Evidence linking sugary drinks to overweight and obesity grows

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Evidence linking sugary drinks to overweight and obesity grows

Posted 26/11/2012 by Amanda Biggs

Evidence has been growing that the consumption of sugary drinks among children is contributing to our increasing rates of overweight and obesity. Sugary drinks include ones artificially sweetened with sugar, such as soft drinks and energy drinks, but also seemingly healthy drinks, such as fruit juice. Sugary drinks are sometimes described as offering ‘empty kilojoules’ because they provide plenty of calories but lack many essential nutrients. Two recent studies into the effect sugary drink consumption has on children's weight, add to a growing body of evidence linking them to weight gain. A recent issue of the New England Journal of Medicine (NEJM) reported on both studies.

 In one trial, a group of normal weight Dutch school children aged 5–12 was given one can of sugary drink daily, while another group was given one can of drink sweetened with a non-calorie sweetener. The trial found that over 18 months body mass index (BMI)—a measure of weight adjusted for height—in the group given the sugar sweetened drink increased significantly more than the group given the artificial sweetener. 

In the second trial, one group of overweight and obese US adolescents received home deliveries of no calorie drinks for one year, while another group of similar profile was given supermarket vouchers, to spend as they please. For the first year, those in the first group consumed fewer sugary drinks and their BMI increased more slowly than those in the second group. However, differences in weight gain disappeared in the second year (possibly due to other changes in dietary habits of both groups).

It has been claimed that the aggressive marketing of soft drinks in Australia is fuelling consumption and contributing to weight gain. But there are significant gaps in our knowledge about levels of sugar consumption. No national survey on consumption of food stuffs has been undertaken since 1998–99, while a national survey on nutrition and dietary habits has not been done since 1995. Other survey data confirms that Australians generally are getting fatter, not exercising enough and are eating poorly, but our level of sugar consumption is not accurately known. Some survey data indicates that children are currently consuming higher than recommended levels of sugar, but trend data measuring consumption over time is lacking.

The 2007 Australian National Children’s Nutrition and Physical Activity Survey (NCNPAS), co-funded by the Australian Food and Grocery Council and the government, surveyed 4487 children aged 2–16 children on their BMI, physical activity, and dietary habits. The survey found all age groups of children were consuming higher levels of sugar than recommended by the national dietary guidelines. On average across age groups, dietary sugar comprised around 23–24 per cent of total energy intake, compared to the recommended level of 20 per cent. NCNPAS also found that 17 per cent of children were overweight and a further 6 per cent were classified as obese. Sugar consumption over time was not measured, nor were findings compared with the 1995 national nutrition survey. 

More detailed analysis of the survey undertaken by researchers from the Telethon Institute for Child Health Research in Western Australia looked at the composition of children’s sugar consumption, including their consumption of sugar sweetened beverages (SSB). SSB included carbonated drinks, sports drinks, flavoured milks, and sugar sweetened fruit juice. Children were classified as a being high, moderate or low consumer of SSB. High consumption of SSB was defined as contributing more than a third of daily energy intake (or 2 glasses of SSB a day). Around 14 per cent of children were considered high SSB consumers, 66 per cent were low-moderate consumers and approximately 20 per cent reported no SSB consumption during the survey period. High consumption of SSB, particularly carbonated drinks, was associated with low levels of education and inadequate fruit and vegetable consumption. Younger children aged 2–3, tended to consume sugar sweetened juice, while older age groups favoured carbonated drinks.  

The researchers concluded that consumption of SSB contributed ‘a substantial amount of energy to the diet of Australian children’. This ranged from 4 per cent in 2–3 year olds to 7.5 per cent in 14–16 year olds. Despite this, the researchers were unable to confirm a ‘significant association between high or regular consumption of SSBs and likelihood of being overweight or obese’ (although they suggest the study design limited their ability to draw valid inferences between SSB consumption and weight gain). 

Sugar remains an essential component of a healthy diet, with current national dietary guidelines (published in 2003) recommending a ‘moderate’ consumption to maintain health. The new national dietary guidelines (to be released early in 2013) are likely to modify this advice, taking into account the ‘strengthening evidence’ of the association between the consumption of sugar sweetened drinks and the risk of excessive weight gain in both children and adults. Indeed, the draft guidelines, issued for public consultation in 2011, recommend people should ‘limit intake of foods and drinks containing added sugars. In particular, limit sugar-sweetened drinks’. Precisely what the term ‘limit’ means in terms of daily consumption may become clearer when the new guidelines are released. 

The evidence from the two trials reported in the NEJM will not settle the contentious debate that has developed in Australia about whether our levels of sugar consumption have been rising and therefore contributing to weight gain. This will require more evidence based on a national survey of dietary habits, and further scientific studies. However, the two trials are valuable because their findings are based on robust scientific methodology—including randomisation and use of control and intervention groups—which has sometimes been lacking. They add to the growing body of scientific evidence that increased consumption of sugary drinks plays a significant role in weight gain. But they do not rule out the role of other factors such as overall diet, physical activity levels, and genetic components, which still also need to be considered.

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