December 13, 2011

Childhood obesity can be prevented - Cochrane

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By BMJ 2011;343:d8014

Strategies to promote healthy eating and physical activity in schools and other settings are effective in preventing childhood obesity, says an updated Cochrane Collaboration review released last week.

The publication is an update of a 2001 review that reached more equivocal conclusions when last updated in 2005. It includes 55 studies of interventions targeting children up to age 18 years, with most involving children aged 6 to 12 years.

The review’s lead author, Professor Elizabeth Waters, the Jack Brockhoff chair of child public health at the University of Melbourne, told the BMJ that the most effective interventions sought to change social and physical environments and norms, rather than just individual behaviour.

These included policies for healthy eating and physical activity in schools and early childcare settings, support for teachers and other staff to do health promotion, and support from parents and at home for children to eat better, move more, and spend less time looking at screens.

The review found that the best estimate of effect on body mass index (BMI) (kg/m2) was a reduction of 0.15, or a 0.4-1.6% reduction in individual weight, which would correspond to a “small but clinically important shift in population BMI if sustained over several years.”

Professor Waters said: “The implication of this is quite remarkable—were these programmes able to be implemented across the population, we can be confident that this would translate into a reduction in body weight that would have substantial effects on the consequent child health concerns, such as the rising rates of diabetes.”

She said that policy makers with responsibility for schools and other settings where children spent time had a responsibility to act.

“By not putting in place these strategies, which we know work, the health of children will be affected as obesity rates are predicted to continue to rise,” she said.

The review’s authors said there was now so much evidence about the impact of interventions in children aged 6 to 12 that further such trials in this age group seemed unnecessary.

“Childhood obesity prevention research must now move towards identifying how effective intervention components can be embedded within health, education and care systems and achieve long term sustainable impacts,” they wrote.

However, the review found “substantial unexplained heterogeneity” in the size of intervention effects, and the authors suggested this could reflect “small study bias.”

Professor Boyd Swinburn, director of the World Health Organization’s Collaborating Centre for Obesity Prevention at Deakin University in Melbourne, said policy makers must now respond to the challenge of rolling out the interventions widely. But he cautioned that the review findings did not absolve governments from taking broader action at a population level to tackle junk food marketing and to ensure better regulation of food labelling.

Jane Martin, senior policy adviser for the Obesity Policy Coalition, an organisation that campaigns for change in policy and regulation to help prevent obesity, said the findings reinforced the importance of such broader policy actions to ensure maximum return from investment in school and community interventions. The strategies identified by the review could be even more effective if not counteracted by the influence of junk food marketing, she said.

“A comprehensive approach at all levels of government and society are so important,” said Ms Martin, adding: “You can control the availability in schools, but governments should be looking at controlling the placement of fast food outlets close to schools and the marketing of unhealthy foods overall.”

The review also identified several gaps in evidence, and the authors called for more studies to develop, implement, and evaluate prevention interventions in young children and adolescents.

They also want better reporting of the impact of interventions on health inequalities and of potential harms of interventions. The review noted that none of the eight studies targeting adolescents explicitly reported unintended outcomes or measures of harm, despite body image sensitivities in this age group.

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