Comparison of prevalence data of obesity in children and adolescents around the world remains difficult because of the lack of standardization and interpretation of indicators of overweight and obesity in these age groups. Usually local or national percentile distributions for weight-for-age, weight-for-height, or BMI-for-age are used. Not only do these differ between regions and nations but they are also subject to change over time. In addition, different percentile cut-off points are used for the definition of overweight or obesity (e.g. 85th, 90th, 95th and 97th percentiles are used in different countries).
Another difficulty with these criteria is that when they are applied to older adolescents they do not correspond to the criteria for classification of overweight based on BMI for adults. Recently Cole et al. (17) used data from six large nationally representative cross-sectional growth studies from various parts of the world. They established centiles of the distribution of BMI by age. Those centile curves that, at age 18 years, passed through the widely used cut-points of 25 and 30 kg/m2 for adult overweight and obesity were then used to define BMI cutpoints by age. These proposed cut-points are less arbitrary and more internationally based than current alternatives.
With respect to the interpretation of criteria of overweight in different age groups it is also important to know whether or not they are predictive of later obesity. It is now generally accepted that body weight before the age of 6 years has very limited predictive power for the chances of becoming an overweight or obese adult irrespective of the family history of obesity (18). Data at this age may, however, be predictive in another way, as has been suggested by Rolland-Cachera and others (19). The BMI-for-age from infancy until adulthood has the form of a J-shape. The nadir of this curve usually is in the age range of 5 to 7 years of age. It has been
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