Evaluation of a 2-year physical activity and healthy eating intervention in middle school children

Abstract

The aim of the present study was to evaluate the effects of a middle school physical activity and healthy eating intervention, including an environmental and computer-tailored component, and to investigate the effects of parental involvement. A random sample of 15 schools with seventh and eight graders was randomly assigned to one of three conditions: (i) intervention with parental involvement, (ii) intervention alone and (iii) control group. In 10 schools, an intervention, combining environmental changes with computer-tailored feedback, was implemented over 2 school years. In five intervention schools, increased parental support was added. Physical activity was measured with questionnaires in the total sample and with accelerometers in a sub-sample of children. Fat intake, fruit, water and soft drink consumption were measured using food-frequency questionnaires. Results showed significant positive intervention effects on physical activity in both genders and on fat intake in girls. Parental involvement did not increase intervention effects. It can be concluded that physical activity and eating behaviours of middle school children can be improved by school-based strategies combining environmental and personal interventions. The use of personalized computer-tailored interventions seems to be a promising tool for targeting adolescents but needs to be further explored.

Introduction

Overweight and obesity among children and adolescents has increased alarmingly and has become a serious public health problem [1]. Factors negatively affecting the energy balance, such as low levels of physical activity [2] and unhealthy eating behaviours [3], are associated with a higher prevalence of overweight or obesity. Therefore, there is a need for effective intervention programmes promoting physical activity and healthy eating in children and adolescents.

Children and adolescents spend high amounts of time at school and the school environment is recognized as having a powerful influence on their physical activity [4, 5] and eating [6, 7] behaviours. Through schools, a direct link can also be established with the home environment. Parental influences are important determinants of adolescents' physical activity behaviours [8–10] and their consumption of healthy food products [11].

To date, many interventions have been delivered through elementary schools [2, 12] and only few through middle schools. In these studies the surplus effects of involving the parents have not been investigated [12]. However, declines in physical activity and unhealthy eating patterns are especially clear during adolescence and are likely to persist into adulthood [13–16].

The health education programme ‘Planet Health’, a 2-year intervention targeting both physical activity and healthy eating in middle school children, was not effective in increasing physical activity in boys and girls. However, this programme was effective in increasing fruit and vegetable consumption in girls, but not in boys [17]. M-span was aimed at increasing physical activity and increasing lower fat food choices by using environmental, policy and social interventions [18]. This intervention resulted in increased physical activity in boys, but no effects on fat intake at school were found [18].

The present intervention was unique in combining changes in the school environment with education through interactive computer-tailored feedback. Computer-tailored feedback is a new health education strategy and was found to be effective in increasing physical activity and decreasing fat intake in adults [19]. Additionally, one study in middle school pupils already demonstrated the positive effects of an Internet/video-tailored intervention for increasing physical activity and decreasing fat intake [20]. Due to the increased personal relevance of tailored feedback, these interventions are supposed to be more effective than general classroom curricula.

The purpose of this study was to evaluate the 2-year effects of an intervention, targeting physical activity and healthy eating in middle schools. The intervention was designed in such a way that later implementation in all Flemish schools would be feasible. This implicates that the intervention was designed to be implemented by the school staff themselves without external financial, material or organizational support. However, during the first intervention year, guidance and support was provided to help schools getting started. The results after the first intervention year were promising with increased physical activity levels in both boys and girls (L. Haerens, B. Deforche, L. Maes et al., in preparation) and decreased fat intake in girls [21]. The second year of intervention was aimed at continuation, external guidance was minimized and schools had to implement the intervention topics independently. Therefore, it was hypothesized that the second intervention year per se would not lead to additional intervention effects but that positive intervention effects found after 1 year of intervention would be maintained after 2 years of intervention. Additionally, it was hypothesized that involvement of the parents would remain important for intervention effects on fat intake in girls, as was found after 1 year of intervention.

Methods

Procedure and sample

A random sample of 15 schools out of the 65 schools with technical and vocational education in West Flanders (Belgium) was selected to participate in this study. The 15 schools were randomly assigned to one of the intervention or control conditions: intervention with parental involvement (n = 5, 1226 pupils), intervention alone (n = 5, 1006 pupils) and control condition (n = 5, 759 pupils). The parents of 2840 (95%) of the 2991 pupils in seventh and eight grades signed an informed consent in which authorization was provided for their child to complete measurements. Data of 704 children were lost through follow-up due to absence at measurements, children changing school or questionnaires filled out inaccurately. Table I presents the baseline and follow-up data of the sample.

Table I

Descriptive characteristics (percentages or means and standard deviations) for baseline sample and 2-year post-sample

	Baseline sample (n = 2840), mean ± SD	2-year post-sample (n = 2287), mean ± SD	Drop-out (n = 704), mean ± SD	Fdrop-out
Age (years)	13.1 ± 0.8	13.0 ± 0.8	13.4 ± 0.8	13.0***
% Girls	36.6 ± 48.2	38.1 ± 48.6	31.8 ± 46.6	0.2
% Overweight	18.5 ± 38.8	18.6 ± 38.9	18.2 ± 38.6	0.1
% Higher SES	32.6 ± 46.9	33.1 ± 47.1	30.7 ± 46.2	0.2
School PA (min/day)	16.8 ± 16.5	17.2 ± 16.5	15.3 ± 16.7	0.5
LTPA (min/day)	68.0 ± 49.2	73.1 ± 49.3	67.2 ± 50.4	0.2
Fat (g/day)	116.1 ± 50.3	114.1 ± 49.7	123.2 ± 52.0	2.8
Fruit (pieces/week)	5.4 ± 5.4	5.5 ± 5.4	5.1 ± 5.3	0.3
Water (glasses/day)	3.3 ± 2.7	3.4 ± 2.6	3.2 ± 2.7	0.2
Soft drink (glasses/day)	3.1 ± 2.5	3.0 ± 2.4	3.5 ± 2.7	4.7*

PA = physical activity; LTPA = leisure time physical activity.

***

P < 0.001,

*

P < 0.05.

From each of the 15 schools, one class of seventh graders was randomly selected for more in-depth measurement of physical activity with accelerometers. This resulted in a sub-sample of 258 children. The study protocol was approved by the Ethical Committee of the Ghent University.

Measurements

Measures were assessed at the beginning of the first school year (Pre-test: September 2003), assessed at the end of the first school year (Post 1: May–June 2004) and repeated at the end of the second school year (Post 2: May–June 2005). All measurements took place at school and questionnaires were filled out under supervision of teachers.

Physical activity questionnaire

Physical activity levels were determined using self-administrated questionnaires based on the Flemish Physical Activity Questionnaire (FPAQ). Data on demographics were collected in the first part of the questionnaire. An estimate of higher and lower social economic status (SES) was obtained by classifying the occupation of the father and mother into white- and blue-collar [22].

A second part evaluated physical activity levels of children. To assess an index of school-related physical activity, minutes spent in active transportation to school and in extracurricular physical activity at school were computed. By adding up time spent in leisure time active transportation and leisure time sports, a ‘leisure time physical activity (LTPA) index’ was created. In a separate study, Philippaerts et al. [23] reported moderate to high reliability of the FPAQ for indexes used in the present study. Test–retest intra-class correlation coefficients exceeded 0.70. To obtain validity measures, data from questionnaires were correlated to data derived from accelerometry. Pearson correlations were significant and ranged between 0.43 and 0.79, indicating acceptable validity of the instrument [23].

Accelerometers

Physical activity levels were also assessed by accelerometers (Model 7164, Computer Science Application, Inc., Shalimar, FL, USA) in the sub-sample of 258 children. Parents of 22 children gave no permission for their child to wear accelerometers. Accelerometers have shown to be valid and reliable tools for assessment of physical activity in children [24–26].

Children wore the accelerometer for 6 days above the right hip-bone, underneath the clothes. Accelerometers were set to measure activity counts in an epoch time of 1 min. Most recently published studies support cut-offs around 3000–3500 for moderate to vigorous physical activity (MVPA) [24, 27]. Cut-off points used in the present study were 0, <800, <3200 and ≥3200 for inactive, sedentary, light and moderate to vigorous minutes, respectively [24].

Children were asked to register in a diary each activity performed without wearing the accelerometer. The physical activity index of moderate to vigorous intensity was inflated by physical activities reported in the diaries.

Fat intake

Fat intake was measured with a self-administered questionnaire developed at the Ghent University together with the Flemish Institute for Health Promotion [28]. Questionnaires were validated in a separate study and were found to be sufficiently reliable and valid as compared with dietary records [28]. The questionnaire consisted of 48 items, representing all important sources of fat in the Belgian diet. Pupils were asked how often they consumed these products during usual days, weeks or months. A coefficient was calculated, representing fat content and portion size of each product. This coefficient was multiplied by the frequency of consumption, leading to fat intake score for each food item. Summation of all food items' fat intake scores lead to the total fat intake score and this was expressed in percent energy from fat [28].

Fruit, water and soft drinks

Food-frequency questionnaires adapted from the validated questionnaire used in the Health Behaviour in School-aged Children study [29] were used to assess fruit, water and soft drink consumption.

Intervention

A school-based intervention programme to promote healthy food and physical activity over 2 school years (October 2003–June 2005) was developed. The intervention was designed to be implemented by the school staff itself with only minimal external support to make later implementation in all Flemish schools feasible. During the first intervention year, schools were guided and supported by the research staff to get started; during the second intervention year, schools had to continue with implementation more independently.

Work group

In each of the intervention schools, a work group was set up. At the beginning of the first intervention year, work group members received background information and guidelines on how to address intervention topics. An intervention manual and educational material were made available. Every 3 months, a 1-hour work group meeting was planned to evaluate implementation and plan further actions.

Physical activity

The physical activity intervention focused on increasing levels of MVPA to at least 60 min a day [30]. In the present study, schools were encouraged to create more opportunities to be physically active during breaks, at noon or during after school hours. Schools were encouraged to vary content of physical activities offered in order to reach all pupils. Organization of non-competitive activities was encouraged to increase engagement of less talented children.

Additionally, extra sports materials were made available. Every school received an intervention box with sports materials like ropes, balls and beach ball sets. Schools were encouraged to make these sports materials available during breaks, at noon and during after school hours. Schools were also stimulated to encourage active transportation.

At the personal level, children received a physical fitness test and an adaptation of the adult computer-tailored intervention for physical activity [31]. The physical fitness test took place once, at the beginning of the second intervention year. During classes, all children had to cycle for 10 min on a computerized cycle ergometer. By means of folders, information was given on their fitness levels and possible ways to improve it.

By using CDs, the computer-tailored intervention was completed once each school year during one class hour. First children had to fill out questions on the computer screen. The first part of questions concerned demographic factors. The second part consisted of a school-based adaptation of the International Physical Activity Questionnaire [31] to measure physical activity. Final questions concerned psychosocial determinants of physical activity behaviours. After completing all questions, tailored feedback was displayed immediately on the screen. First, a general introduction and normative feedback was presented. Normative feedback related children's activity levels to current physical activity recommendations for adolescents [30]. Based on the theory of planned behaviour [32], children got tailored feedback about their intentions, attitudes, self-efficacy, social support, knowledge, benefits and barriers related to physical activity. The transtheoretical model [33] was used for matching content and approach of this feedback to the stages of changes in the same way as with the adult version [31]. Overall, an active lifestyle and participation in sports activities was promoted in an advice of five to six pages. Children could either save the advice on the computer or in some cases immediately print feedback. Afterwards, they had to complete a task with questions concerning their advice.

Food

In the same way as in the physical activity intervention, eating habits were targeted by both environmental and personal approaches. The food intervention focused on three behavioural changes: (i) increasing fruit consumption to at least two pieces a day, (ii) reducing soft drink consumption and increasing water consumption to 1.5 l a day and (iii) reducing fat intake. To facilitate fruit consumption, schools were asked to sell fruit at school at very low price or for free at least once a week. It was also suggested to offer fruit for dessert during lunch break. Furthermore, schools tried to promote drinking water as opposed to soft drinks, by offering it for free by means of drinking fountains or at lower price than soft drinks in shops or vending machines. Children received additional information about health consequences of eating fruit as opposed to snacks and of drinking water rather than soft drinks by means of folders and posters.

Every school year, children got an adaptation of the adult computer-tailored intervention for fat intake during one class hour [28]. Questionnaires concerning demographics, fat intake [28], fruit intake [29] and psychosocial determinants of fat intake lead to a tailored fat advice and normative feedback for fruit intake. In the same way as in the physical activity advice, feedback was based on the theory of planned behaviour [32] and the transtheoretical model [33].

Parent involvement

The goal of parent involvement was to create a supportive environment for healthy behaviours outside school. Schools were asked to invite parents at school for an interactive meeting on healthy food, physical activity and the relationship with overweight and health. Three times a year, information on healthy food and physical activity was published in school papers and newsletters for parents. In addition, parents received a free CD with the adult computer-tailored intervention for fat intake and physical activity [28, 31] for use at home. Through an informative folder, parents were informed that their child completed the same computer-tailored programme. They were asked to discuss results together and to give their child support to create a healthier lifestyle, if necessary.

Statistical analyses

Data were analysed using SPSS 12.0. Preliminary analyses consisted of descriptive statistics of sample characteristics. Linear mixed models on baseline demographics and behaviours were used to conduct drop-out analyses with group (participating and not participating at follow-up) entered as a factor.

To assess effects of the second intervention year per se, linear mixed models were applied on 2-year post-measures of physical activity and eating behaviours, co-varying for 1-year post-measurements (Post 1–Post 2). To assess 2-year post-intervention effects, linear mixed models were then repeated, co-varying for pre-test values (Pre–Post 2). Since 1-year post-intervention effects showed clear gender differences, all analyses were applied in boys and girls separately. Condition (intervention–control) was entered as a factor into the models. Schools were nested within condition to take into account possible school variance. All analyses were adjusted for age and SES. To assess specific differences in effects between intervention with parental involvement and intervention without parental involvement, linear mixed models analyses were repeated. P values ≤0.05 were considered as statistically significant.

Results

Sample characteristics and drop-out analysis

Drop-out analyses comparing baseline demographic and behavioural characteristics of pupils participating and not participating at follow-up showed few significant differences (see Table I). Pupils not participating at follow-up were significantly older and consumed significantly more soft drinks then pupils participating at follow-up.

Intervention effects

Effects of the second intervention year (F_{Post 1–Post 2}) on physical activity and eating behaviours are presented in Table II for boys and Table III for girls. No significant increase or decrease of the intervention effects on physical activity and eating behaviours was found as a result of the second intervention year per se (F_{Post 1–Post 2}). Further analyses exploring effects of parental involvement on fat intake in girls showed that there were no significant differences between the intervention with parental support and that without parental support (F = 0.4, P = 0.6).

Table II

Pre and post values of PA and eating behaviours in boys

	Pre (mean ± SD)	1-year post (mean ± SD)	2-year post (mean ± SD)	FCondition
				FPost 1–Post 2	FPre–Post 2
Self-reported behaviours (n)
School PA (min/day)
I (943)	18.3 ± 18.7	25.9 ± 21.3	25.2 ± 21.4	0.1	3.4*
C (214)	22.6 ± 14.8	22.8 ± 16.2	23.8 ± 16.5
LTPA (min/day)
I (943)	79.6 ± 53.0	73.3 ± 53.6	81.7 ± 56.1	3.1	2.5
C (214)	70.7 ± 46.3	65.7 ± 44.8	86.1 ± 56.9
Fat (g/day)
I (1005)	126.2 ± 52.3	123.3 ± 58.3	123.5 ± 58.0	0.1	0.1
C (214)	115.9 ± 50.2	112.8 ± 50.2	117.2 ± 49.1
% Energy from fat
I (803)	41.2 ± 17.5	38.7 ± 17.4	34.3 ± 16.2	1.3	0.2
C (188)	39.6 ± 16.9	38.4 ± 17.0	34.6 ± 14.4
Fruit (pieces/week)
I (966)	4.9 ± 5.1	4.6 ± 4.9	4.7 ± 5.1	5.4*	3.5
C (227)	6.4 ± 6.0	5.8 ± 5.3	6.4 ± 5.4
Soft drinks (glasses/day)
I (999)	3.4 ± 2.5	3.6 ± 2.7	3.5 ± 2.8	1.0	0.5
C (213)	2.5 ± 2.3	2.7 ± 2.5	2.7 ± 2.5
Water (glasses/day)
I (1000)	3.2 ± 2.7	3.6 ± 2.8	3.7 ± 3.0	0.0	0.1
C (213)	3.7 ± 2.5	4.1 ± 2.8	3.9 ± 2.6
Accelerometer data (n)
Sedentary (min/day)
I (51)	539.6 ± 62.5	518.5 ± 58.6	525.4 ± 55.2	0.1	0.0
C (12)	530.9 ± 39.1	490.8 ± 63.7	521.5 ± 60.7
Light (min/day)
I (51)	121.6 ± 29.6	118.3 ± 26.5	115.3 ± 30.7	1.1	8.6***
C (12)	138.5 ± 29.3	113.3 ± 39.1	99.6 ± 28.9
MVPA (min/day)
I (51)	33.9 ± 19.3	32.1 ± 26.4	34.6 ± 26.2	0.1	3.5(*)
C (12)	53.4 ± 19.0	42.1 ± 28.1	35.0 ± 14.0

PA = physical activity; I = intervention group; C = control group; LTPA = leisure time physical activity; MVPA = physical activity of moderate to vigorous intensity.

***

P < 0.001,

*

P < 0.05,

(*)

P < 0.08.

Table III

Pre and post values of PA and eating behaviours in girls

	Pre (mean ± SD)	1-year post (mean ± SD)	2-year post (mean ± SD)	FCondition
				FPost 1–Post 2	FPre–Post 2
Self-reported behaviours (n)
School PA (min/day)
I (437)	12.7 ± 13.0	17.6 ± 15.9	16.3 ± 15.6	3.0	0.3
C (336)	16.5 ± 12.2	16.6 ± 12.1	17.7 ± 13.7
LTPA (min/day)
I (437)	51.4 ± 37.2	51.0 ± 37.8	60.8 ± 40.0	0.2	0.7
C (336)	52.9 ± 39.1	49.1 ± 34.7	61.6 ± 41.8
Fat (g/day)
I (447)	99.1 ± 40.7	84.3 ± 32.8	79.2 ± 33.0	1.2	5.8*
C (340)	95.6 ± 37.3	91.4 ± 35.1	85.5 ± 34.8
% Energy from fat
I (387)	38.7 ± 16.1	32.0 ± 12.9	29.5 ± 13.0	2.2	13.3***
C (289)	36.7 ± 14.5	34.5 ± 13.9	31.8 ± 12.9
Fruit (pieces/week)
I (421)	5.4 ± 5.0	5.7 ± 5.1	5.8 ± 5.6	1.9	1.1
C (330)	6.7 ± 5.8	6.2 ± 5.2	6.6 ± 5.7
Soft drinks (glasses/day)
I (437)	2.8 ± 2.2	2.6 ± 2.2	2.3 ± 2.1	0.0	0.0
C (341)	2.4 ± 2.1	2.3 ± 2.2	2.1 ± 2.1
Water (glasses/day)
I (437)	3.5 ± 2.6	3.7 ± 2.6	3.8 ± 2.8	0.1	0.5
C (341)	3.6 ± 2.5	3.7 ± 2.7	4.0 ± 2.8
Accelerometer data
Sedentary (min/day)
I (41)	548.1 ± 55.1	529.7 ± 67.8	530.6 ± 64.7	2.3	0.9
C (36)	562.8 ± 63.2	527.1 ± 62.0	549.7 ± 65.8
Light (min/day)
I (41)	109.9 ± 30.5	102.5 ± 24.7	107.7 ± 31.2	1.2	4.6*
C (36)	115.0 ± 32.4	90.6 ± 23.6	95.4 ± 26.7
MVPA (min/day)
I (41)	20.5 ± 17.7	25.5 ± 20.6	24.8 ± 13.6	0.1	0.1
C (36)	18.7 ± 12.7	19.1 ± 15.7	22.9 ± 21.8

PA = physical activity; I = intervention group; C = control group; LTPA = leisure time physical activity; MVPA = physical activity of moderate to vigorous intensity.

***

P < 0.001,

*

P < 0.05.

Two-year post-intervention effects (F_{Pre–Post 2}) are also presented in Table II for boys and Table III for girls. In boys, significant 2-year post-baseline intervention effects on levels of physical activity, but not on eating behaviours, were found. School-related physical activity increased significantly more in the intervention groups compared with the control group (P < 0.05). Accelerometer data revealed a trend for significant lower decreases in physical activity of light intensity in the intervention groups (−6 min/day) compared with the control group (−39 min/day, P < 0.001). Where time spent in MVPA remained stable in the intervention group, it significantly decreased (−18 min/day) in the control group (P < 0.05).

In girls, significant 2-year post-baseline intervention effects were found for both physical activity and eating behaviours. In girls, the physical activity intervention was effective in preventing decreases in physical activity of light intensity. Time spent in physical activity of light intensity decreased significantly less in the intervention groups (−2 min/day) compared with the control group (−20 min/day, P < 0.05). Decreases in fat intake and percent energy from fat were significantly higher in the intervention groups (−20 g/day) when compared with the control group (−10 g/day, P < 0.05). In the same line, percentage of energy taken from fat significantly decreased with 9% in the intervention group and with 5% in the control group (P < 0.001).

Discussion

The purpose of the present study was to evaluate 2-year post-intervention effects of a middle school physical activity and healthy eating intervention. After 1 year of intervention, positive effects on self-reported school-related physical activity and physical activity measured with accelerometers were found in both boys and girls (L. Haerens, B. Deforche, L. Maes et al., in preparation) and in girls fat intake was significantly decreased [21]. The goal of the second intervention year was the continuation of initiatives which were implemented during the first school year. During this second year, more autonomy was given to the schools. This increase in autonomy and decrease in external guidance and support from research staff were aimed at creating a ‘real-life situation’ in which schools can take over the intervention themselves after 1 year of support. Hence, it was hypothesized that the second intervention year would not lead to additional positive outcomes but we hoped that positive intervention effects on physical activity and fat intake would be sustained. In line with the hypotheses, positive effects found after 1 year of intervention were sustained after 2 years of intervention and the second intervention year did not result in an increase or decrease of intervention effects.

After 2 years of intervention, positive effects on physical activity levels measured with accelerometers were found. The intervention remained effective in preventing decreases in physical activity of light intensity in both genders. Even more important is that positive effects on MVPA in boys remained, since participation in MVPA is more essential for improved health and weight control [13]. In boys of the intervention group, participation in MVPA remained stable over 2 school years, while in boys of the control group, time spent in MVPA gradually decreased. Also in girls, time spent in MVPA increased after 2 school years of intervention, but this increase was also seen in the control group. Increases in MVPA as found in girls of the control group are against expectations, since literature states that physical activity declines with age [15].

Increases in self-reported school-related physical activity were sustained after 2 school years. These results reflect that the schools were able to continue with promotion of physical activity autonomously. Implementation of the physical activity intervention in Flemish secondary schools with technical and vocational education should be recommended. In addition, more research is needed to find out if the upper limit for promotion of physical activity at school is reached or if additional input should be given to schools. Especially in girls, time spent in school-related physical activity remained rather low.

However, the school is not the only institute responsible for the promotion of physical activity in youth; physical activity promotion should be a shared responsibility between school, family and community. Especially for increasing LTPAs, efforts from schools alone do not appear to be sufficient. School-based strategies implemented during the first year were indeed not effective in increasing LTPA. During the second intervention year, LTPA increased in boys and girls of both the intervention and control group. These increases against expectations could reflect some reporting bias. It is possible that children over-reported their physical activity levels because they knew they were being studied. This is corroborated with the findings of the accelerometer data that indicated declines in physical activity where the data from the self-reports showed a general increase.

In line with our hypothesis, intervention effects on eating behaviours remained stable after the second year of intervention. The intervention was still not effective in decreasing fat intake in boys. In both the intervention and control group, absolute fat intake remained stable over 2 school years. Designing effective interventions to target fat intake in boys is a challenge for the future.

In girls, positive 1-year post-intervention effects on fat intake were sustained after 2 years of intervention. During the second intervention year, fat intake further decreased, and after 2 years of intervention, mean fat intake decreased with an average decrease of 20 g/day. Fat intake decreased with, on average, 10 g/day less in the control group. Fat intake was the only eating behaviour that was targeted by personalized computer-tailored feedback. It is therefore assumed that the personalized computer-tailored feedback was an indispensable intervention component for addressing fat intake in girls. Computer-tailored interventions are easy to implement: pupils can work through the programme independently and no prior teacher training is required. Hence, investigating the independent effect of the computer-tailored intervention is a priority for future research.

There were no positive intervention effects on fruit, soft drink and water consumption. These findings were in line with expectations, since the same intervention strategies used during the first intervention year were maintained during the second intervention year. Results suggests that creating a real-life situation in which both unhealthy and healthy alternatives are available is not sufficient to promote the consumption of fruit and water. Previous studies indeed revealed that pupils are more likely to consume soft drinks every day if soft drinks are available at school [7]. Our experiences learned that the huge incomes secondary schools receive from shops and vending machines were used as a motive for school boards to neglect the importance of a healthy school environment. Governmental laws restricting availability of unhealthy food products within school environments could be required to create healthy school environments.

Next to the school, the home is a fundamental part of adolescents' living environment. Parents are influencing adolescents' physical activity and eating behaviours considerably [9–11]. In the present study, an extra intervention condition was created in which home-based involvement of parents was aimed at. During the first intervention year, parents received a free CD with the adult computer-tailored intervention for physical activity and fat intake to complete at home. One-year post-results showed that parental support was important to find decreases in fat intake in girls. In contrast to the hypothesis, after 2 years of intervention, fat intake decreased similarly in girls of the intervention group with and without parental support. The lack of process evaluation data on levels of parental involvement, which is a limitation of the present study, makes it hard to draw conclusions. It is not clear whether there were no additional effects of increased parental support or whether parental support was not sufficiently increased during the second intervention year. The adult computer-tailored intervention was provided during the first intervention year, and during the second intervention year, parents were only involved through correspondence in school papers and newsletters.

Some additional study limitations need to be addressed. After 2 school years, there was a relatively high percentage (25%) of drop-outs. However, these drop-outs were not selective for this study, as all students present at the moment of data gathering did participate. Moreover, drop-outs did not differ from follow-up participants for most baseline characteristics: they were only somewhat older and consumed more soft drinks at baseline. A second limitation is the self-reported character of the measurements of dietary intake and physical activity, resulting in possible reporting errors [34]. Finally, in the present study, effects of the whole-school intervention were evaluated. Isolated effects of personalized tailored interventions for physical activity and eating behaviours used in the present study were not yet documented in adolescents. Since it is assumed that the computer-tailored feedback was an indispensable part of the intervention certainly for fat intake, this is a priority for future research.

Strengths of the present study are the randomized controlled design and the fact that the intervention was implemented by the school staff itself which makes implementation in all Flemish schools feasible.

In conclusion, physical activity and eating behaviours of middle school children can be improved by school-based strategies combining environmental and personal interventions, implemented by the school staff itself.

This study was supported by the Policy Research Centre Sport, Physical Activity and Health funded by the Flemish Government. The authors would like to thank the 15 schools participating in this study.

Conflict of interest statement

None declared.