Introduction

Worldwide, evidence shows a considerable increase in the prevalence of childhood obesity in the first stages of life¹,², mainly during the first 1000 days, a period from the fetal/neonatal stage to the first 2 years of life³,⁴. In countries such as the United States, a prevalence of overweight and obesity of 8.1% has been reported⁵; in Mexico, a prevalence of 6.5% is reported in children from 0 to 24 months⁶, which is considered high for this age group.

Obesity in the first years of life has been shown to be a strong predictor of obesity in school age and adulthood⁷; it is also considered a risk factor for the development of diabetes mellitus, arterial hypertension, sleep apnea, and a greater risk of social and psychological problems and premature death¹. As childhood obesity is a preventable disease, prevention efforts during the first 1000 days of life should be a public health priority⁸-¹¹.

Childhood obesity is defined as the excessive and abnormal accumulation of body fat detrimental to health caused by an imbalance in energy expenditure¹. Its etiology is multifactorial resulting from a complex relationship between risk factors of different types, such as genetic, family, environmental, and community factors, among others¹². These risk factors have been systematized in some theoretical models with a socioecological perspective to explain and study how they can influence and interact with the development of obesity¹³,¹⁴.

A widely recommended model in childhood obesity research is the Six-Cs Ecological Model of Obesity by Harrison et al.¹⁴, which states that to understand and explain the problem of childhood obesity, it is necessary to know not only the immediate context in which the child is developing but also the environmental factors beyond its proximal sphere and over time. The model is represented by six spheres and their interactions with each other: cell, child, clan, community, country or state, and culture. Within these spheres, it groups risk factors into five specific zones: Zone 1: nutrition-related opportunities and resources; Zone 2: activity-related opportunities and resources; Zone 3: nutrition-related practices; Zone 4: activity-related practices; and Zone 5: personal and relational attributes. The spheres and zones proposed by Harrison et al. have been studied and found to be predictors of childhood overweight and obesity, and are essential for future research and the development of prevention and health promotion interventions for this age group¹³,¹⁴.

Some published systematic reviews have documented ecological determinants of childhood obesity¹¹,¹⁵-¹⁸. However, the results indicate that most studies have focused on preschool and school-age children from high-income countries; most have addressed only one sphere, and only some have assessed the combined impact of several spheres according to the Six-Cs model. Mexico has the highest prevalence of childhood obesity in the world¹⁹. However, no reviews of published studies that identify risk factors for obesity in children under 2 years of age in the Mexican population and the indicators of overweight and obesity in this age group have been found.

Analyzing the available evidence on childhood obesity factors from a holistic perspective is a good starting point to understand its nature, scope and, above all, to address it effectively. This study aimed to describe published evidence on obesity risk factors by sphere and zone in Mexico, considering the structure of the Six-Cs model, and to determine which of them have been associated with anthropometric indicators of overweight and obesity in children under 2 years of age.

Methods

A scoping review was conducted based on the PRIMSA-ScR extension²⁰. The protocol is registered and published in the Open Science Framework (https://doi.org/10.17605/OSF.IO/UWX8V). This methodology allows to map of a large amount of literature on a topic, to assess its extent, scope, and the nature of different study designs, which improves the results without compromising their reliability, and to identify research gaps.

The following research questions were formulated: What risk factors for obesity have been studied in children under 2 years of age in Mexico, by sphere and area, and which of the factors studied are related to indicators of childhood obesity?

Results

A total of 529 articles were retrieved from the databases previously mentioned. After eliminating duplicate articles (n = 424) and those that did not meet the inclusion criteria (n = 344), a total of 80 articles remained to be retrieved and assessed for eligibility for full-text review. Of these 80 articles, six were excluded due to lack of full-text availability, and 49 did not assess the variables or age group of interest. A total of 25 studies were considered eligible for this review (Figure 1).

Figure 1 PRISMA-ScR flow chart for inclusion of studies in the scoping review. 

When classifying the 25 articles by spheres and zones (Table 3), we identified that the highest percentage (40.4%) studied the child sphere, followed by clan (35.7%), culture (11.9%), community (9.5%), and cell spheres (2.5%)²³-⁴⁷. Some articles studied two or more spheres together: child-clan sphere (n = 7, 2%), family-culture (n = 2, 8.0%), and child-clan-culture (n = 1, 4.0%), child-clan-community (n = 1, 4.0%), and clan-community-culture (n = 1, 4.0%). No article reported the study of the country sphere, thus denoting a relevant disproportionate gap of studies in the country, cell, community, and culture spheres (Figure 2).

Figure 2 Proportion of spheres reviewed in Mexican studies. 

In the analysis by zones, we identified the following percentages: Zone 5: personal and relational attributes (52.6%); Zone 3: nutrition-related practices (36.8%); Zone 1: nutrition-related opportunities and resources (7.8%); and Zone 4: activity-related practices (4.0%). No studies were reported for Zone 2: physical activity-related opportunities and resources. The maximum number of zones studied was three, but minimally (8%).

Table 4 shows the characteristics of the risk factors for overweight and obesity that were studied in each article and the main findings²³-⁴⁷. The most common research design was observational: 14 cross-sectional studies (56%), six cohort studies (24%), a case-control study (4%), a qualitative study (4%), and only three quasi-experimental studies (12%). The sample size of the studies ranged from 17 to 25,075 children. The most studied geographic region in Mexico was the Central region (40%), followed by the North-West (16%), the North region (8%), simultaneously studied North and South regions (12%), and at the National level (24%).

The limited number of risk factors studied by sphere was noticeable. By describing them and their relationship with some indicators of overweight and obesity, our findings showed the following: in the child sphere, most of the risk factors corresponded to characteristics of the child and practices related to nutrition. Those related to some indicators of child overweight and obesity were birth by cesarean section⁴³ and high birth weight²⁶; as for nutritional practices, those related to child overweight and obesity were adiponectin levels in breast milk³¹, higher daily caloric intake²⁷, lower consumption of fruits and vegetables, and traditional diet³⁰. Conflicting data were found on the protective effect of breastfeeding²³,²⁶,³³,³⁹. In addition, children with better mental development²⁹ had a lower prevalence of overweight or obesity.

In the family sphere, the main risk factors for overweight and obesity were mothers with a high body mass index³³, less sleep than recommended²⁷, a high-calorie diet⁴², and those who underestimated their child's weight²⁷. It was also found that children living in single-parent families²⁴, with a stressful parenting style³⁴, and with food insecurity at home⁴¹ tended to gain more weight.

In the community and culture sphere, the following factors were identified as being related to overweight and obesity: living in urban areas and the northern and southern areas of the country²⁸, family income, gender roles, and beliefs about children's preference for ultra-processed products led to greater availability of caloric beverages and foods³⁷.

Discussion

This scoping review on risk factors for obesity in infants in Mexico showed that this topic is emerging but in progressive development. In fact, a significant number of articles highlighted the importance of considering the first 1000 days of life as a key period for obesity prevention⁴⁸,⁴⁹.

In the study of risk factors for obesity in infants, we found that the majority of articles reviewed used observational research designs with a limited number of factors per sphere and zones. Also, an incipient use of quasi-experimental design given that only two phase II (feasibility) studies were identified, despite the importance of promoting a multifactorial study of obesity at this level¹⁴,⁵⁰.

The results identified in this study reveal a great disproportion of studies per sphere. The child and family spheres were the most addressed individually and as a whole, while the community and culture spheres were the least studied. Furthermore, no studies were found to address all spheres. To date, the political sphere has not been studied during the first 2 years of life. These findings are similar to previous systematic reviews, which reported that the most studied spheres to identify risk factors for overweight and obesity are the child and family spheres¹⁸,⁵¹.

The main risk factors related to the weight status in children under 2 years of age in Mexico were in the child sphere and zones related to personal characteristics and nutritional opportunities. The most important factors were as follows: birth by cesarean section, high birth weight, inadequate feeding practices such as daily caloric intake higher than recommended, and lower consumption of fruits and vegetables in the diet; the practice of breastfeeding showed contradictory evidence. In the family sphere, the most important factors were mothers with obesity and underestimating their children's weight, stressful parenting style, and food insecurity at home. In the community and culture sphere, the factors identified were living in urban areas, family income, and mothers' beliefs about children's preference for ultra-processed products. All these factors are consistent with previous literature on risk factors for obesity in the first 1000 days of life¹⁷. Some gaps are apparent in the Community, Culture, and Country domains and in Zones 2 and 4, involving components related to practices, opportunities, and resources related to infant physical activity, sleep, knowledge related to active lifestyles, and parental encouragement of infant activity, practices related to physical activity, such as excessive use of screen devices, and sedentary behavior.

The limited number of studies identified in this review may be due to policy strategies focused on obesity prevention in the first 1000 days of life have recently been published in Mexico⁵²,⁵³. These strategies have been formulated considering evidence on the main identified modifiable risk factors for obesity. These strategies are directed at two stages: The first focuses on antenatal care to optimize maternal health and lifestyle in preparation for pregnancy, achieve recommended weight gain during pregnancy, and prepare mothers for exclusive breastfeeding; the second strategy focuses on the postnatal period. The main focus is on the application of cognitive-behavioral interventions, individually and in family, in clinical settings, at home, or in combinations, using digital technology to promote appropriate feeding practices (breastfeeding, complementary, and perceptual feeding), lifestyle training mainly related to nutrition, physical activity, and sleep quality. Therefore, the number of studies in Mexico should increase and help to identify risk factors that determine the problem of overweight and obesity in the first 1000 days and, in turn, pursue intervention studies.

The limited number of publications selected in this article suggests that this topic is challenging. Time and cost are barriers to designing projects that include more determinants per sphere, which should be mitigated in future studies. Developing strategies and using culturally appropriate tools to measure risk factors are urgent for the pursuit of holistic health, especially for young children. High-income countries are conducting an increasing number of trials to prevent obesity in the first 1000 days, with promising results for preventing childhood obesity⁵⁴-⁵⁶. These studies consider areas and opportunities for research, based on evidence of factors associated with obesity in the first 1000 days, and generate recommendations for health professionals caring for this age group⁵⁷,⁵⁸. Therefore, it would be important to consider these strategies in future research studies on the Mexican population.

To the best of our knowledge, this is the first study to systematically review evidence for obesity prevention in children under 2 years of age using the Six-Cs as an ecological framework for childhood obesity. Our analysis provides a clear description of where research efforts for obesity prevention in the first 1000 days are currently focused and provides a broader understanding of the existing literature and its gaps, which is useful in delineating future research.

This review does not summarize the evidence on the magnitude of associations between determinants in the different Six-Cs spheres and children's weight, which could be considered a limitation. However, this review aimed to quantify and describe the studies according to the Six-Cs spheres and zones, not to identify new risk factors for childhood obesity or to compare the results of the studies. Therefore, studies were included regardless of the study designs, statistical analyses, and definitions of childhood overweight and obesity used.

The determinants of overweight and obesity at the individual and family level in children under 2 years of age are the most studied. However, it is important to recognize that these alone cannot explain children's weight. As aspects of different natures determine childhood obesity, studies should be based on a more holistic perspective, that is, simultaneously addressing aspects of different spheres and zones (socioecological models). The weight status of populations should be followed in longitudinal cohorts to develop informed, evidence-based interventions in the future and try to reduce obesity from an early age for better health in adulthood. This will require new analytical, qualitative methods, and more appropriate quantitative analyses, such as multilevel modeling techniques, to include all relevant determinants of childhood obesity in future research. Despite the research conducted in Mexico, more efforts are needed to conduct studies that integrate socioecological models to reduce the research gap on obesity in the first 1000 days of life and, thus, reduce the risks later in life. In addition, it is important to have policies focused exclusively on this period of life and to implement them throughout the country.