The Health-promotion through Obesity Prevention across Europe (HOPE) project aims to bring the European scientific knowledge on overweight, obesity and their determinants together and use the expertise of researchers across Europe to contribute to tackling the obesity epidemic.

This special issue of Public Health Nutrition presents important results from one of the work packages of the HOPE project that aims at gaining and integrating knowledge on the determinants of nutrition, physical activity and obesity among schoolchildren and adolescents (aged 10–18 years) in different European regions. It includes contributions from Northern Europe (Norway), Central and Eastern Europe (Germany, Poland and the Czech Republic), Southern Europe (Greece) and Western Europe (Belgium and The Netherlands), as well as an overview of the availability of good-quality data on prevalence rates and trends in overweight (including obesity) among adolescents in European Union (EU) countries. The studies that are included report prevalence differences, data on relevant nutrition and physical activity behaviours, as well as potential physical and environmental behavioural determinants.

These papers provide further evidence on differences in obesity and overweight prevalence among different EU regions and countries, and contribute to the further exploration of risk factors that may or should be addressed in obesity prevention efforts for school-aged children and adolescents in EU countries.

To review recent data on objectively measured overweight/obesity in national representative samples of European adolescents (aged 10–18 years), as well as availability of studies assessing trends in overweight/obesity in this target group. Attention was paid to the ability of the data to describe the obesity epidemic, especially in sociodemographic subgroups.

Data on prevalence and trends in overweight/obesity among adolescents in the twenty-seven European Community member states, Iceland, Norway and Switzerland, available as scientific publications as well as reports or unpublished data by the end of 2009, were retrieved. Reports on the most recent objectively measured data from national representative samples were selected and described with regard to the years of data collection, sample sizes, response rates, age ranges included, trends by age, type of measures of overweight/obesity, sociodemographic variables and the sources of information.

Objectively measured data on national representative samples were identified for only half of the countries, and the trend studies were mainly conducted applying subnational samples. Most studies used the criteria from the International Obesity Task Force (IOTF) to define overweight/obesity, but the age ranges studied and the years of data collection varied, and information on sample sizes and response rates were often not presented. Data on trends of overweight/obesity over time are increasing, and the most recent studies indicate that the prevalence rate of overweight/obesity has stabilized. Few studies reported data by sociodemographic subgroups other than gender and age.

Objectively measured data on national representative samples of adolescents appear scattered, and there is a large heterogeneity with respect to the quality and comparability of available data. Increasing use of the IOTF criteria for overweight/obesity contributes to improved comparability across studies. Data by sociodemographic subgroups, and in particular by socio-economic status, are scarce.

To examine the prevalence of overweight and obesity in Polish adolescents in 2005 using both the International Obesity Task Force (IOTF) cut-offs and a national reference; to compare this to data collected in 1995; and to assess whether there were differences in overweight or obesity by gender and place of residence in 1995–2005.

BMI was calculated from measured height and weight, collected in a cross-sectional study in five regions of Poland in 2005. Adolescents were categorised as normal, overweight or obese based on IOTF cut-off values, and by national weight for stature tables, where the 90th and 97th percentiles were used as cut-off values for overweight and obesity.

Population-based study set in Poland.

A two-stage sampling method was used to recruit 8065 pupils (3980 boys and 4085 girls) aged 13–15 years.

The prevalence of overweight and obesity was 12·5 % and 1·9 %, respectively. No significant gender differences were found, either in overweight or obesity. The prevalence of overweight and obesity in 2005 had increased 2 % compared to 1995. Overweight and obesity among adolescents were not related to urban–rural residence, but there were significant regional differences.

Monitoring trends in overweight and obesity among adolescents in all regions of Poland using the same reference criteria is important. Since regional differences in overweight and obesity rates among adolescents were observed both in 1995 and 2005, future research should investigate the potential causes of these differences.

To record the prevalence of overweight and obesity in urban primary-school children in relation to several socio-economic and demographic factors.

Cross-sectional.

A representative sample of 729 schoolchildren (379 male and 350 female), aged 9–13 years, stratified by parental educational level, was examined in the urban region of Athens. Weight and height were measured using standard procedures. The International Obesity Task Force thresholds were used for the definition of overweight and obesity. Several socio-economic and demographic data and the child’s ‘popularity’ score were also recorded with specifically designed standardized questionnaires.

The prevalence of overweight and obesity was 29·6 % and 11·1 %, respectively. Annual family income of €12 000–20 000 (OR = 1·58), residence ownership (OR = 1·63) and the grandmother as the child’s primary caregiver (OR = 1·38) were significantly associated with higher odds of childhood overweight and obesity. Non-Greek parental nationality (OR = 0·72) and higher ‘popularity’ scores of children (OR = 0·42) were significantly associated with lower odds of overweight and obesity. The grandmother as the child’s primary caregiver and an annual family income of €12 000–20 000 remained significantly associated with childhood overweight and obesity after adding all significant correlates of childhood overweight and obesity observed at the bivariate level in a multivariate regression model (OR = 1·51 and 1·61, respectively).

Among family income, residence ownership, child’s primary caregiver, parental nationality and popularity scores that were identified as significant correlates of childhood overweight and obesity at the bivariate level, lower family income and grandmother as the child’s primary caregiver were the only factors that remained significantly associated with childhood overweight and obesity at a multivariate level.

To assess the prevalence of normal weight, overweight and obesity among 10–18-year-old Czech Republic adolescents and to assess the association between energy balance-related behaviours and overweight/obesity.

Cross-sectional data from ‘The 6th Nation-wide Anthropological Survey of Children and Adolescents 2001 Czech Republic’ have been used.

Height and weight were objectively measured. Data on adolescents’ behaviours were assessed with self-reported questionnaires. Background variables were assessed by means of a parental questionnaire. Multi-level logistic regression analyses were conducted to assess behavioural risk factors of being overweight/obese.

Data on 31 228 adolescents aged 10–18 years were included in the present study.

The highest prevalence of being overweight or obese was found among boys and younger adolescents. Boys were more physically active, watched more television (TV) and used the computer more often than did girls. Being on a diet and skipping meals were positively associated with being overweight/obese, independent of gender. In boys (10–14 years old), inverse associations with being overweight/obese were found when being more physically active. Monitoring weight showed inverse relations with being overweight/obese in 15–18-year-old girls. Watching TV more than 7 h a week was positively associated with being overweight/obese in 15–18-year-old girls, and was found to be negatively associated in boys of the same age group.

These behaviours should be targeted when preventing overweight and obesity among Czech Republic adolescents. Studies using better measures of energy balance-related behaviours are needed.

To identify lifestyle clusters in adolescents and to characterize their association with overweight and obesity.

Cross-sectional and longitudinal data of the Kiel Obesity Prevention Study.

Schools in Kiel, Germany.

Cross-sectional data of 1894 adolescents aged 14 years and 4-year longitudinal data of a subsample of 389 children aged 10 and 14 years. Self-reported data of physical activity, modes of commuting to school, media time, nutrition, alcohol consumption and smoking were used to identify lifestyle clusters with two-step cluster analysis. Obesity indices (height, weight, waist circumference and fat mass (FM)) were measured.

Three lifestyle clusters were identified: a ‘low activity and low-risk behaviour’ cluster (cluster 1: n 740, 39·1 %); a ‘high media time and high-risk behaviour’ cluster (cluster 2: n 498, 26·3 %); and a ‘high activity and medium-risk behaviour’ cluster (cluster 3: n 656, 34·6 %). Strictly speaking, none of these clusters was considered to be markedly healthy. The prevalence of overweight and obesity tended to be lower in cluster 3 (15·9 %) than in clusters 1 (20·4 %) and 2 (20·5 %; P = 0·053). Longitudinally, 4-year changes in FM were found to be lowest in cluster 2, but the 4-year incidence rate of obesity was lowest in cluster 3.

Explicit healthy lifestyles do not exist, but an active lifestyle reduces the incidence of obesity. In adolescents, health promotion should take into account the diversity of lifestyles and address specific lifestyle clusters.

Insight into the role of energy balance-related behaviours (EBRB) is of great importance when it comes to prevention of weight gain and design of interventions tailored to target these behaviours.

First, the present study examines the longitudinal association of four EBRB in Norwegian adolescents. Second, it aims to examine whether clusters of EBRB are cross-sectionally associated with being overweight.

The present study is part of the ‘Fruits and Vegetables Make the Marks’ project. The study sample consists of twenty control schools in two Norwegian counties.

Survey questionnaires were completed by 884 pupils with an average age at baseline, September 2001, of 11·8 years. In the follow-up surveys in May 2002 and May 2005, a total of 809 and 724 adolescents participated, respectively. Four EBRB were measured: habitual fruit and vegetable intake, snacking and soda consumption, television and computer use and physical activity.

Results of the associations between EBRB were similar for boys and girls. The odds, ranging from 1·14 to 12·06, were mostly significant. One out of four clusters, the unhealthy cluster, was significantly and cross-sectionally associated with overweight and obesity.

Longitudinal associations of EBRB show that it is important to start early with interventions that aim to prevent unhealthy behaviours becoming habitual. These behaviours should be targeted at the same time as they tend to co-occur. More research, preferably longitudinal and more objective, is needed to investigate associations between health behaviours and body weight among adolescents.

To explore the relationship between several physical activity (PA) and dietary behaviours and BMI Z-score and to investigate the relationship between changes in these variables and in the BMI Z-score over a 4-year period from childhood to adolescence.

Longitudinal study in which children were included in the fifth grade and measured for four consecutive years. Dietary and PA behaviours as well as height and weight were measured by means of self-reported validated questionnaires.

Fifty-nine Flemish elementary schools.

The baseline sample consisted of 51·9 % boys and the mean age was 10 (sd 0·4) years. During the first measurement year (2002), data on 1670 fifth graders were gathered. These measurements were repeated after 1 (n 1557), 2 (n 1151) and 3 (n 807) years.

Significant inverse relationships with BMI Z-score were observed for frequency of breakfast consumption (β = −0·033, se = 0·012) and frequency of sports participation (β = −0·011, se = 0·004) across four time points. Significant inverse relationships between changes in BMI Z-score and changes in frequency of sports participation (β = −0·011, se = 0·006) and hours of physical education (PE; β = −0·052, se = 0·023) were observed, meaning that decreases in sports participation and hours spent in PE were associated with increases in BMI Z-score.

The present study provides an important insight into different dietary and PA behaviours related to (changes in) BMI Z-score during the transition from childhood to adolescence.

To identify the correlates of the home food environment (parents’ intake, availability and food-related parenting practices) at the age of 10 years with dietary patterns during childhood and in adolescence.

Primary-school children of fifty-nine Flemish elementary schools completed a questionnaire at school in 2002. Four years later they completed a questionnaire by e-mail or mail at home. Their parents completed a questionnaire on food-related parenting practices at baseline.

Longitudinal study.

The analyses included 609 matched questionnaires.

Multi-level regression analyses were used to identify baseline parenting practices (pressure, reward, negotiation, catering on demand, permissiveness, verbal praise, avoiding negative modelling, availability of healthy/unhealthy food items and mothers’ fruit and vegetable (F&V) and excess scores) associated with children’s dietary patterns (F&V and excess scores).

Mother’s F&V score was a significant positive independent predictor for children’s F&V score at baseline and follow-up, whereas availability of unhealthy foods was significantly negatively associated with both scores. Negotiation was positively associated with children’s follow-up score of F&V, while permissiveness was positively associated with children’s follow-up excess score. Availability of unhealthy foods and mother’s excess score were positively related to children’s excess score at baseline and follow-up.

Parental intake and restricting the availability of unhealthy foods not only appeared to have a consistent impact on children’s and adolescents’ diets, but also negotiating and less permissive food-related parenting practices may improve adolescents’ diets.

To explore direct associations between home and school availability of fruit and fruit intake, and the mediating role of attitude towards fruit, liking, perceived barriers and self-efficacy.

Cross-sectional study.

Primary schools in nine European countries.

Within the Pro Children study, data were collected on perceived home and school availability of fruit, psychosocial factors related to fruit intake and its frequency among 13 305 11-year-old schoolchildren.

Significant overall associations were found between child-reported home availability of fruit and fruit intake in all countries and in the total sample. School availability of fruit was associated with fruit intake in the pooled sample and in country-specific analyses in Sweden and the Netherlands. Liking (13·2–49·4 %) and self-efficacy (14·0–25·1 %) were the strongest mediators in the home availability–fruit intake relationship, but there was also a direct association between home availability and fruit intake, except in Spain and the Netherlands. Mediating pathways of the school availability–fruit intake relationship could only be assessed for Norway, Sweden and the total sample. Attitude was a significant mediator in Norway (80·4 %) and in Sweden (25·3 %), while in the total sample also liking (38·7 %) and self-efficacy (23·0 %) were identified as significant mediators.

The association between home availability of fruit and fruit intake is at least partly mediated by personal factors such as liking and self-efficacy indicates that fruit intake is not a complete automatic or unconscious behaviour.

To examine the associations of perceived physical environmental factors (availability of physical activity (PA) attributes at home, PA facilities in the neighbourhood, neighbourhood pleasantness and safety) and social environmental factors (parental sports behaviour and parental rule regarding sports participation) with adolescent leisure-time sports participation, and to explore whether the associations found were mediated by individual cognitions as derived from the theory of planned behaviour (TPB).

Cross-sectional study.

In schoolyear 2005/2006 adolescents from seventeen schools in Rotterdam, the Netherlands, completed a questionnaire during school hours that included self-reported measures of leisure-time sports participation, perceived physical environmental factors and TPB variables. Information about parental sports behaviour and parental rule was obtained from a questionnaire that was completed by one parent of the adolescents.

Data were collected from 584 adolescent–parent combinations.

Data were analysed with multi-level logistic regression analyses. Availability of PA attributes at home (OR = 1·26), parents’ sports behaviour (OR = 2·03) and parental rule (OR = 1·64) were associated with a higher likelihood of adolescents’ leisure-time sports participation. These associations were partly mediated by attitude and intention.

Adolescents were more likely to engage in leisure-time sports when PA attributes were available at home, when parents participated in sports activities and had a rule about their offspring participation in sports activities. These associations were partly mediated by attitude and intention. These results suggest that parents can importantly promote sports participation among their offspring by making sports activities accessible and a family routine.