1. Introduction
Childhood obesity is a worldwide public health concern. According to the World Health Organization (WHO), over 340 million children and adolescents aged between 5−19 years were overweight or obese in 2016 [
1]. Obesity in children is linked to cardiometabolic complications that are already present during childhood [
2].
Obesity could be triggered by high energy-dense food consumption [
3], among other factors, in conjunction with other obesogenic risk factors, such as a sedentary lifestyle [
4] and insufficient physical activity [
5]. Free sugars intake has been proposed as one of the dietary contributors to obesity development in children, especially in the form of sugar-sweetened beverages (SSB) [
6]. Sugar-containing soft drinks are likely consumed independent of meals and thus provide additional energy [
6]. Sugars have been classified into intrinsic and extrinsic sugars [
7]. Extrinsic sugars are defined as those that are not present within the cellular structure of food when consumed, which are divided into milk sugars and nonmilk extrinsic sugars (NMES). NMES refers to all mono- and disaccharides added to foods by manufacturing, cooking, and consumers, in addition to sugars that are naturally present in honey, syrup, and unsweetened fruit juice. Under these specifications, lactose is excluded, since it is naturally present in milk and milk products [
8,
9]. Studies have shown that diets high in NMES could result in poor diet quality, such as high energy density [
10]. Noteworthily, the term “NMES” is broadly synonymous with free sugars, and these terms have been adopted in research worldwide [
11]. Most countries take into account the WHO recommendations for free sugars intake [
12]. In 2015, the WHO recommended that the daily consumption of free sugars should not exceed 10% of total energy intake (TEI) [
13], while the Scientific Advisory Committee on Nutrition (SACN) from the UK recommended the free sugars intake to be restricted from 10% of TEI to 5% of TEI [
14]. Different dietary surveys have observed that all population groups exceed this recommendation [
15]. European nationwide surveys (1999–2013) showed that added sugars contributed between 11–17% of total energy intake in children [
16].
Recent studies have shown that soft drinks, confectioneries, biscuits, and cakes are the main sources of free sugars in Europe in all age groups [
16]. In European children, the contribution of free sugars to the total energy intake is higher than recommended, and the main food sources are sweetened beverages such as fruit juices and soft drinks [
16,
17]. In European adolescents from the HELENA study, free sugars intake was 110.1 g/day (19% of total energy intake; 24 h recall), while the main food contributor to free sugars intake was carbonated, soft, and isotonic drinks, followed by nonchocolate confectionaries, honey, jam, and syrup [
18].
Te Morenga [
19] assessed the role of free sugars on obesity development and concluded that free sugars are one of the key determinants for body weight gain in children and adults. High intake of food items containing free sugars or SSB often leads to an excess energy intake, which, if not compensated by energy expenditure, will result in an increase of body fat [
19]. Several studies have found that a diet rich in SSB beverages results in weight gain or obesity [
6,
20,
21]. However, other studies have found an inverse relation between dietary sugars intake from milk and fruits and overweight and obesity in children and adolescents, especially in females [
22]. In the same vein, it was observed that free sugars from liquid sources resulted in higher body mass index (BMI), while solid foods sources alone did not have any adverse impact on obesity parameters in adults [
23].
To our knowledge, there is scarce information on the association between free sugar intake and the risk of obesity development in adolescents. Thus, the aim of this study was to investigate the impact of consumption of total free sugars and their intake from the main food sources on body composition and obesity among European adolescents.
4. Discussion
The present study found a lack of association between total free sugars intake and free sugars from different sources and body composition indices (BMI and FMI) in European adolescents. Also, analyses were performed considering known confounders and adjusting by total energy intake and free sugars residuals.
Different foods have different content of free sugars and, for this reason, they may have a different impact on obesity development. Moreover, the food matrix may also influence free sugars. For these reasons, we analyzed total free sugars intake and free sugars from different food items.
Obviously, the results clearly show that the observed intake of total free sugars is higher than the actual recommendations of WHO and SACN [
12,
14] and does not generally lead to obesity in adolescents. The observed intake of total free sugars is within the range of other European studies investigating adolescents’ diet, which has ranged between 14% and 21% [
42,
44]. On the other hand, New Zealand’s adolescents reported higher intakes (16–26%) [
45]. This high consumption of free sugars in this population group could be due to environmental factors, such as the high availability of foods with high free sugars contents; snack consumption at school; psychological factors, such as knowledge level; perception of sugary drinks and individual choice; social factors, such as their family and friends [
46,
47]; and the fact that preferences for sweet taste are higher in children and adolescents [
48]. However, a meta-analysis of longitudinal studies concluded that sugar, confectionary, and sweets consumption decreases after adolescence [
49].
In this analysis, free sugars from all food groups and total free sugars intake were higher in males than in females, as it was previously observed in the total HELENA study sample [
18] and other European studies [
42,
50,
51]. Also, it has been found that adolescent males consume more free sugars, mainly from sweetened grains, beverages, table sugars, syrups, snacks and candies, and milk products than females [
52]. Females usually have lower intakes of sugars because they tend to seek a slim body image, and most of them have tried dieting at least once by cutting off sugar consumption [
22].
Maternal education is important for dietary behaviors, as mothers guide children to develop and learn both food choices and eating habits. This may reflect their personal attitudes, preferences, and knowledge to understand the benefits of healthy eating [
53]. Several studies have assessed the relation between maternal education and free and total sugars consumption [
18,
54], and have found that lower maternal education level was inversely associated with intake from “sugar, honey and jam”, “carbonated soft drinks”, “cakes and pies”, and “breakfast cereals” groups.
Several systematic reviews and meta-analyses have focused on dietary sugar and body weight in children and adolescents. In these age groups, some advice to reduce SSB and other foods containing free sugars was given as an intervention trial, and researchers did not find any association between advice and BMI or BMI z-score [
55,
56]. Meanwhile, cohort studies in children have confirmed the link between SSB intake and the risk of obesity but have not found a consistent relation between other measures of sugars intake and adiposity [
19].
In our sample of adolescents, total free sugar was inversely associated just with the FMI in females. Some studies have reported an inverse association between free sugars intake and BMI with and without energy adjustment. Williams et al. [
57] observed a significant, inverse relationship between sucrose consumption and BMI at 3–4 years of age when adjusted by total energy intake. When these children were followed-up at 7–10 years of age, the relation remained negative but not statistically significant. Another study in children noticed that free sugars intake was inversely associated with BMI but was not related to body fat [
58]. Similar results were found in children with obesity who consumed less free sugars than overweight or normal-weight children [
59]. Results from the Australian National Nutrition Survey also reported that intakes of total, natural, and free sugars were not associated with BMI in adolescents or children [
60]. Noteworthily, it seems that the combination of both excess fat and sugars predisposes children to childhood obesity [
8].
Among the possible explanations for the results from previous literature and the results of this study, individuals with obesity mainly tend to restrict their intake from high-fat and high-sugar foods when they try to reduce their weight. Meanwhile, children who are overweight or obese are less likely to restrict their dietary intake compared to adults [
59]. Also, subjects with obesity tend to underreport their consumption and provide socially desirable answers, even in adolescence [
61]. However, in the present analysis, under-reporters were not included. Additionally, a possible explanation for the negative result in this study was the adjustment of energy intake, since it is well known that excess energy intake plays an important role in obesity development [
62]. Overall, it has been found that lean, active individuals tend to select high-energy and high-sugar diets [
63]. In contrast, individuals who are overweight seem to prefer diets high in fat but tend to restrict dietary sugars [
64]. In the isocaloric theory, the increase of energy from sugars is followed by lower protein intake [
65]. It seems that, when individuals consume a diet high in free sugars and low in fat and energy density, they do not have excess body fat or adiposity. Meanwhile, when individuals consume a diet low in free sugars and high in both fat and energy, they tend to have higher adiposity [
66]. On the other hand, studies have found that satiety is higher when consuming carbohydrates, including sugars, than consuming fat, and carbohydrates suppress eating for longer periods of time [
67]. However, it was found that body fat changes occur when altering consumption mediated via altering energy intake, since the isoenergetic exchange between sugars and other carbohydrates is not associated with weight change [
19].
In our sample, “chocolate”, “fruit vegetables juices”, and “other sources” showed an inverse association with FMI only in females. In Korean children and adolescents, only total sugars intake from milk and fruits was inversely associated with overweight and obesity among females [
22]. However, in our study, total free sugar residuals were used as a confounding variable, and no significant associations were found between free sugar from different food sources and BMI. The possible explanation is that this method completely controlled for confounding variables by total energy intake, which reduced the risk of bias resulting from categorical adjusted variables and removing the variation caused by total energy intake in the estimation results [
68].
Also, in this study, we found that overweight males with obesity tended to consume less juice as a snack compared to normal-weight males. In a cross-sectional study in children, males consumed more milk, orange juice, and carbonated soft drinks than females. However, in that study, children who consumed more milk and less carbonated soft drinks were leaner, whereas females who drank more SSB were heavier [
69]. In a most recent study in China, researchers observed a weak association between BMI and SSB intake after adjusting for age, sex, total energy intake, pubertal stage, and maternal education level [
70]. A meta-analysis conducted in 2013 confirmed the association between SSB intake and body fat in children, while they did not find any consistent relation between total free sugars intake and adiposity in the same age group [
19]. These results can be explained by the limited number of randomized controlled trials focusing on the reduction of SSB consumption, which leads to poor cooperative reporting in children. In European children, an inverse association was noticed between total sugar intake and total energy intake with z-BMI and z-FMI using the residual method. However, this study provides no indication that increased total sugar intake positively affects BMI on an energy-equivalent basis [
65].
In this study, normal-weight male consumers of free sugars from “cakes, pies, and biscuits” and female consumers of “breakfast cereals” had a lower probability of having obesity compared with non-consumers. The same result was found in another study, which showed that children who consumed the least biscuits and cakes tended to be slightly heavier than others [
71]. Another study found that males who consumed SSB had a lower probability of obesity [
22]. However, these results may be false due to their inability to be reproduced or due to the possibility of under-reporting. Also, as we mentioned previously, people with obesity may tend to practice selective food restriction, mainly excluding this free sugar group. On other hand, this may indicate a real prediction between this free sugar group and obesity.
Moreover, in this study, female consumers of “fruit and vegetables juices” had higher tendency toward obesity. Recent meta-analyses have reported that high intake from SSB is positively associated with weight gain and obesity development [
19,
72]. The main explanation of this result is that SSB may lead to weight gain due to their high added sugar content (on average, it contains about 140–150 calories and 35.0–37.5 g of sugar per 12 oz serving) and low satiety effect. Also, after intake of liquid calories, incomplete reduction in energy intake is compensated during subsequent meals [
73]. In addition, studies have shown that fructose from any source promotes visceral adiposity development and ectopic fat deposition [
74,
75].
This study has several strengths. To our best of knowledge, this is the first study to estimate free sugars intake from various food sources and their potential association with obesity in European adolescents. The sample size was selected with a wide geographical spread from eight European cities with large cultural dietary diversity. The sample collection and several anthropometric measurements were assessed using highly standardized and validated procedures to increase accuracy. Also, we excluded under-reporters and over-reporters using a validated method, which improved the quality of the data. In addition, we used the mother’s education level as a covariable and the residual method to adjust in the analysis, which is considered an isocaloric model, to account for the direct contribution of free sugars to total energy intake. One limitation of this study was that the 24 h recalls were completed during school days. Thus, the information on Fridays, Saturdays, and holidays was not included. Another limitation of this study was its cross-sectional nature, which did not allow us to assess behavior over a period of time and did not provide information in determining the cause-and-effect relationship.