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

BMJ 2004; 328 doi: (Published 20 May 2004) Cite this as: BMJ 2004;328:1237

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Childhood obesity and consumption of fizzy drinks. Both diet and exercise play an important role in obesity

The statement by James et al suggesting that carbonated drinks
contributes to childhood obesity was supported in a cross-sectional study
conducted on 93 Primary School children aged 10-11 from three different
schools in Birmingham in March 2004. The aims of this study were to
examine how large a factor diet and exercise play in determining a child’s
Body Mass Index (BMI).

Questionnaires were given out at random consenting schools across
Birmingham, and parental consent was obtained for each child to be
involved in the study. The questionnaire focused on the lifestyle and
dietary intake of each child. Of the 93 study subjects, 1% were
underweight, 69% were of normal weight, 18% were overweight and 12% were
obese, according to the standard classification of BMI for children1. 39%
of normal and underweight subjects participated in greater than 5.5 hours
of exercise a week, compared to 24% of overweight and obese subjects.
This was not statistically significant, but other studies2 have produced
similar trends which have been significant, suggesting the result is most
likely to be a valid reflection of reality. Analysis by logistic
regression showed that low levels of exercise (<2 hrs/wk) may increase
the risk of obesity by up to 30 times, compared to high levels of exercise
(>5.5hrs/wk). However, a child’s estimation of the time spent doing
various activities may be unreliable due to the difficulties in measuring
this quantity.

The questionnaire also asked about the intake of junk food, which
consisted of carbonated drinks, sweets, chocolates and crisps. Despite
the study showing that low levels of junk food appeared beneficial in
preventing children from becoming obese, no conclusive evidence was found
to link junk food intake with BMI.

Therefore, exercise has been found to play a significant role in a
child’s weight, which corroborates opinions expressed by Des Spence3, in
reference to the study by James et al4. However, contrary to the former’s
belief that “Childhood obesity is not caused by diet”, obesity has a
multifactorial cause5, of which diet plays a significant part; and despite
our study having no conclusive evidence for junk food (which includes
carbonated drinks) affecting a child’s weight, the study population was
not large enough to definitely rule out a large intake of junk food as a
causative factor. Hence, our study offers support to James et al’s
statement that the consumption of carbonated drinks, sweetened with sugar,
contributes to obesity in children.

1 Cole TJ, Freeman JV, Preece ME. Boys and girls BMI chart, Body Mass
Index reference curves for the UK, Arch Dis Child 1995;73:25-29

2 Tremblay MS, Wilms JD. Is the Canadian childhood obesity epidemic
related to physical inactivity? International Journal of Obesity

3 Spence, D. Childhood obesity and consumption of fizzy drinks, diet
is not that important in obesity. BMJ 2004;329:54 (3 July)

4 James J, Thomas P, Cavan D, Kerr D. Preventing childhood obesity by
reducing consumption of carbonated drinks: cluster randomised controlled
trial. BMJ 2004;328:1237 (22 May)

5 Prentice Am. Overeating: The health risks. Obesity research

Competing interests:
None declared

Competing interests: No competing interests

19 July 2004
Amy L Chue
Medical Student
Elen Evans, Victoria Field, Kirsty Murdoch
University of Birmingham