Is BMI or Body Mass Index a good predictor of health and life expectancy?
Body Mass Index or BMI is a screening tool used to help identify adults with possible weight issues.  Individuals who are overweight tend to have more adipose or fat tissue.  It only requires ones height and weight to calculate BMI therefore it is very cost effective tool that can be used by health care professionals and the general public to access an individual’s potential risk for obesity related diseases such as heart disease and cancer. 

Since BMI is a screening tool and not a diagnostic tool several other factors must be taken into consideration when determining risk.  Some of the other factors that need to be evaluated are a person’s waist circumference, blood pressure, activity level and dietary habits.  Assessing all of these things will give the clinician a better idea of an individual’s true risk of developing disease.  For example, one reason that one cannot rely on BMI alone is in the case of an athlete.  Athletes tend to be more muscular so while their BMI based on height and weight may be elevated, the weight distribution favors muscle and not fat. It is more common, however, for individuals with BMI in the obesity range to have increased fat percentage. 

What then is considered a normal BMI?  For adults the following table list normal values:

BMI

Weight Status

Below 18.5

Underweight

18.5 – 24.9

Normal

25.0 – 29.9

Overweight

30.0 and Above

Obese

There are many websites and apps available today to help an individual calculate their BMI by simple plugging in values.  However for those of us wanting to do it the old fashion way and use a calculator the equation is Weight (kg) ÷ [Height (m)]2

Overweight and obese individuals are at increased risk for disease such as heart attack, strokes, diabetes type II, high blood pressure, high cholesterol and triglyceride levels, gall bladder disease, sleep apnea, cancers such as colon and breast and osteoarthritis.  These diseases can not only limit our lifespan but also compromise our quality of life.  An important reason that obesity is thought to contribute to development of these dysfunctions is through increased inflammation.  It has been shown that individuals who are overweight have higher markers of inflammation, such as C-reactive protein, than their normal weight counterparts. This inflammatory process is linked to all of the above illnesses.

Certain forms of fat such as the visceral fat that resides in the abdomen and covers the abdominal organs and the pericardial fat that surrounds the heart have been shown to be even more active in this inflammatory process.  Other factors at play is that obesity tends to limit activity levels, makes the heart work harder and puts undue pressure on the joints.  It can contribute to sleep apnea which in of itself further increases mortality and morbidity.  Another factor that is being investigated is fat tissue’s ability to act as an endocrine organ and contribute to the imbalance of the hormones such as cortisol, insulin, testosterone and growth hormone.