06.01.2017

Why BMI doesn't tell the whole story

BMI stands for body mass index and is measure of body fat based on height and weight. It is used to quantify the amount of tissue mass (muscle, fat, and bone) on an individual, and then classify that person as normal weight, overweight, obese, severely obese, morbidly obese based on that value.

Those classifications are based on the relationship between body weight and disease and death1. Overweight and obese individuals are at an increased risk for the following diseases2:

  • Coronary artery disease
  • Dyslipidemia
  • Type 2 diabetes
  • Gallbladder disease
  • Hypertension
  • Osteoarthritis
  • Sleep apnea
  • Stroke
  • At least 10 cancers, including endometrial, breast, and colon cancer3
  • Epidural lipomatosis4

Among people who have never smoked, overweight/obesity is associated with 51% increase in mortality compared with people who have always been a normal weight.5


The problem with BMI

  • BMI doesn’t distinguish between fat and muscle. Many muscular athletes and bodybuilders may fall into the “overweight” or “obese” category.
  • BMI doesn’t account for fat distribution. A large amount of centralized fat is far more dangerous than even fat distribution throughout the body.6

Enter Waist to Hip Ratio

Waist to Hip ratio (WHR) is the ratio of the circumference of the waist to that of the hips and is used to determine the distribution of fat. Where you store excess body fat says a lot more about your health than the weight on the scale or your ability to perform physical activity. Have a look at the two types of fat distribution below.

 

Another aspect of fat distribution is two types of fat.

Subcutaneous fat vs. Visceral fat

Subcutaneous fat = the fat you can pinch that sits just under the skin & surrounds the body. Too much of it can raise your risk of chronic disease, but it is necessary for us all to have some subcutaneous fat.

Visceral fat = sits deep in the abdominal cavity around internal organs. It is linked to systemic inflammation, high blood pressure, cardiovascular disease, and type 2 diabetes.


Calculating your BMI & Waist to Hip Ratio (WHR)


Click here to do the calculations!

Interpreting the results

  • Look at the BMI results first
  • Men - if your BMI = > 27.7 you should ignore WHR & try to bring down their BMI through healthy eating and exercise.
  • Women - if your BMI = > 26.6 you should ignore WHR & try to bring down their BMI through healthy eating and exercise.
  • If you are a bodybuilder, powerlifter, or professional athlete you can ignore BMI & use WHR.
  • If you BMI is > than the numbers given for your gender than the BMI is more useful to you than the WHR for determining your risk for chronic disease.
  • Men - if your BMI = < 27.7 use WHR to determine your risk for chronic disease.
  • Women - if your BMI = < 26.6 use WHR to determine your risk for chronic disease.

WHR Results


If you were surprised to find yourself in one of the at risk classification on BMI or WHR you aren't alone! According Statistics Canada 14,222,521 Canadians (54% of the population) over the age of 18 self-reported as overweight or obese in 2014.7

Remember that BMI / WHR aren’t perfect predictors of chronic disease. They just happen to be the easiest way to measure and therefore we have lots of data on the correlations between body weight and disease. Start small with habits like drinking more water, cutting out sugary drinks, or eating more vegetables. Then start to add in more movement even if it’s just a 30 minute walk a couple days a week. Be consistent and the results will come!


Tyson Montgomery – Certified Personal Trainer & Nutrition Coach


1. "Physical status: The use and interpretation of anthropometry" (PDF). WHO Technical Report Series. Geneva, Switzerland: World Health Organization. 854 (854): 1–452. 1995. PMID 8594834.
2. "Executive Summary". Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults: The Evidence Report. National Heart, Lung, and Blood Institute. September 1998. xi–xxx.
3. Bhaskaran, K; I, Douglas; Forbes, H; dos-Santos-Silva, H; Leon, DA; Smeeth, L (2014). "Body-mass index and risk of 22 specific cancers: a population-based cohort study of 5•24 million UK adults". Lancet. 384 (9945): 755–65. doi:10.1016/S0140-6736(14)60892-8. PMC 4151483  . PMID 25129328.
4. "Multiple epidural steroid injections and body mass index linked with occurrence of epidural lipomatosis: a case series".
5. Stokes A, Preston SH (2015). "Smoking and reverse causation create an obesity paradox in cardiovascular disease". Obesity. 23: 2485–2490. doi:10.1002/oby.21239. PMC 4701612  . PMID 26421898.
6. Yusuf, S.; Hawken S.; Ounpuu, S.; Dans, T.; Avezum, A.; Lanas, F.; McQueen, M.; Budaj, A.; Pais, P.; Varigos, J.; Lisheng, L.; INTERHEART Study Investigators (2004). "Effect of potentially modifiable risk factors associated with myocardial infarction in 52 countries (the INTERHEART study): case-control study". Lancet. 364 (9438): 937–52. doi:10.1016/S0140-6736(04)17018-9. PMID 15364185.
7. "Body mass index, overweight or obese, self-reported, adult, by age group and sex (Number of persons)". www.statcan.gc.ca. Retrieved 2015-10-07.