What Is Body Composition and Is It More Accurate Than BMI?

Bodyweight, body fat, BMI — what's the difference? Is one measurement better than the others?

As you're well aware, the wellness industry uses a number of measurements to determine your health and fitness levels. And, as you are probably even more aware, each of these measurements comes with its fair share of shortcomings.

Here's why: Measurements such as your weight or body mass index offer one narrow view of your health. Rarely — if ever — do they provide the whole picture. 

This poses a problem when you commit to a certain wellness goal. As the saying goes, you cannot improve what you cannot measure. If you don't have accurate measurements to begin with, it can prove very difficult to move forward.

Today, I answer the question, "What is body composition?" and explain why it provides a more accurate depiction of your health than other measurements.

Please note: This post is meant for informational purposes only, and should not be taken as medical advice.

What Is Body Composition? 

Body composition breaks down your weight into four areas: muscle, fat, minerals, and water. In doing so, you have a more accurate depiction of your health, understanding fat mass, muscle mass, bone density, and body fat.

Here's why body composition matters: When you set a goal, you need to arm yourself with as much knowledge as possible to accomplish that goal. Therefore, if you are a 68-kilogram (150-pound) female, and set a goal of losing 5 kilos (roughly 12 pounds), you'll need to ask yourself the following questions:

  • Is losing 5 kilos healthy? Do I evenhave 5 kilos to lose?
  • At 68 kilos (my current weight), how much is fat? How much is muscle?
  • Do I even want to lose weight? Would losingbody fat be a healthier, more attainable goal?

Unfortunately, many measurements — including BMI (body mass index) and bodyweight — do not help answer these questions.

Where BMI (Body Mass Index) Falls Short 

Many times, the wellness industry uses your BMI, or body mass index, as the gold standard to measure overall health.

Your BMI is calculated by taking your weight (in kilograms) divided by your height (in meters squared). At first glance, this seems like a more accurate depiction of your health than bodyweight alone (which it is), because it understands that a 1.83-meter (6-foot) male will undoubtedly weigh more than a 1.5 meter (5 foot) female.

However, your BMI falls short (pun intended) because it does not take into account your muscle or fat mass. A 1.83-meter (6-foot) male with 6% body fat will have a higher BMI than a 1.68-meter (5-foot, 6-inch) male with 35% body fat, even though he is leaner overall.

Here’s where this causes a problem: The 1.83-meter (6-foot) male simply doesn't have that much weight to lose, because his body fat is so low. However, the man with the higher body fat percentage could lose a significant amount of weight, even those his overall BMI is lower. 

Why Do Doctors Reference BMI if It's Not the Most Accurate Measurement?

Fair question.

Many times, doctor’s offices, physical therapists, and other health professionals reference BMI because it's easy to calculate. To calculate BMI, all you need is a person's height and weight. 

Body composition, on the other hand, is much more difficult to calculate. In fact, there is no easy way to accurately calculate body composition on your own — you will need to have your body composition calculated by a professional (more on this below).

Weight Loss Does Not Always Mean Fat Loss 

When you lose weight, you often lose fat, muscle, and water (not just fat). The vast majority (if not all) of my clients would be thrilled if their weight loss caused a loss in body fat alone, preserving their skeletal muscle mass. Unfortunately, that's just not how it works.

When you first lose weight, you may lose a great deal of lean tissue (muscle) and water weight. If your total body weight and BMI decreases, but you look the same in the mirror, it’s a sign you aren’t losing fat.

Skinny Does Not Always Mean Healthy 

It's entirely possible — and common — to have a low BMI while still having a considerable amount of fat on one's body. 

There are two types of fat: visceral fat and subcutaneous fat. Subcutaneous fat is the fat that lays just below the surface of the skin. Visceral fat, on the other hand, crowds around your organs, and is considered to be far more dangerous to your health. Too much visceral fat on the body can lead to a number of health risks, including certain types of cancer, heart disease, and even diabetes.

A person with a high percentage of visceral fat tissue could appear trim and healthy on the surface (leading to the common phrase, "skinny fat"). Therefore, it's important to understand the percent of total body fat, muscle mass, total body water weight, and bone mineral weight in the body.

5 Ways To Measure Body Composition 

Body composition gives you an accurate depiction of the human body divided between water, fat, muscle, and minerals.

As stated earlier, you will not calculate your body composition on your own, as with your BMI. Instead, you can use the following resources to calculate your body composition:

  • Skinfoldcalipers (pinch test): A skinfold caliper pinches your subcutaneous fat layer. While this method is simple and affordable, it does not measure your visceral fat levels, making it slightly inaccurate.
  • Dexa scan:A dexa scan is a large X-ray machine or full-body scan that measures your bone density. 
  • Hydrostatic weighing:Hydrostatic (underwater) weighing involves submerging your whole body  It calculates your total body fat by your total body volume using the Archimedes’ principle.
  • Air displacementplethysmography: Air displacement measures the volume of the human body according to changes in pressure within a total body  Then, weight and volume are used to calculate bone mass, body fat, and fat-free mass (lean body mass).
  • Bioelectrical Impedance Analysis(BIA): BIA is a method that sends electrical current through an individual's hands or feet to measure body fat, muscle mass, water weight, and bone density,such as Bodypedia Smart Scale.

I Know My Body Composition, Now What?

Once you calculate your body composition, you can use it as your baseline to set long-term health goals. Specifically, you can use your body composition analysis to discover the following:

  • Set realistic goals:Rather than simply saying, "I want to lose 5 kilos," you can set realistic, healthy goals to preserve muscle while losing fat.
  • Determine how many calories you need:An optimal nutritional plan will be based on your BMR (basal metabolic rate) and your TDEE (total daily energy expenditure). Someone with a higher percentage of muscle will need more calories than someone with less lean mass.
  • Workout smarter, not harder:Body composition measurements show how much fat and muscle you have throughout your body. Now, you can determine a workout plan with an optimized mix of strength and cardio training that targets fat loss, not the loss of muscle mass.