Body Mass Index (BMI) is one of the assessments for determining the level of obesity ,  where weight and height are used to find out whether the weight is healthy or not,  It should be noted that this evaluation is often linked to a total Fat mass in the body ; It is more an indicator than a measure of the total level of fat mass in the body, and its height most often indicates an increase in the percentage of total body fat. 
It is worth noting that the basis for determining BMI values is the extent to which excess fat affects disease and death risk, so its height indicates a high risk of developing it, and among the health conditions that are associated with being overweight or obese are: premature death, cardiovascular disease, High blood pressure, degenerative arthritis, diabetes , and some types of cancer, and it is worth noting that the BMI is recommended for children and adolescents as well, as it is measured for them as it is measured for adults and then the result is compared with the percentile ; It is the value of a variable that includes under it a certain percentage of the readings, which we will mention later. 
The body mass index can be calculated by dividing the body weight in kilograms by the square of its height in meters, and the equation in metric units is as follows: 
BMI = weight (in kilograms) ÷ (height (meters)) ²
For example, if a person's weight equals 70 kilograms, and his height equals 1.75 meters, then his body mass index is calculated as follows: 
BMI = 70 kg (1.75 m) ² = 22.9 kg / m²
Semantics of BMI results
The result of the BMI calculation indicates the proportions of the weight to the height; Where this indicator determines if a person is underweight , or if he has a healthy weight or overweight, or suffers from obesity, and therefore if the body mass index is outside the range of the ideal weight index, the health of the body is more at risk. its owner may offer injury to many health problems that we have mentioned previously,  It should be noted that the body mass index is used to express different weights for both sexes from the age of 20 years and above,  and in the table comes illustrates the body mass index values, classification of weight And the interpretation of these values: 
|Body mass index (kg / m²)||Weight rating||Interpretation of the BMI value|
|Less than 18.5||Being underweight or thin||The weight is less than normal, and it may need to be increased to reach a normal weight, and a nutritionist should be consulted|
|18.5--24.9||Weight is healthy||The weight is appropriate for height, and is less likely to have health problems|
|25.0--29.9||overweight||He may need to lose excess weight for health reasons, and a nutritionist should be consulted|
|30.0 or more||Obesity||Excessive weight gain, and health may be at risk if weight is not lost, and a nutritionist should be consulted|
Although the BMI formula is the same for adults and children, its interpretation varies between children and adolescents according to their ages and genders, due to the difference in the distribution of fats in their bodies. : Age growth charts) to determine the body mass index of children and adolescents according to the value of the percentile , so that this value is compared to the BMI result of the child or adolescent with his peers of the same sex on the growth chart, for example a child suffers from obesity if his body mass index is 95 By percentages or more on the growth chart , the interpretation of this is that the child has more than 95% fat percentage of his peers of the same sex and age, The following table shows the adopted values for determining BMI for children and adolescents, and their classification: 
|BMI (in percentile values)||Weight rating|
|Less than 5%||Weight loss|
|5% to less than 85%||Normal weight|
|85% to less than 95%||overweight|
|95% or more||Obesity|
For more information about how to calculate a child's BMI, you can read the article How to know a child's normal weight .
Measuring body mass index (BMI) is one of the methods used by most health care providers. Although it is a simple and inexpensive means of detection, it is not approved for diagnosis, as specialists need further evaluation to assess health risks, and from these evaluations; Body fat percentage , exercise exercise, nutritional history, as well as family health history. 
It is worth noting that BMI is not necessarily an accurate indicator of the level of fat in the body, it may be the same for two different people, but one of them has a higher fat percentage while the other has a higher percentage of muscle mass, in addition to the fact that women's bodies have a higher percentage of fat compared to Men's bodies are on the same measure of body mass index, and the same is true for black people who have less fat than white skinned people, while Asians have a higher fat percentage than white skinned people,  and it is worth noting that those who have muscle mass They have a high BMI without being linked to the risk of health problems. 
Other methods used to determine body size include: the waist-hip ratio , and body composition ; Which calculates the mass of fat and muscle mass in the body, and it is worth noting that these methods focus more on measuring the percentage of fat and its distribution in the body, so using it together with the body mass index may contribute to improving the accuracy of assessing health risks associated with weight. 
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