Assessing long-term impact of dietary interventions: important but challenging.

National and international dietary recommendations highlight the importance of increased fruit and vegetable (FV) consumption for chronic disease prevention and general good health (1, 2). However, many people do not follow these guidelines, and there is a substantial public health need for successful strategies to promote and sustain healthy dietary habits, such as sustained increased FV consumption. Many school-based interventions aimed at increasing FV consumption have been implemented because schools provide equitable access to children and high levels of continual contact, which could be used to promote health and wellbeing (3, 4). Short-term increases in FV intake have been achieved in a number of studies (5–7). Reviews generally indicate that child fruit consumption may be moderately improved by school-based interventions, but studies show minimal success with vegetable consumption (5, 6). Long-term sustained effects on FV consumption, however, are relatively unknown. Interventions that provide free FV snacks to students in school may reduce health inequalities for children from low socioeconomic backgrounds (5). The Stea et al. study in the December 2018 issue of the Journal (8) aimed to assess the long-term effects of 1 y of free fruit in elementary school on fruit, vegetable, and unhealthy snack consumption at 14 y post intervention. In 2001, the Fruit and Vegetables Make the Marks study was conducted in 38 schools in Norway. Nine schools were assigned to the intervention group; 29 schools served as controls. The program provided 1 free fruit at lunch over a 10-mo period to children in the intervention schools. Baseline and postdata collection were conducted with 1950 children in 2001, with follow-up measurements in 2002, 2003, 2005, 2009, and 2016. The current article (8) presents findings based on the 2016 data compared with baseline intake for 982 participants (∼50% of baseline). The major finding was that there was no overall intervention effect 14 y post intervention on fruit, vegetable, or unhealthy snack intake. Gender-stratified analyses showed an increased frequency of fruit consumption (0.38 portions/d) among females in the intervention group compared with females in the control group, and further stratification for gender and educational level showed a stronger long-term effect (0.73 portions/d) among females with low educational attainment in the intervention group compared with those in the control group. The numbers of participants in each of these stratifications were not in the tables. It can be speculated that this could be due to the fact that low-income individuals receive fresh produce via food-assistance programs which increase the home availability of FV and thus consumption. Also, it is known that FV intake, in general, is higher among females than among males (9, 10). No further significant long-term effects were observed. This is the first study to attempt to assess possible sustained effects of an FV intervention post 14 y. Also, the use of Facebook to track the participants is quite an innovative strategy and may have contributed to the relatively high response rate for this follow-up study. As stated by the authors, the study limitations include use of self-reported data and use of different measures of educational attainment at baseline (parental education) and in the 2016 follow-up (participants’ own education levels) as an indicator of socio-economic status. The use of the word “sustained” to report results is also not warranted because it is only one 24-h intake measure. However, a number of other limitations should be recognized in evaluating and interpreting the findings of this study. The study was aimed at assessing the long-term sustained effect of the free fruit intervention. Comparing the 2016 followup data with post-1-y data from 2001 (instead of baseline) would have provided a more relevant assessment of sustainability over time in either the positive or negative direction. Also, an evaluation of 1 y of free fruit intervention reported an increased consumption of FV at 1 y and 3 y. However, the current study does not justify a 14-y follow-up considering that the intervention effect was not sustained at the 7-y follow-up. Furthermore, the study lacks the premise for assessing associations between providing 1 fruit per day with increased vegetable intake and decreased unhealthy snack intake. The 29 schools in the control group cannot be considered truly a control group because students in 9 of the 29 schools received a subsidized fruit snack via the Norwegian School Fruit Program. Although the authors state that the effect of the subsidized fruit was small compared with that of the free fruit in the original study, there was a significant difference in FV intake of subscribers compared with nonsubscribers (11). Thus, it can be speculated that there could still be a certain degree of intervention effect from the subscription program in those 9 control schools, which could have masked intervention effects.