Updated 19th March 2024

What is body composition, and why is it important?

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“Body composition” refers to the relative percentages of fat, muscle, and bone in your body. The term is mostly used by doctors and scientists. 

Increasing or maintaining muscle mass and bone density can help you stay fit and active as you get older.

If your body composition isn’t within a healthy range, reducing your body fat percentage could lower your risk of developing health conditions such as heart disease and type 2 diabetes.

Improving your diet, exercising more, and getting better sleep can all make a difference.

How does it affect your health?

Your body composition can influence your risk of developing a range of health conditions.

Having too much body fat is linked to metabolic diseases, like heart disease and type 2 diabetes, as well as some types of cancer.

As you age, your bones may become less dense and you may lose muscle, though your overall weight may not change. 

Low bone density can significantly increase your risk of fractures.

Muscle loss can eventually affect how well you can perform day-to-day tasks. If this happens, it can increase your risk of falls, illness, and obesity.

Your body composition also influences your basal metabolic rate (BMR). This is the amount of energy your body uses every day for functions like breathing, sleeping, and blood circulation. 

Having more lean muscle tends to increase your BMR, meaning you burn more energy and may store less body fat.

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How can you change your body composition?

Exercise, diet, and sleep all influence your levels of body fat and muscle mass.


If your ratio of fat to muscle mass is too high, doing regular resistance training can help.

Resistance training is also called strength training. It can involve lifting weights, using resistance bands, or doing bodyweight exercises, like squats and push-ups.

Make sure to include all the major muscle groups in your workouts. It’s also a good idea to have some cardio and balance training in your exercise routine.

Learn more about muscle building here.


To gain muscle through exercise — or to slow down muscle loss as you age — you may need more protein. 

The recommended dietary allowance of protein for most adults is 0.8 grams per kilogram of bodyweight per day

But people who regularly do resistance training may benefit from getting more: 1.2 to 1.6 g. And older people may need around 1.2 to 2.0 g.

Healthy sources of protein include:

  • legumes, like peas or beans

  • tofu

  • fish, such as salmon or sea bass

  • lean, unprocessed meats

  • dairy, like milk, yogurt, or cottage cheese

  • eggs

  • nuts and seeds

Try to get your protein in throughout the day. Your body can only use a certain amount to maintain and build new muscle mass, and extra protein may end up as fat.

If you’re looking to reduce body fat, eating patterns like the Mediterranean diet are a healthy approach. They don’t involve restrictive calorie counting.

Research suggests that the Mediterranean diet and similar patterns could reduce overall body fat, waist circumference, and body mass index (BMI)

The Mediterranean diet typically includes: 

  • a wide range of fruits and vegetables

  • plenty of legumes

  • whole grains

  • fish

  • extra virgin olive oil

  • nuts

  • moderate or no alcohol

  • limited red meat and processed meat

  • limited foods and drinks with added sugar

At ZOE, we run the largest nutrition science study in the world. We know that our bodies have unique responses to different foods, so a one-size-fits-all approach to nutrition doesn’t work.

Our at-home test assesses the health of your gut and measures how your blood sugar and blood fat levels respond to food. With this information, our personalized nutrition program can help you eat the best foods for you and your health goals.

Learn more about how it works and take our free quiz.


Many experts think sleep processes influence our body composition in important ways.

Studies suggest that sleeping less, or getting low-quality sleep, is significantly associated with having obesity, higher levels of body fat, and increased waist circumference.

Here are ways to help you sleep better:

  • Go to bed and get up at the same times each day.

  • Try not to sleep during the day.

  • Get regular exercise.

  • Get some natural light each day.

  • Avoid caffeine after lunch.

  • Don’t spend too long in bed when you’re not sleeping.

  • Don’t use your smartphone or watch TV in bed.

  • Make your bedroom quiet, dark, and cool.

What is body fat?

Body fat, or adipose tissue, is more complex than you might think. Beyond fat cells, it’s made up of connective tissue, immune cells, and nerve cells.

There are two types of body fat: subcutaneous fat and visceral fat. Subcutaneous fat is a layer beneath your skin. Visceral fat surrounds your internal organs.

Their layers change as we age. And there are differences when it comes to sex: During and after puberty, visceral fat tends to build up around the waist and belly in males.

In females, subcutaneous fat tends to build up around the hips and thighs. And after menopause, visceral fat levels increase. 

Body fat is a form of stored energy — our bodies use it when it’s needed. It also helps:

  • keep you warm

  • release hormones to regulate your appetite and metabolism

  • produce proteins and enzymes involved in your immune system

Having too much body fat, or not having enough, can contribute to a variety of diseases. The visceral fat around your organs is the type that’s mainly associated with these health issues. 

Too much body fat

Overweight or obesity increases your risk of developing certain health conditions, including: 

  • high blood pressure

  • unhealthy cholesterol and blood fat levels

  • heart disease

  • stroke

  • type 2 diabetes

  • gallbladder disease

  • osteoarthritis

  • breathing problems

  • poor mental health

  • several types of cancer

Too little body fat

Not having enough body fat also increases your risk of some health conditions, including:

  • low blood pressure

  • problems with blood flow around the body

  • low levels of oxygen in the blood

  • eye problems

  • reproductive problems

  • poor wound healing

  • poor mental health 

  • some cancers

You can learn more about how your body creates fat by listening to the ZOE Science & Nutrition podcast on fats and oils.

What is muscle?

Muscle is soft tissue that controls our movements, supports our posture, and helps move things around in our bodies.

Most of your muscles are skeletal muscles. These make up around 40% of your body weight.

Skeletal muscles are bundles of individual muscle fibers. They include everything from the large muscles in your legs and arms to the smaller muscles in your face.

And skeletal muscles are also important for your metabolism.

Reduced muscle mass or quality can make you less efficient at managing your blood sugar, increasing your risk of type 2 diabetes

As we mentioned earlier, you can lose muscle mass and strength as you age. This process is called sarcopenia.

Maintaining a healthy muscle mass as you age can reduce your risk of the associated health issues and protect your quality of life. 

Body composition vs. weight vs. BMI

“Body composition” refers to the different percentages of muscle, fat, and bone in your body. 

Body weight is just a single number, the total mass of all the different types of tissue in your body. It doesn’t take into account any ratios.

So, people with the same weight could have very different levels of muscle and fat.

BMI is your weight divided by the square of your height in meters or feet. It can be an initial indicator of body fat, but it can’t distinguish between muscle weight and fat weight.

This is why some lean, muscular athletes have a high BMI — in the overweight range — even though they’re fit and healthy.

How to measure body composition

If a doctor needs to check your body composition, they might use:

  • Calipers: This tool pinches folds of skin and fat at different points on your body to measure their thickness. Doctors use calipers to calculate your body fat percentage.

  • Bioimpedance: This method involves attaching electrodes to you and estimating your body composition based on the rate at which an electrical current travels through your body.  

  • Dual-energy X-ray absorptiometry: This approach is also called DEXA. It involves using low-level X-rays to analyze the amounts of fat, muscle, and bone in different areas.

  • Magnetic resonance imaging: This is an MRI scan. It involves using a combination of magnetic fields and radio waves to scan your body and identify different types of tissue.

Can you calculate your body composition at home?

You can get an idea of your body composition at home. But these methods aren’t as reliable as clinical approaches:

  • Online calculators: These use your age, weight, height, and other body measurements to estimate your body fat percentage.

  • Bathroom smart scales: These use electrical currents to measure the amount of water in your body. It’s the same principle as a clinical bioimpedance machine but less accurate

  • Waist circumference: Measuring your waist and comparing it to guidelines can help you tell if you’re at risk of obesity-related health conditions.

  • Waist-to-hip ratio: Dividing your waist measurement by your hip measurement gives you a single number. This can help predict your risk of certain illnesses

Healthy ranges

There’s no single expert agreement about a healthy body composition. But some health organizations do have guidelines about body fat percentage. 

The American Council on Exercise, a nonprofit group, lists these ranges for fat: 


  • Fitness: 21–24%

  • Acceptable: 25–31%

  • Safe minimum: 10–13% 


  • Fitness: 14–17%

  • Acceptable: 18–24%

  • Safe minimum 2–5% 

A healthcare charity in the United Kingdom, Nuffield Health, notes that a “normal” body fat percentage depends on your age, but it’s in the range of 33–36% for females and 19–25% for males.

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Body composition is the percentage of fat, muscle, and bone in your body.

These ratios can have a huge impact on your health, influencing your risk of developing chronic and age-related diseases.

The good news is that routine changes, like exercising more, eating well, and getting better sleep, can improve your body composition and your health.

To get an accurate idea of your body composition, speak with your doctor about clinical approaches. 

In the meantime, measuring your waist circumference or calculating your hip-to-waist ratio can give you a broad idea of whether you might need to make some changes to your routine.


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