Food and drink consumption at school lunchtime: the impact of lunch type and contribution to overall intake in British 9–10-year-old children

Abstract

Objective

To examine the differences in dietary intakes of children consuming school meals and packed lunches, the contribution of lunchtime intake to overall dietary intake and how lunchtime intake relates to current food-based recommendations for school meals.

Design

Cross-sectional analysis of overall intake of macronutrients and food choice from 4-day food diaries and school lunchtime intake from the two diary days completed while at school.

Setting

Norfolk, UK

Subjects

One thousand six hundred and twenty six children (aged 9-10 years) attending 90 Norfolk primary schools

Results

At school lunchtime school meal eaters consumed more vegetables, sweet snacks, chips, starchy foods, and milk, and less squash/cordial, fruit, bread, confectionery and savoury snacks than packed lunch eaters. These differences were also reflected in the overall diet. On average school meal eaters met School Food Trust (SFT) food-based standards, while food choices among packed lunch eaters were less healthy. The contribution of food consumed at school lunchtime to overall diet varied by food and lunch type, ranging from 0.8% (milk intake in packed lunches) to 74.4% (savoury snack intake in packed lunches).

Conclusions

There were significant differences in the foods consumed by school meal and packed lunch eaters, with food choices among school meal eaters generally in line with SFT standards. The food choices made at school lunchtime make a significant contribution to overall diet.

Introduction

Food consumed at school, and its potential association with childhood obesity, has received considerable attention from the UK media in recent years, with particular emphasis on the quality of meals from school canteens ¹. In May 2006 the UK government announced new standards for school food. Determined by the School Food Trust (SFT), these included the introduction of interim food-based standards for lunches provided by schools in September 2006, which were finalised, almost unchanged, for September 2008 ². These replaced previous food-based standards introduced in 2001, prior to which no government guidelines or compulsory standards had been in place ³.

Lunches consumed at school make an significant contribution to food intake, providing 25-33% of daily energy intake among primary school-aged children ⁴. Hence improvements in them may have an impact on overall diet, potentially leading to improved health outcomes. Indeed, in adolescents, significant differences have been observed in some cardiovascular risk factors (systolic blood pressure, ratio of total cholesterol to high density lipoprotein cholesterol, plasma glucose, serum insulin, and serum folate) between those usually eating school meals, who appear to have slightly lower cardiovascular risk profiles, and those eating packed lunches ⁵.

There is evidence that the quality of lunches eaten at school varies according to whether the meal is provided by the school (referred to as a ‘school meal’ throughout this paper, with ‘school lunches’ referring to any food consumed at school at lunchtime) or brought in from home (‘packed lunch’), but neither lunch type has previously been seen to be consistently nutritionally better than the other ^6-8. A 1996 survey of Scottish primary school children found poorer nutrient profiles among those eating school meals. This group typically took a lower proportion of their energy from carbohydrates (45.4% vs 53.2%) and a higher proportion from fat (42.3% vs 38.8%) than those eating packed lunches⁴. More recently, but prior to the introduction of current standards, Rogers et al ⁷ found nutritional deficiencies in both lunch types that were worse among those eating packed lunches, who had higher intakes of saturated fat (16.2% of energy vs 12% in school meals) and sugar (20.9% of energy vs 14.2%) and lower intakes of some micronutrients.

Since the introduction of current school lunch standards, two studies ^{6, 8} have compared the quality of school meals and packed lunches in the UK. Both found that school meals are more likely to meet the food-based standards. Rees et al ⁶ reported those consuming school meals were more likely to eat a portion of vegetables and fish, and were less likely to eat chocolate bars, savoury snacks, sugary drinks, and a portion of fruit. Similarly the SFT ⁸ also saw lower consumption of fruit, confectionery, savoury snacks and sugary drinks among those consuming school meals.

Another factor likely to impact on the quality of food consumed in school meals is the degree of choice pupils have at lunchtime ³. The 2001 food-based standards for school meals were framed around providing healthy choices, but these appeared to have little impact on actual intake ³ as children were seen not to take the healthy choices available ⁶.

Although previous work has compared school meals and packed lunches, much of it was undertaken prior to the introduction of the current UK school meal standards. Furthermore, recent studies have used fairly small samples, and have only compared intake at lunchtime on school days. We build on this work by investigating the differences in children’s food intake between school meal and packed lunches and the impact of food choice at lunchtime on overall dietary intake amongst a large well-characterised sample of 9-10 year old school children from Norfolk, U.K completing detailed food diaries. We examine how the food and drink consumed at lunchtime on school days contributes to overall intake and consider whether school lunches are meeting current food-based standards.

Methods

Recruitment

The SPEEDY study (Sport, Physical activity and Eating behaviour: Environmental Determinants in Young people) was instigated to investigate individual and collective correlates of diet and physical activity behaviour of Year 5 (aged 9-10) children across the county of Norfolk, UK. Ethical approval for SPEEDY was obtained from the University of East Anglia local research ethics committee. The study’s methods are described in detail elsewhere ⁹ and so are only briefly recounted here.

Schools across Norfolk with at least 12 Year 5 pupils were sampled according to a stratification by urban/rural status ¹⁰. Ninety-two schools took part in the study, and 2064 children were recruited into SPEEDY; 57% of the 3619 invited to participate. Data collection was performed during the summer term (April to July) of 2007. Teams of trained Research Assistants performed measurements at participating schools according to standard operating procedures, oversaw the completion of questionnaires, and distributed food diaries and parental questionnaires for later completion.

Dietary assessment

Participating children were asked to complete an un-weighed four-day food and drink diary, with the assistance of their parents. Diaries were completed over four consecutive days; either Thursday to Sunday or Saturday to Tuesday depending on when measurement took place at a child’s school. A four day diary was deemed sufficient to determine mean dietary intake without overburdening participants, while also covering equal numbers of weekdays and weekend days. A short questionnaire at the beginning of the food diary asked children about their usual dietary habits, including which one of the following they usually did at lunchtime on school days: eat a meal from the school canteen, eat a packed lunch brought from home, go home for lunch, or not eat lunch. The diary required children to record all food and drink consumed by time of consumption, and to include estimates of portion size (small, medium or large, or specific unit such as a packet of crisps, or slice of cake). Guidance on the completion of the diary was given to the children by research assistants, and full written instructions were included for parents.

Food and nutrient intake was calculated from the food diaries using WISP nutritional analysis software version 3.0 (Tinuviel Software, Warrington, UK) ¹¹, and portions sizes were estimated from previously published data ^12-14. The data entered into WISP were reviewed by a dietician who checked for errors and consistency. For these analyses additional criteria were imposed on the food diaries so that only those with four days’ worth of data, with at least one school day were included. From these data we estimated four-day mean intakes of energy, fat, protein, carbohydrates, and fibre (Non-starch polysaccharides; NSP). The intake of key food types, selected to be comparable with the SFT interim food-based standards for school lunches ² which were in place at the time of the data collection, were estimated as the mean intake of foods consumed between 12 noon and 2pm on school days. This time period covered the lunch-breaks, but no other break-times at all schools. As we did not have a record of whether children were at school on any given day, school days were defined as week days during term-time.

Under-reporting of energy intake was assessed by calculating the ratio of reported energy intake (EI) to estimated energy requirements (EER), which were estimated using equations from the FOA/WHO/UNU Expert Consultation Report on Human Energy Requirements ¹⁵. A 95% confidence interval for the accuracy of EI:EER was calculated by taking into account the amount of variation inherent in the methods used to estimate EI and EER ¹⁶. For the SPEEDY data the 95% confidence interval for EI:EER was 0.71 to 1.30 and therefore those reporting an EI of less than 71% of EER were defined as under-reporters. So as not to distort dietary intake data by excluding children who under-reported energy intake, the EI:EER ratio was included as a continuous variable in all statistical models ¹⁷.

Child and family co-variates

As individual factors are known to be associated with dietary intake ¹⁸, we included gender, and measures of adiposity and socio-economic status (SES) in our analyses. Height was recorded to the nearest millimetre using a Leicester height measure, and non-segmental Tanita scales (type TBF-300A) were used to measure weight. Body Mass Index (BMI = weight(kg)/height(m)²) was calculated for all participants with valid height and weight data. SES was measured based on educational attainment from the questionnaire completed by the parents/carers of all participating children. The individual completing the questionnaire (the mother on 86% of occasions) was asked to indicate their highest educational qualification. Answers to this question were grouped into four categories; no qualifications/school leaving certificate, GCSE (the national school exams in England and Wales, usually taken at age 16) or equivalent, A-Level (the national school exams in England and Wales, usually taken at age 18) or equivalent, and degree or higher.

School policies

The head teacher at each participating school was asked to complete a questionnaire which included questions on physical activity and food related facilities, policies and learning opportunities. This included a question on whether children had any choice in the food they obtained from the school canteen (with the options of either “Yes, they can choose what they want on the day”, “Yes, menus are sent to parents and choices can be made in advance”, or “No”). The questionnaire also asked what percentage of all pupils at the school ate school meals, and whether a hot meal was available every day.

Statistical analysis

All statistical analyses were performed in 2010 using Stata IC version 11 (StataCorp, 2009). We derived mean intake values of the nutrients and food types studied adjusted for sex, BMI, SES, under-reporting and, for food types, total energy intake. Because schools were used as the sampling units in SPEEDY, multi-level regression models (xtreg command in Stata) were used to account for potential school-level clustering in outcomes, with child at level 1, nested within schools at level 2. We modelled the intake of each nutrient and food type based on the co-variates and a variable indicating lunch type (school meal or packed lunch), and used the estimates to predict dietary intake means at mean values of the independent variables for each lunch type group. Adjusted mean intakes were derived in this manner for daily consumption over all four diary days and for lunchtime (12pm-2pm) consumption on school days. To calculate the variance between schools, for the school day models intraclass correlations (ICC) were derived by calculating the estimated between-school variance as a percentage of the estimate of total variance. The moderating effect of choice in school meals was assessed by fitting an interaction term between these two factors (meal choice and lunch type). Where interactions were statistically significant at p<0.1 they were further investigated in stratified models.

Results

Of the 2064 children recruited in the SPEEDY study, 1859 provided valid food diaries. However, a further 233 were excluded as 141 did not complete all four days of the diary, 40 completed the diary over the half term week, and so did not include any school days, 45 did not report their usual school lunch type, and valid height and weight data were not available for seven children. To prevent further loss of cases SES was imputed to the modal category, GCSE or equivalent, for 75 participants who were missing these data. This resulted in a final sample of 1626 children (78.8% of SPEEDY participants), attending 90 schools (two schools were excluded as none of their pupils met the inclusion criteria for these analyses). There was no difference between those included and excluded in terms of sex, BMI and SES (all p>0.05), however those excluded reported lower energy intake, had greater under-reporting, and were more likely to eat school meals (p<0.01).

Summaries of the characteristics of the pupils included in these analyses are shown in Table 1. Slightly more girls (56%) than boys were recruited to the study, and were thus included in these analyses. Girls generally had higher BMI than boys (p<0.05), but there were no significant gender differences in SES, lunch type, or under-reporting. None of the sample reported usually going home for lunch, or not eating lunch, so all participants reported usually eating either a school meal (n=399) or a packed lunch (n=1227). Across the 90 schools, mean uptake of school meals as reported by the head teacher was 32.4% (SD 14.5%). The uptake of school meals by school in the analysis sample ranged from 0% to 100%, with a mean of 24.5% (SD 20.4%). In terms of choice offered, 23 schools (25.6%) gave pupils no choice in school meals, 32 (35.6%) gave choice in advance, and 34 (37.7%) gave pupils some choice on the day (one school did not answer this question). All schools offered a hot meal every day.

Table 1.

Characteristics of the SPEEDY participants included in these analyses

	Mean; standard deviation, or n (%)
	All	Girls	Boys
Number of participants	1626	910 (56%)	716 (44%)
Age (years)	10.25; 0.31	10.25; 0.31	10.24; 0.31
Body Mass Index a	18.21; 3.12	18.51; 3.28	17.83; 2.84
Highest educational qualification of parent
None	107 (6.6%)	62 (6.8%)	45 (6.3%)
GCSE or equivalent	873 (53.7%)	495 (54.4%)	378 (52.8%)
A-Level or equivalent	390 (24%)	220 (24.2%)	170 (23.7%)
Degree or higher	256 (15.7%)	133 (14.6%)	123 (17.2%)
Usual type of lunch on school day
School meal	399 (24.5%)	214 (23.5%)	185 (25.8%)
Packed Lunch	1227 (75.5%)	696 (76.5%)	531 (74.2%)
Under-reporters b	332 (20.4%)	176 (19.3%)	156 (21.8%)

^adifference between girls and boys statistically significant at p<0.05

^bUnder-reporting defined as reported energy intake less than 71% of estimate energy requirement

Participants reported consuming an average of 7355kJ (SE 38kJ) per day, with 48.7% (SE 0.12%) of energy coming from carbohydrates, 37.0% (SE 0.11%) from fats, 14.3% (SE 0.06%) from protein. Average daily intake of NSP was 10.8g (SE 0.07g). Adjusted mean dietary intakes of participants are given by lunch type in Error! Reference source not found. and 3. The adjusted mean differences in food consumption between the two lunch types are displayed in Figure 1. In terms of nutrient intake (Table 2), school meal eaters consumed more NSP, acquired a higher percentage of energy from protein and had a less energy dense diet than packed lunch eaters (all p<0.05).There were no statistically significant differences in total energy consumption, nor percentage energy from fat or carbohydrates between lunch types. The contribution of lunchtime food intake to average daily food intakes varied by lunch type; the school meal group ate much of their vegetables (42.5%), sweet snacks (46.9%), and chips (61.1%) during school lunches, while those taking packed lunch consumed 74.4% of their intake of savoury snacks, 64.0% of their bread and 51.0% of their average daily confectionery intake at lunchtime (Table 3).

Figure 1.

Differences in food intakes between those usually eating school meals and those usually eating packed lunches.

Table 2.

Adjusted mean dietary intake, by reported usual school lunch type calculated over four whole days.

	School meal (n=399)		Packed Lunch (n=1227)
	mean †	SE	mean †	SE
Energy (kJ)	7338.1	16.8	7357.3	11.1
% energy from fat	36.8	0.2	37.0	0.2
% energy from carbohydrates	48.7	0.3	48.8	0.2
% energy from protein ‡	14.6	0.1	14.2	0.1
Non-starch polysaccharides (g) ‡	11.0	0.1	10.7	0.1
Energy density ‡	7.2	0.1	7.6	0.0
Fruit (g) ‡	90.3	4.5	100.2	2.9
Vegetables (g) ‡	112.0	3.2	96.7	2.1
Fruit & Vegetables (g)	202.3	5.9	196.9	3.7
Fruit Juice (g)	139.9	7.6	134.1	4.6
Carbonated Drink (g)	83.8	5.9	81.1	3.7
Squash/cordial (g) ‡	150.1	11.4	191.0	7.1
Savoury snacks (g) ‡	10.2	0.6	14.0	0.4
Sweet snacks (g) ‡	86.2	2.4	75.5	1.5
Confectionary (g) ‡	17.7	1.0	21.5	0.6
Chips (g) ‡	37.7	1.8	30.3	1.2
Bread (g) ‡	60.2	1.6	72.0	1.0
Starchy foods (g) §	161.7	3.3	159.2	2.2
Milk (g) ∥	87.8	5.5	88.0	3.1

^†Means adjusted for Sex, BMI, SES, EI:EER ratio, and, for food types only, total energy

^‡Difference in mean All days; whole day intake between school meal and packed lunch eaters statistically significant p<0.05

^§Starchy foods include: bread, pasta, rice, couscous, noodles, potatoes, sweet potatoes, yams, millet, cornmeal and other cereals not cooked in oil.

^∥Skimmed and semi-skimmed milk only

Table 3.

Adjusted mean dietary intake at lunchtime on school days, by reported usual school lunch type.

	SFT interim food-based standards		School meal (n=399)			Packed Lunch (n=1227)			School-level variance
	Standard (per lunchtime)	Equivalent grams †	mean ‡	SE	% of daily intake	mean ‡	SE	% of daily intake	ICC
Energy (kJ)			2435.4	40.5	33.2%	2549.7	27.5	34.7%	4.9%	**
Fruit (g)	At least one portion	40g	20.3	3.2	22.5%	51.0	2.1	50.9%	4.1%	**
Vegetables (g)	At least one portion	40g	47.6	2.6	42.5%	20.9	2.1	21.6%	15.8%	**
Fruit & Vegetables (g)	At least two portions	80g	69.6	4.0	34.4%	71.9	2.9	36.5%	7.5%	**
Fruit Juice (g)	A ‘Healthier drink’; consumption unlimited	n/a	46.5	4.9	33.2%	46.9	3.2	35.0%	3.3%	**
Carbonated Drink (g)	Not allowed	0g	3.0	1.0	3.6%	1.9	0.6	2.3%	0.0%	ns
Squash/cordial (g)	Not allowed	0g	20.3	5.7	13.5%	82.7	3.6	43.3%	2.7%	**
Savoury snacks (g)	Not allowed	0g	2.5	0.5	24.4%	10.4	0.4	74.4%	4.0%	**
Sweet snacks (g)	Not covered by Standards	n/a	40.5	1.8	46.9%	22.6	1.2	30.0%	6.1%	**
Confectionary (g)	Not allowed	0g	2.8	0.7	15.8%	11.0	0.4	51.0%	0.0%	ns
Chips (g)	Not covered by Standards	n/a	23.0	1.4	61.1%	6.1	1.1	20.2%	19.5%	**
Bread (g)	Provided every day	n/a	19.2	1.4	31.9%	46.1	1.0	64.0%	4.4%	**
Starchy foods § (g)	Provided every day	n/a	61.6	1.9	38.1%	54.7	1.3	34.4%	4.6%	**
Milk (g) ∥	A ‘Healthier drink’; consumption unlimited	n/a	5.9	0.9	6.7%	0.7	0.5	0.8%	0.0%	ns

^†Equivalent grams based on estimated portion sizes used for data entry

^‡Means adjusted for Sex, BMI, SES, EI:EER ratio, and, for food types only, total energy

^§Starchy foods include: bread, pasta, rice, couscous, noodles, potatoes, sweet potatoes, yams, millet, cornmeal and other cereals not cooked in oil.

^∥Skimmed and semi-skimmed milk only

ICC = intraclass correlation; percentage of variance at the school level in multilevel model for lunchtime intake on school days;

** = p<0.01, ns= p>0.05

Where applicable Table 3 gives the SFT food-based standards for the relevant food groups along with the equivalent grams per lunchtime meal based on the portion sizes used during data entry. Among school meal eaters, mean fruit and fruit & vegetable intakes are below the level set by the guidelines (20.3g vs 40g and 69.6 g vs 80g respectively). Packed lunch eaters’ mean consumption of vegetable and fruit & vegetables are also below SFT standards (20.9g vs 40g and 71.9g vs 80g respectively), and among both lunch types there is consumption of prohibited food types (carbonated drinks, squash/cordial, savoury snacks and confectionary) which is generally greater in those eating a packed lunch. The lunchtime intakes of most food types varied significantly at the school level, with ICCs (Table 3) of up to 19.5% (for intake of chips at lunchtime). However, no statistically significant interactions were observed between lunch type and meal choice, so no further stratification was performed.

Figure 1 shows the differences in food intakes between those usually eating school meals versus packed lunches, adjusted for sex, BMI, SES, underreporting and energy intake. It illustrates that overall, and at school lunchtime, school meal eaters consumed more vegetables, sweet snacks and chips than packed lunch eaters. Packed lunch eaters consumed more savoury snacks, confectionery, bread, fruit and squash/cordial (non-carbonated sugary drink). School meal eaters also consumed statistically significantly more starchy food and milk than packed lunch eaters at school lunchtime, although these differences were not seen in overall intake. Some of the differences in mean consumption were considerably larger at school lunchtimes than overall, with the school meal group eating 27g more vegetables (compared with 15g more overall) and packed lunch eaters consuming 62g more squash/cordial and 31g more fruit (compared with 41g and 10g overall respectively).

Discussion

This study investigated the associations between lunch type at school and dietary intake in 9-10 year old children. The contribution of school lunchtime intake to overall intake varied by lunch type and food choice and significant differences in food consumption were observed both at lunchtime on school days and over the whole day between school meal and packed lunch eaters.

Our findings of greater vegetable consumption among school meal eaters and greater fruit consumption among packed lunch eaters are comparable with others who have compared school meals and packed lunches since the introduction of the current food-based standards for school lunches ^{6, 19}. On average, both groups met total fruit and vegetable intake recommendations for school meals (two portions; 80g ²) when fruit juices were included, but only the school meal group reported consuming one whole portion (40g) of vegetables. These differences were clearer during lunchtime on school days, but were also apparent over the whole day. Steps to increase vegetable consumption among packed lunch eaters may therefore be appropriate.

SFT standards promote the provision of ‘healthier’ drinks, including fruit juice and skimmed and semi-skimmed milk, while prohibiting that of others such as sugary carbonated and non-carbonated drinks. In these analyses fruit juice intake appeared to make an important contribution to overall fruit and vegetable intake but did not differ between the two lunch types. Milk consumption was significantly higher among the school meal group at lunchtime but average consumption was very low in both groups (5.9g and 0.7g). Consumption of carbonated drinks at lunchtime on school days was low in both groups, with almost all daily consumption occurring outside of this time. A striking difference in beverage consumption was seen in the consumption of squash/cordial; packed lunch eaters drank almost four times as much as school meal eaters. Such drinks are prohibited by the SFT, but the standards do not apply to packed lunches. The same pattern of beverage consumption to the current study was reported by the SFT ¹⁹, who found that school meal eaters drank ‘healthier’ drinks exclusively, compared to only 69% of packed lunch eaters.

SFT standards are focused around savoury snacks (potato, cereal, soya, nuts, seeds, fruit or vegetable snacks with added salt or sugar) and confectionery (sweets and chocolate, or products containing, coated or flavoured by chocolate), neither of which are permitted in school meals ²⁰. In accordance with these recommendations, we saw much lower consumption of both these food types among school meal eaters, both at lunchtime on school days, and over the whole day compared to packed lunch eaters. The fat, sugar and salt contents of these foods could lead to similar nutritional discrepancies as those reported by Rogers et al ⁷; higher intakes of saturated fat (16.2% of energy in packed lunches vs 12% in school meals), sugar (20.9% of energy vs 14.2%) and sodium (805mg vs 607mg). However, we also considered a third group of foods, sweet snacks, including cakes, biscuits, puddings and desserts, which are not explicitly covered by the SFT guidelines. Such foods may form part of a school meal menu where their presence has been associated with higher BMI among pupils ²¹. We observed that the school meal group consumed significantly more of these than packed lunch eaters. For all these food types, the differences seen at lunchtime on school days were also apparent in overall diet, and school lunch appeared to make a substantial contribution to overall consumption, especially for packed lunch eaters, who consumed 74.4% of their savoury snacks and 51.0% of their confectionery during this period. This raises the possibility that reducing the consumption of these foods at lunchtime could have an impact on overall intake.

At the time of our survey, food-based recommendations for school lunches required that starchy food (not cooked in oil/fat) be provided to children every day, with bread made available as an extra item. We observed that school meal eaters consumed more starchy food compared to packed lunch eaters, although a lower proportion of that was from bread. Neither school lunch group consumed a full portion of starchy foods a day (based on average portion sizes of 80g of rice, and 100g of mashed potato ¹³). Starchy foods are promoted as a means of satiating hunger without excessive consumption of fat ², and higher consumption may help children meet the SFT recommendation of at least 50% of food energy coming from carbohydrates ²². Although chips are not specifically part of current school lunch recommendation, they were considered here as such deep fried, high fat foods have been implicated as a potential contributor to obesity ²³ and their presence on school menus has been associated with higher BMI among pupils ²¹. Unsurprisingly, the school meal group consumed more chips, both at lunchtime and over the whole day, although the average weight consumed at lunchtime is quite small; 23.0g for school meal, which equates to roughly a portion every 3.9 days, based on a typical portion size of 90g ¹³. Some chips also appeared to be eaten by the packed lunch group at school lunchtime. This could indicate that some the SPEEDY participants who reported usually eating packed lunches actually had a school meal on one or more of the food diary days, or that in addition to eating a packed lunch, obtained food from the school canteen.

The results of the current study demonstrate that the food eaten at lunch time in schools clearly has an impact on children’s food intake. Lunchtime intakes of all food types, except carbonated drinks, milk, and confectionery, showed statistically significant variation at the school level, which contributed up to 19.5% (chips) of the overall variation in intake. This is perhaps unsurprising given that schools are likely to provide largely the same foods to all children taking school meals, but may also indicate that the choices schools make about the foods they provide are associated with children’s intake. No significant interactions were seen between school meal and pupil choice in the current study. The lack of an interaction could be explained by the relatively small numbers in the school meal group (399 school meal eaters compared with 1227 packed lunch eaters) so that once children had been divided into the three choice categories, the numbers could have been too low to detect differences in intake. The provision of pupil choice has been suggested as a potential barrier to improved dietary intake in school meals ³. This is likely to be dependant on the nature of the choices given, and future studies may collect more detailed information about the foods offered by schools to further investigate this.

This study has a number of strengths and weaknesses. In terms of strengths, we recruited a large number of schools and pupils to the study, and collected a range of measurements from them. We assessed their dietary intake using detailed diet diaries over four whole days (not just during school hours), and included both two weekend days and two week days. The week days covered varied by school so all days except Wednesday were included in the sample. However, the two school days recorded were not sufficient to give a reliable picture of typical nutrient intake ²⁴, and so our analysis focused on the types of foods consumed.

Although food diaries give a valid measure of food intakes in this age group ²⁵, the diary used in SPEEDY was not validated. Food diaries, are subject to a number of potential errors. We did not ask participants to weigh the food and drink they consumed and children have been seen to experience difficulty in estimating portion sizes ²⁶. Under-reporting is a problem in self-reported dietary assessment but we were able to adjust for underreporting of energy intake. Another weakness is that we did not know which lunch type children had on a given week day or if they had actually been at school, only the type of lunch they reported usually consuming, which may have led to some misclassification. However, these potential errors are likely to result in an attenuation of differences between the two groups, and so are unlikely to explain the differences in intake we observed.

In terms of generalisability, the SPEEDY schools and children were broadly representative of the Norfolk population, although with a slightly higher proportion of girls, and lower proportion of obese children taking part ⁹. However, schools in Norfolk have a low proportion of non-white pupils, which potentially limits the generalizability of our findings to more ethnically diverse populations.

In conclusion we found statistically significant differences in food intake between children consuming school meals and packed lunches and these differences were also observed in overall diet. On average those usually taking school meals met current food-based standards for school lunches, while the food choices of packed lunch eaters typically fell short. The uptake of school meals was low (less than 25% in this sample, but currently just over 40% in English primary schools ²⁷), so it appears more needs to be done to encourage similar standards in packed lunches. School lunches appear to have an impact on overall diet, but further work is needed to establish how this translates into nutrient intake and health outcomes.