BMI is an approximation of the degree of fat, or an estimation of the body’s composition whereas body fat is the body’s measurement of lean body tissue to body fat tissue. BMI is a simple and easy way to approximate the degree of body’s fat, instead of focusing solely on weight. Like waist to hip ratio, they both measure locations of fat deposits which can be used to indicate the risk of disease and a person’t fitness level. Either can be used as a baseline comparison useful in assessing the potential for health-risk factors. Knowledge of health history related blood pressure, cholesterol, and heart health should be tracked because of the relationship between body fat and chronic disease. The higher the BMI the higher the risk for morbidity and mortality.
A BMI of ≥25 is considered overweight, while a BMI of ≥30 is considered obese. Unfortunately, those with really large muscular builds and frames tend to score high on BMI charts classifying them in the overweight and obese category despite how fit these individuals really are. For that reason, it is always best to check BMI with another body composition assessment forms body fat. BMI is preferred because it’s quick and easy to do with minimal equipment.
How to Calculate Your BMI
BMI is calculated as the ratio of weight to height, or simply divide your weight in kilograms, by your height in squared meters.
BMI = Weight (kg)/Height² (meters)
To convert pounds to kilograms, divide by 2.2
To convert inches to meters, multiply inches by 0.0254
BMI = Weight (lb) x 703/Height (inches)/Height (inches)
BMI is a convenient and popular method used to index the adiposity, but not always considered the most accurate. Some healthy adults can be labeled overweight or even obese based on their BMI. For example, large sized field athletes, football players, and just anyone with a seemingly muscular build are usually misdiagnosed because these individuals have large amounts of lean muscle that weighs more per unit than fat. For this reason, body fat percentage is a better index number to track. BMI is still the method of choice because its pretty simple to obtain the two numbers for comparison and it correlates with more technical measures.