Obesity means the proportion of your total body weight that is made up by fat exceeds a predetermined level. To determine if a person is overweight or obese, doctors often use the body mass index (BMI). The BMI is an indirect measure of the portion of your body that is made up of fat. This is also the measure most often used to determine your risk of diseases related to excess weight such as type 2 diabetes and heart disease.

Your BMI takes into account your height and weight; higher numbers mean you carry more fat. If your BMI is above 25 but below 30, you are considered “overweight.” If your BMI is between 30 and 39 you are considered “obese,” while a BMI of 40 or above is considered extremely or “morbidly obese.” Notice that the terms “overweight” and “obese” are not synonyms; medically, they refer to distinct categories of excess weight. You can calculate your own BMI. The formulas for calculating BMI are:

• BMI = (weight in pounds/height in inches squared) x 703
   — or — 
• BMI = weight in kilograms/height in meters squared

Alternatively, if you know your height and weight, you can determine your BMI using a BMI table such as the one found on the National Institute of Diabetes and Digestive and Kidney Diseases Weight-control Information Network (see the external resources).