WHAT IS BODY MASS INDEX (BMI)
Body Mass Index (BMI) is an index or number which is calculated from ones weight and height. Knowing your BMI gives one a fair idea about his/her body fatness. Research indicates that BMI correlates with direct measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry (DXA). BMI can be considered as an alternative for direct measures of body fat.
BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems like Hypertension, Dyslipidemia (high Low Density Lipoprotein (LDL) cholesterol, low High Density Lipoprotein (HDL) cholesterol, or high levels of triglycerides), Type 2 diabetes, Coronary heart disease, Stroke, Gallbladder disease, Osteoarthritis, Sleep apnea and respiratory problems and some cancers (endometrial, breast, and colon).
One of the best methods for population assessment of overweight and obesity is the calculation of BMI. Its calculation requires only height and weight; it is also inexpensive and easy to use for clinicians and for the general public. The use of BMI allows people to compare their own weight status to that of the general population.
Other methods of measuring body fatness include skinfold thickness measurements (with calipers), underwater weighing, bioelectrical impedance, dual-energy x-ray absorptiometry (DXA), and isotope dilution but these methods are expensive, not always readily available, need highly trained personnel and can be difficult to standardize across observers or machines, complicating comparisons across studies and time periods.
HOW IS BMI CALCULATED AND INTERPRETED
|Measurement Units||Formula and Calculation|
|Kilograms and meters (or centimeters)||
Formula: weight (kg) / [height (m)]2|
With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters.
Example: Weight = 68 kg, Height = 165 cm (1.65 m) Calculation: 68 ÷ (1.65)2 = 24.98
|Pounds and inches||
Formula: weight (lb) / [height
(in)]2 x 703|
Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703.
Example: Weight = 150 lbs, Height = 5’5″ (65″) Calculation: [150 ÷ (65)2] x 703 = 24.96
Interpretation of BMI for adults
For adults 20 years and older, BMI is interpreted using standard weight status categories that are the same for all ages and for both men and women. For children and teens, on the other hand, the interpretation of BMI is both age- and sex-specific using growth charts.
|18.5 – 24.9||Normal|
|25.0 – 29.9||Overweight|
|30.0 – 34.9||Obese (Class I)|
|35.0 – 39.9||Obese (Class II)|
|40 and Above||Morbid Obese (Class III)|
HOW IS BMI FOR AN ATHELETE OR A MASCULAR PERSON INTERPRETED
The BMI weight status categorizes individuals with BMI over 25 and 30 as overweight and obese respectively. It is however important to remember that BMI is not a direct measure of body fatness. An individual’s weight includes both muscle and fat. In this regard, some individuals may have a high BMI but not have a high percentage of body fat. For instance, highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness. Although some people with a BMI in the overweight range (from 25.0 to 29.9) may not have excess body fatness, most people with a BMI in the obese range (equal to or greater than 30) will have increased levels of body fatness.Weight is only one of the factors related to risk for disease. If you have questions or concerns about the appropriateness of your weight, you should discuss them with your Nutritionist.
How reliable is BMI as an indicator of body fatness?
The relationship between BMI and body fatness is fairly strong but varies by sex, race, and age. These variations include the following examples:
• At the same BMI, women tend to have more body fat than men.
• At the same BMI, older people, on average, tend to have more body fat than younger adults.
• Highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness.
One should bear in mind that BMI is only one of many factors related to risk for disease. For assessing someone’s likelihood of developing overweight- or obesity-related diseases, the National Heart, Lung, and Blood Institute guidelines recommend looking at two other predictors:
• The individual’s waist circumference (because abdominal fat is a predictor of risk for obesity-related diseases).
• Other risk factors the individual has for diseases and conditions associated with obesity (for example, high blood pressure or physical inactivity).