Body Composition: Definition and Insights into Health
Medically reviewed by Ashley Baumohl, RD
Body composition refers to the distribution of fat, muscle, bone, and other tissues that make up your body. It is often expressed as the percentage of total body weight that consists of fat and/or lean body mass. Body composition offers numerous insights into health, fitness, and nutritional status.
Body fat plays a key role in hormone production, insulation, and other important body processes. While the optimal amount of body fat differs from person to person, having too much body fat increases the risk of various health issues, from joint problems to heart disease.
Fortunately, there are several strategies to improve body composition and your overall health. This article discusses what body composition is, why it's important, and how to improve yours.
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What Is Body Composition?
Body composition is the term used in the fitness and health community to refer to the percentage of fat, water, bone, muscle, skin, and other lean tissues that make up the body.
While checking your weight on the scale can be helpful for seeing your total weight, it doesn’t tell you how the weight is distributed in your body.
Body composition is typically broken up into two groups:
Fat mass refers to the body's stored fat. Fat insulates the body, surrounds your organs, and is used for energy.
Non-fat mass refers to all of your body's components except fat. Non-fat mass includes bones, liver, kidneys, intestines, muscles, and other organs and tissues your body needs to function.
Many health risks are tied to the ratio of fat mass to non-fat mass. Research shows that the risk of premature death is greater in people who have higher percentages of fat compared to non-fat mass.
In comparison, people with higher percentages of non-fat mass compared to fat mass tend to be leaner with more muscle. These individuals have a lower risk of many diseases.
Related: Body Fat Percentage: Charting Averages in Men and Women
Importance of Measuring Body Composition
Body composition is a valuable tool for assessing:
Health status: Body composition assesses the percentage of fat in the body. Having excessive body fat, especially fat around organs (visceral body fat), increases the risk of many health conditions, including heart disease, diabetes, and several cancers.
Fitness levels: Athletes and fitness enthusiasts can use body composition as a tool to track their lean muscle building progress. Body composition helps athletes optimize their strength, endurance, and overall athletic performance.
Nutritional status: Body composition can help you and your healthcare provider understand if you have too much or too little body fat relative to your weight. This information can be used to design a safe and effective diet intervention or meal plan.
Metabolic health: Having excess fat increases the risk of metabolic health issues, including insulin resistance, imbalances of cholesterol and triglycerides, high blood pressure, uncontrolled blood sugar, and slowed metabolism. Body composition is therefore an effective tool for monitoring and reducing these risks.
Weight control: Weight loss is often accompanied by a loss in lean body mass, especially muscle, which can impede long-term weight loss by slowing metabolism and increasing fatigue. Monitoring body composition helps maintain lean body mass while also shedding body fat.
Body Composition vs. Weight and Body Mass Index
BMI is a screening tool commonly used to assess a person's weight in relation to their height. The tool provides a general evaluation of a person's health risks relative to their weight. But, unlike body composition, it does not provide specifics about the distribution of a person's weight.
BMI is calculated by taking total body mass in kilograms (kg) and dividing it by height in meters (m) squared. The results are written as kg/m2.
The number is then put into a chart to find the category. The BMI categories include:
BMI less than 18.5 = Underweight
BMI 18.5 to 24.9 = Normal
BMI 25 to 29.9 = Overweight
BMI 30 to 34.9 = Obese class I
BMI 35 to 39.9 = Obese class II
BMI more than 40 = Obese class III
Whereas BMI measures weight relative to height, body composition measures fat in proportion to lean body mass. For this reason, body composition offers a more accurate and comprehensive insight into a person's overall health.
Take, for example, an athlete with excessive muscle and very little fat. This individual will likely have a high BMI. In this instance, though, having a high BMI does not mean they have obesity, or a greater risk of health conditions that are associated with obesity.
In order to get an accurate evaluation of how much fat, muscle, and all-around lean mass this individual has, an evaluation of their body composition is needed.
How do you figure out your healthy body weight?
Many calculations for finding healthy body weight use factors like age, sex, and height. These measures can be limited and provide an estimated range. Still, finding your height on a BMI chart can give you an idea of what a healthy weight may be for you.
Calculating Body Composition
Body composition is measured using tools to estimate your body fat percentage. The ways to measure body composition vary. Some are more accessible but may be less accurate, while others may be harder to access and more accurate. Here are different ways body composition is measured.
Skinfold Measurement
Skinfold measurements use a special type of caliper tool designed to measure the thickness of a skinfold. It's done by gently pinching the skin and fat under the skin on several body parts.
Skinfold measurements are usually done on the following:
Stomach
Side of the torso
Chest
Upper thigh
Beneath the shoulder blade
Hip
Tricep or upper arms
This type of measurement is accurate. However, there is a large possibility of "user error" if the person performing the test doesn't have proper training.
Body Circumference
Body circumference or waist circumference measurements are a simple and easy way to estimate body fat. It uses a tape measure to see how wide around specific body parts are. Circumference is often assessed on body parts like the waist, arms, chest, thighs, and hips.
Research suggests carrying more weight on your abdomen is associated with an increased risk for health problems. The circumference method helps assess the risk for disease based on the weight you carry on your belly.
However, this method may not be the best if your goal is to assess your overall body fat percentage because it only measures the circumference and not the percentage of fat and muscle.
Dual Energy X-ray Absorptiometry
The dual energy X-ray absorptiometry scan, known as a DEXA scan, uses low-energy X-rays to accurately measure the weight of bone, muscle, and body fat. After the scan, you receive an assessment of your bone density, body fat percentage, and mass of each body part.
Many professionals consider the DEXA scan the gold standard for measuring muscle mass. However, it can be harder to find a place to have a DEXA scan done depending on where you live, and it may be a more expensive option.
Hydrostatic Weighing
Hydrostatic weighing measures the water displacement when someone is fully submerged in water. Because fat floats and lean tissues sink in water, the more lean body mass you have, the heavier you’ll be under water.
Hydrostatic weighing was long considered the gold standard for assessing body composition until other methods, like DEXA scans, were developed. While this method is accurate, some people find it difficult to stay submerged in water long enough for the assessment, and it may not be accessible.
Bioimpedance Analysis
A bioimpedance analysis (BIA) uses a painless, low-energy electrical current to assess fat mass, muscle mass, and hydration (water mass).
Muscle contains more water than fat, so it conducts the energy current better than fat. Fat tissue impedes the movement of the current. The BIA scanner can assess body composition based on how the energy moves through the body. This test tends to cost less and may be easier to find than other types of scans.
However, the accuracy of this assessment changes based on how hydrated you are. If you drink too much water before the test, you could appear leaner than you are. If you’re dehydrated, the test may say you have more body fat than you do.
Other Methods
Some other methods of assessing body composition include:
BodPod: Uses air displacement to determine body composition.
Magnetic resonance imaging (MRI): Uses strong magnetic currents to generate an image.
Computed tomography (CT) scan: Uses X-rays and a computer to generate an image.
How to Improve Body Composition
The best way to improve your body composition is to make healthy changes, like:
Dietary Changes
Eating a diet full of highly processed foods that provide large amounts of sugar and fat is associated with gaining weight and body fat. To improve your body composition, you’ll have to focus on healthy diet changes.
Try to be mindful of how much you’re eating and aim to fill your plate with mostly:
Vegetables
Fruit
Whole grains
Lean proteins
Healthy fats
Related: Principles of Healthy Eating
Physical Activity
Moving more and exercising regularly helps improve body composition.
Research shows all types of exercise programs help improve the body composition of people who are sedentary. Strength training programs that develop the whole body have the biggest impact on body composition while also improving bone density.
Here are some tips to help you increase your physical activity:
Try group fitness classes.
Find a type of exercise you enjoy.
Meet with friends to exercise.
Find an accountability partner.
Hire a trainer.
Walk during part of your lunch break.
Take the stairs.
Related: What Is Aerobic Exercise?
Sleep Quality
The amount of time you sleep and your sleep quality can greatly impact your body composition.
A 2018 study found poor sleep quality was associated with:
Lower bone mineral density
Lower muscle mass
Higher body fat mass
So, if you’re looking to improve your body composition, you may want to place a higher priority on sleep.
Here are some tips to help increase your sleep quality:
Have a consistent bedtime routine, including going to bed and waking up at the same time daily.
Sleep in a cool, dark, quiet environment.
If you need background noise, use a fan or noise machine for a consistent sound.
Avoid caffeine and alcohol before bed.
Exercise regularly.
Related: How to Improve Sleep
Lifestyle Changes
In addition to the above lifestyle changes, other changes that may help your body composition include:
Limiting the amount of alcohol you drink.
Prioritizing your mental health.
Summary
Body composition is a measurement of the amount of body fat and lean tissue in your body. It’s important because having more body fat is associated with an increased risk for some chronic diseases and health problems.
Body composition can be measured with tests like skinfold assessment, DEXA scan, body circumference, hydrostatic weighing, and bioimpedance analysis. In addition, you may be able to improve your body composition by focusing on lifestyle changes like a healthy diet, exercise, sleeping better, and managing stress.
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