Results from this study showed that serving of a free, healthy school meal for one year had a significant effect on the total daily intake of vegetables on sandwiches in the intervention group compared to the control group at the end of the intervention but not in the middle of the intervention. The intervention did not lead to other statistically significant changes in the intervention group compared to the control group with regards to other vegetables, fruits or unhealthy snacks.
The increased intake of vegetables on sandwiches in the intervention group is important because bread is an essential staple of the Norwegian every-day diet. Children, as do adults, have a high frequency of consumption of bread based meals, with 82%, 85% and 61% consumption for breakfast, lunch and supper, respectively (29). Since the intake of bread is so high, the use of vegetables on sandwiches might be a potential way to increase vegetable intake, which we know is lower than the dietary recommendations (20). Since vegetables commonly used for sandwiches (lettuce, tomatoes, cucumber, peppers) were part of the free school meal, it is likely that the significantly increased intake of vegetables on sandwiches in the intervention group may be due to what the children ate at school. However, it is also possible that the increased intake may be explained by an increased consumption at home and during leisure time. This could potentially be explained by habit theory, in that repeatedly performing a behaviour, i.e., intake of vegetables on sandwiches at school every day for one year, might result in it becoming a habit (30, 31). We did not observe this effect at follow up1, and this might be explained by the fact that the intervention may have changed the home environment, but that it took time to do so.
The average intake of unhealthy snacks among the participating children was relatively low at both baseline and the follow-up assessments. The lack of intervention effect might therefore be due to little possibility for improvement with regards to the intake of unhealthy snacks, as it was already low at baseline. Also, the intervention did not target intake of snacks specifically, as it was a free healthy school meal intervention, and this may be an explanation why we did not notice any change. There has been a clear decrease in sugar intake among Norwegian children since the turn of the millennium (18, 19). The lack of intervention effect might therefore be due to a general decrease in sugar intake in the Norwegian child population, and not the intervention itself, and might also explain the difference in results from this study compared to the free school fruit study (22), which was done early 2000.
The former study by Ask et al found that a free school lunch for four months did not improve the intake of fruit, vegetables, low-fat milk and wholegrain bread, or reduce the intake of unhealthy snacks (24). The yearlong intervention period in the current study posits a larger potential for intervention effect as it gives more time to detect a possible effect. This might explain why the current study had a positive effect on vegetable intake, while the study conducted by Ask, et al. did not lead to any improved measures on diet.
Strengths and limitations of the study
There are several strengths and limitations to this study. Strengths are the long intervention period of one year, a high participation rate, and having a control group and an intervention group. It is also a strength that the study has three data collection points, which makes it possible to assess how the intervention effect develops over time. The same research assistants conducted the data collection at all timepoints.
Limitations to this study are non-randomization, small sample size and self-reported data. The control group was selected based on similarities to the intervention group, making it reasonable to assume that possible differences are very limited. Analyses conducted also reveal that the two groups generally do not differ significantly. The fact that the intervention group was located at the same school as part of the control groups represents a substantial limitation. However, the children in the intervention group were in a totally different part of the school building than the control group, minimizing the chance of bias. They also ate the school meal in the classroom, and not a school canteen, making it less visible to the control children. Minor differences in age as well as differences in group size between the intervention group and the control group constitute another limitation. Large sample sizes are preferred in quantitative research, but the nature of this intervention made a larger sample unrealistic. The FFQ used in this study was quite limited, both regarding the lack of details in fruits and vegetables eaten and the lack of portion sizes, and a better dietary method would have strengthened the study. Self-reported data may be biased if respondents do not fully remember what they have eaten, or if they over/under-report their intake (32). Children in the School Meal Project were aware that improved diet quality was a desired outcome. This might have made them report healthier habits than they really have, which is a common phenomenon known as “social desirability bias” (33).