The Body Mass Index (BMI) is a method used to calculate body size based on height and weight. Referencing tables devised in 1959 by the Metropolitan Life Insurance Company, and later modified in 1983, the BMI attempts to illustrate healthy and/or unhealthy weight levels based on body composition. The measurements are determined by dividing the weight in kilograms by the height in meters squared. The subsequent results place people in either underweight, normal weight, overweight or obese categories. BMI does not account for or differentiate between fat mass and fat-free mass, or lean body mass. Plainly, a person who has a lean, muscular build and is the same height and weight of another person who carries a higher fat percentage is classified as having the same health status of that person with the higher fat percentage.
Underweight
Having a BMI less than 18.5 is considered underweight. Although there are some exceptions, such as bodybuilders and boxers, a low BMI usually equates to an unhealthy level of body fat. In women, excessively low levels of body fat can cause amenorrhea, a disturbance in the menstrual cycle.
Normal
The ranges for the normal weight classifications are 18.5 to 24.9. Purportedly, in this range, risk for disease is relatively low.
Overweight
To be considered overweight based on the BMI, you must fall in the range of 25.0 to 29.9. There are two levels of disease risks in this classification based on waist circumference. Essentially, for men, if your waist is equal to or less than 40 inches, you have an increased risk for disease such as heart disease or diabetes. However, if your waist circumference is greater than 40 inches, you're considered a high risk for disease. For women, the risks are equal to or less than 35 inches or greater than 35 inches, respectively.
Obese
The obese classification has three subcategories. The disease risk assessments for obesity are subject to the aforementioned protocols for waist circumference. Obesity 1 is characterized with a range of 30.0 to 34.9 BMI. Risks for disease are high and very high, respectively. Obesity 2 has a range of 35.0 to 39.9 and risk levels of very high and very high. Finally, Obesity 3 or extreme obesity is a BMI equal to or greater than 40. Its risk level for disease based on waist circumference is extremely high.
References
- "Essentials of Personal Training," National Strength and Conditioning Association; 2004.
- "Sports and Fitness Nutrition," R. Wildman and B. Miller; 2004.
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