The body mass index, or BMI, is a scale that provides an indication of your overall body composition and fat. Your basal metabolic rate, or BMR, is a measure of the amount of energy your body requires to perform its normal vital functions at rest. Your BMI and BMR are related in the sense that a lager body composition is generally associated with a higher BMR.
Calculating BMI
You can calculate your BMI by dividing your weight in pounds by your height in inches squared, then multiplying the result by the number 703. For example, if you are 5 feet 10 inches tall and you weigh 175 lbs., you would have a BMI of about 25.1. You can also calculate your BMI by using an online calculator.
BMI Scale
A normal BMI falls in the range of 18.5 to 24.9, while a BMI below 18.5 is underweight, and a BMI of 25 to 29.9 is overweight. A BMI of 30 to 34.9 is obesity I, 35 to 39.9 is obesity II, and a BMI of 40 or more is obesity II, or morbid obesity. Each BMI classification beyond normal is associated with a progressively increasing risk of cardiovascular disease, and morbid obesity may be a fatal condition.
BMR Basics
Several factors go in to determining your BMR, including your age, sex, body composition and diet. Your BMR has the most significant impact on your body's daily energy requirements, accounting for about 60 to 75 percent of your total metabolism. The frequency and type of food you eat accounts for about 10 to 20 percent, and your physical activity level accounts for 20 to 30 percent of your body's daily energy needs.
Calculating BMR
Calculating your BMR is a bit complicated, and the formula is slightly different for males and females. The easiest way to calculate your BMR is to use an online calculator. The result will provide an indication of how many calories your body needs each day to perform simple functions such as breathing and digesting food. You can also calculate your BMR based on how much physical activity you typically get, using a formula called the Harris Benedict Equation.
Using BMI and BMR
If you have a BMI that falls outside the normal range, you can use your BMR to accurately determine the number of calories you need to consume each day to either gain or lose weight. You need to accumulate a positive or negative energy balance of 3,500 calories to gain or lose 1 lb. of fat. For example, if you have a BMI of 25 to 30, you are about 10 percent over your ideal weight. If you weigh 175 pounds and have a BMI of 25.1, your ideal weight is roughly 158 lbs., and you would need to accumulate a negative energy balance of 61,250 calories to reach this weight.
References
- "Essentials of Strength Training and Conditioning"; Thomas R. Baechle and Roger W. Earle (editors); 2008
- BMI Calculator: BMR Formula
- American Heart Association: Body Composition Tests
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