We developed and validated a food-based diet quality score based on Dutch dietary guidelines to estimate overall diet quality of children. Using this score, we evaluated diet quality of over 4700 children at the age of 8 years in a population-based cohort in the Netherlands. We observed that diet quality in this population was suboptimal and none fully adhered to the guidelines. Factors that correlated with a higher diet quality in this group were, amongst others, a higher socioeconomic status and no maternal smoking. We observed only weak tracking of diet quality between the ages of 1 and 8 years.
Interpretation of findings and comparison with previous research
Diet quality was suboptimal in our study population of 8-year-old children. This is consistent with studies in the US, Brazil, and the UK that showed less than optimal diet quality in similarly aged children [
9‐
11]. Compared to the American population aged 7–9 years [
9], level of adherence was similar for the fruit and vegetable components, however, for the dairy component adherence was lower in our study population. This might be explained by the difference in scoring, as we only included recommended food items in the dairy component, whereas in the US-based study all dairy items were included [
9].
As expected from previous studies [
27], socioeconomic status was positively associated with diet quality. A strong association was observed particularly for maternal educational level, independent of household income and other factors. Previous studies indicated that individuals with a higher educational level could have more nutritional knowledge [
4,
27,
28]; our study suggests that this also translates to the diet provided to their children. Furthermore, families with a higher income may be more able to buy healthy, more expensive, food products [
29,
30], explaining our association of household income with child diet quality, independent of educational level. A previous study among households in Canada showed that access to dairy, fruit, and vegetables, which are food groups that positively contribute to our diet score, may be constrained by low income irrespective of educational level [
31]. Unfortunately we did not assess food security in our study, which may partly explain the association between socioeconomic status and diet quality found in our study.
The negative association of maternal smoking with diet quality score is consistent with previous research among 515 children aged 2–17 years in the U.S., which showed that children from low-income families with parents who smoked, had a poorer diet quality than children from low-income families with non-smoking parents [
32]. We also observed a negative association between maternal overweight and child’s diet quality score, which is in line with a previous study among 1640 children aged 3 years in the UK [
33]. These findings for maternal smoking and overweight suggest that an unhealthy lifestyle of the mother negatively influences their child’s diet quality, independent of socioeconomic status.
Independent of these maternal factors, we also found an association between children’s lifestyle and their diet quality. Being more physically active and having less screen time were associated with a higher diet quality in children, which is consistent with previous research, that showed that sedentary behavior is associated with a less healthy diet [
27,
33]. However, we did not observe this association for the group with the highest levels of physical activity. Finally, in our fully adjusted models, we observed that children with a Moroccan ethnic background had a higher diet quality score than those with a Dutch ethnicity. Children with a Moroccan ethnicity had higher intakes of fish, legumes, and nuts and a lower high-fat and processed meat intake, suggesting a more Mediterranean-style diet [
34].
In our study population, we found only weak tracking of the diet quality score and its individual components between the ages of 1 and 8 years. Studies on tracking of diet from early life to later childhood are limited [
35]. One previous study found moderate to fair tracking of the intakes of fruit, vegetables, and sugar-sweetened beverages from the age of 18 months to 7 years [
35]. A review by Nicklaus and Remy (2013), showed moderate tracking of eating habits after the first year of life [
36]. Combined, these results suggest that tracking of diet may start after the age of 1 year.
Methodological considerations of the diet quality score
The diet quality score was positively associated with intake of micronutrients, indicating adequate construct validity, since dietary recommendations are, amongst others, developed to provide a sufficient supply of nutrients [
24]. We included both healthy and unhealthy components in the score, which may better capture overall diet quality than including healthy or unhealthy components only, as eating healthy foods is not necessarily inversely related to eating unhealthy foods [
37]. Further research is needed to examine whether this combined score is indeed associated with child health. Another strength of our diet score is the use of cut-off values based on current dietary recommendations instead of using a population-specific cut-off value such as a population-specific median intake, which may not be related to an actual healthy intake level [
24]. Finally, a strength of our diet quality scoring system is that we used a continuous scale, which provides more detail and is more accurate in ranking children with respect to diet quality than a dichotomous scoring system [
24].
Constructing an overall diet quality index involves many choices [
24]. Although it may have been preferred to ascribe greater weights to components that have a greater effect on health, not enough information on the overall health effects of individual components was available, so we chose not to apply any weighting. In addition to the number and weights of components, another aspect to consider is the type of components included in the diet index. Most diet indices are based on intake of nutrients, food groups, or a combination of these, and some indices also include measures of dietary variety [
24,
38]. We chose to construct our diet quality score on the basis of intake of food groups only, in line with the Dutch dietary guidelines, but we also observed positive associations of the diet score with intake of micronutrients, suggesting it represents an overall healthy diet. When diet quality score components are similar to each other or when they are strongly correlated, they contribute more heavily to the score [
24]. However, in our diet quality score, we observed low correlations between the diet score components (
r − 0.13 to 0.08). Finally, because our diet quality score is based on Dutch recommendations, important food groups may be absent for children with another ethnic background. However, the Dutch recommendations are comparable to recommendations in other countries [
39]. Furthermore, a systematic review conducted by Gilbert and Khokhar (2008) showed that after moving to a Western country, the majority of ethnic groups change their eating habits to a more Western diet [
40]. Also, we did not find major differences in diet score between the different ethnic groups in our population, suggesting that the Dutch recommendations and our diet score were also suitable for the study participants with another ethnicity.
Strengths and limitations
Major strengths of the Generation R Study, in which we applied our diet quality score, are the population-based prospective cohort design and the large number of subjects. Also, we had information available on many parental and child sociodemographic and lifestyle factors for which we could examine their correlation with diet quality. However, there may be other correlates of diet quality that were not assessed in our study. Unfortunately, we had no detailed information on physical activity of the children. We used the amount of time participating in organized sports as a proxy for physical activity, which may not be an optimal measure, because it does not take into account other sources of physical activity. In addition, not all correlates were assessed at the same moment as dietary assessment, which may have influenced the associations. However, there was a high correlation of most variables throughout childhood, and we expect that any changes in these correlates are only limited. Therefore, we chose the time point that was the closest to our moment of dietary assessment. Furthermore, non-response analyses showed that non-responders to the FFQ more often had characteristics associated with a lower diet quality score, such as a lower educational level, suggesting that diet quality might be even lower in the children in Rotterdam than observed in the study population for which we had data available.
Another limitation of the study was the assessment of dietary intake with an FFQ. Limitations of FFQs in general are that they contain a limited amount of food items, and recollection of the consumed foods and portion sizes can be sources of error [
41]. The FFQ used in our study was validated against the doubly labeled water method, regarded as the golden standard for the determination of total energy expenditure in free-living subjects, and this validation showed a reasonable capacity of the FFQ to rank subjects with respect to energy intake [
17]. However, the FFQ was not validated for the intake of specific foods or food groups. Finally, for our analyses on tracking of diet quality, a limitation was that diet quality was not scored in exactly the same manner at the ages of 1 and 8 years and that no data on dietary intake were available for the period in between these two age categories.
Implications
The results of our study suggest that overall diet quality among 8-year-old children in our study population in an urban multi-ethnic setting in the Netherlands is suboptimal and that none of the children fully adhered to the dietary guidelines. This is undesirable as a healthy diet is important for healthy growth and development of the child [
1]. However, future research is needed to assess whether a higher overall adherence to the dietary guidelines is indeed associated with a better health and to evaluate diet quality in other populations of children. Although the observed effect estimates for the correlates of diet quality were relatively small on an individual level, these may be relevant for public health strategies. We observed for example that children from higher educated mothers had an 0.3 higher diet quality score (scale 0–10) than children whose mothers had not completed higher education. Most of the observed correlates of diet quality in our study are in line with previous research. Consistent with other studies, we found low socioeconomic status to be a strong predictor of a lower diet quality [
27], emphasizing the need to target child dietary interventions especially to families with a lower socioeconomic status. Interventions should focus on promotion of healthy food products and increase the accessibility of these foods for these groups. Additionally, interventions should also discourage the consumption of unhealthy food products. Adherence to the recommendations was particularly low for the moderation components in our study population, underlining the importance of discouraging the intake of sugar-containing beverages and high-fat and processed meat. As previous evidence showed tracking of diet between mid-childhood and adulthood [
14], dietary interventions targeted at children are expected to not only improve diet quality during childhood, but also their diet quality into adulthood. However, we observed only weak tracking of diet quality from early to mid-childhood. Therefore, further research is needed to establish the optimal age and also the best target groups (e.g., children, parents, and/or schools) for dietary interventions in order to improve long-term diet quality.