Is Body Mass Index (BMI) all that?
Body Mass Index (BMI) is one of the most common measurements used to assess for weight status and fitness. BMI is a quick measure that is easily obtained with relatively little cost. Weight (kilograms) is divided by Height (meters squared). BMI is then expressed as an index. Websites such as nhlbisupport.com/BMI have an online calculator to that will let you calculate BMI by entering in an individual’s information in inches and pounds.
The indexes of body ranges include:
Underweight: < 18.5
Normal Weight: 18.5 – 24.9
Overweight: 25.0 – 29.9
Obese: > 30
Pros:
- BMI is an easy and quick way to assess weight status and body fatness for most people.
- No additional cost or training is required. BMI can be calculated with a pencil and paper or an online BMI calculator.
- It provides real time feedback for in office assessment as other methods such as DEXA, underwater weighing and Bioelectrical Impedance Analysis (BIA) are expensive and may not be readily available to the patients in medical offices.
Cons:
- BMI does not differentiate fat mass from lean mass. Athletes and the elderly may have the same BMI but have totally different fat and lean mass percentages. Muscular individuals will have a higher BMI and less body fat. Some individuals may have a normal BMI but have an increased body fat percentage.
- BMI may not be the best numerical index to determine fitness with or use as a health predictor. Assumptions should not be based on a single index. Composition of the weight may impact health risks more than the overall individual weight.
Well, what does this mean?
Medical practitioners need to look for new or additional tools that will make fitness and health status evaluations more accurate and meaningful to the patient.
Bioelectrical Impedance Analysis (BIA) equipment is becoming more available to medical practitioners for assessment of body composition. BIA is a noninvasive method to measure lean mass and body fat percentages. A safe low level current is sent through the body and the body’s ability to conduct an electrical current is measured. Percent of body fat present may be a more accurate marker for health risk than measuring height and weight alone. It is expected that overweight and obese individuals will have a higher percentage of body fat and be more at risk for medical comorbidities associated with excess adiposity. It is not expected that individuals with a BMI in the normal weight index range would have fat content similar to an overweight or obese individual. BIA will be able to detect “normal” weight obesity. Staff training for BIA equipment use is easy to facilitate and the results from the BIA are available to the patient immediately following the test. Counseling to assist in decreasing health risk factors and to improve health predictors can be done as the results are reviewed by the healthcare provider and the patient together following the test.
Medical evaluation should not stop with an elevated BMI and weight management suggestions. Further assessments should be ordered to evaluate health status and potential health risks. These include BIA, lipid panel, HgA1c, vitamin level assessment and a diet and physical activity history. A multifactoral approach to health status evaluation will provide the most accurate clinical picture for any needed interventions to promote and maintain good health.