Your BMI, or Body Mass Index, indicates whether you have a healthy weight for your height. Your BMI value also indicates your risk for obesity-related diseases, such as diabetes, heart disease and metabolic disorders. Hospitals and organizations such as the Mayo Clinic, the Cleveland Clinic and the National Heart Lung and Blood Institute recommend that adults calculate their BMI and discuss this value with their doctors. You can use the BMI formula to determine the normal or healthy weight range for a person of your height.
BMI Basics
The BMI formula takes your weight and height into consideration to predict your fitness level and your risk for obesity-related diseases. To calculate your BMI, divide your weight in pounds by your height in inches, squared, and multiply the resulting value by a conversion factor of 703. For example, if you measure 5 feet 6 inches tall and weigh 120 pounds, divide 120 by 66 squared, or 4,356, to get .0275. Multiply that value by 703 to get 19.4. This value represents your BMI.
Weight Classifications
The National Heart Lund and Blood Institute classifies BMI values according to five categories. BMI values below 18.5 indicate that a person is underweight. BMI values between 18.5 and 24.9 indicate a healthy weight. BMI values between 25.0 and 29.9 indicate that a person is overweight and BMI values between 30.0 and 34.9 indicate that a person is obese. BMI values over 35 indicate morbid obesity.
Ideal Weight Range
Calculate the ideal weight range for a person of your height using the same formula you used to calculate your BMI. Plug your height in inches and the lowest healthy BMI value, 18.5, into the formula to calculate the lowest possible healthy weight for a person of your height. For example, to calculate the lowest healthy weight for a person measuring 5 feet 6 inches tall, divide 18.5 by 703 and then multiply by 4,356. You should get 114.6. To calculate the highest healthy weight for a person measuring 5 feet 6 inches tall, divide 24.9 by 703 and then multiply by 4,356. You should get 154.3. Thus, a 5 foot 6 inch tall person must weigh between 114.6-lbs. and 154.3-lbs. in order to have a healthy BMI.
Weight Loss
Use the calculations described in the previous sections to set a weight loss goal. Many adults set unrealistic weight loss goals that, if reached, would put them in the underweight BMI category. By calculating the ideal weight range for your height, you can set realistic and achievable goals, rather than striving to be too thin.
Expert Insight
BMI values can sometimes fail to predict unhealthy weight. According to the National Heart Lung and Blood Institute, older adults who have lost muscle mass might have unhealthy body fat levels even if their BMI values indicate that they have a healthy weight. The Mayo Clinic points out that BMI often underestimates body fat in women, who typically have higher body fat percentages than men. On the other hand, highly trained athletes with dense muscle mass might have a healthy weight but a high BMI that indicates they are overweight. The Mayo Clinic also warns that the BMI system can underestimate body fat in adults of both genders. Many adults with healthy BMI values have an unhealthily high body fat percentage. The Mayo Clinic describes this condition as normal weight obesity.
Considerations
Because of the limitations of the BMI system, you should consider other measurements and factors when determining your risk for obesity-related diseases. Have your doctor measure your body fat percentage or your waist circumference. These measurements can serve as a more accurate predictor of health risks for some adults. The Mayo Clinic warns that men with body fat percentages above 20 and women with body fat percentages above 30 face much higher risks of obesity-related diseases than adults with healthy body fat levels.
References
- National Heart Lung and Blood Institute: Assessing Your Weight and Health Risk
- Cleveland Clinic: Overweight and Heart Disease
- Mayo Clinic: Normal Weight Obesity---An Emerging Risk Factor for Heart and Metabolic Problems
- MayoClinic.com: BMI May Underestimate Obesity in Women
- BMI Calculator: BMI Formula
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