A two- to nearly fourfold increase in the prevalence of childhood obesity has been reported from different countries all around the world [9, 10]. Table 1 summarizes studies performed in 14 selected countries. These studies were selected because they offer – with certain limitations – the opportunity to compare different global regions. Although nearly all studies reported an increase in the prevalence of childhood obesity, the individual prevalence rates and the degree of increase differed considerably between the different countries. There was a range of prevalence rates of overweight from 1.9% (Ghana) to 30.4% (USA) and from 1.7 to 15.5% for obesity, respectively. The annual increase of prevalence rates differed from a maximum of 28% in Haiti to a decrease by 9% in Russia. This variability may indicate true differences in prevalence rates or increments of the respective rates. Data quality may be variable between the countries, but most studies covered at least 80% of population [8]. Therefore, selection bias is an unlikely explanation. Different classification criteria used in the respective countries, however, must be considered. Nine of 14 studies used the definition of the Childhood Obesity Working Group of the International Obesity Task Force (IOTF). The cut-off values for overweight and obesity for different age groups are presumed to represent the widely used cut-off points of 25 and 30kg/m2 for adult overweight and obesity [11]. In adults these cut-off values mark a critical threshold beyond which typical overweight-related diseases and health problems appear and are presumed to be of similar relevance in children. The BMI values of the 90th and 97th percentiles, recommended by the European Childhood Obesity Group (ECOG) as cut-off values in Germany [12] match with those for overweight and obesity in the IOTF definition [13], whereas those for the UK [14] and France [15] differ. The US definition, however, refers to the 85th and 95th percentiles of the CDC growth charts [16, 17]. In table 1 only the publication of Ogden et al. [18] is based on this definition. This explains in part the higher prevalence values compared to the other study in US children [19]. The publication of de Onis and Blössner [8] uses the WHO criteria: overweight is defined as weight for height above 2 SD of an international population [20]. As percentiles are always relative values that underlie alteration with time, it is important, which standard population is used for comparison. In the report of de Onis and Blössner [8] a global prevalence of 2.3% is expected, since 2.3% of values of a normal distribution lie beyond two standard deviations. As the standard population in that study was not the actual world population, but a historical population, a global prevalence of 3.3% was extrapolated to depict the world population of today. In table 1, the respective cut-off criteria are indicated for each study described. In order to make the different countries comparable despite of the diverse time intervals of observation, the increase of overweight was also given as percentage per year. Another possible explanation for spurious differences in the increase rates are the different starting points. While in industrialized countries already high prevalence rates of overweight are found, developing countries started with lower values, but had remarkably high rates of increase in the past years. In a very recent study de Onis and Blössner [8] used the WHO Global Data Base on Child Growth and Malnutrition (Geneva) and found notably high prevalence rates of overweight in preschool children in North Africa (especially Algeria, Morocco and Egypt) with 8.1%, and Latin America (4.4%) [8] compared to the global prevalence of 3.3%. The lowest figures of obesity are reported for southcentral Asia (2.1%), south-eastern Asia (2.4%) and western Africa (2.6%). These are also the regions with the highest rates of underweight. Despite the growing obesity issue the most important nutrition-related problem of developing countries remains malnutrition and underweight, as emphasized by the authors. In that study, data for trends in overweight were available for 38 countries. Of these, 16 countries showed a rising prevalence of childhood overweight (e.g. Bolivia, Ghana, Nigeria, Morocco, Egypt).
An example of rapidly developing countries is the Seychelles in the Indian Ocean (table 1). Some 12.6% of the children are overweight and 3.8% are obese. These figures are as high as in industrialized countries like England or Germany [21], which indicates that rapidly industrializing countries undergo similar cultural changes as Western countries did in the past years.
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