body composition scales

What is body composition?

Almost everyone knows roughly what their body weight is or where they fall on the BMI scale, but these factors don’t always give us an accurate picture of overall health.

Body composition, e.g. the breakdown of protein, fat, minerals and body water in our bodies can be a better and more useful health indicator. Read all about it in this guide.

What is body composition and why is it important?

First, let’s take a look at Oxford Dictionary’s body composition definition:1 ‘The chemical constituents or tissues of which a living organism is composed; especially the relative proportion of fat and lean tissue in the body of a human or animal.'

To put it in simpler terms, our body composition is the measurement of proteins, fats, minerals and water in our bodies.

Why is body composition measurement important?

The diet and fitness world tend to be overly obsessed with weight – focussing on how many lbs people could / should gain or lose. However, body composition proves that weight is certainly not the be-all and end-all when it comes to health and our appearance. For example, two women may have the same body weight but look completely different: one may have more muscle mass and be a few dress sizes smaller than the other woman who has more fat mass.

Knowing your body fat and muscle mass percentage can also be invaluable if you are strength training so you can accurately track how your body is changing and becoming stronger, instead of relying on a scale which can fluctuate wildly.

Some other body composition benefits include:

  • Helps you find out if you need to lose, maintain or gain muscle and fat to be healthy
  • Allows you to focus on fat loss not weight loss
  • Helps you to set personalised health and fitness goals

What the scale alone can’t tell you

Most of us have been there when trying to lose weight – we follow a diet to the T and pop over to the gym a few times a week only to see the scales rise, which can kill all motivation and have us heading for the biscuit tin. The fact is: weight can’t tell us everything and can often be detrimental to our own body perception.

One week the scale may shoot up for an ‘unknown’ reason because your body is retaining water – a natural reaction to your muscles tearing and growing in size. Also, once that muscle has grown in size – however small it may look - it will naturally weigh more than it did before. This is because muscle tissue is much denser than fat, and growth in muscle size could equal weight gain or maintenance – even if you’re simultaneously losing fat.

If you know your body composition and get it checked regularly, weight fluctuations like this are less likely to curb your motivation or hinder your progress because you will have a better idea of what your body is doing on the inside.

How is body composition different than BMI?

BMI is one of the most common methods to assess an individual’s health and is calculated by comparing their body weight and height. You get given a number between roughly 9 and 65 which gets correlated with the following categories:

  • Underweight
  • Healthy
  • Overweight
  • Obese
  • Morbidly obese
Using BMI alone to determine if you’re ‘healthy’ has its fallbacks, namely its inability to identify what your body weight is made up of. Some athletes and naturally muscly people will wrongly be put in the ‘obese’ category as they naturally weigh more due to their increased muscle mass. Also, it’s worth noting that BMI was created on the model of Caucasians, so it doesn’t necessarily translate as well to other racial / ethnic groups.2 In the same way, just because your BMI is in the ‘healthy’ category and you are seen as ‘thin’ or ‘skinny’ it doesn’t mean you are healthier than an ‘obese’ person. Although BMI is a relatively sensible indicator of health, it is totally possible for you to be placed in the ‘healthy’ BMI category, be visibly thin on the outside and be metabolically obese on the inside.3

Does skinnier always mean healthier?

No, being ‘skinny’ does not mean somebody is healthy. Although society tends to demonise ‘overweight’ and ‘obese’ people, ‘thin’ people can also be at risk of conditions seemingly reserved for visibly overweight people like:

  • High cholesterol
  • High blood pressure
  • Diabetes
  • Cardiovascular disease
This is because it’s the visceral fat we can’t see – that surrounds our abdominal organs – which can cause these conditions.4 Someone could simultaneously have a ‘healthy’ BMI, be carrying too much visceral fat and lacking in muscle.

What’s more, skinny people are typically unaware of the potential health problems they could face as it will usually go undetected, whereas an overweight person with a high percentage of fat is likely to be more aware of the risk they face.

How can body composition measures help?

Body composition allows everyone to find out how balanced their fat and muscle mass are and identify if they need to make any changes to be healthier.

What body composition method is best?

Here are some of the most popular ways of measuring body composition

  1. Skinfold Callipers: also known as a pinch test, this method is used to estimate your total body fat percentage. The callipers pinch your subcutaneous fat layers to measure the thickness on different points on the body. To get the most accurate estimate, you need to make sure you have a competent measurer. Please note: although this method is accessible for many, it may not be accurate for people whose fat distributions vary.

  2. Hydrostatic Weighing: this method calculates total body fat by weighing you normally and then underwater and comparing the two to find your volume. Most professionals consider this method as one of the best for measuring body composition.

  3. Air Displacement Plethysmography: similar to underwater weighing, this method measures the volume of your body, and consequently your body fat, by changing the pressure in a chamber and noting the differences.

  4. Duel Energy X-Ray Absorptiometry (DEXA): this highly accurate method involves X-raying the body with two different X-rays to measure bone density, muscle mass, and body fat.

  5. MRI (Magnetic Resonance Imaging): this method uses a high-strength magnet to scan the body and measure skeletal muscle mass and fat mass – it can even distinguish between visceral and subcutaneous fat.

  6. Bioelectric Impedance Analysis: you may have scales or machines with this technology in your gym or your weighing scales at home. This method measures how much water you have in your body using alternating electrical currents. It’s not as scary as it sounds, though! This none-invasive method requires electrodes to be placed on a person’s hands, feet or both so a low-level electrical current can be sent through the body – which is affected by the volume of water in the body. The signal also passes through muscle easily but is slowed down by fat – which helps this method measure your body composition.

What is a healthy body composition?

A healthy body composition will be different for everybody, but body fat is one of the most important and easiest factors to manipulate for health, hence why many methods measure this.

One person’s ideal body fat will be different to another’s, with variables like age, fitness levels and body goals coming into play. Women also naturally require more fat percentage than men.

Healthy body fat percentage

According to the American Council on Exercise, (the NHS likes to focus on BMI), these are the body fat percentage ranges for different classification groups:5



Classification Women (% body fat) Men (% body fat)
Essential fat 10 – 13% 2 – 5 %
Athletes 14 – 20 % 6 – 13%
Fitness 21 – 24% 14 – 17%
Average 25 – 31% 18 – 24%
Obese 32% + 25%+

The final word

We hope this has helped explain what body composition is, what it means for your health, how to measure it and how it differs from BMI.

Please take this advice with a pinch of salt and discuss it with your GP before making any big changes in your lifestyle.

Last updated: 20 October 2020 

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