1. Introduction
In recent decades, childhood obesity has grown globally and is now a major public health problem [
1]. In 2016, over 50 million girls and 70 million boys were obese at a global level [
2]. Excess body fat has been attributed to both a high intake of energy-dense, nutrient-poor foods and beverages, such as chips, salted snacks, sweets and soft drinks, and a sedentary lifestyle [
3]. In Europe, a North–South obesity gradient has been observed. Italy, particularly the Southern region of the country [
4], has one of the highest prevalences of childhood overweight and obesity in the European WHO region [
5]. Growing evidence indicates that environmental and socio-economic factors play a relevant role among determinants of the childhood obesity epidemic. Parental habits can influence children’s habits early in life [
6,
7]. Growth from childhood to adolescence is strongly influenced by the interaction between genetic [
8], social, nutritional and environmental factors, that increasingly come from the world outside the family, and in particular from school and the community [
9]. Therefore, the study of the interaction between family or environmental factors and body weight is important to identify determinants [
10] and potential intervention targets for childhood obesity [
11].
The present study sought to investigate the influence of parental physical activity, dietary habits, obesity level, sociocultural factors and the interaction with the geographic area, on the weight status of children and adolescents in Italy.
4. Discussion
These data shed new light on the regional differences of BMI in Italy, showing that (1) there is a direct relationship between the BMI of children and parents that is independent of a geographical area; (2) the eating or physical activity habits of parents are transmitted to their children even if they do not directly affect the BMI of the children; (3) geographical area is not in itself a determinant of the BMI of students.
Diet and physical activity are among the best-known and studied factors that influence a person’s weight. Adherence to the Mediterranean Diet (MD) and physical activity were reported to reduce the risk of developing cardiovascular risk factors (hypertension, diabetes, dyslipidemia) and chronic non-communicable diseases from childhood onward [
23,
24,
25]. Family environment is therefore now considered an important target for prevention of childhood obesity, which often tracks into adulthood [
26]. Excess body fat has been attributed to both high intake of energy-dense, nutrient-poor foods and beverages, such as chips, salted snacks, sweets and soft drinks, and a sedentary lifestyle [
27]. The World Health Organization (WHO) indeed recommend associating adherence to the MD with at least 60 min of daily moderate-to-vigorous physical activity for children and adolescents in order to reduce the risks of obesity [
28] and to achieve proper psychomotor development [
29]. Unfortunately, the MD appears to be followed less and less by younger generations in most Mediterranean countries [
30,
31], sedentarism is spreading [
32,
33] and childhood obesity is on the rise. In Europe, childhood obesity has a North to South gradient [
4,
5], also observed at a national level in Italy [
4]. The search for the determinants of these differences is of great interest for prevention strategies.
Parents’ habits are among the main factors that shape the lifestyle habits of their children, influencing their respect for healthy patterns especially at a developmental age [
33]. It has, in fact, been reported that the adherence of parents to the MD favorably conditions the eating behavior and food choices of their children [
34,
35,
36,
37,
38]. It must be said that other studies showed a moderate or weak association in dietary habits, with remarkably varied results [
39]. In the present study, the adherence of parents to the MD favorably affected the students’ MD, although an inverse association was observed with age. This pattern may suggest a deviation from family habits during the transition from childhood to adolescence, a stage characterized by marked shifts in cognitive development and an increased sense of autonomy in decision-making about own eating patterns [
37]. Thus, combined with evidence that eating behavior is established early in life, these findings suggest that childhood and adolescence are better stages for establishing healthy dietary habits to prevent obesity [
40]. In the present study, the amount of physical activity practiced by children was also affected by parents’ habits, as described in previous studies [
33]. Parents can influence children’s physical activity through modelling, providing support for physical activity in the home environment and establishing rules or expectations for physical activity [
41].
When considering geographical differences, the prevalence of obesity was found to be higher in Calabria, a Southern Italian region, than in Tuscany, in line with recent data [
4]. However, in the multivariate regression analysis, the geographical region was not selected as an independent determinant of student obesity, even though Tuscan children moved more than Calabrian children. In contrast to a previous study in Italy [
42], no regional differences in MD habits were found.
Importantly, in the present study adherence to the MD and physical activity do not emerge as determinants of childhood obesity. This observation agrees with a recent systematic review where an inverse association of MD adherence with BMI values or the prevalence of overweight and obesity was observed in only 10/26 papers investigating children and/or adolescents [
43]. Exploring the relationship between the MD and overweight/obesity is indeed complex. Cross-sectional design studies do not permit the inference of causal relationships between MD adherence and anthropometric variables. Secondly, BMI is not a clear indicator of abdominal adiposity or fat mass. Finally, self-reported measurement studies could have been influenced by the fact that obese individuals are more likely to under-report their body weight.
To the best of our knowledge, this is the first study to explore the relationship between nutritional knowledge and obesity in adolescents and their parents. Interestingly, there appears to be a discrepancy between the level of nutritional knowledge and obesity in adults and students. More precisely, the lower nutritional knowledge of students in Calabria than in Tuscany was closely associated with a higher degree of obesity. Conversely, regional differences in obesity were independent from nutritional knowledge among adults. Although proper knowledge of nutrition does not necessarily translate into a healthier BMI [
44], other cultural descriptors, such as the level of education of parents, could help to better explain these findings. The influence of regional differences on students’ BMI indeed disappears when the education level of parents, the only socioeconomic indicator available in this study, is introduced into the model. At this point the only variable that continues to influence students’ obesity is the phenotype of the parents. If parents are obese, children are more likely to also be obese. In the context of the family environment, socio-cultural aspects were found to play a key role; children from low socioeconomic status were reported to be at the highest risk of obesity [
45]. According to Nau et al. [
46], social factors mainly operate through physical activity and dietary factors. In Italy, regional differences exist in the availability of sports facilities and of trained personnel for various sports; in the amount of caloric intake; in the level of education of the parents, which was observed to be different in the two populations [
47]. The combination of these factors affects the BMI of both children and parents. In conclusion, even though the transmission of virtuous habits appeared to occur from parents to children, parent–child BMI remained the only strong association found. Parental obesity can therefore be the point of convergence of the complex interactions between parents’ and children’s habits and should be one of the most important factors to look for.
This study has several potential limitations. First, this study does not allow for a clear analysis of the role of socio-economic factors. In fact, it was not possible to use the income parameter in a study with these characteristics. The level of education is not a reliable proxy in countries such as Italy where the degree of education is not necessarily associated with income. Second, the participation rate was low although in line with current reports. Third, biases inherent in the use of referred data, such as anthropometry, eating habits and level of physical activity, are possible. Fourth, the use of a convenience sample and the small number of schools examined do not allow us to generalize our results. Studies based on large random samples that are representative of the Italian adolescent population are obviously warranted. Finally, the Mediterranean Diet score investigates the frequency of food consumption by disregarding the total amount of food consumed and excluding other factors that may affect childhood obesity such as snack food and sweetened beverages.