Body Mass Index is a convenient way of measuring how your weight relates to your height—in other words, it tells you if you are too fat, too thin, or just right! The formula sounds complicated, but it is easy to work out if you know your height in meters and your weight in kilograms.
BMI is the weight in kilograms divided by the square of the height in meters (wt/ht2). If you know your height in inches, multiply that by 2.54 for centimeters and divide by 100. This gives you your height in meters. Likewise, if you know your weight in pounds, multiply that by 0.4536 to give you your weight in kilograms. Take as an example a man of 5 feet 10 inches and who weighs 177 pounds. Therefore he is 1.778 meters tall, and weighs approximately 80 kilograms. The square of his height (1.778 x 1.778) equals 3.16. Now divide 80 (his weight) by the square (3.16) and the answer is 25.3.
This figure of 25.3 is the man’s BMI. It is just above the limit of normal, so shows that he is just a pound or two overweight. However, a BMI of 27 or more could be considered overweight enough to do something about it.
Here are the general BMI ranges:
• Below 20 is probably too thin
• 20-25 is within acceptable limits
• 25-30 is overweight
• 30-plus is obese
In the British Regional Heart Study, men above the average of 20-25 for BMI were at higher risk than average of having a heart attack.
However, a high BMI is closely related to a high cholesterol level, high blood pressure, and another measure of fats in the blood—a high triglyceride level. When these were taken into account in the British Regional Heart Study analysis, the BMI alone did not appear to exert an extra effect on heart disease over and above them. Some people have taken this to mean that obesity does not really matter, as long as you keep your blood pressure and blood fat levels under control. This is not true, and in any case is very difficult to achieve, as obesity, fat, and blood pressure are all bound up together. So if you are overweight and have angina, it is best to lose the extra weight.