What Is Body Composition & Why It’s Vital for Health & Fitness

What is body composition, and why is it important?

When you get on the scales to see how much weight you have lost (or gained!), the scales tell you one thing and one thing only – your total body mass.

No differentiation is made between the various components that make up your weight.

While your total weight is an interesting thing to track and can be used to monitor the success of your workout program and diet, it doesn’t really tell you the whole story, and while your weight can and will change, this isn’t always a good thing.

Because of this, a lot of exercisers track their body composition, which is more commonly known as your fat percentage.

What is body composition?

Rather than focus on just bodyweight, it’s useful to know what percentage of your weight is made up of fat and what percentage is made up of other fat-free substances.

This is called your body composition and is correctly expressed as a percentage.

Most body composition assessments simply split your weight into fat and fat-free mass, so you might get a reading of 24%, which simply means that 24% of your weight is fat, and the rest is fat-free.

But what does this fat-free mass consist of? Let’s have a look!

Fat-free mass includes the weight of your…

• Muscles
• Skin
• Internal organs
• Brain
• Bones
• Blood
• Minerals
• Water
• Muscle and liver glycogen
• Food in your stomach and small intestine
• Waste material in your large intestine

Simply put, your weight could go down because you empty your bowels or bladder, sweat off some water, lose some muscle, deplete your glycogen, experience a reduction in bone mass, or donate a unit of blood.

Likewise, it could go up because you gain some muscle, drink some water, or eat a large meal.

Your weight can fluctuate up or down, often quite significantly, while your body fat percentage stays exactly the same.

Seeing as its fat that most people need to lose and muscle that they want to gain, it’s worth differentiating between fat mass and fat-free mass for a more accurate indicator of what’s going on inside your body.

How do you do that? Good question!

There are several methods you can use to assess your body composition – some being better than others.

Magnetic Resonance Imaging (MRI)

Magnetic resonance imaging machines are usually found in hospitals.

They can be used to take an accurate three-dimensional picture of your body so that you can see exactly what your body mass is made up of.

On the plus side, an MRI is very accurate and will provide a precise assessment of your body composition.

However, such tests are costly, are not readily available, are very noisy, claustrophobic, and time-consuming.

Hydrostatic weighing

Fat floats and muscle and bone do not; that’s the basic premise of hydrostatic or underwater weighing. You are weighed in water and then again on land, and the difference is applied to a mathematical calculation to predict your fat versus fat-free mass.

Considered to be very accurate, hydrostatic weighing was once the “gold standard” to which all other methods were compared. However, more recently, it has been superseded by MRI and other high-tech methods.

To do hydrostatic weighing, you need specialist weighing scales, an appropriate pool, a trained operator, and a willingness to be submerged in water. However, things like undigested food, intestinal gas, and difficulty completely empty your lungs of air can all affect the accuracy of the results.

Bioelectrical impedance

Muscle contains a lot of water and is, therefore, a good conductor of electricity. In contrast, fat does not hold much water and conducts electricity poorly. By passing a current through your body, it is possible to measure the resistance to the flow of electricity and estimate your body composition. And no, you won’t be able to feel the electricity coursing through you!

Bioelectrical impedance is very non-invasive and easy to apply but is not always very accurate. Your hydration levels can have a significant effect on your readings and, for women, so too can the time of the month.

Accuracy also depends on the machine you use. Some bioelectrical impedance machines only pass electricity through your legs, arms, or one side of your body, so the results are at best, calculated guesses.

That said, for convenience, bioelectrical impedance testing is hard to beat, and there are machines specifically designed for home use.

Skinfold measurements 

Skinfold measurements involve pinching and measuring the thickness of fat stores at strategic locations around your body using special calipers. By comparing the total number of millimeters to a chart, it is possible to estimate your body fat percentage.

There are numerous systems for taking skinfold measurements. Some use as few as two test sites, while others use ten or more. The more areas tested, the more accurate the test is likely to be, but the more invasive the assessment becomes.

Testing also requires a skillful operator, as even the smallest measuring error can significantly alter the result. Skinfold measurements are most accurate on lean people and almost impossible to do with anyone who is significantly overweight.

Personal trainers often know how to take skinfold measurements but, if you buy a set of calipers and are prepared to learn and practice, this method of body composition assessment is also suitable for home use, although you won’t be able to test yourself!

Air displacement

This method uses a similar principle to hydrostatic weighing, except air takes the place of water. Air displacement is a quick, easy, and accurate way to assess body composition. You simply strip down to your underwear, get into a so-called Bod Pod unit, which is then pressurized, and the amount of air displaced measured.

From this, the machine estimates your body composition. While easy to use and accurate, Bod Pods are very expensive and quite rare, so not many people will have access to this type of equipment. Some gyms and medical centers have Bod Pods.

Dual Energy X-Ray Absorptiometry – DEXA

DEXA uses two types of X-ray to measure and differentiate between muscle, fat, and bone. This is a very low dose of radiation and is relatively safe. DEXA tests take around 12-minutes and are very accurate and non-invasive. But, on the downside, they can be very expensive and are not widely available.

Body composition – interpreting the results

Once you have completed your chosen body composition assessment, you will be told your body fat percentage. This figure, remember, is the percentage of your body weight made up of fat.

Compare your reading to the body fat percentage recommendations from the National Academy of Sports Medicine (NASM):

And to the American Council on Exercise:

Accuracy versus consistency

It’s clear that some methods for assessing body composition are more accurate than others. The tolerance for some tests can be as much as +/- 10-percent. At first glance, this can make it appear that some of the tests are worthless, but actually, even an inaccurate test can be useful.

So long as a test produces consistent results, it can still be used to track your progress. As an unreliable bathroom scale still shows weight loss or weight gain, an inaccurate body composition test can still show fat loss or fat gain.

However, because of the inaccuracies of each individual method, it would be pointless to compare your skinfold measurement with your bioelectrical impedance measurement.

Why is Altering Your Body Composition Important?

Here are some pretty fantastic reasons why improving your body composition is vital for your health and fitness:

1. Look and feel better – sometimes you might be unrecognizable to your friends and family!
2. Raise your metabolism fat-burning engine throughout the day
3. Decrease your risk of obesity, high blood pressure, cardiovascular disease, and type 2 diabetes
4. Improve your sleep
5. Less stress on your body and internal organs
6. Reduce your risk of joint pain and injury
7. Greater freedom of movement and functional mobility helps you enjoy the many benefits of physical activity for your health and fitness
8. Once you experience the benefits, you won’t fall off the fitness wagon!
9. Improve your overall health, wellness, and lifespan
10. Ratchet up your self-confidence and self-esteem

As published by the National Institute of Health:

“Excess body weight and fat cause insulin resistance, inflammation, and numerous other alterations in metabolic and hormonal factors that promote atherosclerosis, tumorigenesis, neurodegeneration, and aging. Studies in both animals and humans have demonstrated a beneficial role of dietary restriction and leanness in promoting health and longevity.” ¹

Tips for improving body composition

Now you know what body composition is, how to measure it, and why it is significant, how do you improve it? Try these handy tips!

1. Build muscle –

Increasing your muscle mass while maintaining or decreasing your body fat will improve your body composition score even if your weight doesn’t change. A 180lb person with 13% body fat looks very different to a 180lb person with 30% body fat.

2. Eat more protein –

If you want to gain muscle and lose fat, protein can help. Protein is filling, can help preserve your existing muscle mass, and also has a high thermogenic effect. This means that eating it increases your metabolic rate for faster fat burning. Make sure you consume around one gram per pound of bodyweight to improve your body composition.

3.  Use but don’t abuse cardio –

Cardio burns fat, but it can also cause muscle catabolism or breakdown. This means it can help you lose weight, but your body composition could remain unchanged if you lose as much muscle as you do fat. Combine cardio with strength training to lose fat while maintaining or even gaining muscle.

4. Try some interval training –

Interval training can help you burn fat while preserving muscle, which is the perfect recipe for decreasing your body fat percentage. This type of workout involves alternating brief periods of high-intensity exercise with either active or passive rests. For example, you could sprint for 30 seconds, sit, walk, or jog for 60 seconds, and repeat ten times. Not only is this a good workout for burning fat, but it’s also very time efficient.

5. Get more sleep –

Lack of sleep will undermine your diet, increase carb and sugar cravings, decrease your willpower, and rob you of energy to work out. If you are serious about improving your body composition, you need to get serious about sleep too. Do your best to clock up eight hours of sleep every night.

See the recommended fitness gear to improve your body composition & more.

What is body composition – Final Thoughts

Many people live and die by the number on their scales when, really, scale weight only tells a small part of the story. Rather than get hung up on what you weigh, it’s better to care about what that weight is made up of – your body composition.

You can be heavy but lean, and you can be light but fat, and the only way to determine the difference is through body composition assessment.

But, even if you don’t know your exact body composition percentage, your aim should always be to lose body fat while maintaining or gaining muscle. Losing muscle will have an adverse effect on how you look, feel, and perform, even if you end up weighing less.

What’s Next

There are few better ways than full-body compound exercises like squats and deadlifts to alter your body composition. Total body resistance training targets the major muscle groups of your entire body.

See 27 Sensational Ways How Deadlifts Change Your Body for a real-life example of the power of the deadlift.

Last, there is no easier way to help remodel your body than eating, yes, that’s right, eat your way to getting leaner and stronger with this free guide – How to Lose 20 Pounds in 3 Months Using 5 Simple Steps.

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Footnotes:

¹ Optimal body weight for health and longevity: bridging basic, clinical, and population research