Body composition: what it reveals that scales can't

Weight and BMI are often used as simple ways to assess whether someone is carrying too much or too little weight. But neither tells you how much of that weight is muscle, fat, water or bone.

Body composition measurements look at these different elements of your body, providing more detail than your weight alone. They can also show how much body fat you have, including visceral fat, and give an estimate of your muscle mass.

For this reason, body composition can be useful when you're trying to understand changes in your weight, fitness or general health.

What is body composition?

Body composition describes what your body is made up of, including fat, muscle, bone and water.

Two people can have the same weight but very different body compositions. Someone who exercises regularly, for example, may have more muscle and less body fat than someone of the same weight who is less active.

This is one of the limitations of looking at weight or BMI alone. BMI can be a useful screening measure, but it cannot distinguish between weight from body fat and weight from muscle, or show where fat is stored.

What does a body composition scan measure?

A body composition scan can provide several measurements that aren't available from ordinary scales.

Bluecrest's body composition scan measures or estimates:

• Body fat: the proportion of your body made up of fat
• Muscle mass: an estimate of the amount of muscle in your body
• Visceral fat: an estimate of fat stored around your internal organs
• Body water: an estimate of the amount of water in your body
• Bone mass: an estimate of bone mineral mass
• Basal metabolic rate (BMR): an estimate of the energy your body uses at rest
• Metabolic age: an estimate based on measurements including your BMR and body composition

The scan uses bioelectrical impedance analysis (BIA), which sends a weak electrical signal through the body to help estimate its different components.

Together, these measurements can help put your weight into context.

Why doesn't weight tell the whole story?

Your weight can change for many reasons. A change on the scales could reflect changes in body fat, muscle, water or a combination of these.

For example, someone who starts strength training may gain muscle while losing body fat. Their weight might change very little, even though their body composition has changed.

The opposite can happen too. Someone can lose weight without maintaining all of their muscle mass.

This is why changes in weight can be more useful when considered alongside other measures.

What does visceral fat tell you?

Not all body fat is stored in the same place. Visceral fat is stored deeper inside the abdomen, around internal organs. It is different from the fat stored just beneath the skin.

Higher levels of fat around the waist are associated with a greater risk of health problems including type 2 diabetes and cardiovascular disease. This is why waist measurements can provide useful information alongside BMI.

The NHS recommends trying to keep your waist measurement to less than half your height.

A body composition assessment can provide an estimate of visceral fat, giving you another measure to consider alongside your weight, BMI and waist measurement.

What is metabolic age?

Metabolic age can be one of the more surprising results on a body composition assessment.

It isn't your biological age and it isn't a clinical measurement. Metabolic age is an estimate based on your basal metabolic rate (BMR). It compares your BMR with the average BMR for different age groups, and gives the age whose average is closest to yours.

A metabolic age that's higher than your actual age doesn't automatically mean that you're unhealthy. Equally, a lower metabolic age isn't proof that you're healthier.

The result is best considered alongside your other body composition measurements rather than on its own.

If you'd like to understand more about the number, Bluecrest has a separate guide to metabolic age and what it can and can't tell you.

What can affect a body composition result?

Body composition measurements are estimates, so the conditions under which they're taken can matter.

Many body composition devices use bioelectrical impedance analysis (BIA). The electrical signal behaves differently as it passes through tissues such as muscle, water and fat, allowing the device to estimate the different components of your body.

Hydration can influence BIA measurements, which is one reason it can be useful to take measurements under similar conditions if you're monitoring changes over time.

Your body composition can also change naturally. Activity levels, diet, age and changes in muscle and body fat can all contribute to differences between assessments.

Rather than focusing too heavily on a single reading, look at the wider pattern.

Does body composition replace BMI?

Not necessarily. BMI and body composition tell you different things.

BMI uses your height and weight to provide a simple measure that can be useful when assessing weight at a population or individual level. But it cannot distinguish between muscle and fat or show where fat is stored.

Body composition measurements provide additional information that can help put your weight and BMI into context.

Waist-to-height-ratio can also give you an indication of how much fat you're carrying around your middle. As a general guide, your waist measurement should be less than half your height, giving a waist-to-height ratio below 0.5.

Looking at several measures together can therefore provide a more complete picture than relying on one number.

How can you support a healthy body composition?

There isn't one ideal body composition that applies to everyone. Age, sex, genetics, activity levels and other factors all play a role.

If you're looking to support a healthy body composition, focus on habits that benefit your health as a whole.

Include muscle-strengthening activity

Resistance exercise can help build and maintain muscle. NHS guidelines recommend muscle-strengthening activities that work all the major muscle groups on at least two days a week. This could include lifting weights, using resistance bands, bodyweight exercises or other activities that challenge your muscles.

Stay active

Walking, cycling, swimming and other forms of aerobic activity can support cardiovascular health and help you stay active.

The NHS recommends that adults aim for at least 150 minutes of moderate-intensity physical activity a week, or 75 minutes of vigorous activity. You don't have to do it all at once. Finding ways to build more movement into your usual routine can help you stay active throughout the week.

Eat a balanced diet

A varied, balanced diet provides the nutrients your body needs to support muscle function, energy, and overall health. Rather than focusing on a particular food or supplement to change one measurement, aim for a healthy pattern of eating that you can maintain over time.

Give your body time to recover

Sleep and rest are also part of looking after your health. Your body needs time to recover from physical activity, while consistently poor sleep can affect many aspects of your wellbeing.

How should you interpret your body composition results?

The most useful approach is to look at your results as a group.

Your weight and BMI provide one starting point. Body fat, muscle mass and visceral fat add more detail, while measurements such as BMR and metabolic age provide further context.

If you're tracking changes over time, look at the direction of several results rather than reacting to one number. A change in weight, for example, means something different if you've also gained muscle or lost body fat.

It's also worth remembering that body composition measurements are estimates. They can help you understand changes in your body, but they don't diagnose health conditions or replace advice from a healthcare professional.

Frequently Asked Questions

What is the difference between body composition and body weight?

Body weight is the total weight of your body. Body composition looks at what that weight consists of, including fat, muscle, bone and water.

Can you have a healthy weight but high body fat?

Yes. Weight and BMI don't show how much of your weight comes from fat or muscle. Body composition measurements can provide additional information about the proportion of fat in your body.

Does muscle weigh more than fat?

A kilogram of muscle and a kilogram of fat weigh the same. The difference is that muscle is denser than fat, so the same weight of muscle takes up less space.

What is visceral fat?

Visceral fat is stored around the internal organs in the abdomen. Higher levels of central or abdominal fat are associated with an increased risk of conditions such as type 2 diabetes and cardiovascular disease.

Can body composition change without your weight changing?

Yes. You can gain muscle and lose body fat while your overall weight changes very little. This is one reason why weight alone doesn't always reflect changes in your body.

Look beyond the number on the scales with Bluecrest Wellness

Your weight is only one part of the picture. Bluecrest's Body Composition Scan provides a more detailed look at your body composition, including body fat, muscle mass, visceral fat, body water, bone mass, basal metabolic rate and metabolic age.

The scan is non-invasive and is included as part of Bluecrest's full body health check packages.

Explore Bluecrest's Body Composition Scan.

Need help? Call free on 0800 652 2183 to speak to one of our team.

This article is for general health information purposes and does not constitute medical advice. If you have concerns about your health assessment results, please speak with a healthcare professional.