, fruit and vegetables were consumed. Intakes of Na were higher on the days larger portions of white bread, luncheon meats, frying meats (i.e. bacon, sausages, pudding) and cheese were consumed, and were lower on the days larger portions of chips and chocolate were consumed. Intakes of Ca were higher on the days larger portions of ready-to-eat breakfast cereals (RTEBC), whole and reduced-fat milks and cheese were consumed, and were lower on the days larger portions of chips, crisps and sugar-sweetened beverages were consumed. Intakes of Fe were higher on the days larger portions of RTEBC and baked beans were consumed, and were lower on the days larger portions of sugar-sweetened beverages were consumed. Intakes of vitamin D were lower on the days larger portions of chips and sugar-sweetened beverages were consumed.
Discussion
Saturated fat
Lower intakes of saturated fat were observed on the days larger portions of white bread, boiled potatoes, fruit, sugary sweets and sugar-sweetened beverages were consumed. In this, there appears to be some evidence for the ‘sugar–fat see-saw’ phenomenon, whereby as sugar intakes (total, added or non-milk extrinsic) as a percentage of total energy increase, fat intakes decrease( Reference Gibson 31 – Reference Gibson 33 ). The significance of this is that dietary guidance for these population groups must be carefully considered, as goals recommending simultaneous reductions in the proportion of energy coming from saturated fat and sugar may be difficult to achieve( Reference Overby, Lillegaard and Johansson 34 , Reference Rugg-Gunn, Hackett and Jenkins 35 ). As might be expected, intakes of saturated fat were higher on the days larger portions of whole milk, cheese, butter and chocolate were consumed. There was a marked difference between the saturated fat intakes of consumers of whole and reduced-fat milks, regardless of the portion size consumed; a similar difference was observed between consumers of butter and reduced-fat spreads. In both groups, the highest saturated fat intakes recorded were observed on the days larger portions of cheese were consumed.
Added sugars
Intakes of added sugars were significantly higher on the days larger portions of sugary sweets and sugar-sweetened beverages were consumed in children, but not in adolescents. In both groups, however, intakes of added sugars were highest on the days large portions of sugary sweets were consumed (23·0 and 18·7 %TE, respectively). These values were above mean intake values for the cohorts as a whole (15·0 and 12·7 %TE, respectively) and well above the population goal of a maximum of 11 %TE from added sugars daily( 36 ).
Dietary fibre
Intakes of dietary fibre increased significantly with increasing portion size of baked beans in both children and adolescents. Children and adolescents who consumed large portions of baked beans had mean dietary fibre intakes of 30·2 and 34·9 g/10 MJ, respectively, on the days they were consumed; these are the highest intakes reported for dietary fibre in the current analysis and are significantly higher than the mean values reported for the cohorts as a whole (18·3 and 19·1 g/10 MJ, respectively). In both groups, intakes of dietary fibre increased significantly with increasing portion size of brown (but not white) bread. Children and adolescents who consumed brown bread had higher dietary fibre intakes on the days it was consumed compared with the mean values for the cohorts as a whole, and were among a minority of consumers to meet the European Food Safety Authority’s dietary fibre recommendation of 2 g/MJ daily( 37 ). This finding provides further support for the current dietary guidance in Ireland, which is to choose ‘mostly wholegrain’ breads for digestive health( 38 ).
Sodium
In both children and adolescents, intakes of Na were significantly higher on the days larger portions of frying meats were consumed. Children and adolescents who consumed large portions of frying meats had mean Na intakes of 4051 and 3939 mg/10 MJ, respectively, notably higher than the mean Na values for the cohorts (3007 and 3107 mg/10 MJ, respectively). Current dietary guidance in Ireland does address this in recommending that ‘processed meats such as bacon or ham’ be limited due to their high salt content( 38 ). In both groups, intakes of Na were higher on the days larger portions of white (but not brown) bread were consumed.
Micronutrients (calcium, iron and vitamin D)
Larger portions of RTEBC were associated with increased intakes of Ca and Fe (and a range of B-vitamins for which results are not published) on the days they were consumed in both children and adolescents, agreeing with previous findings on the beneficial effects of RTEBC consumption on micronutrient intakes in children aged 4–15 years( Reference Albertson, Anderson and Crockett 39 – Reference Albertson, Franko and Thompson 41 ). This is likely to reflect both the fortification of RTEBC and the additional milk that tends to be consumed with them. Ca intakes were higher in both groups on the days larger portions of whole and reduced-fat milks and cheese were consumed. Fe intakes were significantly increased in both children and adolescents on the days larger portions of baked beans were eaten. In both children and adolescents, decreased intakes of Ca, Fe, vitamin D (and a range of other micronutrients for which results are not published) were observed on the days larger portions of sugar-sweetened beverages were consumed. Interestingly, however, no such effect was observed with increasing portion size of non-sugar-sweetened beverages in either group, despite comparable portion weights of both beverage types being consumed (Table 1). Increased intakes of sugar-sweetened beverages have previously been linked to micronutrient dilution in both children and adolescents( Reference Johnson, Wilks and Lindroos 29 , 37 , 38 ). There were relatively few relationships observed between intakes of vitamin D and portion sizes of any foods. This may be explained by the fact that dietary intakes of vitamin D are known to be largely influenced by the use or non-use of a vitamin D-containing supplement, rather than dietary intake, in Irish children and adolescents( Reference Black, Walton and Flynn 10 ).
Dietary energy density
In the current study, DED was significantly lower on the days larger portions of boiled potatoes, fruit and vegetables were consumed in both children and adolescents. It has previously been observed that Irish and Swedish children and adolescents in low DED tertiles are more likely to be consumers of potatoes, fruit and vegetables, and to have higher energy-adjusted intakes of these foods( Reference O’Connor, Walton and Flynn 12 , Reference Patterson, Wärnberg and Poortvliet 42 ). In the current work, DED was significantly higher in both children and adolescents on the days larger portions of sugar-sweetened beverages were consumed. As DED was calculated to include foods only (and exclude beverages) however, the sugar-sweetened beverages themselves cannot be responsible for the increased DED. Instead, it would seem that they are markers for the consumption of other foods that, in turn, affect DED. Interestingly, on the days larger portions of non-sugar-sweetened beverages were consumed, there was no increase in DED in either children or adolescents.
Reasons for observations described
There appear to be three discernible trends with respect to the observations described in the present study. First, larger food portion sizes may be associated with increased intake of a nutrient as a consequence of the composition of the food itself (e.g. larger portions of high-salt frying meats were associated with increased Na intakes on the days they were consumed). Findings may also occur as a result of ‘food associations’ resulting from typical patterns of consumption. This might explain, for example, why DED was significantly higher in both groups on the days larger portions of sugar-sweetened beverages were consumed, although beverages themselves were excluded from the calculation of DED. Lastly, some observations may be explained by food displacement. For instance, children who consumed large portions of sugary sweets had decreased intakes of many micronutrients on the days they were consumed. As the sweets cannot be responsible for the decreased micronutrient intakes per se, it may be that the consumption of large portions of sweets displaced other micronutrient-dense snacks, such as fruit or yoghurt, from the diet on the days they were consumed.
Strengths and limitations of the work
The current analyses are based on food intake data that have been collected from nationally representative samples of the population and very carefully quantified, and therefore are based upon a set of high-quality and reliable portion weight data. The work is novel for its focus on food portion size in relation to dietary quality (rather than energy intake), and for examining a wide range of foods, rather than just energy-dense foods, which are more typically involved in discussions on food portion size. A limitation of the work is that it did not take into account the number of eating occasions per day of any the foods examined. A recent study using cross-sectional data to examine the relative contributions of portion size, energy density and number of eating occasions to increased daily energy intakes in adults in the USA (1977–2006) found that changes in portion size and number of eating occasions had accounted for most of the change( Reference Duffey and Popkin 43 ), and so inclusion of this information would have provided a more complete picture on the relationship between food portion size and dietary quality. Since it was not possible to know by which means energy under-reporting had occurred, and some provision had been made to help minimise its effect on outcomes (by energy-adjusting), we believe that the inclusion of all reporters in the current study is acceptable. Additionally, as the aim of the study was to describe eating patterns in a nationally representative sample, the exclusion of all under-reporters could have introduced a secondary ‘selection bias’ to the work( Reference Livingstone and Black 44 ).
Policy implications and practical uses for the work
Reduction in portion size, particularly for energy-dense foods, to reduce DED and energy intake and to help tackle the obesity epidemic is increasingly addressed in healthy eating guidelines. The findings of the current study provide a useful evidence base to support the portion size guidance related to DED and dietary energy intake currently available for Irish children and adolescents. The study also identifies potential effects on dietary quality (both positive and negative) of varying portion sizes of different energy-dense foods, as well as other foods. This may help to further develop guidance on food portion sizes, e.g. relating guidance to foods that may be appropriate to consume in larger quantities. Findings from the study will also be of use to policy makers in devising strategies to target intakes of specific nutrients going forward, particularly if considered in conjunction with previously published data on the typical portion weights of foods consumed by these groups( Reference Lyons and Giltinan 45 ).
Conclusions
The current study describes observations between food portion sizes and indicators of dietary quality in Irish children and adolescents on the days the foods were consumed. Energy under-reporters (32 % of children, 64 % of adolescents) were not excluded from the analysis. Lower DED and saturated fat intakes, and higher dietary fibre intakes were observed on the days larger portions of fruit and boiled potatoes were consumed. Higher DED and lower micronutrient intakes were observed on the days larger portions of sugar-sweetened beverages were consumed. Findings from the current work will form an evidence base from which more specific dietary guidance relating to portion size may be developed and may be of use where strategies are being devised to target intakes of specific nutrients going forward.
Acknowledgements
Financial support: The study was funded by the Irish Department of Agriculture, Food and the Marine under the Food for Health Research Initiative 2007–2012, supported by the Irish Department of Health and the Health Research Board. The funding bodies had no role in the design, analysis or writing of this article. Conflict of interest: None. Authorship: J.L. was involved in the collection and analysis of data and preparation of the manuscript; A.F. was involved in the conception of the work and was a grant holder; J.W. was involved in the design and implementation of the studies. Ethics of human subject participation: The NCFS and NTFS were conducted according to the guidelines laid down in the Declaration of Helsinki. All procedures involving participants were approved by the St. James’ Hospital and Federated Dublin Voluntary Hospitals Joint Research Ethics Committee (NCFS) or the University College Cork Clinical Research Ethics Committee of the Cork Teaching Hospitals (NTFS). Written informed consent was provided by the participants, as well as their parents/guardians.
