Assessment of risk for overweight by monitoring body mass index is now recommended in developed countries and more recently in urban areas of less developed countries. Body mass index is known to track significantly from childhood, to adolescence, and then to adulthood.1 Body mass index should therefore be assessed and monitored during childhood and adolescence to allow for early, and perhaps more effective, intervention strategies. Tim Cole and colleagues' validated thresholds or cut offs for body mass index, recommended by the International Obesity Task Force to define and identify overweight and obesity in childhood,2 are internationally recognised.

Rather less attention has been paid, however, to the importance of assessing body mass index to monitor undernutrition. In this week's BMJ, Cole and colleagues extend this work to provide cut offs for body mass index to define “thinness” in children and adolescents.3

Malnutrition, or …