The Complete Guide to Body Mass Index (BMI)
Body Mass Index (BMI) is a scientifically derived value based on the mass (weight) and height of a person. It is defined as the body mass divided by the square of the body height, expressed in units of kg/m². Invented in the 1830s by Adolphe Quetelet, BMI remains the premier screening tool used by healthcare professionals worldwide.
Why Measure BMI?
BMI provides a quick, inexpensive, and reliable way to screen for weight categories that may lead to health problems. It helps categorize individuals into groups: underweight, normal weight, overweight, and obesity.
Understanding the Math
- Metric Formula: Weight (kg) ÷ [Height (m)]². This is the standard method used globally.
- Imperial Formula: [Weight (lbs) ÷ [Height (in)]²] × 703. This is primarily used in the USA and UK.
Who Should NOT rely on BMI?
BMI is a general screening tool, but it has limitations for specific groups:
- Athletes: Muscle is denser than fat. Athletes may have a high BMI but low body fat percentage.
- Elderly: Older adults tend to have more body fat than younger adults for the same BMI.
- Pregnant Women: Weight gain during pregnancy skews BMI calculations significantly.
Health Risks of High BMI
Being in the "Overweight" or "Obese" category increases the likelihood of:
- Type 2 Diabetes and Insulin Resistance.
- Cardiovascular diseases like high blood pressure and stroke.
- Respiratory problems such as sleep apnea.
- Joint issues like Osteoarthritis.