Claire N. Tugault-Lafleur, Jennifer L. Black, Susan I. Barr

Food, Nutrition, and Health, Faculty of Land and Food Systems, University of British Columbia, Vancouver, BC V6T 1Z4, Canada.

Received February 24, 2017. Accepted June 14, 2017.

Applied Physiology, Nutrition, and Metabolism, 2017, 42(10): 1064-1072, https://doi.org/10.1139/apnm-2017-0125

Understanding how dietary intakes vary over the course of the school day can help inform targeted school-based interventions, but little is known about the distribution or determinants of school-day dietary intakes in Canada. This study examined differences between school-hour and non–school-hour dietary intakes and assessed demographic and socioeconomic correlates of school-hour diet quality among Canadian children. Nationally representative data from the Canadian Community Health Survey were analyzed using 24-h dietary recalls falling on school days in 2004 ( n = 4827). Differences in nutrient and food-group densities during and outside of school hours and differences in School Heathy Eating Index (School-HEI) scores across sociodemographic characteristics were examined using survey-weighted, linear regression models. Children reported consuming, on average, 746 kcal during school hours (one-third of their daily energy intakes). Vitamins A, D, B 12 , calcium, and dairy products densities were at least 20% lower during school hours compared with non-school hours. Differences in School-HEI scores were poorly explained by sociodemographic factors, although age and province of residence emerged as significant correlates. The school context provides an important opportunity to promote healthy eating, particularly among adolescents who have the poorest school-hour dietary practices. The nutritional profile of foods consumed at school could be potentially improved with increased intake of dairy products, thereby increasing intakes of protein, vitamin A, vitamin D, calcium, and magnesium.

Missing data were handled with case-wise deletion. Therefore, analytical sample sizes varied slightly across analyses. Sampling weights were applied to all analyses to generate nationally representative estimates. The 500 sets of bootstrap weights supplied by Statistics Canada were used to derive robust standard errors ( Statistics Canada 2008 ). All analyses were conducted using Stata 13 (LP Stata Corp, Texas, USA), with significance defined as p value < 0.05 (Bonferroni-adjusted p value <0.05/ n , with n being the number of comparisons).

To examine differences in school-hour diet quality by select demographic and socioeconomic characteristics, simple linear regression models were used with a Bonferroni adjustment to account for multiple comparisons in regression models with multiple dummy variables (e.g., province of residence). These models did not include an energy term since the algorithm for the C-HEI and School-HEI already computes scores based on age- and sex-specific food and nutrient requirements. Since age group emerged as a significant predictor of school-hour diet quality, we also estimated mean School-HEI total and subcomponent scores (for example, School-HEI subscores for whole fruit) and NRF scores by age group.

Descriptive statistics (survey-weighted means and robust standard errors of the mean (SE)) were used to obtain average absolute dietary intakes and dietary contributions (in percent) from school hours relative to whole-day intakes. Because energy intake during school hours was significantly lower than non-school hours, densities (nutrient and food group amounts per 1000 kcal) were calculated for foods consumed during school hours and during non-school hours. Survey-weighted simple linear models then tested for significant differences in nutrient and food-group densities across time period using a dichotomous variable for school hours as the independent variable. Since nutrient intakes are measured in different units (e.g., carbohydrate in grams vs. vitamin C in milligrams), a common unit of comparison was needed to compare the magnitude of the differences between school and non-school hours. Results were therefore expressed as percent differences from school hours relative to non-school hours. This was calculated by taking the estimated mean difference in nutrient or food-group density between time periods divided by the nutrient or food-group density during non-school hours. The difference was then multiplied by 100 to express this difference in relative terms.

To compare our results with another composite measure of diet quality, findings were compared with Nutrient Rich Food (NRF) index scores ( Fulgoni et al. 2009 ). The NRF index is a composite nutrient-based diet quality indicator that calculates a score based on the sum of the percent consumed of the reference United States daily values for nutrients to encourage (i.e., protein, fibre, vitamin A, vitamin C, calcium, iron, magnesium, and potassium) from which is subtracted the sum of the percent consumed of reference daily values for nutrients to limit (saturated fat and sodium), expressed per 100 kcal ( Fulgoni et al. 2009 ).

To compute C-HEI scores adapted specifically for school hours, the scoring criteria for each component were scaled to reflect the mean energy contribution from school hours (0900–1400 h) to daily energy intake (see Table 1 for a list of the components of the School HEI (School-HEI)). The food group components’ scoring criteria for the School-HEI were scaled to reflect one-third of the total daily servings recommended for each age and sex group, based on preliminary analyses confirming that foods consumed during school hours provided, on average, one-third of the daily calories consumed. For example, the scoring criterion for total fruit and vegetables for earning maximum points on the subscore for children aged 6–8 years (whose recommended daily intake is 5 servings/day) was 1.67 servings. This approach is similar to the standards set by the United States National School Lunch Program, which uses one-third of the 1989 Recommended Daily Allowances for energy, protein, iron, calcium, vitamin A, and vitamin C as minimal nutritional quality criteria for school meals ( United States Department of Agriculture 2012 ). A similar approach has also been used in previous Canadian studies that used one-third of the daily recommended intakes as nutritional criteria for meals consumed at school ( Taylor et al. 2012 ; Neilson et al. 2017 ). For the C-HEI, diet quality categories have been previously established ( Garriguet 2009 ). A “high quality diet” is defined as above 80 points, a diet “requiring improvement” falls within 50–80 points, and a “poor quality diet” is <50 points. Similar to the C-HEI, scores for the School-HEI range from 0 to 100 points, so the same categories were used for interpretation of School-HEI scores.

Dietary intake variables included the amounts of energy, nutrients, and food groups consumed during and outside of school hours on school days, and the relative contributions (percentage intake) from school hours relative to total daily intakes (TDIs). To address the multidimensional nature of diet quality, we adapted a validated measure of diet quality for Canadians (the Canadian Healthy Eating Index (C-HEI) ( Garriguet 2009 )). The C-HEI is based on the United States 2005 HEI ( Guenther et al. 2008 ), with modifications to reflect how well diets comply with Canadian dietary guidance from the most recent 2007 version of Canada’s Food Guide (CFG) ( Health Canada 2007 a ). The C-HEI contains 11 components (maximum score = 100 points), reflecting both the adequacy and moderation dimensions of a healthy diet. The C-HEI components are based on daily intake standards (e.g., 2 servings of milk and alternatives/day recommended for children age 6–8 years) to provide subscores for each of its components.

Foods reported to be consumed between 0900 to 1400 h were classified as those consumed during school hours. Time of consumption was used to classify foods and beverages as either falling within or outside of school hours as the CCHS 2.2 did not ask respondents to state where the food or beverage was consumed ( Statistics Canada 2008 ). Since public school hours vary by Canadian jurisdictions ( Government of Canada 2009 ), it was not possible to determine the exact time window that would include school hours for all Canadian children. The 0900 to 1400-h timeframe was chosen since it was most likely to include school hours for the majority of Canadian children and this study aimed to capture dietary intakes occurring within school food environments. Sensitivity analyses confirmed that widening this time period by 30-min increments did not result in substantial increases in energy intake up until 1500 h, which is when Canadian schools are often at or near closing time and hence a substantial number of children are likely to be consuming food at or en route home (see Supplementary Table S1 1 ).

Analyses included respondents ( n = 4945) age 6 to 17 years who reported attending school full-time and who completed a valid first 24-h dietary recall, which fell on a Canadian week day (Monday through Friday) but excluded recalls that fell on the last week of December or the first week of January (typical Christmas/winter breaks), other statutory/national holidays, or during summer months (June 21 to September 7). Diet recalls with daily energy intakes reported either above or below 3 standard deviations from the mean (>6365 kcal/day or <486 kcal/day) were considered extreme outliers and were excluded ( n = 28 children). Children who did not report consuming any energy during school hours or outside of school hours were also excluded from these analyses ( n = 90). The final analytical sample consisted of 4827 children.

Nationally representative data were obtained from the 2004 Canadian Community Health Survey Cycle (CCHS) 2.2, which used a complex multistage stratified cluster sample nationally representative for age, sex, geography, and SES ( n = 35 107; response rate, 76.5%) ( Health Canada 2006 ; Statistics Canada 2008 ). The survey targeted residents of all ages living in private dwellings in Canada’s 10 provinces. A computer-assisted 24-h dietary recall method asked respondents about all foods and beverages consumed in the past 24 h, including types and amounts of foods consumed, eating occasion (e.g., breakfast, lunch, snack), and time of consumption ( Health Canada 2006 ). The approach used for the 24-h recall was based on the United States Department of Agriculture Automated Multiple-Pass Method (AMPM). The AMPM is an automated questionnaire that guides the interviewer through a series of questions and probes to maximize the interviewees’ opportunities for remembering and reporting foods eaten in the previous 24 h ( United States Department of Agriculture 2016 ). Although a second telephone-administered dietary recall was performed in a subsample of participants, this study used only the first interviewer-administered 24-h recall. Interviews for children aged 6 to 11 years were conducted with parental/caregiver assistance, while children aged 12 years and above were interviewed alone. All foods and beverages were analyzed using the food composition data from the 2001b version of the Canadian Nutrient File database ( Statistics Canada 2008 ). Owing to the nature of the study design (secondary data analysis) and the lack of personal identifiers, the present study was exempted by the Research Ethics Board of the University of British Columbia.

Table 6 shows total and subscores for the School-HEI, stratified by age group. The average total School-HEI score was 53.4 points, suggesting that mean diet quality during school hours for Canadian children “required improvement” (School-HEI 50–80 points). School-HEI scores (means ± SE) by age group ranged from 58 ± 0.7 points (children aged 6–8 years) to 49 ± 0.6 points (children aged 14–17 years) and were significantly different between young children (6–8 years) versus pre-adolescents (9–14 years) and adolescents (14–17 years). Children age 6–13 years had significantly higher School-HEI scores for total vegetables and fruit, whole fruit, and meat and alternatives compared with children aged 14–17 years. Compared with children aged 9–17 years, children aged 6–8 years also had higher School-HEI subscores for milk products. Compared with children aged 14–17 years, children aged 6–8 years had significantly higher School-HEI subscores for dark green and orange vegetables (although these subscores were, in absolute terms, low for all age groups), and percent energy from minimally nutritious foods. NRF 8.2 scores declined significantly with age, with children aged 6–8 years having significantly higher NRF 8.2 scores compared with children aged 9–17 years.

Table 5 shows the results from linear regression analyses testing associations between school-hour diet quality with select demographic and socioeconomic characteristics. Age, household-level education, and province of residence were associated with statistically significant differences in school-hour diet quality. Children aged 6–8 years had, on average, school-hour diet quality scores that were 9 points higher than 14–17-year olds. Children in Quebec had, on average School-HEI scores that were at least 5 points or higher compared with children living in Newfoundland and Labrador, Nova Scotia, Ontario, and Manitoba. No differences in School-HEI scores were observed across any of the other demographic or socioeconomic characteristics (sex, ethnicity, residential location, income, or food-security status). Moreover, none of these models had a large (>0.05) coefficient of determination ( R 2 ), suggesting that with the exception of age, none of the other characteristics examined explained a substantial proportion of the variation in school-hour diet quality.

Mean nutrient and food-group densities (amounts per 1000 kcal) for both school and non-school hours and relative percent differences between school and non-school hours are shown in Table 4 . Statistically significant differences were found in nutrient and food-group densities between school and non-school hours for the majority of dietary outcomes. However, the magnitude of these differences was often small (≤20% relative difference between school hours and non-school hours). Larger differences (>20%) were observed for cholesterol, vitamin A, vitamin D, vitamin B 12 , calcium, and milk-product densities, which were all lower during school hours, while vitamin C density was higher during school hours. Vitamin D and milk-product densities emerged as those with largest relative percent differences between time periods (54% and 33% lower during school hours, respectively). For milk products, this translated into an estimated difference of 0.4 servings/1000 kcal consumed between time periods.

On average, children consumed 2.5 servings of grain products, 1.5 servings of vegetables and fruit (including fruit juice), and 0.6 servings each of milk products and meat and alternatives during school hours. Children also consumed on average 175 kcal from “other” foods (foods not part of the 4 core food groups from the CFG and typically minimally nutritious foods such as candy bars and salty packaged snacks) during school hours, providing 37% of total daily calories from minimally nutritious foods. The contribution from grain products was higher (37% of TDI) whereas the contribution of milk products was lower (25% of TDI) during school hours.

Mean school-hour dietary intakes and their relative contributions to whole school-day dietary intakes are shown in Table 3 . The mean energy from foods and beverages consumed during school hours was 746 kcal, representing 33.6% of the total daily energy consumed on school days. The relative dietary contributions of total carbohydrates, fibre, total sugars, total fats, and saturated fats were similar to the energy contribution. However, intakes of polyunsaturated fatty acids and linoleic and linolenic fatty acids provided higher contributions during school hours (defined as providing ≥36% of their TDIs) while contributions from protein and cholesterol were lower (defined as providing ≤31% of their TDIs). Foods consumed during school hours provided lower contributions of vitamin A, vitamin D, riboflavin, vitamin B 6 , vitamin B 12 , calcium, phosphorus, magnesium, zinc, and potassium (all ≤31% of their TDIs) but higher contribution of vitamin C (38% of TDI).

Table 2 provides the sample characteristics of Canadian children aged 6–17 years whose first 24-h dietary recall fell on a Canadian school day in 2004. Young children (6–8 years) comprised approximately a quarter of all children surveyed, 43% were aged 9–13 years, and close to one-third were older adolescents (14–17 years). Fifty-one percent of participants were male. The majority of children identified themselves as having European ethnicity, lived in urban areas, and had at least 1 household member who had completed some post-secondary education (college or university). Close to 9% of children were classified as “food insecure” while slightly over one-third lived in a low-income household.

In this paper Top of page Introduction Materials and methods Results Discussion « References

Discussion

Findings revealed that in 2004, foods and beverages consumed by Canadian children between 0900 to 1400 h provided close to one-third of the total energy consumed on a school day. While relative intakes of most nutrients and food groups were proportional to the contribution to energy intake (∼33%), dietary intakes from milk products, and key nutrients found in milk (protein, vitamin A, D, B 12 , calcium) during school hours provided smaller contributions to TDIs. Moreover, nutrient densities for these outcomes were significantly lower during school hours. Finally, only age group was a substantive predictor of school-hour diet quality (although school-hour diet quality required improvement for all age groups).

To our knowledge, this is the first Canadian study to compare dietary intakes between school hours and non-school hours on school days and few other studies are available for comparison. In a sample of Swedish children in grades 2 and 5, the mean energy contribution of school lunches was 27% of daily intake, and the mean nutrient contributions were either proportional or higher than the caloric contribution, with the exception of carbohydrates that provided a relatively smaller contribution (24%). In contrast, Canadian findings here suggest that total carbohydrates (and grain products) represented a similar or higher dietary contribution relative to the mean energy contribution. In the United Kingdom, Nelson and colleagues compared the lunch-time contributions from foods across school-meal participation status and between elementary and secondary school students (Nelson et al. 2007). In contrast to our study, the contributions from protein and calcium were close to the energy contribution regardless of age or school-meal participation status. Another United Kingdom study comparing the lunch-time contributions from foods by school-meal–participation status revealed the dietary contribution for the majority of nutrients was similar to the energy contributions with the exceptions of vitamin C (lower for both boys and girls regardless of school-meal participation status), vitamin A (lower among girls eating a home-packed lunch), and folate (lower among boys, regardless of school-meal participation status) (Prynne et al. 2013). Although it is not possible to directly compare our findings to these studies because of methodological differences on how dietary contributions were defined (contributions from the lunch meal vs. all foods consumed during school hours), our findings suggest important nutritional quality differences between time periods in Canada. Most notably, substantially lower intakes were reported for key nutrients such as vitamin A, D, calcium, phosphorus, and magnesium during school hours compared with non-school hours. Between-country differences could reflect differences in patterns of foods consumed at lunch-time by school-age children and differences in access to school meal and milk programs.

Canada remains the only G8 country without a national school meal program (McKenna 2010; Godin et al. 2017), and some advocates have proposed a federally funded school meal program (Jeffery and Leo 2007; Kimmett 2011; Anonymous 2013; Hyslop 2014; Collier 2015). Moreover, wide variation in provincial and local-level school nutrition policies and guidelines (Godin et al. 2017) and funding and capacity for school meal programs (Jeffery and Leo 2007) has been reported. In the United States, the beneficial effects of children’s participation in universal school meal programs on dietary outcomes are well-established (Clark and Fox 2009; Hanson and Olson 2013). Understanding where Canadian children acquire foods from during school hours and whether lunch-time food source is associated with dietary quality is important for informing debates about school meal programs for Canadian children. Next steps in our research will explore these associations using national dietary data.

Our findings indicate that specific aspects of in-school dietary patterns could be improved. Mean School-HEI score for Canadian children was 53 points out of a possible maximum score of 100 points. Similar to previous United States studies characterizing the quality of foods consumed in the school context (Cullen et al. 2011; Au et al. 2016), the lowest School-HEI subscores (for all age groups) were for green and orange vegetables, whole fruit, whole grains, and milk products. Hence, Canadian school-based nutrition policies and program should focus on improving access to and affordability of healthy food choices (particularly vegetables, whole fruit, whole grains, and milk products) in Canadian schools.

We also found that vitamin A, vitamin D, vitamin B 12 , calcium, and milk-products densities were at least 20% lower during school hours compared with non-school hours. These findings align with other Canadian studies reporting low intakes of milk products at school (Woodruff et al. 2010) and low frequency of milk consumption during school hours (Ahmadi et al. 2015; Velazquez et al. 2015). Considering that in 2004, more than one-third (37%) of children aged 4–9 years and up to 61% of boys and 83% of girls aged 10–16 years did not meet their recommended daily servings of milk (Garriguet 2006), the school context represents an opportunity to increase intakes of milk products among Canadian children and youth.

Age was a meaningful predictor of diet quality during school hours, with mean School-HEI scores declining as children aged. Younger children (aged 6–8 years) also reported proportionally fewer calories from minimally nutritious foods compared with adolescents. These findings align with other studies reporting declining diet quality as children age (Garriguet 2006, 2009; Larson et al. 2007; Riediger et al. 2007; Velazquez et al. 2015). No differences in School-HEI scores were reported across ethnicity, residential location, household-level income, and food-security status. Although the association between School-HEI scores and parental education was significant (p = 0.04), the low R2 (<1%) suggests it did not explain a meaningful proportion of variation in school-hour–diet quality. The lack of association between household income and school-hour–diet quality was not surprising. A large repeat cross-sectional study among United States children and adolescents reported no association between parental income and United States HEI-2010 scores over a 13-year period (Gu and Tucker 2017). Similarly, the associations between food insecurity and diet quality among young children in Canada remain unclear. Food security is thought to impact diet quality by limiting access to resources to purchase more expensive food items such as fresh produce and dairy products (Dachner et al. 2010). Previous analyses using the CCHS 2.2 have confirmed differences in nutritional adequacy between food-secure and food-insecure households, but only among adolescents and not younger children (Kirkpatrick and Tarasuk 2008). It is possible that the effect of food insecurity on household members may differ whereby parents compromise their own intake to buffer younger children (Glanville and Mcintyre 2006). Children living in food-insecure households may also have access to local school-based meal programs in some regions. However, the CCHS 2.2 did not include any questions on children’s participation in a local school meal program, which could have allowed us to examine their potentially buffering effect.

Strengths of this study included its large, nationally representative sample and the use of a composite diet-quality indicator to capture the multidimensional nature of diet quality in the specific context of school hours. However, some limitations should be acknowledged. First, we did not assess whether differences in dietary intakes observed on school days were similarly observed on weekend days (when children are not in school), so it is not possible to determine whether these differences are solely due to the school context. This could reflect specific sociocultural patterns in the types of foods typically eaten at lunch compared with the remainder of the day (regardless of whether lunch is consumed on a week day or a weekend day) since our analysis focused on school days. Another limitation was the use of self-reported data. The accuracy of dietary recall methods among children can vary widely depending on children’s age and interview conditions (e.g., the retention period, type of prompting, and use (or not) of parental assistance) (Sharman et al. 2016; Tugault-Lafleur et al. 2017). Studies conducted among children have also confirmed substantial under-reporting of energy intake (McPherson et al. 2000; Burrows et al. 2010). Dietary recall methods can also be affected by social desirability bias, a type of systematic error when subjects selectively misreport certain foods because of their norms and beliefs about what they should eat (Hébert 2016). However, it is reasonable to believe that both the recall and social desirability biases would be similarly distributed during school and non-school hours for older children who completed the recall without any parental assistance. Yet for children aged 6–11 years who completed the recall with parental assistance, the presence of a parent could have been a selective confounder. The parent would know what was in a home-packed lunch, but the child might have been reluctant to report that he/she had not eaten part of the lunch.

Implications for school-based nutrition programs in Canada Given that foods eaten during school hours for Canadian children represent one-third of the total daily energy consumed, the school context provides an important opportunity to promote healthy eating among Canadian children. Energy-adjusted intakes of vitamin A, vitamin D, vitamin B 12 , calcium, and milk products were substantially lower during school hours compared with non-school hours. The quality of Canadian children’s dietary intakes at school could potentially be improved by increasing intake of nutritious foods including dairy products, thus increasing the intake of key nutrients such as protein, vitamin A, vitamin D, calcium, and magnesium. Mean school-hour–diet quality scores required improvement for all age groups and declined as children aged. School-based health promotion strategies should target lunch meals for all children, but particularly among adolescents who are at highest risk of poor diet quality at school.