Primary care Preventing childhood obesity by reducing consumption of carbonated drinks: cluster randomised controlled trial

Objective To determine if a school based educational programme aimed at reducing consumption of carbonated drinks can prevent excessive weight gain in children. Design Cluster randomised controlled trial. Setting Six primary schools in southwest England. Participants 644 children aged 7-11 years. Intervention Focused educational programme on nutrition over one school year. Main outcome measures Drink consumption and number of overweight and obese children. Results Consumption of carbonated drinks over three days decreased by 0.6 glasses (average glass size 250 ml) in the intervention group but increased by 0.2 glasses in the control group (mean difference 0.7, 95% confidence interval 0.1 to 1.3). At 12 months the percentage of overweight and obese children increased in the control group by 7.5%, compared with a decrease in the intervention group of 0.2% (mean difference 7.7%, 2.2% to 13.1%). Conclusion A targeted, school based education programme produced a modest reduction in the number of carbonated drinks consumed, which was associated with a reduction in the number of overweight and obese children. Introduction Obesity in children has reached epidemic proportions. Ultimately energy imbalance is the reason for excessive weight gain, whether the main cause is genetic, endocrinal, or idiopathic. A contributory factor seems to be the consumption of carbonated drinks sweetened with sugar. These have a high glycaemic index and are energy dense. Children who drink one regular carbonated drink a day have an average 10% more total energy intake than non-consumers. In the United Kingdom more than 70% of adolescents consume carbonated drinks on a regular basis. Although school or family based programmes that promote physical activity, modification of dietary intake, and reduction of sedentary behaviours may help reduce obesity in children, few have been effective. Recently the United Kingdom based active programme prompting lifestyle in schools (APPLES) reported the effects of multiple interventions on obesity in children. The programme included teacher training, modification of school meals, action plans within the curriculum, changes to the tuck shop, physical education, and playground activities. Despite these initiatives there was only a modest increase in consumption of healthy foods such as vegetables without any change in obesity rates. In contrast, there is a paucity of studies on single factors considered to be important in obesity in children. We aimed to determine if a school based educational programme for reducing consumption of carbonated drinks could prevent excessive weight gain in children. Participants and methods The Christchurch obesity prevention project in schools (CHOPPS) took place between August 2001 and October 2002 over one school year. The project was based in six junior schools in children aged 7 to 11 years. Outcome measures Anthropometric measurements were taken at intervals of six months. Height (without shoes) was measured by one investigator (JJ) to the nearest 0.1 cm with the Portable Leister height measure (Seca, Marsden, United Kingdom). Weight (in light clothing) was measured to the nearest 0.1 kg on medical scales (Seca 770, Marsden). Waist circumference was measured according to published centile charts. We converted body mass index (weight (kg)/(height (m))) to standard deviation scores (or z scores) and to centile values using the British 1990 growth reference disc (Child Growth Foundation, London). The children completed diaries at baseline and at the end of the trial on drinks consumed over three days. Records were made over two weekdays and one weekend day. Collecting dietary data in this way has been shown to provide comprehensive results. Intervention One investigator (JJ) delivered the programme to all classes. The main objective was to discourage the consumption of “fizzy” drinks (sweetened and unsweetened) with positive affirmation of a balanced healthy diet. We thought the children would respond best to a simple, uncomplicated message so they were told that by decreasing sugar consumption they would improve overall wellbeing and that by reducing the consumption of diet carbonated drinks they would benefit dental health. A one hour session was assigned for each class each term. Teachers assisted in the sessions and were encouraged to reiterate the message in lessons. The initial session focused on the balance of good health and promotion of drinking water. The children tasted fruit to learn about the sweetness of natural products. In addition, each class was given a tooth immersed in a sweetened carbonated cola to assess its effect on dentition. The second and third sessions comprised a music competition; each class was given a copy of a song (Ditch the Fizz) and challenged to produce a song or a rap with a healthy message. The final session involved presentations of art and a classroom quiz based on a popular television game BMJ Online First bmj.com page 1 of 5 Cite this article as: BMJ, doi:10.1136/bmj.38077.458438.EE (published 27 April 2004) Copyright 2004 BMJ Publishing Group Ltd show. The children were also encouraged to access further information through the project’s website (www.b-dec.com). Statistical methods We undertook a cluster, randomised controlled trial. Clusters were randomised according to a random number table, with blinding to schools or classes. Sample size was estimated based on data from a pilot study conducted in the same geographical area. In the pilot, 54% (n = 149) of children gave consent, of whom 71% (n = 108) completed drink diaries. From this we predicted that we needed an average of 12 children in each class. The standard deviation of carbonated drink consumption in the pilot was 0.6 glasses (average glass size 250 ml) a day, therefore a study of this sample size (31 clusters with an average of 12 children) would have 90% power to detect average reductions each day of 0.9, 0.7, and 0.6 glasses over three days using intracluster correlations of 0.1, 0.05, 0.01, and 0.001. Data were analysed using SPSS (version 11) with a 5% significance level. Data for interval scaled measurements for each cluster were derived by averaging all individual measurements for the children in the cluster, and dichotomous data were derived by calculating the proportion in the cluster. These were our summary measures, with clusters as the unit of analysis. All measures were normally distributed. We used the independent sample t test to establish significance between intervention and control clusters and the paired t test to establish the significance of changes within clusters. Intracluster correlation coefficients and 95% confidence intervals were calculated by using Searle’s method, with adjustment for variable cluster size.