The calculation for determining BMI (Body Mass Index) is: weight (in pounds) divided by height (in inches) divided by height (in inches) multiplied by 703. For example, the body mass index of a person who weighs 164 pounds and who is 5 feet 9 inches, would be calculated, 164 ÷ 69 ÷ 69 x 703 = 24.2, which may be rounded to 24.
A body mass index of less than 18.5 is below normal: People with a BMI below this level are considered underweight. A BMI slightly below 18.5 is not necessarily unhealthy unless the reason for it is because of malnutrition, an eating disorder, or other underlying or unknown health issues. A BMI of 16 or less is considered starvation: People with a BMI this low may need medical intervention to help increase their weight to a healthier level.
A body mass index between 18.5 and 24.99 is considered normal; however, it is important for people with a BMI near the upper limit of the normal range to be extra vigilant in following a healthy lifestyle to ensure that their BMI does not increase. Once the BMI rises above 24.99, specifically between 25 and 29.99, a person is considered overweight. For a person with a BMI at the low end of this range, a few minor changes in diet and exercise may lower their BMI into the normal range. People at the high end of this range are at risk of passing over the threshold into obesity unless they make immediate changes in their lifestyle. People with a BMI in the overweight range carry a higher risk of developing health problems than people with a BMI in the normal range.
People with a body mass index between 30 and 30.99 are considered obese. Significant changes in lifestyle may be necessary to reduce the risk of weight related health problems. A BMI above 40 indicates that a person is morbidly obese. People with a BMI this high live with an extreme risk of developing a number of severe health problems. Some studies have indicated that many morbidly obese people may be predisposed to extreme weight gain: genetics and brain chemistry imbalances may play a part in this. Whatever the cause, genetic or otherwise, life expectancy is greatly reduced in most cases.
It is widely accepted that as a person's body mass index increases above normal levels, the risk of health problems related to obesity increases as a result; however, a number of variables must be taken into account when determining the possible risk. Age, body shape, the ratio of fat to muscle, pregnancy, and an active or sedentary lifestyle are among the important considerations when making an accurate assessment of BMI and how it relates to overall health. The body mass index should be used only as a general guide for assessing possible health risks associated with obesity: It is by no means a definitive tool. Body mass index is, however, becoming increasingly utilized to gauge progress in weight management rather than conventional "ideal weight" charts.