PAPER Prevention of obesity - Nature

International Journal of Obesity (2001) 25, Suppl 1, S66–S74 ß 2001 Nature Publishing Group All rights reserved 0307–0565/01 $15.00 www.nature.com/ijo

PAPER Prevention of obesity — more than an intention. Concept and first results of the Kiel Obesity Prevention Study (KOPS) ¨ ller1*, I Asbeck1, M Mast1, K Langna¨se1 and A Grund1 MJ Mu 1

Institut fu¨r Humanerna¨hrung und Lebensmittelkunde, Christian-Albrechts-Universita¨t zu Kiel, Kiel, Germany

OBJECTIVE:Obesity prevention is necessary to address the steady rise in the prevalence of obesity. Although all experts agree that obesity prevention has high priority there is almost no research in this area. The effectiveness of different intervention strategies is not well documented. There is also no structured framework for obesity prevention. DESIGN: Based on (i) our current and limited knowledge and (ii) the idea that prevention of childhood obesity is an effective treatment of adult obesity, the Kiel Obesity Prevention Study (KOPS) was started in 1996. Concept, intervention strategies and first results of KOPS are reported in this paper. KOPS is an ongoing 8 y follow-up study. We first enrolled a large scale cohort of 5 to 7-y-old children, providing sufficient baseline data. KOPS allows further analyses of the role of individual risk factors as well as of long-term effectiveness of different intervention strategies. RESULTS: From 1996 to 1999 a representative group of 2440 5 to 7-y-old children was recruited (ie 30.2% of the total population of 5 to 7-y-old children examined by the school physicians) and a full data set was obtained from 1640 children. Of the children, 340 (20.7%) were considered as overweight and obese, 1108 children (67.6%) were normal weight, and underweight was found in 192 children (11.7%). Of the normal-weight children, 31% or 346 (21.1% of the total population) were considered to have a risk of becoming obese. Cross-sectional data provided evidence that (i) there is an inverse social gradient in childhood overweight as well as health-related behaviours and (ii) parental fatness had a strong influence on childhood overweight. We observed considerable changes in health-related behaviours within 1 y after combined ‘school-’ and ‘family-based’ interventions. Interventions aimed to improve health-related behaviours had significant effects on the agedependent increases in median triceps skinfolds of the whole group (from 10.9 to 11.3 mm in ‘intervention schools’ vs from 10.7 to 13.0 mm in ‘control schools’, P < 0.01) as well as in percentage fat mass of overweight children (increase by 3.6 vs 0.4% per year without and with intervention, respectively; P < 0.05). CONCLUSION: First results of KOPS are promising. Besides health promotion, a better school education and social support seem to be promising strategies for future interventions. International Journal of Obesity (2001) 25, Suppl 1, S66 – S74 Keywords: childhood obesity; prevention; Kiel Obesity Prevention Study (KOPS); nutrition education; school intervention; family intervention; social gradient

Introduction The prevalence of overweight, moderate obesity and severe obesity has been steadily increasing over the last 50 y. Overweight and obesity now represent a major public health concern. Current estimates indicate that the prevalence of obesity is still rising. Obesity, once established, is difficult to treat. Therefore prevention of obesity and its comorbidities

¨ ller, Institut fu ¨ r Humanerna¨hrung und *Correspondence: MJ Mu Lebensmittelkunde, Christian-Albrechts-Universita¨t zu Kiel, ¨ sterubrooker Weg 17, D-24105 Kiel, Germany. Du E-mail: [email protected]

are high priority research goals. However, at present, there is no structured framework for obesity prevention and numerous proposals for research and future directions have been suggested.1 – 3 Despite the national importance of obesity and costs to health services there are no nationally coordinated strategies for research and development in this area. Up to now only a few human studies have investigated the prevention of obesity. This may be explained by (i) lack of effective prevention strategies; (ii) underfunding of public health and obesity research; (iii) problems identifying risk individuals and groups; (iv) limited knowledge about the pathophysiology of obesity; and (v) practical preventive skills and public health training are not regular parts of

Prevention of obesity MJ Mu¨ller et al

S67 medical education. The latter point is in part due to public health professionals, many of whom regard their subject as population-based and outside the clinical domain. Vice versa clinicians sometimes feel that epidemiology and public health are inferior to clinical research. Obesity is a public health problem and needs to be addressed from a population or community perspective as well as with respect to the individual subject.2 In practice different levels of prevention strategies aimed at multifactorial conditions such as obesity have been used. First, intervention strategies are directed at everyone in a community with the aim to stabilize or to reduce the mean body mass index (BMI) in a population (ie universal prevention2). In addition, selective prevention is directed at high risk individuals (eg children of obese parents). It is concerned with improving the knowledge and skills of people to increase autonomy and thus prevent weight gain. Third, targeted prevention is directed at overweight and obese individuals to prevent further weight gain and=or to reduce body weight. At present there are no comprehensive population-wide strategies to specifically tackle the problem of obesity. Obesity prevention strategies have been integrated into community-wide programmes preventing coronary heart disease (eg the North Carelia Project.4) These interventions consisted of mass media education, and worksite and school-based programmes to integrate prevention strategies into community structure. Although capable of significantly reducing coronary heart disease risks and mortality, universal prevention was without effect on BMI in the North Carelia Project.4 Most authors consider selective prevention as prevention of weight gain in children and in adults in schools and in the wider community,5,6 and various degrees of effectiveness were reported. Few researchers7 – 9 have shown effective management of overweight and obese children as a measure of prevention of adult obesity. These authors were most successful when children were treated together with their parents. In that study the follow-up period lasted up to 10 y.9 The effectiveness of these family-based and lifestyle interventions was well documented by weight changes, a reduced prevalence of obesity as well as lifestyle changes.10 The studies mentioned above can be summarised as follows: although all experts agree that obesity prevention has high priority there is almost no research in this area. The effectiveness of different intervention strategies is not well documented. Regarding universal prevention little rigorous evaluation has been carried out. Selective prevention exhibited various degrees of effectiveness but at present definitive statements cannot be made because of the limited number of studies as well as limits in study design. Finally, targeted prevention produced promising results in children when compared to no treatment. There is no clear idea about comprehensive interventions studying combinations of different strategies. It is tempting to speculate that predictors of treatment outcome (eg psychological and sociodemographic factors) may serve as barriers to preventive strategies, but this has not yet been investigated.

Some authors assume that early intervention in a paediatric population is superior to intervention strategies directed at adults.1 – 3,11 Specific periods for the development of overweight and obesity have been identified in children. These include the prenatal period, the period between the ages 5 and 7 (so called adiposity rebound) and adolescence.11 Although most people become obese as adults there is a significant association between BMI in childhood or adolescence and in adults.12 – 15 The persistence of obesity into adulthood appears to rise linearly throughout childhood. In addition childhood overweight was shown to be predictive for adult morbidity and mortality.14 – 16 Antecedents of adults disease (hypertension, hyperlipidemia, abnormal glucose tolerance) occur with increased frequencies in obese children and adolescents. However there is a lack of longterm follow-up data spanning childhood to adulthood period.15 Taken together these data suggest life-long persistence and health consequences of overweight and obesity in many children. Preventive strategies should therefore consider critical periods of early onset of obesity. It has been proposed, that prevention of paediatric obesity may be the only effective treatment of adult obesity.1 Prevention strategies aimed at childhood obesity are based on the knowledge of risk factors. Risk factors of childhood obesity included parental fatness, social factors, birth weight, timing or rate of maturation, physical activity= inactivity, dietary factors (including early infant feeding practices), and other behavioural and psychological factors.15 These risk factors are related but their relationship is unclear at individual as well as at population level. Although most risk factors for obesity seem to be self evident, their confounding or cumulative effects on the development of obesity as well as their clustering and their effects over time on the casual pathway to the development of obesity remain unclear with respect to a given individual as well as with respect to a greater population of obese subjects. From a public health point of view some of the risk factors are modifiable but others cannot be changed and, thus, are not a target of intervention strategies. It is generally accepted that action is primarily required at societal level to counter the environmental influences on physical activity and dietary intake. Regarding obesity prevention emphasis is now more on physical activity rather than on dietary changes. Based on (i) our current and limited knowledge and (ii) the idea that prevention of childhood obesity is an effective treatment of adult obesity, the Kiel Obesity Prevention Study (KOPS) was started in 1996. Concept, intervention strategies and first results of KOPS are reported in this paper. KOPS is an ongoing 8 y follow-up study. We first enrolled a large scale cohort of 5 to 7-y-old children providing sufficient baseline data. These cross-sectional data will be further extended by longitudinal data sets allowing analyses of changes over time and intraindividual comparisons of the parameters obtained. A control group and two intervention groups are followed. Interventions took=take place at schools for all children, parents and teachers as well as in families of overweight International Journal of Obesity


S68 and obese children and parents. KOPS allows further analyses of the role of individual risk factors as well as of longterm effectiveness of different intervention strategies.

Methodology Setting The KOPS is being conducted in collaboration with the school physicians as well as the teachers at different schools in the city of Kiel, northwest Germany. In addition a sports programme for overweight children was developed together ¨ r Sportwissenschaften der Universita¨t Kiel with the Institut fu (chair Professor H Rieckert).

Study participiants Five to 7-y-old children were=will be recruited from 1996 to 2002. Data were randomly sampled in different parts of Kiel, the capital of Schleswig Holstein, northwest Germany, a city with about 231 000 inhabitants. There were no eglibility criteria except willingness to participate. General recruiting took place as part of health examinations by the school physicians. The study was approved by the local ethical committee. All parents gave their informed written consent. Every year about 30% of the total population of 5 to 7-y-old children in Kiel examined by the school physicians could be enrolled. Up to 1999, 2440 5 to 7-y-old children were recruited. Basement recruitment included (i) assessment of the nutritional state by anthropometric methods as well as bioelectrical impedance measurements;17 (ii) dietary assessment by a standardised food frequency questionnaire;18 (iii) assessment of physical activity and social state by different questionnaires,19 – 21 risk factors (blood pressure, blood glucose, cholesterol, triglycerides by standard procedures) and

Figure 1

Flow chart of the Kiel Obesity Prevention Study (KOPS).

International Journal of Obesity

resting as well as 24 h energy expenditure, physical activity, muscle strength and physical fitness in a subgroup of children.22,23 Representativity of the cohorts was tested and assured by comparing sociodemographic as well as nutritional data (body weight, height, BMI) with the total group of 5 to 7-y-old children born in 1989 in Germany and investigated by the school physicians in Schleswig Holstein.24 This group consisted of 25 338 5 to 7-y-old children (12 289 girls, 13 049 boys) which were 92.6% of all children born in Schleswig Holstein, the capital of Schleswig Holstein, in 1989. Using 1978 reference data for height and weight of children in northwest Germany25 the prevalence of overweight and obesity was estimated to be 17.6 and 18.5% in girls and boys, respectively.24 In KOPS, overweight and obesity were defined by triceps skinfold thickness (TSF) as a parameter of fat mass. The present data were compared with a 1978 database for children in northwest Germany;25 the 90th TSF percentile (14.5 and 12.9 mm for girls and boys, respectively) was used as a cut-off value.

Study design The flow chart of the study is presented in Figure 1. All children will be reinvestigated after 4 and 8 y. In 2000 we had just started to re-investigate the 1996 cohort of KOPS. Following basement assessments (between 1996 and 2002) two different interventions were performed (see Asbeck et al26 for further details of the different intervention strategies). First, a school intervention aimed at nutrition education and health promotion for all children, their parents as well as their teachers was performed in three schools (‘intervention schools’) every year. Data obtained in the ‘intervention’ schools were compared with data obtained in three sociodemographically matched ‘control’ schools. Every alternat-


S69 ing year schools changed and the ‘control’ schools became ‘intervention’ schools and vice versa. In addition family intervention plus a structured sports programme were offered to families with overweight or obese children and also to families with normal-weight children but obese parents. Because of different levels of acceptance it was not possible to randomise family intervention. All subjects are going to be re-investigated after 4 (at 9 – 11 y) and after 8 y (at 13 – 15 y) using identical study measures (see below). We assume a 15% loss of subjects per a 4 y period. The primary hypothesis being evaluated is that participants of the intervention groups will gain less body weight and fat mass over the course of the study than those in the control groups. We hypothesised that the prevalence of overweight increases spontaneously from 22% (5 to 7-y-old children) to 25% (9 to 11-y-old children) and 35% (13 to 15y-old children). The cumulative incidence of overweight in an at risk group (children of obese parents) was assumed to be 12.5% per year. We also assume that about 10% of normal weight 5 to 7-y-old children without risk become overweight at the age of 9 – 11 and 13 – 15 y, respectively. Other questions of interests are whether: (i) the effects of the interventions differ between individuals with different baseline characteristics; and (ii) attitudes of behaviour or other factors (eg familar disposition for overweight and obesity) are predicitive for weight changes, individually or in combination with intervention assignment.

Intervention The intervention programme of KOPS is based on the assumption that attitudes of behaviour or other factors (eg familar disposition for overweight and obesity, low social state) are predicitve for weight changes. Thus, in general prevention of overweight is possible by a healthy lifestyle. This message is important for all people but it is of particular interest for those carrying a risk (eg familar disposition for overweight and obesity, low social state). Life-style changes are accomplished by increased knowledge, self monitoring, increased self esteem and personal autonomy. Healthy lifestyle can be supported by counseling, education and social support. Within KOPS26 the same behavioural and educational messages are given to all children and their parents. These are (i) eat fruit and vegetables each day, (ii) reduce the intake of high fat foods, (iii) keep active at least 1 h a day, and (iv) decrease TV consumption to less than 1 h a day. These messages were delivered to all primary school children within their first year in three representative schools in Kiel. An 8 h course of nutrition education including socalled ‘active breaks’ was offered by a skilled nutritionist together with a teacher. The messages were also addressed to their parents on a school meeting (parents evening). In addition the teachers were trained regularly by a structured nutrition education programme within a continuation class ¨ r Theorie and Praxis in der Schule (IPTS), Kron(Institut fu

shagen, Germany). In addition to ‘school interventions’ for all children, parents and teachers, families with overweight and obese children and=or obese parents (BMI >30 kg=m2) were offered a face-to-face counselling and support programme within the family environment. The family intervention consisted of three to five home visits organised by a nutritionist. Family counseling considered personal preferences of individual family members and was based on the strucure, organisation and lifestyle (diet, activity) of children and parents within the family. Parents were instructed to monitor food intake and activity of the children using a protocol. Reinforcement and corrections (eg in the case of so-called externality of eating as in the case of eating in response to food availability or social eating) were done on the basis of the individual behaviours. Individual counselling and organisation within families (eg ‘shopping’, ‘cooking’, ‘resetting the family table’) was performed at three to five different occasions within a period of 3 months. Special attention was paid to healthy food choices for between-meal eating. In 1997 and 1998 a 6 month structured sports programme (twice a week) was also offered to overweight ¨ r Sportchildren. This was organised in the Institut fu wissenschaften (Sportsciences) of the Christian-AlbrechtsUniversita¨t zu Kiel. Materials used for education and ¨r counselling were purchased from the Bundeszentrale fu Gesundheitliche Aufkla¨rung (BzGA, Bonn, Germany), ¨ r Theorie and Praxis in der Schule (IPTS), KronsInstitut fu ¨ nchen, Germany and hagen, Germany, Institut Danone, Mu ¨ r Erna¨hrung, Frankfurt, Germany. Deutsche Gesellschaft fu The materials and programme were used for school education as well as for face-to-face interventions within families. Available materials were used because it is our intention that interventions of KOPS, if proven beneficial, can be easily repeated by other authors.

Study measures Demographics. Age, education, current marital state, employment, social state and ethnicity (by questionnaire), were recorded. Nutritional state. Body weight, height and BMI (children, parents, grandparents), body composition (anthropometry, bioelectrical impedance analysis in children) were measured. Diet and activity. Food frequency and activity questionnaires were administered. Assessment of energy expenditure, physical activity and fitness by indirect calorimetry, 24 hheart rate monitoring and spiroergometry was carried out in a subgroup of children. Risk, comorbidities. These comprised birth weight, duration of pregnancy, lactation, development of weight and height (children); smoking, alcohol, drugs (parents); blood pressure, blood cholesterol, triglycerides, glucose (children); diseases (children, parents, grandparents). International Journal of Obesity


S70 Study participation and acceptance. Study participation was defined as the percentage of complete datasets (measurements plus questionnaires). Regarding intervention, participation was defined for those who attented all meetings. Acceptance was defined as percentage positive responses= changes from the participants.

Statistical analysis All analyses were done using standard statistical software (Excel 5.0, SPSS, Statview). Baseline characteristics of the participants of the study were examined. The following analyses were performed. First, using baseline data the characteristics described (demographics, lifestyle habits, risks and comorbidities) were compared between groups of children differing with respect to their nutritional state. Second, baseline characteristics plus nutritional state were compared with respect to social state. Third, the effect of intervention was assessed after a 1-y follow-up by intraindividual comparisons. The primary outcomes were changes in BMI and fat mass. Secondary outcomes were changes in health-related behaviours and comorbidities. Demographics, nutritional state, risks, comorbidities and baseline diet and exercise were used as covariates. Changes in BMI and fat mass as well as health-related behaviours were also compared between children in ‘intervention’ and in ‘control schools’.

First results of KOPS Baseline measurements From 1996 to 1999 a representative group of 2440 5 to 7-yold children were recruited (ie 30.2% of the total population of 5 to 7-y-old children examined by the school physicians in Kiel) and a full data set was obtained from 1640 children. From these children 340 (20.7%) were considered as over-

weight and obese, 1108 children (67.6%) were normal weight and underweight was found in 192 children (11.7%). Of the normal weight children, 31% or 346 (21.1% of the total population) were considered to be at risk of becoming obese because of parental obesity (BMI of at least one parent above 30 kg=m2; n ¼ 109, 6.6% of the total population), high birth weight (>4000 g in 135 or 8.2%) or stunting (ie below the 10th percentile for age adjusted body height; n ¼ 105 or 6.4%). In addition children with low birth weight ( < 2500 g at a gestational age of 38 – 42 weeks; n ¼ 40 or 2.4%) were also considered to be at risk for nutritionrelated diseases. Based on these data and ongoing recruitment up to the year 2002 we assume a total KOPS population of 3890 children (856 overweight and obese, 2645 normal weight and 389 underweight; 817 normal weight children are considered to be at risk of becoming overweight and=or obese). There were no sex differences in the prevalence of overweight as well as in the different risk groups. Body composition analyses showed that comparing recent data with previous reference data the 90th TSF percentile increased by 10.3 and 13.2% in girls and boys, respectively (Figure 2). Our cross-sectional data did not provide evidence for the ideal that attitudes of food intake are predictive for overweight.18,21 The frequency of individual food choices as well as an overall diet quality index did not differ between overweight, normal weight and underweight children. By contrast mean BMI as well as the prevalence of overweight were increased in children with low activity as well as in children with a high TV consumption (>1 h when compared to < 1 h per day).19 Children with a high TV consumption more frequently had unhealthy food choices, suggesting a accumulation of unhealthy behaviours.19 A high level of physical inactivity together with unhealthy food choices were more frequently seen in children from families with a low social

Figure 2 Distribution of triceps skinfolds (TSF) in 1640 5 to 7-y-old children (847 boys, 793 girls). KOPS data were obtained between 1996 and 1999. These data were compared with reference for 5 to 7-y-old children in northwest Germany from 1978 published by Reinken et al.25



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Figure 3 Social gradient of the prevalence of obesity (left panel) and BMI (right panel) in 1350 5 to 7-y-old children investigated between 1996 and 1998. Social state was characterised by parental school education according to the highest achieved school level of either mother or father. Low, 9 y, middle 10 y and high 13 y of school education. The differences are significant (w2-test: P < 0.05; Kruskal – Wallis test: P < 0.05).

state.20 In 5 to 7-y-old children there is a linear social gradient in unhealthy behaviours.20 In addition an inverse social gradient is observed for BMI and the prevalence of obesity: the highest prevalence of overweight as well as the highest mean BMI is observed for low social class children (Figure 3). The social gradient is more pronounced in chil¨ ller, dren of obese parents (K Langna¨se, M Mast, MJ Mu unpublished data).

Interventions Between 1996 and 2000 school interventions targeted a total of 414 children and their parents as well as 30 teachers. In addition, 92 out of 368 eglible families completed the family intervention programme. The acceptance of school intervention reached 87%, 75% and 100% of children, parents and teachers. In all, 48% of eglible families were visited at least for one session; 25% of the families completed the programme. The short-term effects were studied for all children within 3 months after the end of the interventions. As a result of school interventions good nutrition knowledge (as assessed by a questionaire) was observed in 60 instead of 48% of the children (ie an increase in 25%). In addition daily physical activities were reported by 65 instead of 58% (ie an increase by 12%). Concomitantly, a further 28% of the children became members in a sports club. Regarding family intervention daily fruit and vegetable consumption increased by 50% (from 40 to 60% of the children). Concomitantly the

frequency of daily intake of low fat food increased from 20 to 50%. Daily physical activity also increased and was observed in 68 instead of 50% of the children. This increase was associated with a decrease in TV watching from a mean value of 1.9 h to 1.6 h=day. All changes became significant at P < 0.05. The nutritional state of children in the ‘intervention schools’ was reassessed after a period of 1 y. Data were compared to nutritional state of children in ‘control schools’. Figures 4 and 5 show the 1 y changes in anthropometrically derived fat mass in overweight children in ‘intervention’ as well as in ‘control’ schools. During 1 y there is a significant change in fat mass in both groups. When compared with children of ‘intervention schools’ children of ‘control schools’ showed disproportionate increases in (i) the median TSF (mean values of 13.0 vs 11.3 mm at 1 y follow-up, P < 0.01; Figure 4) as well as in (ii) percentage fat mass of overweight children (increase by 3.6 vs 0.4%, P < 0.05; Figure 5).

Discussion There are only a few studies on obesity prevention in children.7 – 9,27 – 35 Although different with respect to study populations, study design and intervention strategies, most studies showed some improvement in health-related behaviours as well as nutritional state of children. The strategies applied are targeted prevention directed at overweight and obese children. In addition strategies aimed at school International Journal of Obesity


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Figure 4 Distribution of triceps skinfold (TSF) in 297 children (136 in the intervention group and 161 in a sociodemographically-matched control group) at baseline and after 1 y with or without school-based intervention. When compared with the control group there is a significant shift in the distribution of TSF 1 y after intervention (P < 0.01), whereas no group differences in the distribution of TSF were observed at baseline.

Figure 5 Anthropometrically derived percentage fat mass in overweight and obese children (n ¼ 25) before and 1 y after intervention. Data were compared with data obtained in children of sociodemographically-matched ‘control schools’ (n ¼ 25). See text for further details (P < 0.01) in ‘control schools’, P < 0.05 in ‘intervention schools’ for intraindividual changes before and after 1 y. P < 0.05 for group differences in changes of % fat mass.



S73 children populations were used. Targeted prevention in overweight and obese children was most successful when children were treated together with their parents. There is only one long-term follow-up study on a total population of 76 (entrance) and 61 (follow-up) obese children aged 6 – 12 y.9 In that study, follow-up period lasted up to 10 y. Families were randomised to three different groups and were provided with eight weekly meetings and six additional meetings during a period of 6 months. The effectiveness of family-based and lifestyle interventions was well documented by decreases in percentage overweight (77.5 vs þ 14.3%9,10). These are promising results. However the data also reflect the limits of prevention strategies. The mean values of changes in nutritional state and health habits may camouflage that preventive strategies are more effective in some but without or even negative effects in other subjects. At present we do not have measures to identify suitable responders for intervention strategies. When compared to the studies mentioned above, KOPS offers unique opportunities (Figure 1). It combines different prevention strategies directed at a group of 5 to 7-y-old children. In a representative cohort of 5 to 7-y-old children in Kiel KOPS aims to reduce the mean BMI in the whole population by concerted school interventions directed at children, parents and teachers. In addition, family intervention is directed at high risk individuals (eg children of obese parents) as well as at overweight and obese individuals to prevent weight gain and=or to reduce body weight. KOPS is a longitudinal study. First results of a short-term follow-up (up to 1 y after intervention) are promising. They show some improvement of health-related behaviours as well as nutritional state in children (Figures 4 and 5). The baseline data of KOPS document that overweight and obesity is a considerable and increasing problem even in the group of young children (Results, Figure 2). The first analysis of our data also shows that we have to deal with a heterogenous group of children. Regarding health-related behaviours low physical activity and high inactivity but not unhealthy food choices were associated with a higher prevalence of overweight. The lack of association between unhealthy diet and overweight may be in part explained by (i) the weakness of a food frequency questionnaire and (ii) the fact that we analysed cross-sectional instead of longitudinal data. We would like to discuss these points as follows: (i) at present there is no quantitatve instrument for the assessment of nutrient intake in 5 to 7-y-old children; and (ii) we are just reinvestigating the first cohort of KOPS which gives us the opportunity for a longitudinal analysis of diet and activity data. Given that our cross-sectional data are a true reflection of risk factors contributing to overweight and obesity in children, a low level of physical activity and high physical inactivity seem to be more important than diet. Thus, regarding obesity prevention emphasis should be paid more on physical activity rather than on dietary changes. However since both diet and activity are variable in children and

obviously could not explain most of the variance in fat mass (see Results) further determinants of childhood obesity have to be considered. In KOPS familar disposition and social state are considered as further covariates. It is obvious from our first analysis of data that besides health-related behaviours parental obesity and a low social state are associated with an increased mean BMI and a higher prevalence of overweight in children (Results, Figure 3). Both covariates add to each other and the highest mean BMI is seen in children with two obese parents ¨ ller, and a low social status (K Langna¨se, M Mast, MJ Mu unpublished data). These differences between children differing with respect to parental fatness could not be fully explained by differences in health-related behaviours. A similar and linear social gradient was seen in children differing with respect to parental fatness. These data suggest that there is an inverse social gradient in unhealthy behaviours. The manifestation of health risks in terms of overweight is strongly affected by parental fatness. Thus, simple messages (eat fruit and vegetables each day, reduce the intake of high fat foods, keep active at least 1 h a day and decrease TV consumption to less than 1 h a day) may not counter the whole problem. It is tempting to speculate that a simplifying approach (which is necessary in preventive medicine) will weaken the success of the intervention. At present we feel that targeted intervention directed at children with obese parents and a low social class should be encouraged. However it is well documented that middle and high class as well as intact families were able to benefit better from treatment than families sharing other characteristics.9 Part of these experiences may be due to prevention strategies promoting diet, nutrition and exercise education. Future interventions should therefore consider that, besides traditional counselling and information, we should use other strategies directed at social support of individual families as well as better school education for children. In the long-term these strategies will help to improve the knowledge and skills of individuals and hopefully reduce the steady rise in the prevalence of obesity. Obesity prevention is necessary to address the steady rise in the prevalence of obesity. However there are almost no studies in this area. The results of previous studies as well as first results of KOPS are promising. Simple messages cannot solve the whole problem. Conventional prevention strategies are of limited value in high risk groups. Besides health promotion, a better school education and social support seem to be promising strategies for future interventions.

Acknowledgements The authors wish to thank all coworkers, teachers, parents and children as well as the school physicians of the city of Kiel. KOPS was supported by Deutsche Forschungs¨ 714 5-1 and 5-2), Schwartauer gemeinschaft (DFG Mu Werke AG, Bad Schwartau, Team Success AG, Selent, Else ¨ ner Stiftung, Bad Homburg, Hansa Tiefku ¨ hlmenu ¨ , Hilter, Kro International Journal of Obesity


S74 Data Input, Frankfurt and Wirtschaftliche Vereinigung Zucker, Bonn.

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