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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The first study, ‘Preventing obesity by reducing consumption of carbonated drinks: cluster randomised controlled trial’ (James, Thomas, Cavan and Kerr, 2004) aims to reduce the consumption of carbonated drinks in 615 children aged 7-11 years old via the delivery of a focused educational programme on nutrition in schools. This study utilises a cluster, randomised controlled experimental design. The actual procedure is really rather complicated and lacks detail as in it leaves the reader with more questions than answers and because of this, accurate replication would likely be difficult. For example, it is not clear precisely how much time and method of delivery was devoted to each component; discouragement of ‘fizzy’ drinks, affirmation of a balanced healthy diet, drinking water, presenting art, writing songs/raps outlining healthy messages. And as a result of this it is impossible to identify which aspects were actually effective and which were unnecessary. There is no effort to detail exactly how these messages were delivered to the participants apart from the considerations they made with regards to the young age of the participants. The researchers tailored the study in many ways to try to make the programme accessible to children. Firstly they did this by keeping the message simple; ‘by decreasing sugar consumption they would improve overall well-being’, to presumably help the children understand the message though this is not explained and there is no reference to previous research to justify this. Secondly, the study incorporates a music competition for the participants to write a song or rap with a healthy message and also produce and present pieces of their own art. Once again there is no rationale for this but is probably used to get the participants involved and thinking about the message and to hold their attention. Clearly this would not be likely to be utilised in a study using adults as participants and is more appropriate to childhood intervention. The song writing and art presentations sound like very appropriate methods for this intervention and demonstrate the importance of the Lifespan approach when designing interventions to reach children but unfortunately there is absolutely no indication of how these were implemented or more importantly the impact that they might have had. It would have been very interesting to read feedback of a qualitative nature about any difficulties they had implementing this and whether the children really became involved or not. In a perfect world one could imagine all the children in a class competitively and enthusiastically painting and singing and drinking water in their element but is that a realistic approximation? After all, the interpretation of the results hinges on these details.

On the positive side, the participants in the sample were representative of the target population as this is aimed at reducing/preventing childhood obesity and the size of the sample was large enough for the number of measures and the effect size. The clusters (in this case class) were randomly associated to either intervention or control group and written consent was sought from both parents and participants. It is claimed that each group were similar and equally distributed in terms of age, sex and consumption of sweetened carbonated drinks but there is no statistical test to confirm this. One problem with the sampling, which the researchers point out, is that school s contained classes both in the experimental and the control group and therefore it is possible that ‘transfer of knowledge may have taken place outside the classroom’ with participants discussing the different conditions amongst themselves.

The measures taken are very empirically dubious. The participants were asked to keep a three day diary both at the beginning and at the end of the intervention (over one school year) and keep record of the drinks that they consumed. It is doubtful whether this could be regarded an appropriate method of collecting data considering the sample used. Is it feasible to ask a 7 year old to keep an accurate diary indicative of the complete beverages they have consumed? This is a poor method of measurement with participants as young as this and indeed this was reflected in the low number of completed diaries they received both at baseline and the climax of the intervention. This resulted in a biased result as the only data they received was from children motivated to keep the diary and it is questionable how accurate these will have been in any case. The anthropometric measurements were however a more appropriate method of measurement. After the year long intervention the percentage of obese/overweight participants had reduced in the intervention group whereas the percentage had increased in the control group. This does indeed indicate that the intervention did have a positive effect on the participants’ health; it is just unclear precisely which elements are responsible for this as the intervention aimed at healthy eating as well and reducing carbonated drinks. Also, teachers in the intervention group were asked to ‘encourage and reiterate the message in lessons’. This alone could be responsible for the difference and is completely out of the researchers’ control. Some teachers may encourage the health promoting message frequently and others less so if at all. This study could be described as being an amalgamation of multiple attempts to deliver the health promotion message of reducing carbonated drinks and healthy eating to children in various forms with flimsy description of precise procedures but actually in the end it is reasonably successful. It has some interesting methods of engaging the children and because it is multi- faceted it seems to bombard the messages and the results seem to suggest that the do influence the participants’ eating and drinking behaviour.

In line with the Lifespan approach, this study is important because it is targeting children at a time when the instance of childhood obesity is on the increase. By successfully equipping children with the ability to avoid becoming obese, you automatically reduce incidence of future adults becoming obese and techniques that will make a difference over the lifespan. Magarey et al (2003) found that over 70% of obese children went on to become obese adults. Therefore it is important to target children with obesity prevention messages in order to prevent the next generation being obese. This research targeted reduction of carbonated drinks as its main message. This is interesting because children have fairly limited control over what they eat and drink. This is because they are not old enough to shop and cook independently and are therefore likely to be eating similarly to their families or what is available at school. This intervention target carbonated drinks as hey are arguably within a child’s control of consumption. This is therefore highly appropriate along with the general healthy eating message. This study does contribute to existing research as it is set in the school setting and thus reaches its targeted population. There are very few other school based obesity interventions (Ebbeling, 2006)

Competing interests: None declared

Competing interests: None declared

Stephen D East, MSc Health Psychology student + Dual Diagnosis Support Worker

TS10 1RD

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10 May 2006

Please note that the email address for the corresponding author has changed.

Competing interests: None declared

Competing interests: None declared

Janet L James, Diabetes Development Nurse

Bournemouth Diabetes and Endocrine Centre, Royal Bournemouth Hospital, Bournemouth BH7 7DW

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Is there a working explanation for this result in view of the non caloric carbonated drinks?

I have had a personal interest in this concept for some time. For example, what explains the negative impact of carbonated beverages with seborrheic dermatitis? Clearly this is a systemic effect.

I offer the thought of investigating the possible effect of surface disruption of the oral and gastric surfaces by the carbonation and what the consequences of this even may be.

I have some additional thoughts but I'll leave it at a general concept at this point.

Kenneth B. Peterson MD Internal Medicine

Competing interests: None declared

Competing interests: None declared

Kenneth B. Peterson MD, Medical Director at a disease managment firm.

SHPS, 14770 N. 78th Way, Scottsdale, AZ, 85258, USA

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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 2003;27:1100-1105

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 2001;9:S234-S238

Competing interests: None declared

Competing interests: None declared

Amy L Chue, Medical Student

Elen Evans, Victoria Field, Kirsty Murdoch

University of Birmingham

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It's common knowledge that fizzy drinks are bad for you.It is said that a glass of cola contains about 7-8 teaspoons of sugar.Diet colas containing artificial sweetners are equally bad providing just empty calories.If this is the case its no wonder that drinking them increases obesity. Its quite sad to overweight children knowing the health problems they are going to have as adults.But what is more important is what we can do about it?

Its not easy to convince children that something they like and enjoy so much is not good for them especially with the pull of peer pressure and television advertisments.It would be next to impossible in those children whose parents are regular cola drinkers-after all children do learn from their parents!

Its not possible to come up with a magic wand to stop children drinking cokes but we could try our best to develop a healthy diet when they are quite young in life.The first and the most important thing would be for parents to set a good example for their kids.Switch the fizzy drinks for some fresh juice or milk shakes.Take kids out to play,encourage them to enjoy the outdoors instead of spending time in front of the television/ computer.Its time we seriously start thinking of what obesity is going to do for our next generation.

Competing interests: None declared

Competing interests: None declared

sheena surindran, clinical observer

Cottingham 2, kettering general hospital, northants. nn16 8uz

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This study directly targets one very well known factor, i.e., consumption of carbonated drinks rich in sugar in the etiology of obesity in school children, which is a major public health problem and also reported to have multiple biopsychosocial consequences in adulthood, some of which such as myocardial infarction and strokes are fatal while others such as diabetes, musculoskeletal disorder, depressions and eating disorders are chronic in nature. Notably, schools are the places where effective educational messages as evident in this study (1) can get through a large number of targeted population of children and adolescents who have tendency to become pathologically obese.

Certainly, a proportion of children in schools are not obese at all, though they are cosuming carbonated drinks like their counterparts who are obese. Likewise, a proportion of children are obese, though they are not consuming rather avoiding carbonated drinks. Thus, four groups of children could be identified in schools, 1) obese drinking carbonated drinks, 2) obese but not drinking carbonated drinks, 3) not obese but drinking carbonated drinks, and 4) neither obese nor drinking carbonated drinks. Hence, accordingly this study has only addressed and targeted about one quarter of population of school children. One interesting question emerges is that why children not obese and drinking carbonated drinks should or should not continue driking such enjoyable drinks? Simply the answer is "no" because over a two year period or so they are also likely to be obese.

Finally, I feel that the preventive strategies targeting only single etiological factor in the complex disorder like obesity will not have much successful and sustained effective effects on longterm basis.


Janet James, Peter Thomas, David Cavan, and David Kerr. Preventing childhood obesity by reducing consumption of carbonated drinks: cluster randomised controlled trial BMJ 2004; 328: 1237-0

Competing interests: None declared

Competing interests: None declared

Dr.Naseem A. Qureshi MD, IMAPA, LMIPS, Medical Director(A), Director CME&R

Buraidah Mental Health Hospital, Postcode:2292, Saudi Arabia

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Childhood obesity is no doubt a serious health care concern with its deleterious effects on the society as a whole. Measures to decrease its menace should focus at promoting overall healthy lifestyle habits in children rather than focussing on any one aspect responsible for it. Reduction of carbonated drinks undoubtedly reduces the energy consumption and thereby the obesity levels in young children. However an analysis of factors responsible for an increase in these drinks needs to be done to prevent their overconsumption. Studies(1,2) have found out that an increase in the indoor activities like television viewing, working on computers etc. has brought about an increase in the consumption of junk foods and carbonated drinks. This also means a reduction in the outdoor playing activities thereby decreasing the total energy expenditure by the children. These problems are being aggravated by the parental pressures to perform well on the academic front thereby decreasing further the time spent in outdoors by the children. A strategy thus needs to be developed comprising of healthy eating habits, maximising outdoor activities and restricting the number of television viewing hours thereby decreasing the factors responsible for the consumption of junk foods and carbonated drinks and hence their effects on the health of children.

References: 1)Matheson DM, Killen JD, Wang Y, Varady A, Robinson TN.Children's food consumption during television viewing. Am J Clin Nutr. 2004 Jun;79(6):1088-94.

2)Crespo CJ, Smit E, Troiano RP, Bartlett SJ, Macera CA, Andersen RE.Television watching, energy intake, and obesity in US children: results from the third National Health and Nutrition Examination Survey, 1988- 1994. Arch Pediatr Adolesc Med. 2001 Mar;155(3):360-5.

Competing interests: None declared

Competing interests: None declared

Amit K Kapoor, Johnson and Johnson Fellow in Arthroplasty

Sasidhar Yeluri, Jayashree Panwar, Guneesh

Center for Knee Surgery, Baroda, India-390001

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EDITOR--It was interesting to read the paper of James et al (BMJ 2004;328:1237), Preventing childhood obesity by reducing consumption of carbonated drinks: cluster randomised controlled trial.

My comment:
Recently there were many papers on three areas which have psychological, physical, and social consequences on the person concerned and the Society. They were published in different medical journals among which is the BMJ. I was surprised recently about the content of caffeine in many of the popular drinks like Coca Cola and Pepsi! I think the Govermental authorities of which the Health authority is one of them ought to take that seriously before further deterioration.

Thanking you

Competing interests: None declared

Competing interests: None declared

AK Al-Sheikhli, Psychiatrist

Medical centre,Nuneaton,CV11 5HX,UK

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As Professor Greenhalgh aptly notes in her response, perhaps the greatest difficulty ahead will be to disentangle commercial interests of the food industry from the services and needs provided by those in supportive or nurturing roles.

Commercial interests extend to a marketing opportunity for all occasions including dietary regimes for weight loss. Weight-loss and “healthy eating products” are sometimes anything but nutritious if you examine the overall salt, sugar and fat listed in the ingredients.

Currently the mixed health messages on Obesity and nutrition overlook a significant subsection of the adult population who are targeted by media and mimetic desire of next to transparent role models, or through poverty stand beyond it.

I refer you to SACN findings of the national diet and nutrition survey

Perhaps noting: Page 5 Item 12/ Page 11 Item 51/ Page 13 Item 67

Which comments on the shocking rise in soft drink consumption. Though you may also care to consider:

Page 13 Item 69.

Obesity is a very visual measure of unhealthy nutritional status, there is good cause to examine less apparent sectors of the population who may be overlooked by this measure alone (1) You will note that the survey did not encompass those over the age of 64 for whom soft or carbonated drinks may not figure largely in their overall intake. Were they or are they to be considered as a separate and distinct entity in a parallel or future survey for the non-economically productive?

Perhaps an overall goal of achieving an entire population with both equal access to health information and economic ability to purchase affordable nutritionally desirable foods (2) which are not always the most inexpensive, without the accompanying raucous food industry advertising strategies designed to tap into self-image, status desire or inappropriate sponsorships.

Though instigation and maintenance of adequate early nutritional balance is a key message, from a lay “gardening” perspective, any stressor on my tomato plants throughout their lifecycle will alter the nature of the fruit produced, be it shrivelled, swollen or split.

(1) BMJ 1997;315:338-341 (9 August) Evaluation of validity of British anthropometric reference data for assessing nutritional state of elderly people in Edinburgh: cross sectional study Bannerman et al

(2) taf/DynaPage.taf?file=/ejcn/journal/v58/n6/abs/1601889a.html

Dietary intakes of adults in the Netherlands by childhood and adulthood socioeconomic position

Competing interests: None declared

Competing interests: None declared

MC Feliciello, N/a


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27 May 2004

Great study, and underscores clinical intuition about why kids are more obese these days. Wearing my hat of school governor, I've been trying to introduce a healthy eating policy to our local school. It was relatively easy to get the catering contract changed to a company that guarantee to use fresh veg, low salt, less fat etc, but it was much more difficult to influence the policy on soft drinks machines. Reason - the latter are a critical source of income for a cash-strapped school that has seen its budget squeezed in real terms year on year. Sales from vending machines are now used to pay for books and equipment - and I suspect it won't be long before the school advertises for a 'Coca-Cola head of chemistry' or a 'Fanta French teacher'.

Perhaps it's time the BMJ launched a new journal: 'Sugar Control'?

Competing interests: None declared

Competing interests: None declared

Trisha Greenhalgh, Professor of Primary Care

University College London

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