weight for age ratio (P / E): This indicator reflects body mass relative to chronological age. It is influenced by the child's size and weight, which complicates their interpretation because of its composite nature. The low weight for age indicates risk of malnutrition, and high values of weight for age should be classified as excess and not as overweight or obese. height for age ratio (T / E): This indicator reflects linear growth achieved, defects and deficiencies indicate cumulative health or long-term nutrition. This parameter measures chronic malnutrition as a process of deficit in time or stunting, as its rate of increase is slower by environmental influences, for long periods of illness, emotional deprivation or poor diet that is linear growth delay. weight to height ratio (P / T): This indicator is used in the clinical assessment of obesity in children and adolescents. It is considered normal in a standard percentage of 90 and 110, and overweight in excess of 120% of ideal weight for height according to the tables of the NCHS. Some epidemiological studies classified as overweight> 1 and <2 percentile> 85 and obesity ≥ 2 D.E. or ≥ 95 percentile. Body mass index (BMI) or Quetelet Index: This index was derived in 1972 by Keys, the Belgian astronomer Quetelet equation (1869), which relates weight in kilograms by height in meters squared (kg/m2 ). BMI reflects corpulence, and according to many researchers, is an indicator of adiposity by its high correlation with body fat and independence with size, so it can be used as an indirect measure of obesity. According to WHO, a BMI greater than or equal to 25, determines overweight, and a BMI equal or greater than 30, determined obesity. BMI provides the most useful measure of overweight and obesity in the population, because it is the same as for both sexes, and for adults of all ages.In children and adolescents overweight and obesity are defined differently than adults.
Because children are still growing and boys and girls mature at different rates, the BMI of children and adolescents compares height and weight growth charts that take into account age and sex. This comparison is known as percentile of BMI for age. The percentile of BMI for age of a child or adolescent shows how comparing the BMI of the child with other children of the same age. It has the graphics percentile of BMI for age of 2-20 years and sex developed by the National Center for Health Statistic (NCHS) in collaboration with the National Center for Chronic Disease Prevention and Health Promotion the United States, developed in 2000, it should be noted that these charts are a reference standard used in a developed country with high prevalence of overweight and obesity.The recommended BMI calculation only if the P / T is above +1 standard deviation DE that is, should be used only to detect overweight or obese. We suggest a careful analysis when either reflect that status indicators, taking into account that children are in a period of rapid growth, and that an inappropriate restriction in the diet can affect it.
The International Obesity Task Force (IOTF) in an international workshop, set cut points for BMI, to identify degrees of overweight in children and adolescents, according to European recommendations Chidhood Obesity Group and National Center for Health Statistics (NCHS). One of the most important decisions of the workshop was to use the cutoffs for overweight a BMI of 25kg / m² and for obesity a BMI of 30 kg / m² in adults, which in late adolescence were the cutoffs for identification of childhood overweight.
Difficulties in the use of BMI charts for assessing thinness and obesity in children and adolescents are not clear if the excess weight is due to accumulation of fat or more muscle mass development. The great variability of weight and lean and fat components during growth and does not take into account the average age of biological maturation, early or late pubertal development during the classification criteria for overweight NHANES II: those with a BMI> to 85th percentile, and severity slightly overweight P85-95, P90-95 moderately overweight and P ≥ 95 obesidad213. To define overweight and obesity have not been established BMI cut-off points, therefore, different epidemiological studies defined obesity through higher percentiles of 85 and no greater than 95th percentile for age and gender