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Body mass index (BMI) is a person’s weight in kilograms divided by the square of their height in meters. The standard formula would be pounds divided by inches squared. The BMI formula combines the two measurements into one number that can provide a standardized measurement for overall health risk in humans.
Lambert Adolphe Jacques Quetelet had the idea almost 200 years ago to implement a standard to identify human obesity. He was from Belgium, and his human samples consisted of western Europeans. He had a variety of interests. However, he was not a doctor or health care practitioner in any form.
By convention, BMI provides an estimate of healthy body weights for individuals and helps to identify when someone may be underweight or overweight. It can also help monitor changes in body composition over time. However, BMI does not account for age, gender, body frame, genetics, or other characteristics that have a profound effect on health risks associated with normal values. These may also include individual choices such as tobacco use, alcohol consumption, and sedentary lifestyles.
It has been widely accepted as a reliable indicator for estimating population means related to obesity since its introduction over 100 years ago. However, the index may not give accurate results when applied to individual patients due the factors mentioned earlier . Despite this, BMI remains an effective “screening tool” allowing doctors to determine a persons current health status. However, other factors such as family history and blood lipid testing will be required for the best overall health status of all humans at any given time.
The World Health Organization (WHO) has established the following categories for BMI to help differentiate between different levels on a population basis:
Underweight – below 18.5 kg/m2; Normal Weight range – from 18.5 kg/m2 to 24.9 kg/ m²; Overweight 25–29 .9kg / m² ; Obesity 30+ Kg/. M² plus Morbid obesity 40 + Kg / M² .
While most online resources list BMI classifications in metric, this free .pdf chart lists classifications using standard USA customary measurements.