Olds et al.1 recently described the trends in the prevalence of overweight and obesity from 1985 to 2008 from a meta-analysis of 41 studies conducted in Australian children and adolescents. They showed that the increase in the prevalence of overweight and obesity among Australian children has slowed and plateaued over the past 10 years. Olds et al.1 reported that the findings were consistent with several recent reports from Australia, Sweden, France, the United States and New Zealand. They failed, however, to comment on a unique study conducted on over half a million male adolescents aged 18 years from Sweden.2 In that study, Neovius et al.2 observed that severe/morbid obesity (body mass index (BMI)⩾35 kg m−2; hereinafter called morbid obesity, following the terminology used by Neovius et al.) increased faster than moderate obesity (BMI=30.0–34.9 kg m−2) during the last 35 years (period studied 1969–2005). Unfortunately, these interesting analyses have never been replicated, probably because of the fact that the prevalence of morbid obesity in young people is rather low, and consequently large sample sizes are need to address this question. As Olds et al.1 have managed to put together raw data on BMI from 70 758 Australian young people, we encourage the authors to conduct additional analyses to further understand whether the trends reported by Neovius et al.2 are the same in other cohorts. The authors made a first attempt to address this question by examining the mean BMI values within weight-status groups. They observed no increase in mean BMI in the obese group; however, it is possible that increases in the high section of the BMI spectrum could be balanced by decreases in the low section of the spectrum, resulting in similar mean BMI values.
Neovius et al.2 used the International BMI cutoffs for adult population (BMI⩾35 kg m−2), as their sample was aged 18 years; yet, this cutoff cannot be applied to Olds et al.'s population (aged 2–18 years). As there are no international sex- and age-specific BMI cutoffs available to define morbid obesity in children and adolescents, other statistical approaches should be explored. The prevalence of obesity was similar in both studies (ranging from 1–2% to 5–6%).1, 2 Neovius et al.2 observed that the percentage of morbid obese participants ranged from 0.1 to 1.3%. Taking an arbitrary averaged percentage of 0.5%, a sex- and age-specific 95th percentile could be used to define morbid obesity; yet, sensitivity analysis should be conducted. A figure plotting the BMI values corresponding to the sex- and age-specific 99.5th percentile (y axis) from the first to the last examination year (x axis) will provide information on whether the prevalence of morbid obesity has increased in Australian children and adolescents over the past years. We are aware that the sample sizes representing the morbid obese group will be small (that is, 70 758 × 0.005=354, a number that should be further divided by examination-year surveys). As the health risks and costs of obesity-related morbidity increase disproportionately with morbid obesity, it is important to assess morbid obesity in prevalence studies, and the present Australian study provides a good opportunity to do so.
Olds TS, Tomkinson GR, Ferrar KE, Maher CA . Trends in the prevalence of childhood overweight and obesity in Australia between 1985 and 2008. Int J Obes (Lond) 2010; 34: 57–66.
Neovius M, Teixeira-Pinto A, Rasmussen F . Shift in the composition of obesity in young adult men in Sweden over a third of a century. Int J Obes (Lond) 2008; 32: 832–836.
The authors declare no conflict of interest.
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Ortega, F., Ruiz, J. & Labayen, I. Trends in the prevalence of morbid obesity in Australian children and adolescents from 1985 to 2008: what do we know about?. Int J Obes 35, 1331 (2011). https://doi.org/10.1038/ijo.2011.127
International Journal of Obesity (2011)