Body Mass Index (BMI) versus Body Fat Percentage

Do you know the difference between BMI and Body Fat Percentage? Do you know when to use each? We know it can be a bit confusing. Here is an explanation what each, as well as the pros and cons of using each measure. 

Where does Body Mass Index (BMI) come from?
  • The Quetelet Index was developed in 1832, with no specific interest in identifying obesity.
  • After World War II, the rising incidence of mortality and morbidity of overweight and obese life insurance policy holders resulted in renaming the Quetelet Index as BMI and validating it as an index of relative body weight, but not body fatness.
  • Ancel Keys who validated the Quetelet Index cautioned against using BMI for individual diagnoses, since the equation overlooks variables such as age and gender.

Criticism with BMI?
  • BMI uses height and weight to classify people as overweight or obese and nothing else.
  • This is despite males and females and people of different ages looking different.
  • Researchers have in the recent past started to scrutinise the reliability of BMI in accurately predicting overweight and obesity.
  • BMI was never intended for individuals, it was intended for mass screening of large groups.
  • Two people with exactly the same BMI can have very different patterns of body fat distribution and thus different risk of developing cardiovascular disease (CVD).

How is body fat percentage different?
Body fat percentage is different as it eliminates muscle mass but it also takes into consideration that individuals with too much body fat have greater health risks.

When comparing BMI to body fat percentage:
  • BMI classified 95% of people incorrectly in terms of their body fat percentage.
  • As such, BMI would have classified a person with a perfect body fat as overweight or obese 95% of the time.
Conclusion
  • BMI should not be used as a risk stratification indictor due to its lack of accuracy in explaining percentage body fat.
  • By incorrectly classifying individuals, it can result in harm by assigning incorrect interventions.
  • As such, body fat percentage measurements should be used to indicate potential health risks.
  • Body fat has been found to be a substantial risk factor in CVD, but also a myriad of other diseases such as diabetes and certain types of cancers. Furthermore, a high body fat percentage is inevitably associated with numerous other risk factors such as high blood pressure, abnormal cholesterols, etc.
  • Even too low body fat has been found to be linked to a myriad of health conditions including CVD.

If you are making lifestyle changes to reduce your risk of CVD, you might also want to read this article on fad diets to learn how to differentiate between diets that work and those that are a set up for failure from the beginning.