Effect of sugar-sweetened beverages on body weight in children: design and baseline characteristics of the Double-blind, Randomized INtervention study in Kids

Abstract

Background

Intake of sugar-sweetened beverages is associated with overweight in observational studies. A possible explanation is that liquid sugars do not satiate and that their intake is not compensated by reduced caloric intake from other foods. However, evidence from intervention studies for this hypothesis is inconclusive because previous studies were not blinded. Hence results may have been influenced by expectations and behavioral cues rather than by physiological mechanisms.

Methods

We designed the Double-blind, Randomized INtervention study in Kids (DRINK) to examine the effect on body weight of covertly replacing sugar-sweetened by sugar-free beverages. Children were only eligible if they habitually drank sugar-sweetened beverages. We recruited 642 healthy children (mean age 8.2, range 4.8–11.9). We designed, tested and produced custom-made beverages containing 10% sugar and sugar-free beverages with the same sweet taste and look. Children receive one 250 mL can of study beverage daily for 18 months. We perform body measurements at 0, 6, 12 and 18 months. The primary outcome is the z-score of BMI for age. The maximum predicted difference in this score between groups is 0.72, which corresponds with a difference in body weight of 2.3 kg.

Discussion

The double-blind design eliminates behavioral factors that affect body weight. If children gain less body fat when drinking sugar-free than when drinking sugar-sweetened beverages that would show that liquid sugar indeed bypasses biological satiation mechanisms. It would also suggest that a reduction in liquid sugars could decrease body fat more effectively than reduction of other calorie sources.

Introduction

Obesity in children has become a major health problem worldwide. In the past three decades the prevalence of overweight in children has increased dramatically [1]. Recently the prevalence of high body mass index in children appeared to plateau [2] but the number of overweight children remains high. Obesity in children is a risk factor for adult obesity, type 2 diabetes, cancer, cardiovascular diseases and death before 55 years of age [3], [4], [5], [6], [7], [8]. Obesity in children also has negative health consequences during childhood itself such as insulin resistance, hypertension, dyslipidemia and type 2 diabetes [9].

The increase in prevalence of obesity coincided with a large increase in consumption of sugar-sweetened beverage in children [10]. Energy intake among children increased substantially between 1977 and 2001 in the US, and energy from sugar-sweetened beverages accounted for more than 50% of this increase [11]. Sugar-sweetened beverages, also known as liquid sugars, are thought to be more fattening than sugars in solid form because they do not satiate [12]. As a result children would not compensate for the intake of liquid calories by eating less of other foods and drinks. Therefore sugar-sweetened beverages might increase total energy intake and cause overweight.

Indeed, in several observational studies intake of sugar-sweetened beverages was associated with weight gain both in adults [13], [14], [15] and in children [16], [17], [18]. However, some studies failed to find such an association [19], [20], [21]. Also, an association between sugar-sweetened beverages and weight gain may be due to confounding because people who drink more soft drinks often also eat more fast food and exercise less. Although most studies adjust statistically for known confounders, residual and unmeasured confounding are of increasing concern in observational nutrition studies [22], [23]. Hence trials are needed for conclusive evidence about causality.

Results of trials of the effect of liquid sugars on overweight are inconclusive, with some finding an increase in weight [24], [25], [26], [27] while other trials found equivocal results [28], [29], [30]. The lack of conclusive evidence may be due to a lack of proper placebo treatments, small samples sizes, short duration and lack of individual randomization. Also, none of these trials was properly blinded. Blinding is crucial because without it, results may be biased by effects on food intake of behavioral cues and expectations rather than by physiological mechanisms [31].

Hence there is a need for conclusive evidence whether liquid sugars fail to evoke compensatory changes in food intake and are therefore more fattening than other sources of calories [32], [33]. We designed DRINK – the Double-blind, Randomized INtervention study in Kids – to examine the effect of covertly replacing sugar-sweetened beverages by sugar-free beverages on body weight. This allows us to study biological compensatory mechanisms independent of behavioral cues and voluntary changes in intake. In this article we describe the rationale, design, methods and baseline characteristics of this study.