We explored the relationship between sugar and quality of life in children and adolescents as an attempt to challenge the conventional realms of a relationship between sugar and health. In contrast to our initial hypothesis, we found consistent adverse associations across most of the studies between sugar intake and measures of QoL, including sleep, food security, and health-related QoL, despite the limited number of papers and the high variability in the sugar exposure and outcome measures. Besides giving further support to the inverse association between sugar intake and health-related outcomes underlying the current dietary reference values and Food Based Dietary Guidelines [10,11,12, 17], this finding may underline the importance of embracing the multidimensional aspects of health, taking into account of the broad range of exposures and outcome measures or measurement tools.

Common behaviors of consuming sugar-rich foods containing added sugar were presumed to be associated with the context of social gathering, relaxation, and comfort, which may be tightly associated with QoL. Sweet and fatty foods have previously been associated with feelings of pleasure in adult populations [48]. High SSB consumption, in contrast, was shown to be driven by multiple factors, from the children’s preference and behaviours (e.g. screen time, snack consumption), parental factors (e.g., lower SES, lower age, SSB consumption, using food as reward, etc.) [49], which may differ from factors driving sugary food consumption. This study hence highlights the multidimensionality of both sugar intake and QoL. Embracing the full complexity of both sugar intake and QoL taking into account all different aspects surrounding this relationship is hence necessary, despite challenges in merging the highly variable exposure and outcome measures, which interestingly, seemed consistent in this study.

Since most of the included studies were cross-sectional, it is important to remember the possibility of reverse causation, i.e., higher sugar intake in those with lower QoL, especially in case of food insecurity. However, the consistent associations in almost all the included studies may imply underlying causal relationships, which deserves further investigations. Embracing the full complexity of QoL taking into account all its different aspects is necessary, despite challenges in establishing the causal relationship and merging highly variable outcomes.

The populations in the studies that were included in the present scoping review represented children between 4 and 8 years of age and adolescents aged 12–19. Intake of sugar-sweetened foods and beverages is of concern to children and adolescents, especially due to the low nutritional value of these foods. These foods contain energy and replace the more nutritious foods in children’s and adolescent’s diets [50]. Eating behavior and food choices are highly complex processes driven by physiological (i.e. genotypes, phenotypes, metabolic functions, homeostatic balance), psychological (i.e. mood, hedonic), as well as surrounding socioeconomic factors [51]. These aspects affect not only how much, but also when and on which occasions people eat. Many choices affecting sugar intake are shaped by interpersonal relationships and social activities, which may vary from one culture to another. Similarly, sugar may be one of the most affordable sources of energy, which may encourage its preferred intake over other dietary components with higher nutritional quality. As the juvenile/adolescent period has been shown to be an important period for the development of food preferences and habits with long-lasting health consequences [18,19,20], the high intake of sugar-rich foods and beverages becomes a concern if it is retained throughout life.

The adolescent period is an important period which may determine the onset of anxiety later in life [52]. Consumption of hypercaloric diet has been proposed to influence the neuroendocrine stress systems and the maturation of neural circuitry supporting emotion regulation [52]. Additionally, children and adolescent may be exposed to marketing of sugar-rich foods that may contribute to health-detrimental eating behaviors [53]. In a meta-analysis of randomized trials it was shown that children exposed to advertisement of energy-dense sugary products were more likely to consume those foods and increase their dietary intake, especially in the younger age group (≤ 8 years of age) [54]. The fast foods and sugar-rich foods and beverages may also be consumed in connection to stressed situation or along with emotional eating in adolescent population [55, 56]. The opposite direction seemed to also apply, as the consumption of imprudent diets rich in sugar-rich beverages, processed foods, and foods rich in saturated fatty acids was linked to an increased risk of depression in adolescents [57, 58].

Similar adverse associations between sugar intake and various measures of QoL have been previously reported in adult populations. Among university students aged 18–25 year old, higher intake of added sugars and SSB was observed in students with food insecurity [59, 60]. In another study conducted at university students, overconsumption of high-fat and high-sugar food was associated with poor sleep quality [61]. Higher consumption of SSB in Spanish adults has also been associated with lower score in the physical component of a validated questionnaire of health-related QoL [62]. Despite limited number of studies and lack of systematic review in this field, this finding hence showed a good concordance between children and adult populations, which may deserve a future in-depth examination on the association between sugar intake and QoL.

Most of the studies in our literature review did not include information about the amount of actual sugar intake because we did not aim to establish the cut-off limit nor expect to observe a linear dose–response relationship between sugar intake and lower QoL. The intake of SSB or other sugar-rich foods was measured either by using FFQ or 24-h foods recall, with no well-validated scales, scores (such as HEI with added sugar) or questionnaires developed for the purpose. One of the possible reasons could be due to challenges in quantifying sugar intake from sugar-rich foods and beverages, especially when the exposure in focus was dietary patterns. Additionally, included studies in this review did not classify added sugar intake as according to the cut-off values often used in official recommendations. In the recently published EFSA scientific opinion on a tolerable upper intake level for dietary sugars, challenges of identifying studies with intake of less than 10% energy intake were mentioned [63]. Thus, we cannot use current study to estimate the actual amount of sugar associated adversely with QoL.

In the research literature, the agreement on how to measure children’s QoL seems lacking. The outcome related to quality of sleep such as sleep bruxism; sleep duration and sleep disturbance may have a strong impact on the QoL. However, studies are not easily comparable with differing sleep-related outcomes and with differing methods used, such as parts of the questionnaires from the previous studies, the observations of the parents, or sleep habits questionnaire or sleep quality index. Other outcome measures were mental well-being, oral health, physiological well-being, or food security. Food insecurity as the outcome was measured differently in the studies. For example, parent reports and child food security assessment tools (CFSA) were used. The difference in methods may interfere with the interpretation and reliability of our findings.

Despite the lack of quantitative measures in both exposures and outcomes, the consistent inverse association between sugar intake and measures of QoL across these studies was striking. Because of the high heterogeneity of sugar exposure and QoL outcome measures, our attempt was to find emerging patterns from included studies and highlight the knowledge gaps in the field instead of estimate the strength of the association between sugar intake and QoL. We were surprised by the number of studies appearing during the secondary literature search, which may imply a growing interest in this field, or emerging interdisciplinary approaches in solving nutrition-related challenges in the past few years. Given the findings of our study, we are convinced that inclusion of multidimensional aspects enabled by collaborations with other fields will capture a wider perspective to better understand underlying relationship between diet and health, which will provide stronger evidence for policymaking, including formulation of nutrient recommendations and dietary guidelines.

There are several lessons learned from this review. First, we observe a gap in the scientific literature for additional understanding of the role of sugar in QoL and well-being. Many previous studies focus on hard endpoints such as risk of cardiometabolic diseases, indirect risk markers, or other quantifiable measures. Nevertheless, health is not merely about being free of disease or being responsive to health disturbance and treatment of symptoms, but the capacity to respond to challenges within the windows of homeostatic balance [21]. Additionally, health comprises not only the physical aspect, but also the emotional, social, and psychological well-being. QoL was picked based on the availability of quantifiable measures using validated questionnaires. However, in this study we observed that QoL also embraces the positive and active aspects in health maintenance and prevention strategy as well as various aspects of life, such as sleep quality, social aspects (mood, behaviour, emotional and depression symptoms), and food security. Some of the measures are well described with validated methods, while some others may not be quantifiable with validated questionnaires or other quantitative measures. This exercise hence shows how current nutrition science practices are skewed towards mostly quantifiable physical aspects of health, which overlook other aspects shaping one’s physical and mental well-being. Given the intricacy involved, reductionist approaches that solely focus on quantitative aspects of medical sciences may fall short in offering a comprehensive understanding of nutrition science.

Our scoping review suggests that inclusion of different methodologies and endpoints measuring both physical and mental health from different angles such as QoL illustrates the value of adding additional layers to the existing as a way towards a more holistic approach. Although no study with qualitative behavioral data was included in this review, inclusion of a more wholistic lens in the future is highly encouraged. Based on our findings from sugar and health, we argue that when considering the complexity, reductionist approaches focusing only on quantitative aspects of medical sciences may not suffice to provide wholistic insight on nutrition sciences. To this end, we hypothesize that by complementing currently practiced reductionist approaches with additional layers inherent in nutrition, we will arrive at a more wholistic approach where important new dimensions of the relationship between nutrition and health may lead the field of nutrition science forward.

Second, the quantitative aspects of nutrition science as derived from medical studies always require exposure/dosage information. This information, however, may not always be applicable as people would have different levels of e.g., energy intake, energy expenditure, and factors behind dietary choices. None of the included studies mentioned the actual amount of sugar intake, but SSB (10 studies), sugar-rich food and beverages (4 studies), or dietary patterns (7 studies), which hinder translation of the current review to draw any dose–response relationship or recommend the maximum amount of intake without possible harmful consequence. Though no advice on sugar intake in children and adolescents related to their QoL can be derived using our approach, we underline some of the challenges that were also depicted by the EFSA’s scientific opinion on the sugar intake [63].

We acknowledge that we ended up with a relatively low number of studies, which may represent the high proportion of studies with reductionist approach or be attributable to traditional medical point-of-view in article screening with restricted inclusion criteria, study population, or outcome measures. Similarly, many of the studies stemmed from other disciplines than nutrition sciences, which may have influenced methodologies. Most (18 of 21 studies) were cross-sectional as only a limited number of other study designs were screened. In those studies, higher sugar intake coexists with other unfavorable health behaviors, such as lower physical activity, higher screen time [31], lower dietary quality [24,25,26, 31], including high frequency of SSB intake. Therefore, we cannot resolve if the SSB intake was the cause, effect, or an effect modifier of the low-quality diet. Despite moderate to good correlation between frequency of SSB intake and sugar intake [64, 65], it may not suffice to represent total sugar intake due to varying SSB consumption patterns among individuals and populations, varying sugar content in SSBs, and other sources of added sugars in diets than SSBs. Additionally, food insecurity may act as exposure instead of the outcome of the high sugar intake. As most of the studies were cross-sectional, no directionality or causality can be inferred from these studies, although the consistent associations across studies may infer underlying causal relationship among the included variables. Moreover, the long-term impact of sugar consumption cannot be concluded, either. Not all the included studies reported SES of the study participants, although SES may confound the associations between sugar intake and e.g., food insecurity and other aspects of QoL. Also, the measures of exposures and outcomes differed by age group, e.g., filled by parents for smaller age group and by the adolescents themselves. The immense variation in the study populations, designs, exposures, measurement tools, and main outcomes made it challenging to merge the findings and draw a generalizable conclusion, despite strikingly similar adverse association over such high variations. Considering this diversity, inference was then made based on the observed patterns across study.

Based on the studies reviewed, we suggest that a higher consumption of sugar-rich foods and beverages are likely to have detrimental association with QoL, although no causality and time-related relationship can be established and lacking information on the actual amount of consumed sugar. Many of the studies took insights from other disciplines such as behavioural or social sciences, bringing out contexts where sugar-rich foods and beverages may be related with other outcomes, such as food security, health-related quality of life, and sleep quality. In combination with metabolic and physiological outcomes, these aspects may add a value which may also be of interest for consumers and clients in the healthcare system. In the future, multidimensional aspects of nutrition, considering both reductionist and wholistic approaches, e.g., intervention studies with continuous monitoring of QoL components, and inclusion of other interdisciplinary approaches, such as health perception, more subjective health outcomes, taking into account socioeconomic status, cultural values, and other factors in the society, are hence encouraged. An extra caution is required to overcome challenges of merging both quantitative and qualitative measures to reflect health to fully embrace the complexities in nutrition science and support the translation of nutrition science into food- and nutrition policies, to health professionals, and for communication to the public.