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The ins and outs of BMI (and my personal opinion)

health and fitness Aug 01, 2022

BMI is a common term in the health community. You may have heard it at a recent medical appointment, or it may be something you are monitoring on your own to help measure your progress. While BMI is a great measurement tool, it has its limitations when looking at the whole picture of your health.

What is BMI? 

BMI stands for Body Mass Index, a screening tool used to help identify and categorize people with an increased risk for health issues related to higher body fat. BMI scores fall into 1 of 4 categories:

  • Underweight = Below 18.5
  • Healthy weight = 18.5 to 24.9
  • Overweight = 25.0 to 29.9
  • Obese = 30 or higher

How do we calculate what a person’s BMI is? 

BMI is used to help measure a person's body fat. Medical professionals use a simple formula to compare a person’s height and weight to help place them in one of the above categories. 

What is BMI used for? 

Once a person’s BMI has been calculated, it gives healthcare professionals a good starting place for developing a plan that best fits their health needs based on their score. It also gives them a quick and easy metric to help identify patients at an increased health risk since research has indicated that a higher BMI score often correlates with a person carrying more body fat.

The categories of “overweight” and “obese” are generally considered higher risk categories by most healthcare providers. Once the category is determined, the provider will work with the patient to recommend exercise, nutrition, and even some lifestyle modifications to help the patient reach a lower BMI, which, in turn, will lower an individual's potential risk for future health complications.

What are some misconceptions about BMI? 

Too often, people use BMI as a one-size-fits-all approach to determining whether or not someone is healthy. A low BMI score is generally associated with good health, while a high BMI score is more often associated with poor health. BMI is a great tool, but it doesn’t always give us the complete picture of a person’s health.

What are the limitations of BMI? 

While BMI is a great measurement tool and starting point for figuring out where a person is on their health journey, it is not without its faults. Some of the limitations of using BMI as a metric of health include:

  • BMI does not diagnose a person’s health. Although a higher BMI is typically correlated with higher overall body fat, BMI is based only on a person’s height and weight. This does not leave any extra room to account for the difference between body fat and lean body mass, a portion of which is skeletal muscle mass. So, it can be feasible for someone to have a high BMI but otherwise be totally healthy.
  • A low BMI may give a false sense of health to those individuals falling into the "healthy weight" category but who have very little skeletal muscle mass and increased body fat. What does this mean? It means someone may look thin but are not as healthy as they could be.
  • A person actively engaged in a weight loss journey may give a false sense of sustainable progress. A lower BMI score does not account for a person’s "fat to muscle" ratio. What that means is that without additional methods, like one of those mentioned below, it is impossible to know if the decreased body weight is primarily the result of a loss of body fat (healthy) or the result of losing skeletal muscle mass (not fit). This is just an example to help paint a picture of a significant limitation. The main caveat is that it is common for people to lose some skeletal muscle while decreasing body fat, especially if they are significantly overweight. This circles back to the importance of regular, accurate testing that reflects body fat and muscle mass so that a person or coach can make the necessary adjustments in their nutrition and/or exercise program to retain as much muscle mass as possible while still losing weight in the form of fat.

What's the solution? 

  • Prioritize body fat percentage instead. Body fat percentage is a more accurate reflection of a person's progress and can help give you a better picture of health.
    • For example, monitoring progress using BMI would not reflect a 4-pound reduction of body fat and a 4-pound increase in lean body mass because the body weight would stay the same, despite an improvement in a person's overall body composition.
  • More robust testing methods provide a more accurate reflection of a person's health and progress. Some examples include:
    • Skinfold Calipers
    • Hydrostatic Weighing
    • DEXA Scan
    • Bioelectric Impedance Analysis (BIA) - a tool to help get an accurate measurement of body fat mass, body fat percentage, skeletal muscle mass, and total body water weight, among other stats. I have this tool personally and regularly use it to measure progress and overall health.

Can BMI determine if a person is healthy? 

BMI can be a warning sign for an overweight individual who is not currently taking steps to improve their health and body composition. Still, BMI alone should not be used to determine if a person is or is not healthy. Further testing is required to understand a person’s overall health. BMI should not be used to determine an individual's progress in fitness and nutrition programs focused on helping a person lose weight. Instead, body fat percentage would be a more accurate indicator of a person's health and progress.

If you’re interested in taking the next steps on your own health journey, book a discovery call with me today. I offer consults worldwide

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