The body mass index is a chart that uses your height and weight to determine if you are at a normal weight, overweight or obese. Similarly, your body fat percentage will also tell you if you are normal, overweight or obese, but it based on the percent of body fat you have, as well as a few other factors that the BMI doesn't account for. Both are ways of measuring body composition, but they are not the same thing.
Body Mass Index
Body mass index is one of the most useful ways to estimate body composition. It's easy to calculate and it doesn't require any special equipment. Your BMI is your weight in kilograms divided by your height in meters, squared. First convert your weight from pounds to kilograms by dividing it by 2.2. Next, convert your height from inches to meters by first multiplying it by 2.54, then dividing that number by 100, and finally squaring it . For example, if you are 6 feet tall and weigh 200 lbs., you would divide 90.9 by 3.34 to get a BMI of 27.2.
BMI Categories
The normal and healthy weight range on the BMI scale is 18.5 to 24.9. Numbers between 25 and 29.9 are considered overweight. Any number above 30 is considered obese and with that comes a great number of health risks, such as diabetes, hypertension, heart disease and high cholesterol. Because the body mass index is just a calculation of weight versus height, without accounting for the actual percentage of lean and fat tissue, the results could possibly be skewed for people that are more muscular. Due to this, ACE suggests performing some sort of body fat analysis in conjunction with BMI to get a better idea of your actual body composition.
Body Fat Percentage
Body fat percentage is just that, the percent of fat mass versus non-fat mass, such as bones, lean tissue, muscle and organs. Like the body mass index, height and weight are factors for determining body fat percentage. It also takes age and sex into account. There are various methods of finding body fat percentage, with some being more reliable than others and each having its own specific equations. Hydrostatic weighing is the most accurate, but is very costly. You can often find the more reasonably priced electrical impedance and skin-fold calipers in most gyms, as well as in many sporting good stores, if you desire one for your own personal use.
Ideal Percent Body Fat
Like the BMI, there are body fat percentage categories. The difference is that the body fat percentage takes into account your sex, because men naturally carry less fat than women. The fit and normal range for a woman is between 21 and 31 percent while it is a little lower for guys at 14 to 24 percent. Any number above 32 percent for a woman, and 25 percent for a male is considered obese, with the potential for the same health risks as a person with a higher than normal BMI. Athletic women will have a lower body fat percentage averaging between 14 and 20 percent while most athletic men will range between 6 and 13 percent.
References
- "ACE Personal Trainer Manual"; American Council on Exercise; 2003
- MayoClinic.com: Normal Weight Obesity: A Hidden Health Risk?
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