Body image perception and body composition in early adolescents: a longitudinal study of an Italian cohort

A longitudinal study design was chosen, and data were collected and analysed in a sample of 134 children (64 males and 70 females) attending middle school in the Emilia Romagna region (northern Italy). The students were measured three times at regular intervals: at first measurement mean age was 11.8 ± 0.3 yrs. in males and 11.9 ± 0.3 yrs. in females, then they were measured after 1 year and after 2 years. Only children who received parental written consent and agreed to participate were allowed to take part in the study, without any compensation. The study was approved by the Bioethics Committee of the University of Bologna (approval n. 2.18). A flow chart regarding the selection of the sample is shown in Fig. 1. Only native Italian adolescents with no missing data in all the three measurements were included in the study. Immigrant subjects were excluded since they were not a uniform group, but belonged to different ethnic groups. A trained operator directly collected the anthropometric measurements according to standardized rules described in the Procedures section.

General information about demographic (e.g. sex and age) and sport participation (sport practice - considered as club sports, namely planned sports activities led by staff) and the amount of time involved (hours per week) were collected by a questionnaire. The sport practice frequency of each subject was determined by the hours of sport training during a typical week as declared by the subject.

The data analysis was performed using Statistica for Windows, version 8.0 (Stat Soft Italia SRL, Vigonza, Padua, Italy).

The suitability of the sample size for each analysis was assessed using the G-Power software 3.1.9.2. An a priori power analysis was conducted to ensure that the number of participants was representative for the purposes of this study. To identify the sample size for the study, we assessed an ‘a priori: computer required sample size- given α, power and Effect Size’ by G*Power (3.1.9.2, Universität Kiel, Germany). A repeated measures ANOVA was selected as the F test of all the test family, imputing the following parameters: α = 0.05; (1 − β) = 0.95; Effect Size f = 0.25; number of groups: 2; number of measurements: 3. The outcomes parameters thus calculated detected a sample size of 44 participants, but additional subjects were involved to ensure availability of data in case of problems with data collection.

Variables normality was verified with the Shapiro–Wilk test. The means and SD of the baseline data (1^stclass) and in the following years (2nd and 3rd classes) were calculated. Percentage frequency was determined for qualitative variables (weight status).

Repeated measures ANOVA was used to assess differences between the values carried out on subjects in each of the 3 years of measurement (from first class to third class), while non parametric ANOVA was used to evaluate the differences among body image parameters, since they are not normally distributed.

Differences in the frequencies were tested by the chi-squared test. Since in the present study the comparison between the weight status consisted of multiple pairwise comparisons (three groups), according to Bonferroni correction, the results were considered statistically significant if p was < 0.05/3 or 0.017.

Backward multiple regression analysis was carried out to assess possible predictors of FID and FAI. Anthropometric variables, sex, weight status and maturity status were included into the model. Predictors input into the model were those found to have significant associations with FID and FAI (i.e., p < 0.05), while those with p > 0.05 were removed from the model.

Table 1 shows the anthropometric and body composition characteristics of the sample during the three consecutive years in both sexes. Considering sex differences, ANOVA showed significant differences in body proportion (leg length and cormic index), in waist and hip circumferences and relative indexes (WHR and WHtR), in three skinfold thicknesses (suprailiac, medial calf and thigh) and in the sum of skinfolds.

Greater are the differences connected with the variation of the measurement over time. Except for cormic index, WHtR, three of skinfold thickness and %F, all the other characters presented a significant variation with age.

Analysing these variations in more detail, considering also the post-hoc, we can observe some different trend in the two sexes. In males, from the 1st to the 3rd class, height increment was 13.43 ± 4.24 cm, sitting height increment 6.21 ± 3.48 cm, leg length increment 7.23 ± 2.45 cm and weight increment 11.03 ± 4.15 kg.

Ninety-two percent of males practiced club sports. This percentage was constant in the first 2 years, with a slight decrease (90%) in the 3rd class. Weekly amount of club sports increased with age, with significant difference between the 1st and 3rd class.

In females, from the 1st to the 3rd class, height increment was 7.32 ± 3.51 cm, sitting height increment 4.40 ± 2.55 cm, leg length increment 2.92 ± 2.45 cm and weight increment 8.88 ± 4.15 kg. The cormic index did not show any significant variation with age, even though a tendency to increase was observed. BMI showed a significant increase between all the age classes (p < 0.001). Waist and hip circumferences showed a significant increase with age (p < 0.05), so that WHR showed a slight decrease with age, but not significant. WHtR did not show any significant differences during the 3 years, and also the subjects with values above the cut off remained stable over the 3 years (9.52%).

Sports were practiced by 89.9% of the girls in the first class, passing to 87.1% in the second class and to 90% in the 3^rdclass. Weekly amount of club sports slightly increased during the 3 years, but not significantly.

Considering the prevalence of weight status in males (Table 2), no significant differences were observed among the 3 years. Normal weight prevailed in all the considered classes, showing an increasing trend with age. A small percentage of obese boys were observed in the 1st class, but this category disappeared in the following years, and a reduction of overweight subjects was observed.

Similarly, in females the weight status prevalence did not significantly differ among the 3 years and normal weight subjects prevailed (Table 2). Contrarily to males, in the 1st and 2nd classes a small percentage of underweight girls were observed. Even if the differences were not significant, a slight increase in the prevalence of overweight in the 3rd class was observed.

According to equation of Mirwald et al. [45] the mean age at PHV of the male sample was 14.00 years (SD = 0.62). The majority of the boys were average maturers (91.9%), only 3.2% were early maturers, and 4.8% late maturers. In the 3rd class about 93% of the subjects were approaching the PHV (distance from PHV = ± 0.5 years).

With reference to females, data regarding age at menarche showed that in the 1st class, 29.0% of the sample had reached it; this percentage increased to 62.9% in the 2^ndclass and to 74.3% in the 3rd class. The mean age at menarche was 11.97 (SD = 0.94 years).

Body image perception showed significant differences between sexes (Table 3). The difference in the choice of perceived current figures was significant, since females have chosen thinner silhouettes than males. Body image dissatisfaction (FID) is greater in females. Males presented a greater misperception of their weight status, showing a greater underestimation than females.

Body image parameters did not show any significant variations with age (Table 3). In all 3 years, on average, males chose normal weight silhouettes both for the perceived current figure and the ideal figure. As a consequence, the FID score indicated no dissatisfaction with their body, especially in the 3rd class. As regards the misperception of their weight status, FAI score indicated no variations with age; a tendency to underestimate the weight status was observed in all the three considered years.

On average, the perceived current figure chosen by girls (Table 3) belonged to the normal weight category, but it was in the upper extremity (nearly overweight). The mean ideal figure chosen also falls into the normal weight category, but presented lower values than the perceived current figure, as testified by positive mean values of FID, indicating a desire to be thinner. FAI score approximated zero, indicating no inconsistency in the perception of weight status, even though with a slight tendency to underestimation, testified by negative mean values.

We performed different multiple linear regression models to evaluate the impact of age, sex and BMI on body image dissatisfaction (assessed by FID score) and on inconsistency of weight status (assessed by FAI score) in the adolescents during their 3 years of middle school (1st class, 2nd class, and 3rd class). The results of these predictive models are presented in Table 4.

As regards FID, both sex and BMI are significantly associated with FID and both are positive predictors. Body image dissatisfaction increases as BMI increases and being a female increases the dissatisfaction. The models explain 16% of the variance in the 1st class, 39% in the 2nd class and 52% in the 3rd class; all models have highly significant R².

Being females is associated with a higher overestimation of one’s own weight status, as shown by the significant and positive association between sex and FAI (Table 4). In the transition to the 2nd class and 3rd class, the adolescents showed an increase of overestimation as their BMI increased. The models explain 5% of the variance in the 1st class, 17% in the 2nd class and 20% in the 3rd class; all models have highly significant R².

The present study considered the trends in body composition and in the prevalence of overweight and obesity, assessed using the Cole cut-off values [37, 38], in Italian adolescents followed longitudinally over the 3 years of middle school. In addition, another aim was to determine whether body composition and weight status during adolescence were associated with the risk of developing body image disturbance. To our knowledge, this study is the first to evaluate the longitudinal association between these parameters in young Italian adolescents.

As regards the first aim, the longitudinal variations in body composition of the subjects of the two sexes are connected with the phase of maturation they were approaching.

The male sample during the 3 years was approaching the growth spurt, and in the last year of measurement about 93% of the boys were near the time of PHV. This is reflected in the great height increment and in the prevalence of leg length growth in comparison with trunk growth. Differential timings of growth of height, sitting height and leg length are in fact known, since with growth a change in relationship between leg length and sitting height is observed. The growth of leg length precedes the PHV, while sitting height growth occurs after PHV [32]. The trend in parameters connected with body composition confirmed this specific stage of growth. During the 3 years, the sum of skinfolds showed a tendency to decrease in males, and, as a consequence, a significant decrease of %F with age was observed, accompanied by a significant increase of FFM were observed. These data are in accordance with the body composition and fat distribution changes that occur during male adolescence [32].

The percentage of mature girls increased with age, changing from 29.0% in the 1^stclass to 74.3% in the 3rd class. The mean age at menarche was 11.97 (SD = 0.94 years). A significant increase with age was observed for all the considered parameters, with height, weight, waist and hip circumferences showing significant differences among all the considered age classes. The height increment was lower than that observed in males, while the sitting height increment was higher than that of leg length: this reflects the different phase of maturation of the two sexes, with girls ahead compared to males.

Also connected with sexual dimorphism is the trend of parameters connected to body composition: skinfold thicknesses generally showed a significant increase in girls during the 3 years; it follows that the %F significantly increased from 19.55% in the 1st class to 22.19% in the 3rd class.

In males, BMI remained quite stable during the three school years. The percentage of normal weight males was lower than the national data [51], which reported an incidence of 75.9% in 11-years-old boys and 78.4% in 13-years-old boys, but it tended to approach these values with age. Percentages of overweight boys in the present sample were higher than the national data, but a tendency to decrease with age was observed. Obesity is slightly higher in the 1st class, but disappeared in the following years. Contrarily to the national data, there were no underweight subjects in the present sample. In girls, BMI showed a significant increase. Even if the weight status prevalence did not significantly differ among the 3 years and normal weight subjects prevailed, a reduction in underweight prevalence and a slight increase in the prevalence of overweight with age were observed. The percentage of normal weight girls was comparable to the national data [51], but the percentage of overweight girls was higher, and obese and underweight subjects were lower. Regarding sex differences in weight status, females showed a higher incidence of normal weight, and a lower incidence of overweight and obesity.

The latest data [52] from the WHO Childhood Obesity Surveillance Initiative (COSI) reveal that in countries like Italy, Portugal, Spain and Greece, there has been an important decrease of obesity, which is attributable to a very significant effort that these countries have made in recent years in the management and prevention of childhood obesity [53], although rates are still high. Despite the fact that the incidence of overweight in the present sample was high, the percentage of subjects engaged in sports practice (about 90% in both sexes) suggests that the issue of prevention was taken into account. Low levels of PA in adolescents is a critical cause for the obesity epidemic in developed countries [53, 54], and obese adolescents are generally less physically active (PA) than normal-weight adolescents [55]. As a consequence, increasing physical activity is probably one of the best strategies to reduce the prevalence of overweight and obesity in youth [56]. In addition, fat distribution may have more significant implications for health than the total amount of body fat. In the present study only a small percentage of subjects of both sexes presented a WHtR higher than cut-off. Visceral fatness or the accumulation of intra-abdominal adipose tissue increases cardiovascular risk in children, and it has been shown that that the most active individuals have the lowest visceral fat after adjusting for total body fat. This suggests that PA may elicit a proportionally larger decrease in fat stored in the intra-abdominal cavity than in other regions in people with visceral fatness [57, 58]. Cross-sectional data also suggest that PA could promote a reduction of visceral fat and trunk fat in pre-pubertal and pubertal children [59, 60]. In this longitudinal study, sports practice is high and regular, and once again this can be traced back to the preventive campaigns that the region in which the study took place [61] has put in place to encourage the spread of a healthy lifestyle among children and adolescents.

The second aim was to assess whether the change in body composition parameters and weight status influence body image perception. In both sexes, body image perception did not show any significant variations with age and both the perceived current figure and the ideal figures were chosen fall into the category of average in normal weight silhouettes. Nevertheless, females tend to choose a thinner ideal figure than the perceived current figure, as also testified by the FID. The average FAI index of both sexes is close to 0, implying a correct perception of their own weight status.

The data of the present study strengthen the notion that body image dissatisfaction and perception are mostly influenced by moderating factors such as sex and BMI, which should be considered in studies regarding youth. The results of the multiple linear regression analysis showed that BMI is a common denominator for both sexes, and as it increases also body dissatisfaction increases. With the increase of BMI, in the adolescents of the 2nd class and 3rd class, increases the overestimation of their weight status. In addition, girls are more vulnerable than males for both dissatisfaction. In girls, fat mass increases more rapidly than in boys during adolescence. Important variations in body composition, which are influenced by age and sex, and which include BMI, subcutaneous fat and relative fat distribution [31, 62‐64] can be sources of dissatisfaction in body image perception.

The results of the present study are in accordance with those of other Authors [65‐67], which showed that increased BMI is a key point in influencing body image perception. It is associated with lower self-perceptions of social acceptance and physical appearance, and subjects who demonstrate low perceptions of self-concept are also generally less willing to participate in activities with peers [68‐70].

The strength of this study is the three-year longitudinal design in which anthropometric parameters of the adolescents were directly measured by an expert anthropometrist, and not self-reported.

A limitation of this study could be connected to the use of standardized body silhouettes instead of computerized assessments, which allow to assess separate characteristics of body image, such as overall size or shape. This technological method presents a good flexibility to visually represent how users perceive themselves, compared to fixed silhouettes. In addition, it allows detailed information to be gathered regarding the assessments of individual body areas [71, 72]. Even if the silhouettes used in the present study are widely utilized in the literature [73, 74] they do not allow the assessments of muscularity, an important aspect considered in studies on older subjects [75, 76].