Ashley Braun, MPH, RD, is a registered dietitian and health content writer with over 5 years of experience educating patients on chronic diseases using science-based information.

Ashley Baumohl, MPH, RD, CDN, CNSC is a surgical dietitian. She provides medical nutrition therapy at Lenox Hill Hospital and is based in New York, New York.

Most diets focus on body weight and weight loss over maintaining healthy body composition. Your body composition is the percentage of body fat, muscle, bone, and other tissues. Read on to understand what body composition means and why physical fitness is preferable to weight loss. 

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 the composition of your body.

Typically, people break body composition into two groups: fat mass and fat-free mass. Fat mass is the amount of body fat. Fat-free mass is all the lean tissues in your body like muscles, organs, bone, water, etc. 

Body mass index (BMI) is another popular term used in the medical and health community to describe body measurements. 

Body composition is different from body mass index because BMI focuses on how your whole body weight compares to your height. BMI is calculated by taking total body mass in kilograms (kg) and dividing it by height in meters (m) squared. The results are written with unit kg/m2.

The number is then put into a chart to find the category. The BMI categories include:

The problem with BMI is it doesn’t accurately show your body composition. Many athletic people with high muscle mass and low body fat percentage may fall into the overweight or obese categories. But that doesn’t mean they have the same health risk factors as someone with the same BMI and a high body fat percentage.

Body composition and body fat percentage may better predict health risks than simple obesity classification based on BMI. A healthier body composition is a higher percentage of lean tissue and a lower percentage of body fat. 

Body composition is important because it can give you a better idea of your health risk, especially if you fall in the overweight or obesity category for BMI because you have more muscle and lean tissue.

While weight loss and watching the number on the scale can help, it doesn’t tell you whether you’re losing body fat or muscle mass.

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 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:

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 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. 

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 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. 

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.

Some other methods of assessing body composition include:

The best way to improve your body composition is to make healthy changes, like:

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:

Moving more and exercising regularly helps improve body composition.

Research shows all types of exercise programs helped improve the body composition of people who were sedentary. The results showed strength training programs that develop the whole body had the biggest impact on body composition and improving bone density.

Here are some tips to help you increase your physical activity

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:

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:

In addition to the above lifestyle changes, other changes that may help your body composition include:

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.

Body composition can give you a better understanding of your current fitness and health level. In addition, repeating the body composition test over time can help you track your progress on your wellness journey. 

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.

All types of exercises can help with body composition, especially if you weren’t very active before. Strength training and interval training may have a bigger impact on raising your muscle mass and lowering your body fat percentage.

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By Ashley Braun, MPH, RD Ashley Braun, MPH, RD, is a registered dietitian and public health professional with over 5 years of experience educating people on health related topics using evidence-based information. Her experience includes educating on a wide range of conditions including diabetes, heart disease, HIV, neurological conditions, and more. 

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