What is body composition?

Body composition is a method of breaking down the body into its core components: fat, protein, minerals, and body water. It describes your weight more accurately and provides a better glimpse into your overall health than traditional methods. Body composition analysis can accurately show changes in fat mass, muscle mass, and body fat percentage.

Why is body composition important to measure?

Our conversations on diet and fitness tend to focus on the amount of weight that we want to gain and lose. What they fail to consider is that two people of the same sex and body weight may look completely different from each other because they have a different body composition. Body composition describes the amount of fat, bone, water, and muscle in the body. Measuring your body composition will tell you your own body’s unique makeup and help you identify areas to work on to improve your overall health and wellness.

Body composition analysis is a method of describing what the body is made of, differentiating between fat, protein, minerals, and body water to give you a snapshot of your health. InBody is in the business of body composition analysis, and we’re here to teach you the importance of it today’s day and age to help you reach your health goals from the inside out.

How can BMI be inaccurate and misleading?

You may not have heard of body composition before, but you’re probably familiar with BMI. What’s the difference? Body Mass Index (BMI) is a common method used to assess the health of an individual by comparing the amount of weight they carry to their height: BMI – kg/m2

Despite the widespread use of BMI in clinical practice, BMI has many limitations and is a poor tracking tool for weight change because there’s no way to identify if changes in your weight are in fat or muscle. Predicting health or mortality using a single number such as BMI oversimplifies health risks and ignores important factors that contribute to positive health.

When you’re trying to get healthier, you’re most likely focused on losing fat and gaining muscle. Scales or BMI cannot tell you how much of your weight loss is fat, muscle, or body water, but body composition can.

Why do you need to understand your weight in terms of muscle and fat?

You may be aware of the normal weight ranges, but how do you get there? If you only focus on losing weight, you may end up losing muscle mass and eventually sabotage your efforts. By differentiating between muscle and fat, body composition removes the guesswork of determining what your weight fluctuations mean, be it muscle gain, fat loss, or anything in between.

Whatever your goals may be, an important thing to keep in mind during your health journey is that skinny does not always equal healthy.

Does skinny always equal healthy?

It’s common to assume that having as little fat as possible is healthy. However, being thin does not automatically reduce one’s health risk—“skinny fat” people can carry the same elevated health risks as an obese person.

People who are skinny fat may look thin and healthy because they have an acceptable amount of subcutaneous fat—the type of fat stored just under the skin—but they have increased health risks due to an excessive amount of visceral fat and too little muscle mass.

What’s more, those classified as skinny fat are typically unaware of their potential health risks because, unlike subcutaneous fat, visceral fat cannot be measured with BMI and scales so it goes undetected. Whether you fall into one of the above categories, or you just want to know how you start making healthy changes, understanding your muscle-balance is a great place to start.

A healthy balance of fat and muscle is a vital component of long-term health. Having sufficient muscle mass helps bolster the immune system to fight off illnesses, support good posture, enhance mobility, and prevent frailty in old age.

What are the benefits of understanding your body composition?

  • Find your baseline so you know what you need to lose, gain, or maintain
  • Assess your Percent Body Fat so you can focus on fat loss, not just weight loss
  • Maximize your workout routine to fit your unique health and fitness goals
  • Calculate your caloric needs and create a personalized nutrition plan
  • Set realistic goals, accurately monitor progress, and stay motivated
  • Make more educated decisions to improve your body composition

How do you track your progress with body composition outputs?

With body composition, you can easily track progress and measure the effectiveness of your diet and exercise regimen.
There are several essential body composition outputs that you can use to track your progress over time:

Percent Body Fat (PBF)

Percent Body Fat is a more accurate indicator of your health than your body weight or BMI because it tells you exactly how much fat makes up your total body weight. For a healthy body fat level, aim for a PBF within 10 – 20% for males, or 18 – 28% for females.

Skeletal Muscle Mass (SMM)

Skeletal Muscle Mass is important for mobility, posture, and strong immunity for long-term health. Body composition analysis shows you precisely how much Skeletal Muscle Mass you have in each body segment, so you can focus on building more muscle or correct imbalances to ensure you have a healthy muscle mass balance.

Body Water

Your Total Body Water (TBW) is divided into two groups: extracellular water (ECW), which is the water located outside your cells, and intracellular water (ICW), which is the water located within your cells. A healthy balance of body water is critical for good health. With body composition analysis, you can identify any changes and address them to maintain a healthy balance.

Methods of Body Composition Analysis

There are many ways to determine your body composition. Some are quick and easy, but provide basic information only. Some are lengthy and expensive, and require the assistance of a trained technician to administer a test. Here are a few methods that are used to determine body composition:

Skinfold Calipers

One of the anthropometric methods used for measuring body fat is the skinfold test. It is also known as pinch test. As the name implies, this method involves pinching the subcutaneous fat layer with fingers and measuring the thickness using a caliper.

Calipers easily portable, and measurement is simple and inexpensive. However, this method involves estimating the total Percent Body Fat (PBF) based on subcutaneous fat.

Although a large portion of body fat is subcutaneous fat, the measurement may not be accurate for people whose body fat distributions vary. Also, measurement is difficult if the subcutaneous fat layer thickness is 5 cm or more and reproducibility of the result varies greatly depending on the skills of the measurer.

Image Credit: Flickr

Hydrostatic Weighing

Underwater weighing calculates the total body fat by the density of the body. It is based on Archimedes’ principle: when an object is submerged in water, the difference between the mass of the object in the air and its mass in water is the object’s volume.

Body density = Mass of air /(Mass of air – Mass of water )

Underwater weighing is regarded as the gold standard for body composition measurement as it is one of the only body composition technologies that have been compared directly to cadaver analysis.

Image Credit: Texas A&M

Air Displacement Plethysmography

This method measures the volume of a human body by measuring the volume of air according to the changes in pressure in a chamber.

First, weight and volume of the person are used to calculate body density and then Percent Body Fat and the fat-free ratio.

  • Density = Mass / Volume
  • Percent Body Fat = (495 / Density) – 450 
  • Fat free ratio = 100-BF%

Time required for measurement is relatively short at 3-5 minutes and the examinee can continue breathing in the chamber as opposed to underwater weighing. This method is known as a gold standard because it allows body composition analysis and produces accurate measurements using volume just like underwater weighing.

Image Credit: U.S. Air Force photo by Joel Martinez

Dual Energy X-Ray Absorptiometry (DEXA)

DEXA is an imaging method that measures the body weight in terms of BMC, lean, and fat based on the decrement of X-ray on the images obtained by exposing to two different X-rays. With the patient lying down, photons of the X-ray beams of different energy levels scan the patient. It takes about 5 to 30 minutes.

As a standard method for body composition analysis, DEXA has high accuracy along with hydrodensitometry. Its advantage is that it can measure the body composition of bone density, body fat and muscle mass for different parts. Advancements to the technology affords DEXA the ability to differentiate lean and fat, allowing this technology to advance from a 2 compartment model to a 3 compartment model.

In order to get a DEXA scan performed, you will typically need to make an appointment with a hospital or clinic that has a DEXA device. You may need to do some research; not all hospitals and clinics will have DEXA devices.

Image Credit: Wikipedia

MRI (Magnetic Resonance Imaging)

Magnetic resonance is a form of imaging technique where the body water may be mapped (but not quantified). The body is scanned in segmental (slices) scans are used to predict whole-body values. MRI is considered to be the most accurate tool for in vivo quantification of body composition. It is an ideal evaluation tool for measurement of skeletal muscle mass and adipose tissue (and can divide adipose into visceral and subcutaneous depots).

MRI’s use a high-strength magnet, thus all metal must be removed. Individuals with metallic chips, materials, surgical clips, artificial joints/prosthetics, pacemakers, metal implants, artificial heart valves, metallic cochlear implants, bullet fragments, or insulin pumps should not test. However, since there is no ionizing radiation, this is a preferable option for many (elderly, children, etc.)

A whole-body scan is roughly 25-30min for scan and 3 hours to analyze via computer software.

Image Credit: Northwest Radiology

Bioelectric Impedance Analysis (BIA)

Bioelectrical Impedance Analysis (BIA) is a method of measuring impedance by applying alternating electrical currents to a user to measuring their volume of water through impedance values.

This non-invasive method involves the placement of electrodes on a person’s feet, hands, or both. A low-level electrical current is sent through the body, and the flow of the current is affected by the amount of water in the body. BIA devices measure how this signal is impeded through different types of tissue (muscle has high conductivity but fat slow the signal down).

As BIA determines the resistance to flow of the current as it passes through the body, it provides estimates of body water from which body fat is calculated using selected equations.


Learn how InBody's BIA technology works
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