The term "Obesity" is used to define a weight 20% above the healthy weight limit set by the World Health Organization.

Each person's healthy weight limit obviously depends on their height. For example, the taller a person is the higher the weight which is considered healthy. This creates a challenge for the comparison of weight levels among populations so researchers created an index which adjusts body weight for height to produce a single number.

This index is called the Body Mass Index or BMI. It is calculated by dividing a person’s weight (in kilograms) by the square of his or her height (in meters). Using U.S. weight measures the calculation is weight (in pounds) divided by the square of height (in inches) times 703.

Here is an example of this calculation for an individual who is 6 feet tall (72 inches) and weighs 200 pounds.

   **  200 divided by (72 x 72) = 0.03858. Then 0.03858 x 703 = 27.12  **

So the BMI for this individual is 27.12.

The World Health Organization has set the healthy weight limit for BMI as 25.0 so this individual would be considered overweight. A BMI of 30 and above (30 is 20% above 25) is labeled as obese.

So, to summarize, here is how the World Health Organization labels different Body Mass Index levels:

• BMI of 18.5 and less: Underweight
• BMI between 18.5 and 25: Healthy Weight
• BMI of 25 to less than 30: Overweight
• BMI of 30 and above: Obesity

However, it is important to understand that Body Mass Index is just a crude population measure of excess fat. Although these cut-off points are often used to provide a general reference for individual assessment, this index was not developed for that purpose.

Instead, BMI is meant to broadly categorize populations for research and statistical purposes. For individuals, its accuracy in relation to actual levels of body fat is easily distorted by such factors as fitness level, muscle mass, bone structure, gender, and ethnicity. For example, it doesn't accurately distinguish between lean and fat tissue. So individuals with significant lean muscle mass can be categorized incorrectly. For example, Arnold Schwarzenegger's BMI has been calculated as 33 and 97% of NFL players have a BMI over 25.

The above information about overweight, obesity and Body Mass Index provide the necessary background for understanding the articles below concerning obesity research and public policy related to addressing the "obesity epidemic."