The relationship between body mass index and body size dissatisfaction in young adolescents: spline function analysis

Cortese, Samuele, Falissard, Bruno, Pigaiani, Yolande, Banzato, Claudia, Bogoni, Giovanna, Pellegrino, Maristella, Vincenzi, Brenda, Angriman, Marco, Cook, Solange, Purper-Ouakil, Diane, Dalla Bernardina, Bernardo and Maffeis, Claudio (2010) The relationship between body mass index and body size dissatisfaction in young adolescents: spline function analysis. Journal of the American Dietetic Association, 110 (7), 1098-1102. (doi:10.1016/j.jada.2010.04.001).

Abstract

This study assessed how body size dissatisfaction (BSD) varies in relationship to specific body mass index (BMI) values in a sample of preadolescents. A novel statistical approach based on spline function, suitable to assess in detail how two variables are related, was used. The study was conducted between December 2004 and March 2005. Students (aged 11 to 14 years) from seven selected secondary schools in Verona, Italy, were invited to participate. The final study group included 678 subjects. BSD was assessed using the Body Image Assessment Procedure. BMI values were expressed as z scores. It was found that, in the total sample, slightly underweight subjects (BMI z scores=?0.5) had no BSD. BSD progressively increased (current body size > ideal body size) for BMI z scores >?0.5 and became negative (ideal body size > current body size) for BMI z scores <?0.5. In boys, average weight subjects had no BSD. BSD progressively increased for BMI z scores >0 and became negative for BMI z scores <0. In girls, moderately underweight subjects (BMI z scores=?1) had no BSD. BSD progressively increased for BMI z scores >?1 and became negative for BMI z scores <?1. Although sex significantly moderated the relationship between BMI and BSD (P<0.001), socioeconomic status did not (P=0.459). Because average weight and slightly underweight young girls desired a thinner body, our study suggests that these subgroups should receive particular attention in public health programs as well as in dietetics clinical practice.



Body image relates to a person's perceptions, feelings, and thoughts about his or her body, and is usually conceptualized as incorporating body size estimation, evaluation of body attractiveness, and emotions associated with body shape and size (1). Concerns with body image, including body size dissatisfaction (BSD), are common among adolescents (2, 3, 4 and 5). They are associated with emotional distress, low self-esteem, and increased risk for eating disorders (6 and 7).

Most (8, 9, 10, 11 and 12), although not all (13 and 14), studies have reported a significant positive correlation between body mass index (BMI) and BSD. However, these studies used statistical analyses suitable to estimate only whether BMI and BSD are associated. No epidemiologic studies have investigated in detail how BMI and BSD are associated. Such a detailed analysis would provide information on the specific BMI categories that display BSD. This, in turn, would offer insight into what factors might be useful to include in health programs that target specific weight groups. Such analysis would also provide useful insights for clinical practice, suggesting which weight categories should receive particular attention in the management of BSD.

Moreover, it is still unclear how sex (3) and socioeconomic status (SES) (15, 16 and 17) moderate the inter-relationship between BMI and BSD in preadolescents.

The aim of our study was to assess how BSD relates to specific BMI values and the influence of sex and SES on this relationship. It was decided to only include young adolescents to collect data that could potentially be useful for prevention programs addressing BSD in this young population.

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Contributors

Author: Samuele Cortese

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