The Body Mass Index Isn’t As Accurate As You Think!
As you delve into the world of muscle building and fitness you often come across stark contrasts with current medical opinion. Those who tend to push the envelope on the competitive side as they ascend through to the professional ranks often look great, but epitomize what it means to be unhealthy. It’s just the way it is. However, most of us exist somewhere in the mediocrity and do indeed live a healthy and fit lifestyle.
One tool the medical world has used to assess obesity is the Body Mass Index, or more commonly referred to as BMI. According to the Center for Disease Control & Prevention BMI is defined as “a number calculated from a person’s weight and height. BMI is a reliable indicator of body fatness for people. BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry (DXA).1, 2 BMI can be considered an alternative for direct measures of body fat. Additionally, BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.”
This was obviously very disheartening but fortunately a recent study published in the International Journal of Obesity has shed some light on this conundrum. They clearly state that the BMI rankings has severe limitations in both sexes and doesn’t accurately describe the relative obesity in severely obese subjects either. Thankfully, a well respected journal has gone against the grain of popular medical opinion to bring these truths to light. If you feel you or your children have been diagnosed with a high BMI without just cause please present the following citation to them. After all, life is a never ending learning process and those of living the fitness lifestyle certainly are not AVERAGE.
1Division of Cardiovascular Diseases, Mayo Clinic College of Medicine, MN, USA.
Background: Body mass index (BMI) is the most widely used measure to diagnose obesity. However, the accuracy of BMI in detecting excess body adiposity in the adult general population is largely unknown.Methods: A cross-sectional design of 13 601 subjects (age 20-79.9 years; 49% men) from the Third National Health and Nutrition Examination Survey. Bioelectrical impedance analysis was used to estimate body fat percent (BF%). We assessed the diagnostic performance of BMI using the World Health Organization reference standard for obesity of BF%>25% in men and>35% in women. We tested the correlation between BMI and both BF% and lean mass by sex and age groups adjusted for race.Results: BMI-defined obesity (>/=30 kg m(-2)) was present in 19.1% of men and 24.7% of women, while BF%-defined obesity was present in 43.9% of men and 52.3% of women. A BMI>/=30 had a high specificity (men=95%, 95% confidence interval (CI), 94-96 and women=99%, 95% CI, 98-100), but a poor sensitivity (men=36%, 95% CI, 35-37 and women=49%, 95% CI, 48-50) to detect BF%-defined obesity. The diagnostic performance of BMI diminished as age increased. In men, BMI had a better correlation with lean mass than with BF%, while in women BMI correlated better with BF% than with lean mass. However, in the intermediate range of BMI (25-29.9 kg m(-2)), BMI failed to discriminate between BF% and lean mass in both sexes.Conclusions: The accuracy of BMI in diagnosing obesity is limited, particularly for individuals in the intermediate BMI ranges, in men and in the elderly. A BMI cutoff of>/=30 kg m(-2) has good specificity but misses more than half of people with excess fat. These results may help to explain the unexpected better survival in overweight/mild obese patients.
February 21, 2008 at 3:06 am
I am classed as overweight with a BMI of 26. My height is 5′7" and weigh 166lb.
Now do i look overwieght in my pics…… ?
I never thought this was an accurate measure but some people do.
Nice Blog Dan.
February 21, 2008 at 5:23 pm
BMI is a complete joke. Since I carry more muscle than the average woman, I am classified as overweight until I am precontest, when I am in normal range. When considered normal I am in single digit bodyfat, which is anything BUT normal for a healthy female.
April 16, 2008 at 8:18 am
No the BMI is not accurate if you are in good shape. If you lead a fairly seditary life the BMI could serve as a wake up call that you should seek another opinion.
April 24, 2008 at 10:58 am
This is some generalization nothing is asked of body dimensions or anything like that. It seems to be a ploy by some corporation to lure the unsuspecting novice into spending some cash.