"Skinny Fat" is Dangerous

August 3, 2016

The BMI (Body Mass Index) scale, to be honest, hasn't been universally accepted for some time now. An arbitrary relationship between an individual's height and weight, and the theoretical level of "health" based on this magical formula has received much scrutiny in the past. Despite the lack of faith put in this system by many experts in the field of health and fitness, it still receives a fair bit of attention from physicians and health care workers looking to promote a healthy lifestyle amongst patients.


It is not uncommon that individuals who use even a moderate amount of resistance training in their workout program can be pushed into the "overweight" or even "obese" category on the BMI scale. Fat free mass, such as muscle, is very dense, which can increase an individual's overall weight and therefore skew their BMI score.


On the other end of the spectrum, and a topic that has been studied recently in the American College of Physicians publication, is that despite having a "normal" BMI, one can still be considered unhealthy and have a greater risk of all-cause mortality.

Relationship Among Body Fat Percentage, Body Mass Index, and All-Cause Mortality: A Cohort Study


Background: Prior mortality studies have concluded that elevated body mass index (BMI) may improve survival. These studies were limited because they did not measure adiposity directly.


Objective: To examine associations of BMI and body fat percentage (separately and together) with mortality.


Design: Observational study.


Setting: Manitoba, Canada.


Participants: Adults aged 40 years or older referred for bone mineral density (BMD) testing.


Measurements: Participants had dual-energy x-ray absorptiometry (DXA), entered a clinical BMD registry, and were followed using linked administrative databases. Adjusted, sex-stratified Cox models were constructed. Body mass index and DXA-derived body fat percentage were divided into quintiles, with quintile 1 as the lowest, quintile 5 as the highest, and quintile 3 as the reference.


Results: The final cohort included 49 476 women (mean age, 63.5 years; mean BMI, 27.0 kg/m2; mean body fat, 32.1%) and 4944 men (mean age, 65.5 years; mean BMI, 27.4 kg/m2; mean body fat, 29.5%). Death occurred in 4965 women over a median of 6.7 years and 984 men over a median of 4.5 years. In fully adjusted mortality models containing both BMI and body fat percentage, low BMI (hazard ratio [HR], 1.44 [95% CI, 1.30 to 1.59] for quintile 1 and 1.12 [CI, 1.02 to 1.23] for quintile 2) and high body fat percentage (HR, 1.19 [CI, 1.08 to 1.32] for quintile 5) were associated with higher mortality in women. In men, low BMI (HR, 1.45 [CI, 1.17 to 1.79] for quintile 1) and high body fat percentage (HR, 1.59 [CI, 1.28 to 1.96] for quintile 5) were associated with increased mortality.


Limitations: All participants were referred for BMD testing, which may limit generalizability. Serial measures of BMD and weight were not used. Some measures, such as physical activity and smoking, were unavailable.


Conclusion: Low BMI and high body fat percentage are independently associated with increased mortality. These findings may help explain the counterintuitive relationship between BMI and mortality.


What the study found was that despite an individual being within a "healthy" or "normal" weight range on the BMI scale, a greater body fat percentage was linked to a greater risk of all-cause mortality.


In other words, the term "skinny fat" has been used in the media before which this study exemplifies. Just because you are within a healthy weight range for your height does not meant that you are at an advantage health-wise.


What this tells us is that it is important to focus more on keeping a body fat percentage within a healthy range rather than focusing on overall weight. Not only that, but resistance training an adequate protein consumption are extremely effective tools to promote the growth of fat free mass, improving our overall health.


Tyler Robbins B.Sc. CSCS
Director of Fitness
Head of CrossFit

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