Taken from the official translation of the German Sustainable Development Strategy
The body mass index (BMI) is a benchmark that is used to identify excess weight and especially obesity. It is calculated by dividing the body weight in kilograms by the square of an individual’s height in metres (kg/m²). This calculation does not take account of age- and gender-specific differences or of an individual’s body mass composition. Since the ratio of height to weight constantly changes in children and adolescents, there is no single threshold value for all age groups for the classification of excess weight and obesity. Excess weight and obesity among children and adolescents are defined by using an individual’s age and gender to compare his or her BMI with those of a predefined reference population. The percentile reference values proposed by Katrin Kromeyer-Hauschild are used as a comparison, as recommended by the Childhood Obesity Federation (AGA). In this method, children and adolescents are said to be overweight if their BMI is above the 90th age and gender-specific percentile of the reference population (> P90), that is to say if they fall within the range of those 10% of the reference group with the highest BMIs. A BMI above the 97th percentile of the reference population (i.e. as high as the 3% of children and adolescents with the highest BMIs) is classified as obesity (> P97). For example, girls and boys aged three with a BMI of 18.8 kg/m² are considered to be obese. These reference values are based on details of body size and weight that were recorded between 1985 and 1998 in various regions of Germany, using different methods.
The data for the indicator was collected by the Robert Koch Institute. The German Health Interview and Examination Survey for Children and Adolescents (KiGGS) for the period 2003 to 2006 delivered the first nationwide representative findings. Comparable measurement data are available for the period from 2014 to 2017 from the second follow-up of the KiGGS study (KiGGS Wave 2). To allow proper data comparison, the findings were standardised on the basis of extrapolated population data for 31 December 2015.
For the 2014-2017 period, 3.9% of the 3 to 10-year-olds and 8.0% of the 11 to 17-year-olds were classed as obese. While there were no differences between the sexes in the 3-10 age group, the rates for the 11 to 17-year-olds were 7.2% for girls and 8.7% for boys. In the period from 2003 to 2006, the proportion of 3 to 10-year-olds with obesity was about 5.2%; among the 11 to 17-year-olds, it was about 8.3%. In that period too, girls and boys in the 3-10 age group were equally affected. The figure for the 11-17 age group broke down into 8.2% of the girls and 8.4% of the boys. The obesity rate has therefore fallen more sharply among 3 to 10-year-olds than in the 11-17 age group. While it fell by 1.0 percentage points among girls aged 11 to 17, it showed a slight increase of 0.3 of a percentage point among boys in that age group.
The percentage of overweight 11-17-year-olds (> P90) had not changed substantially since the 2003-2006 period, showing a decline of 0.6 of a percentage point to 12.3% in the 3-10 age group and an increase of 0.6 of a percentage point to 18.7% among 11 to 17-year-olds.
Key factors in becoming overweight are nutrition and exercise habits, which vary considerably when the findings are examined in the light of socio-economic status (SES). The findings of KiGGS Wave 2 confirm that 3 to 17-year-olds with a low socio-economic status more often have an unhealthy diet and more rarely take part in sport than their contemporaries with a higher socio-economic status. The risk of excess weight and obesity among 3 to 17-year-olds with a low socio-economic status are about three to four times greater than in the high status group; each group comprises about 20% of the sample population.