What Is Body Composition?

The human body is made up of trillions of cells. These cells comprise of everything in your body from your muscles, bones, organs, fat, and nerves. Your body composition specifically can break down the percentages of how much of your cells make up your lean mass and your body fat. Measuring your body composition offers helpful information about the state of your overall health that other measures (like body weight and body mass index) can't offer.

What Does Body Composition Measure?

Your body composition measures two important factors: your body fat and your lean mass.

• Body fat:  There are multiple different types of fat, but when thinking about body composition, it’s helpful to understand the difference between essential body fat and excess body fat. Essential body fat appears in your organs, muscles, and brain, and helps regulate important functions. The most harmful type of fat is known as visceral fat, which can collect around your digestive organs, liver, and heart. Having an excess amount of visceral fat increases your chance of heart disease and other health issues.
• Lean mass: Your lean body mass is made up of your muscles, bones, organs, and water percentage. Several types of muscles also contribute to your lean body mass, including your skeletal muscles (or, muscles that you can control, such as flexing your fingers or kicking your legs), smooth muscles (or, muscles found in your organs and help with their automatic functioning), and cardiac muscles (or, muscles that control your heart and ensure that your heart is pumping properly).

The Difference Between Body Composition, Weight, and BMI

The weight on your scale measures how heavy you are in pounds or kilograms. Your BMI is a common measurement that healthcare providers use to quickly analyze your health data. It's worth noting that the BMI measure is outdated and flawed because it makes assumptions about your overall health by only considering two factors: your height and weight. Specifically, your BMI is a ratio of your weight and height. A BMI chart breaks down this ratio into four categories:

• Obese: BMI higher than 30
• Overweight: BMI between 25 and 29.9
• Healthy weight: BMI between 18.5 and 24.9
• Underweight: BMI lower than 18.4

While your BMI can signal that you might be at a higher risk of certain health conditions, it’s an incomplete and sometimes incorrect measurement of your health—as BMI doesn't account for differences in body mass or consider factors like age or sex.

For example, muscle weighs more than fat, which means that someone with a higher muscle mass could score highly on the BMI scale and be categorized as “overweight” or “obese", even if they are metabolically healthy.

Body composition offers a much more thorough assessment of your health than body weight or BMI because it measures what percentages of fat and lean mass make up your total weight. While two people might weigh the same, they could have completely different body compositions.

Importance of Body Composition

Having a well-balanced body composition sets you up for long-term health success. It’s especially important to make sure you’re carrying a healthy amount of body fat. Body fat is necessary for survival and helps insulate (protect) you from extreme temperatures, cushions your organs, and stores energy.

However, too much body fat can decrease your quality of life by putting you at risk of sleep apnea, breathing problems, and body aches. If your body has a higher body fat percentage, you may also be at an increased risk of developing cardiovascular (heart) diseases, type 2 diabetes, several types of cancer, and premature (or, early) death. That said, keeping your body fat low is more important than having a lower body weight.

Unlike BMI, there isn’t a consensus on the healthiest amount of body fat you should have. However, most researchers generally recommend that people assigned female at birth should have at least 10% body fat, and those assigned male at birth have at least 3% body fat. Your body fat can also vary by age. Your provider can also take all of these factors into account when helping you learn about your body composition and identify imbalances in body fat and lean mass you may have.

How Do You Measure Body Composition?

There are several different tests to measure body composition. Your healthcare provider can help you decide which assessment is best for you. Your options may include:

• Skinfold thickness assessment: For this method of measurement, your provider can use a caliper (an instrument that measures the thickness or distance of an object) to measure double folds of your skin in different areas of your body. Skinfold assessments are typically inexpensive and are one of the more common assessments for body composition.
• DXA (dual-energy x-ray absorptiometry) scan: During this test, your provider asks you to lie down as a medical imaging scanner quickly captures images of your bones, lean body mass, body fat and measures bone density. These tests, like skinfold thickness assessments, are rising in popularity.
• Bioelectrical impedance: This measurement involves the use of an electric current that gets sent through your body. Your provider can determine your body composition by looking at the speed at which the current took to pass through your body. Generally, the current passes through more quickly in lean mass than body fat.
• Bod Pod: This test requires you to sit inside an egg-shaped capsule, called the “Bod Pod.” The machine measures your body density and volume to calculate your body fat percentage.

It's important to note that some people use weight scales to measure their body composition. However, experts say you shouldn’t count on them. One study even compared the results from three different commercially available scales to a DXA scan and found the weight scales were inaccurate.

Factors That Affect Body Composition

A variety of factors can affect your body composition. Unlike the BMI, your body composition takes the following factors into consideration:

• Age: Research shows that as people age, they gain body fat and lose muscle mass and bone density.
• Sex: People assigned female at birth naturally hold more body fat than people assigned male at birth, especially in the hips and thighs.
• Hormones: Hormonal changes can also have an effect on your body composition. Menopause, for instance, can cause a stark increase in your body fat.
• Genetics: Your genes can sometimes have an influence on your body composition up to a certain point. One study found that children showed similar body composition to their parents. However, lifestyle patterns ultimately had more of an effect as the children got older and reached adolescence.

Tips for Changing Your Body Composition

Everyone’s body composition is unique. Your healthcare provider can help you better understand important details about the percentage of body fat and lean mass in your body and offer advice on how to move forward. If you want to change your body composition (either by increasing lean mass or reducing body fat), here are some safe, effective ways to do so: 

• Exercise: You can often burn fat and build muscle simultaneously through consistent exercise. One study found that high-intensity interval training (HIIT), which includes sprints and cycling classes, is an effective way to lose fat and build lean body mass. Strength training, or resistance training, can help you build muscle at any age. In older adults, this type of training can also help reduce frailty and bone loss.
• Increase your protein intake: If you’re trying to build muscle, increasing your protein intake can help. When paired with resistance training, research shows that upping your protein can lead to larger muscular gains and limit age-related muscle loss.
• Avoid processed foods: To lose fat, experts recommend eating a balanced diet filled with whole foods and healthy fats, like the Mediterranean diet, which can help reduce inflammation and the likelihood of developing health conditions like type 2 diabetes or heart disease.

A Quick Review

Body composition is the breakdown of body fat and lean mass that you carry. Unlike the BMI which only considers your height and weight, factors like your age, sex, hormone levels, lifestyle habits, and genetics all play a role in your body composition.

If you want a holistic assessment of the state of your health, knowing your body composition is more useful than just knowing your body weight or BMI. By looking at the breakdown of lean mass compared to fat in your body, you and your healthcare can develop a plan to make certain lifestyle changes that can help you reach your health goals and lower the risk of developing certain health conditions.