Robert Scragg and Jim Mann: Pop drink studies tip the scales

The opinions on sugary drinks and obesity by Associate Professor Wayne Cutfield and Dr Paul Hofman are not supported by the full range of scientific evidence. They say that the evidence between sugary drinks and obesity is weak, based on their review of three papers.

However, the evidence is much broader than this. A review of childhood studies on sugary drinks and obesity was carried out last year for the Agencies for Nutrition Action, and can be downloaded from their website (www.ana.org.nz).

That report, which one of us co-authored, identified 17 papers on children, of which 12 found a positive association between sugary drinks and obesity and five found no association.

Importantly, there were no studies that found that children who have a high sugary drink intake have lower obesity levels (ie a negative association), which supports the conclusion of a real association between sugary drinks and obesity.

If there was truly no association between sugary drinks and obesity, researchers would expect on the basis of chance to find studies across the range of all three possible types of association - positive, none and negative - which did not happen.

When we looked at the better quality studies, four out of five cohort studies found a positive association between sugary drinks and obesity, as did the single experimental study.

What makes the scientific evidence more convincing for New Zealanders is that we have data from the 2002 national children's nutrition survey which show a positive association between the frequency of sugary drink intake and obesity.

The body mass index (BMI) in children who had three or more sugary drinks per day was 0.9 units higher than in children drinking less than four sugary drinks per week.

This BMI difference is equivalent to an extra 2.5kg in weight (or five tubs of margarine). We can be cautious about overseas studies, but can we afford to ignore such compelling evidence collected from our own children?

Cutfield and Hofman also contend that children get little of their energy from sugary drinks. However, this is not supported by evidence from a survey we are doing in South Auckland high schools.

Out of about 3500 students surveyed, 20 per cent reported they drank three cans (1 litre) of regular non-diet soft drinks on their last school day, with 7 per cent drinking six cans (2 litres) or more. Only 10 per cent reported they had no regular soft drinks in the past five school days.

Given that each can of soft drink, such as Coca Cola, has about 38g of sugar, the above consumption patterns of three and six cans per day contain about 115g and 230g of sugar a day respectively. Since each gram of sugar contains about 16 kilojoules of energy, this represents 19 per cent and 38 per cent of the average daily energy intake of 9500 kilojoules by boys and girls aged 11-14 years reported in the 2002 national children's nutrition survey.

Thus, the scientific evidence shows that a large proportion of New Zealand children get substantial amounts of their daily energy intake from sugary drinks.

Soft drink consumption has increased 45 per cent over a recent five-year period and New Zealanders are now the 11th highest consumers of soft drinks per capita worldwide.

Besides obesity, soft drinks also contribute to tooth decay in our children. Some soft drinks also have high levels of caffeine which can stimulate children to be more hyperactive and aggressive at school.

We strongly support moves by the Minister of Health to get soft drinks out of all schools by 2008.

The World Health Organisation has released advice to reduce consumption of sugary drinks which is now included in the recommendations of many countries to reduce childhood obesity.

The New Zealand public can rest assured that the scientific evidence shows increased sugary drink consumption contributes to obesity and should support the common sense strategies required to limit soft drink consumption. Other benefits from this strategy include improved dental health and calmer children in class rooms.

* Robert Scragg is Associate Professor in Epidemiology at Auckland University and Jim Mann is Professor of Human Nutrition at Otago University.