Body Composition: Definition, Examples, and Measurement

Jennifer E. Engen

When it comes to diets, most people favor losing weight over maintaining healthy body composition. But stepping on the scale will only tell you how much you weigh, whereas your body composition is the proportion of fat and non-fat mass in your body.

Often, people measure their body composition at the start of a fitness program and then check it periodically to monitor their progress.

In this article, you will learn what body composition means and why physical fitness is preferable to weight loss. 

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What Is Body Composition?

Your body is composed of two types of mass, body fat and non-fat mass. Here are some key differences between the two:

  • Body fat: Some fat is necessary for overall health. “Essential fat” helps protect internal organs, stores fuel for energy, and regulates important body hormones. But you may also have excess stores of fat and non-essential body fat.
  • Non-fat mass: This includes bone, water, muscle, organs, and tissues. It may also be called lean tissue. Most non-fat mass tissues burn calories for energy, while most body fat does not.

Weighing yourself on a regular bathroom scale does not assess your body composition. A regular scale cannot tell how much of your total weight is comprised of water, fat, or muscle. 

How Is Body Mass Index Different?

Body mass index, or BMI, is another measure of body weight and mass that is often mistaken as a measurable guide to body fat. However, BMI is simply a weight-to-height ratio, which has limitations; it doesn’t take into account a person’s age, race/ethnicity, or non-fat mass.

BMI assigns a number based on a comparison of your weight and height. This number then places you in a category to determine whether you are underweight, at a healthy weight, overweight, or obese for your height. Higher weight categories are considered to be at higher risk for certain illnesses, such as high blood pressure and high cholesterol.

Body composition distinguishes fat from muscle and calculates the percentage of fat in the body. While BMI is a rough estimate of body fat, body fat percentage is a more accurate number for determining overall health.


Your body is composed of two types of mass, body fat and non-fat mass. Non-fat mass includes bone, water, muscle, organs, and tissues. BMI is often mistaken as a measurable guide to body fat. However, BMI is simply a weight-to-height ratio. Body composition distinguishes fat from muscle and calculates the percentage of fat in the body.

Why Body Composition Is Important

A healthy balance between fat and muscle is vital for health and wellness throughout life. Scientific evidence shows that healthy body composition is associated with an increase in expected lifespan because it can help reduce the risk of heart disease, cancer, diabetes, and insulin resistance. Plus, healthy body composition may increase energy levels and improve self-esteem.

With a better understanding of body composition, individuals and healthcare providers can work together to develop a complete health assessment that includes monitoring body fat levels and muscle growth. This will provide a more complete picture of body changes, and facilitate making targeted adjustments to exercise, diet, and lifestyle habits accordingly.

How Is Body Composition Measured?

There are several ways to measure body composition, some are basic and can be done at home, others require specialist equipment.

Skinfold Measurement

Taking skinfold measurements is a method that is sometimes used by fitness trainers or as part of a weight loss program. Skinfold calipers measure the thickness of your subcutaneous fat—the fat underneath the skin—at certain body locations. A calculation helps translate them into a body fat percentage.

It’s worth noting the accuracy depends on the skill of the person performing the assessment, and that skinfold measurement is being replaced by methods such as bioelectrical impedance analysis (BIA) to estimate body fat content.

Body Circumference

Body shape varies from person to person, and the shape of your body can provide information about your body fat. Measuring the circumference of certain body parts is a simple method of estimating body fat percentage. However, the accuracy of this method can vary widely and is not considered an ideal method of measurement.

Dual Energy X-ray Absorptiometry

A dual-energy X-ray absorptiometry (DEXA) scan is performed in a medical setting and can also be used to check for bone density. DEXA is more accurate than many other methods of assessing body composition, but it’s often unavailable to the general population, fairly expensive, and not practical for regular testing.

Hydrostatic Weighing

Hydrostatic weighing estimates your body composition based on its density and requires you to be fully submerged in water. This method is only available at a limited number of facilities.

Bioelectrical Impedance Analysis (BIA)

Bioelectrical impedance analysis (BIA) can be measured by handheld units and BIA body fat scales that you step onto like a regular scale. These tools pass a small electrical current through your body. Fat, water, and lean tissue impede the current differently to give the reading.

However, BIA requires a constant state of hydration (water content) in the body in order to be reliable and reproducible; therefore, it is not usually used in a clinical setting to measure body fat content.

Other Methods

Other ways to measure body composition include:

  • Air displacement plethysmography (ADP): Similar to hydrostatic weighing, ADP estimates your body fat percentage based on the density of your body. However, ADP uses air instead of water.
  • 3D body scanners: 3D body scanners use infrared sensors to get a detailed look at the shape of your body.
  • Magnetic resonance imaging (MRI): Similar to a DEXA scan, an MRI is also performed in a medical setting and can provide quantification of total fat tissue and its location (under the skin, in the muscle, or around body organs). But an MRI is expensive and not practical for regular testing.


There are several ways to measure body composition. Some use handheld tools and measurements, others involve expensive tests and machinery. The method you use to measure body composition will depend on your budget and how accurate you’d like the reading to be.

How to Improve Body Composition

If your body fat percentage is too high, you may want to try to decrease it to improve your health and wellbeing. If your body fat percent is below the level of essential fat, you may also want to make changes to increase it, as that will reduce your health risks as well.

To change your body composition for better health and fitness, aim to increase muscle mass and decrease excess fat mass. You can do this by changing your diet, starting an exercise program, or combining both methods.

Dietary Changes

In very basic terms, if you consistently eat more calories than your body uses, you will gain weight— typically as fat. Likewise, if you consistently eat fewer calories than your body uses, you will lose weight. But the types of foods you eat are just as important as the number of calories you consume.

Protein is important for everyone, but you may need more protein if you are active or trying to gain muscle or lose fat. It is more satisfying than carbs or fat, and your body also burns more calories processing protein than these other nutrients.

Physical Activity

Physical activity and exercise are other crucial components for improving body composition. They not only increase the calories your body uses, but they are also necessary for optimal muscle growth.

The U.S. Department of Health and Human Services Physical Activity Guidelines for Americans state that adults should do at least 150 minutes to 300 minutes a week of moderate-intensity aerobic activity for substantial health benefits. Preferably, aerobic activity should be spread throughout the week.

While these recommendations focus on body weight, it is important to remember that some forms of exercise will build muscle while you are losing fat. This is another example of why thinking about your body composition, rather than just body weight, is a good idea.

Sleep Quality

There is some evidence that people who have poorer sleep quality have a worse body composition than those with good sleep quality. However, it isn’t clear whether good sleep improves your body composition or if having a better body composition improves your sleep.

Lifestyle Changes

Alcohol consumption is another factor that may affect body composition. Alcohol is loaded with sugar and extra calories, which the body stores as fat. Since alcohol contains calories, it can contribute to excess calorie intake and fat gain.


Body composition tells you how much of your body is fat, and how much is non-fat mass like bone, water, muscle, organs, and tissues. Therefore, body composition is a more accurate way of tracking fat loss when on a diet and fitness regime and can be measured in a number of ways.

You can improve body composition by making changes to your diet, exercising, getting enough sleep, and cutting down on alcohol.

A Word From Verywell

Your body composition and body fat can be important measurements because the number you see when you step on the scales is not the whole picture. You could be successful in losing fat and gaining muscle without seeing your weight go down. Tracking your weight loss and fitness efforts with body composition measurement is a good way to see your progress.

Frequently Asked Questions

  • How do you figure out your ideal body weight?

    The traditional ideal weight calculation is essentially a rule of thumb rather than being based on health research or a comprehensive study of population averages.

    • For women: Ideal body weight (in kilograms) = 49kg + 1.7kg for each inch over 5 feet
    • For men: Ideal body weight (in kilograms) = 52kg + 1.9kg for each inch over 5 feet

    Remember that ideal weight is not an absolute target for either appearance or health. The values in charts and equations are estimates and may not take into account factors like muscle mass or health conditions that affect weight.

  • Are certain exercises good for body composition?

    All forms of exercise burn calories. But body composition exercises combine activities to burn fat and activities to build muscle. That way, you replace fat with lean, strong muscles.

    So what is the best way to burn fat and build muscle? A combination of aerobic activity (sometimes called cardio) and strength training (such as lifting weights). Aerobic activity is any exercise that gets your heart pumping. You’ll notice real changes to your body composition when you begin strength training. The purpose of strength training is to build and shape the muscles.

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