Are you confused about body fat percentage vs. BMI?  Maybe why doctors are talking about BMI and everyone else only cares about body fat percentage.  You’re confused for good reason.  There’s a lot of information about the two out there and which one is healthy.  Let’s find out with one is better for you and how you can measure it.

BMI, Your Weight, and the Scale

You go into most homes in America and you’ll most likely be able to find a bathroom scale or some version of a tool that measures weight.  It’s been a staple of our measurement of health for such a long time, of course it’s widely regarded as the method most people trust for assessing the health of their body (at least without the resources of a doctor’s office).

But what does weight really tell us, specially in the context body fat percentage vs. BMI?

BMI, or body mass index, is a very generic measure that groups people based on height and weight.  The formula is:

Imperial:

  • BMI = weight (lb) ÷ height2 (in2) × 703

Metric:

  • BMI = weight (kg) ÷ height2 (m2)

Where your bodyweight is simply a measure of the mass of your tissues.

The Problem With BMI

Your bodyweight includes:

  • Lean mass
    • Muscle
    • Bones
    • Organs
    • Connective Tissue
  • Water
  • Fat mass
    • Visceral (surrounding organs)
    • Subcutaneous (under the skin)

You can see that there are a lot of factors that determine your weight, and there is quite a bit of variability between individuals within these components.

The amount of water in our bodies typically doesn’t affect our health (unless you have way too little or too much).  When we eliminate the water component, that leaves us with the main things that determine our body’s weight;

  • lean mass
  • fat mass

This brings us to body composition, which is the relationship between fat-free mass (lean) and fat mass in the body.

Key takeaway:

Despite being used for a very long time, especially in the medical industry, the scale has proven to be a very flawed tool for truly assessing one’s physical health because of the complexity of components that comprise our body’s weight.

Body Fat Percentage vs. BMI

For men, the healthy body fat percentage range is 8-19% (2).

For women the healthy body fat percentage range is 21-33% (2).

Body Fat Percentage

Body fat percentage is typically measured with calipers, handheld calculators, or fancy equipment like a DEXA scanner.  All of these methods are fairly flawed in one way or another, and typically you can figure similar results with simply looking at pictures of yourself.

If you are measuring a number for body fat, it can help you realize progress with respect to weight loss or fat loss with the following:

Pounds of body fat is found by dividing your percentage of fat by 100, then multiplying times your bodyweight.

  • Example: 20% body fat for a 150 pound individual.
    • 20/100 = .2
    • .2 x 150 = 30
    • Pounds of body fat = 30 pounds
  • If this individual stays at 150 pounds, but drops to 18% body fat, the scale will obviously read the same, but that individual would have 2% less fat than previously.
    • 18/100 = .18
    • .18 x 150 = 27
    • Pounds of fat = 27
  • So without “losing any weight” the individual has dropped 3 pounds of fat (30-27) and thus has changed their body fat percentage for the better.

Body Fat Percentage vs. BMI

Let’s compare the measure of body fat percentage vs. BMI.  Take those two individuals from before.  The ones with the same height and weight and therefore, same BMI.

Let’s say that one of them is a professional athlete, and one works a 9-5 and is physically inactive.

Although their height and weight is the same, I’m going to guess that you’re picturing two very different looking individuals.  One might have a serious amount of muscle and look fairly athletic, while the other might have a bit of a belly, look unathletic, and generally unhealthy.

Looks aside, research tells us that BMI does not have a correlational or linear relationship with health risks or all-cause mortality (1, 2, 3).  In fact, it was found that individuals with a lower BMI were actually at HIGHER risk for mortality than individuals with moderate BMI (4).

This same study (4) found that when adjusted for BMI and body fat percentage, higher body fat percentage was associated with increased mortality in both men and women.

On the high end, you most likely have obesity, and on the low end, you have the concept of skinny fat, where your body weight and BMI are “healthy” but your body composition is not (an idea has been reinforced from years of emphasis on a poor tool for measuring health).

Skinny Fat

I can’t say for certain, but I’d be willing to bet this man weighed more (and hence had a higher BMI) in the picture on the right than he did on the left.

Most importantly, the findings that low BMI and high body fat percentage/BMI are independently associated with an increased risk of mortality tells us that the BMI measure is flawed and we should instead focus on the relationship of lean mass to fat mass in our  bodies.

Key takeaway:

When comparing body fat percentage vs. BMI, we find that assessing our body fat percentage to be a far greater method of assessing health and risk.  BMI alone has been proven to be flawed because of it’s reliance on the scale and often has a counterintuitive relationship with mortality.

Wrap it up:

You most certainly are not a number.  You are not the weight you see on the scale, you are so much more.  Now is a good time to take a step back and assess whether we, as a whole, put too much emphasis on weight and a number on the scale.

When you look at the data when considering body fat percentage vs. BMI, we find that the better measure of health is to look at body fat percentage, hands down.

Yes there are times when an individual will be overweight and need to lose some of that weight, but the general idea is that people need to focus less on that number, and more on their body composition.

This means building muscle and losing fat and has everything to do with your level of activity, eating healthy foods in adequate amounts, maximizing recovery and reducing stressors.

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