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Definition of obesity

Obesity is an excess of body fat that frequently results in a significant impairment of health. Obesity results when the size or number of fat cells in a person's body increases. A normal-sized person has between 30 and 35 billion fat cells. When a person gains weight, these fat cells first increase in size and later in number. One pound of body fat represents about 3500 calories.

When a person starts losing weight, the cells decrease in size, but the number of fat cells generally stays the same. This is part of the reason that once you gain a significant amount of weight, it is more difficult to lose it. However, some recent studies seem to imply that fat cells can be destroyed as a result of certain medications and that a decrease in fat cell number may occur if a lower body weight is maintained for a prolonged period of time.

Each fat cell weighs a very small amount (about 0.4 to 0.6 micrograms but can be as small as 0.1 micrograms to as large as 1.2 micrograms). In other words, it would take about 5 million fat cells to get just 1 ounce of fat. However, the weight of billions and billions of fat cells does add-up. Obviously, it is not practical to count the number of fat cells in a person's body, so science has come up with easier methods to determine if a person is owerweight or obese.

Earlier methods involved tables of desirable weights at various heights that were derived by life insurance companies. These tables were based on illnesses and death rates.

A better method was developed that more closely correlates with body fat and the metabolic complications of obesity. This is the Body Mass Index ("BMI") and it is calculated as follows:

BMI = Weight (in kg.) / Height (in meters) Squared (ht. x ht).

For example, a man who is 5' 10"(1.78 meters) tall and weighs 285 lbs. (~130 kgs.) would have a BMI of 130/(1.78 x 1.78) = ~ 41.

You can use the input form on the next page to automatically calculate your BMI and your resting metabolic rate (the rate at which you expend energy in a resting state in calories per 24 hours).

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