Soft drink consumption and excess weight gain in Australian school students: results from the Nepean study

Abstract

We studied the relation between soft drink/cordial (a sweet, flavoured, concentrated syrup that is mixed with water to taste), fruit juice/drink and milk consumption in mid-childhood, and body mass index (BMI) status in early adolescence in a contemporary Australian cohort. In 1996/7, 268 children (136 males) were recruited from western Sydney at baseline (mean±s.d.: 7.7±0.6 years), and at follow-up 5 years later (13.0±0.2 years). Height and weight were measured at both time periods and overweight and obesity defined using the International Obesity TaskForce criteria. Beverage consumption was calculated from a 3-day food record at baseline. Median carbohydrate intake from soft drink/cordial was 10 g higher (P=0.002) per day in children who were overweight/obese at follow-up compared to those who had an acceptable BMI at both baseline and follow-up. Intakes of soft drink/cordial in mid-childhood, but not fruit juice/fruit drink and milk, were associated with excess weight gain in early adolescence.

Introduction

Increased consumption of sweetened beverages, including soft drink, cordial (a sweet, flavoured, concentrated syrup that is mixed with water to taste) and fruit juice, may contribute to the development of obesity in children.¹ However, it is not clear if obesity is related to the total amount of sweetened beverages consumed or consumption of a specific sweetened beverage, and whether sweetened beverage intake displaces milk intake. The aim of this study was to determine (a) the relation between soft drink/cordial and fruit juice/drink consumption in mid-childhood, and body mass index (BMI) status in early adolescence, and (b) whether sweetened beverage intake displaces milk intake, in a contemporary Australian cohort.

Subjects

In 1996/7, 436 healthy children were recruited at baseline and followed up 5 years later. The median time between baseline and follow-up was 5.4 (4.0–6.6) years. The children were self-selected from the longitudinal ‘Nepean Study’ that was designed to investigate the effects of birth size, body size and genes on blood pressure and bone mass. All children were born at term at Nepean Hospital, in western Sydney, between August 1989 and April 1990 and were part of a birth cohort whose details and selection criteria have been published previously.² Food records were completed by 281 of the children (141 males) at baseline who participated in the follow-up. The mean (±s.d.) age of the children at baseline and follow-up was 7.7±0.6 and 13.0±0.2 years, respectively. At baseline, there was no significant difference in the mean height (P=0.663), weight (P=0.133) or BMI (P=0.082) between the children who completed the food record and those who did not.

Methods

Written informed consent was obtained from participants’ parents and both The Children's Hospital at Westmead Ethics Committee and the Ethics Committee of the Wentworth Area Health Service approved the study.

Height and weight were measured at both time points and BMI (kg/m²) calculated.³ Body mass index Z-scores were calculated from age- and sex-specific reference values to standardise for the effect of age and sex on childhood BMI.⁴ The International Obesity TaskForce BMI criteria were used to define overweight and obesity.³ Participants were categorised into groups based on BMI: (1) acceptable BMI at both time points; (2) BMI gainers – acceptable BMI at baseline, but overweight/obese at follow-up, (3) BMI losers – overweight/obese at baseline, but acceptable BMI at follow-up and (4) overweight/obese at both time points.

Beverage consumption and carbohydrate intake from sweetened beverages consumed were calculated from an estimated (household measurement) 3-day food record at baseline. Beverages of interest were categorised into: (1) soft drink/cordial (sugar sweetened), (2) fruit juice/drink and (3) milk. Non-nutritively sweetened beverages were not included. The dietary data were analysed by a dietitian (SPG), using Diet/1, version 3.10 (Xyris software, Queensland, Australia).

Data were analysed and assessed for normality using the Statistical Package for Social Sciences, version 11.5 (SPSS, Chicago, IL, USA). Differences between groups were assessed by analysis of variance if data were normally distributed; otherwise, a Kruskal–Wallis test was used.

Results

Median carbohydrate intake from soft drink/cordial was 10 g higher (P=0.002, Mann–Whitney U-test) per day in children who were overweight/obese at follow-up compared to those who had an acceptable BMI at both baseline and follow-up, and 23 g higher (P=0.019, Mann–Whitney U-test) per day compared to those who were overweight/obese at baseline but had an acceptable BMI at follow-up. There were no associations between BMI status and carbohydrate consumed from fruit juice/fruit drink, or milk intake (ml) (Table 1 ).

Table 1 Body mass index (BMI) status and beverages consumed

Discussion

Soft drink/cordial intake at age 8 years is associated with excess weight gain 5 years later, suggesting that consumption of these beverages may contribute to the development of adolescent obesity. These findings are consistent with published data in American children, reporting that a high intake of soda, or soft drinks, predicted the development of obesity over 19 months in 12-year-old children.⁵ Ludwig et al.¹ estimated that for each can of soft drink consumed daily, the child's risk of obesity increased by 60%. Interestingly, children who were overweight/obese at baseline but had acceptable BMI at follow-up consumed significantly lower amounts of soft drink/cordial compared to children who were overweight/obese at follow-up, further substantiating a role for soft drinks in excess weight gain. In contrast to findings from earlier studies,^{6, 7} increased sweetened beverage did not displace milk consumption in the current study.

It is unclear why increased soft drink/cordial consumption is associated with increased weight gain. It is hypothesised that increased consumption of sweetened beverages may influence body weight because of a failure to reduce food energy consumption in response to the additional energy provided by sweetened beverages.¹ Alternatively, soft drink/cordial consumption may be a proxy for a range of obesogenic factors, including a less healthy diet, physical inactivity and increased television viewing. In adolescents, soft drink intake is highly correlated with snacking on energy dense foods, as well as time spent viewing television, suggesting that obesity-related behaviours may act in a synergistic manner.⁸ As previously reported in younger children,^{9, 10} no association was found between fruit juice/drink and BMI status. We speculate that fruit juice/drink consumption may reflect an overall healthier diet and lifestyle.

The prevention of obesity in children requires a multi-faceted approach. Limiting the consumption of soft drinks and cordials, in conjunction with promoting healthier food choices, increasing physical activity and reducing sedentary behaviour may prevent excess weight gain in adolescents.