Body Composition: What It Is & How To Test

This article we will discuss the importance of body composition, why it’s important to health and how to measure your body composition.

What is body composition

Body composition is a way to describe what a person’s body is made up of. Body composition analysis can show changes in fat mass, muscle mass, and body fat percentage.

Measuring body composition is more accurate than body mass index (BMI) as BMI only measures height and body mass whereas body composition gives us a deeper understanding of the amount and distribution of body fat, as well as the quantity and make up of lean muscle mass which are crucial factors for health (Wells & Fewtrell, 2006).

For instance, two people with the same gender and body mass may have a similar BMI however, they may look completely different from each other, this is because they have a different body composition.

Let’s delve further on why understanding your body composition is important for your health. 

Why is body composition important?

We are currently grappling with a widespread obesity epidemic that affects both adults and children more than ever before. The repercussions of excessive fat are widely recognised, as it constitutes a significant health risk, contributing to conditions such as heart disease, stroke, hypertension, type II diabetes, specific cancers, and various other illnesses.

While many associate minimal body fat with good health, it’s crucial to understand that being “thin” doesn’t inherently mitigate an individual’s health risks. “Thin” typically refers to weighing less than recommended values based on age-height-weight charts. On the other hand, being “lean” implies having a higher proportion of muscle mass. Therefore, differentiating between what is considered healthy and what is not, especially concerning body fat, is pivotal in assessing an individual’s health.

This distinction holds importance not only for individuals but also for healthcare professionals. Gaining a comprehensive grasp of the differences between thinness, leanness, overweight, and obesity benefits both parties.

Armed with a better understanding of body composition, individuals and healthcare practitioners can collaborate to conduct thorough health assessments, monitor changes in body fat and muscle development, and tailor exercise, dietary, and lifestyle adjustments accordingly. This collaborative approach empowers individuals to take more effective control of their health.

Body Composition: Key Terms

To get a greater understanding of body composition, let’s explore the terms we have used further;

  • Height: Height is the measurement of how tall a person is from the bottom of their feet to the top of their head. It is typically measured in units like centimeters or inches.  
  • Body Mass: Body mass refers to the total weight of a person’s body, including all its components, such as bones, muscles, organs, and fat. It is usually measured in kilograms (kg) or pounds (lb).
  • Lean Muscle Mass: Lean muscle mass, often referred to as lean body mass, represents the weight of all the body’s components except for fat. It includes muscles, bones, organs, and tissues that are not fat. It is a critical component of body composition and is typically measured in kilograms.
  • Fat Mass: Fat mass is the weight of the body’s fat tissue. It includes both essential fat, which is necessary for normal bodily functions, and excess fat, which can contribute to health problems when accumulated in excess. It is typically measured in kilograms.
  • Muscle Mass: Muscle mass refers to the total weight of a person’s muscles. Muscles are the contractile tissues in the body responsible for movement and support. Muscle mass is an essential component of body composition and is typically measured in kilograms.
  • Body Fat Percentage: Body fat percentage is the proportion of an individual’s total body weight that is made up of fat. It is expressed as a percentage and indicates how much of a person’s weight is attributed to fat tissue. It is often used as a more accurate measure of a person’s fitness and health compared to just body weight.

How to measure body composition?

There are various methods available for assessing body composition, ranging from sophisticated and costly techniques to simpler, yet effective, equipment. In the following section, we’ll delve into the different approaches for measuring body composition and evaluate the pros and cons of each method:

  1. Bioelectrical Impedance (BIA)
  2. Anthropometric inc. skinfold callipers
  3. Dual-energy X-ray absorptiometry (DEXA)

Body composition tests

Bioelectrical Impedance (BIA)

Bioelectrical Impedance Analysis (BIA) is a widely used method in clinical practice for evaluating body composition. BIA estimates body composition, encompassing fat mass and fat-free mass, by passing a low-level electrical current through the body.

This method exploits the fact that various bodily tissues, such as muscle, fat, and bone, have different electrical conductivities due to their distinct water content levels. Consequently, the electrical current traverses these tissues at varying speeds. With this information, the device computes impedance, denoted as the resistance of the electrical current, and then proceeds to estimate body composition.

However, BIA has notable limitations, especially when applied to overweight and obese individuals. These limitations arise from two main factors:

  1. The use of BIA equations was initially developed for healthy-weight individuals, which may not be suitable for overweight or obese individuals.
  2. The distinct distribution of body water in individuals with severe obesity, which can affect the accuracy of BIA measurements.

This can lead to bias, particularly in individuals with high hydration levels and a BMI exceeding 35. Nonetheless, BIA remains appealing due to its cost-effectiveness, portability, simplicity, speed, and ability to replicate measurements (Radu et al., 2022).

BIA is typically used in commercial gyms however, it may not provide precise individual or repeatable measurements for athletes. However, if you do use BIA, it’s recommended: 

  1. Complete the assessment at the same time of day for reliability.
    Body mass and alterations in body water content can happen after meals, fluid intake, or due to environmental changes. The body’s circulation of water can also lead to shifts in water distribution throughout the day. To ensure accurate results, it is advisable to conduct repeat tests in consistent conditions, within the same environment, and at the same time of day as the initial assessment.
  2. Remove any jewellery
    Accessories such as jewelry may interfere with the electrical conductivity, remove your before the testing. 


The core elements of anthropometry are height, body mass, head circumference, body mass index (BMI), body circumference to assess for adiposity (another word for body fat) (waist, hip and limbs), and skinfold thickness. 

Utilising skinfold thickness as a predictor of body fat percentage represents one of the most common field anthropometric techniques employed in assessing body composition. Skinfold thickness measurements have been extensively used to estimate body density and fat content.

The primary objective of skinfold measurements is to assess overall fatness and the distribution of subcutaneous adipose tissue. This involves pinching the skinfold at specific body sites, including the triceps, biceps, abdomen, iliac crest, just below the scapula, the thigh, and the chest, using specialised callipers designed for precise subcutaneous tissue measurement. Skinfold measurements are incorporated into various equations to predict percentage body density. 

When administered correctly, skinfold measurements yield accurate results. These methods find widespread application in both clinical and field studies due to their ease of use for large groups and cost-effectiveness, requiring minimal equipment such as skinfold callipers, a tape measure, and an anthropometer.

We must note you must be highly skilled to take accurate skinfold measurements, there are courses available by The International Society for the Advancement of Kinanthropometry (ISAK), they hold international standards for anthropometric assessment and have guidelines on how to take skinfold measurements. 

Dual-energy X-ray absorptiometry (DEXA)

Dual-energy X-ray absorptiometry (DEXA) is a highly utilised method for assessing body composition. It operates on the physical principle of X-ray transmission and attenuation at two different energy levels within the body. Following a full-body scan, the X-ray beam’s attenuation data allows for the categorization of the body into two main compartments: bone and soft tissue.

It’s important to note that a DEXA scan provides more than a mere estimation of body fat; it offers a precise breakdown of both fat and muscle composition. DEXA, was originally developed for measuring bone density. However, by leveraging a straightforward calculation, it utilises the body’s absorption properties to discern fat from muscle tissue.

Unfortunately, DEXA scans are not always considered cost-effective and may not represent the most accurate approach to measuring body composition. While they provide prompt results, they necessitate an initial appointment and a visit to a scanning facility. Furthermore, the cost associated with DEXA scanning may make it inaccessible to many individuals.

What is a healthy body composition? 

According to the American Journal of Clinical Nutrition, recommended body fat percentages vary by age. For individuals aged 20 to 39, women are advised to aim for a body fat percentage between 21% and 32%, while men should target 8% to 19%. Those in the 40 to 59 age range should ideally have body fat percentages ranging from 23% to 33% for women and around 11% to 21% for men. For individuals aged 60 to 79, the recommended body fat percentages are 24% to 35% for women and 13% to 24% for men.

Success in various sports often hinges on the physical characteristics of athletes, leading to distinct demands and variations in body composition requirements across different sports (e.g. Gymnastics estimate 13-16% in females and 3-6% in males). Therefore, body composition may vary between sports and it has been highlighted its importance to monitor the absolute change of each individual relative to their baseline measurements.  

It’s noteworthy that women naturally possess higher body fat percentages than men, and this percentage tends to increase as they age. Additionally, men typically have approximately 60% more muscle mass than women, which underscores the importance of considering these gender-based differences when making comparisons.

Taking Caution when assessing body composition

We must highlight that caution must be taken when assessing body composition.

Measuring body composition in athletes is a delicate process that should be approached with caution. While it can offer valuable insights into an athlete’s physical condition and performance potential, it can also have negative repercussions on body image and contribute to disordered eating behaviours.

Athletes are often under intense scrutiny to maintain specific body compositions to excel in their sports, and inaccurate or misinterpreted body composition measurements can lead to unnecessary stress, anxiety, and pressure to conform to unrealistic standards. It’s essential for athletes, coaches, and healthcare professionals to prioritise the holistic well-being of athletes, including their mental and emotional health, when assessing and discussing body composition to foster a healthier and more sustainable approach to sports performance.

Factors that contribute to your body composition

Several factors play a pivotal role in determining an individual’s body composition. 

  1. Genetics undoubtedly influence how our bodies store and distribute fat, impacting our natural body shape and fat-to-muscle ratio. 
  2. Diet and nutrition choices significantly affect body composition, as the consumption of calories, macronutrients, and micronutrients can influence fat mass and muscle development. 
  3. Physical activity and exercise routines also have a profound impact, as they directly affect muscle mass, fat loss, and overall body composition. 
  4. Hormonal fluctuations, particularly in puberty and during menopause, can trigger changes in fat distribution. 
  5. Lifestyle factors such as sleep quality, stress levels, and even environmental exposures can contribute to variations in body composition. 

Recognising the multifaceted nature of these factors is crucial for understanding and managing one’s body composition effectively.

How to change your body composition?

Changing your body composition involves altering the proportion of fat, muscle, and other tissues in your body to achieve a healthier and more desirable balance.

We recognise we are not experts in this field and it would be wrong for us to provide you comprehensive details on how you can do this. We advise you should consult with a professional such as a registered dietitian, or healthcare provider for personalised guidance and support in achieving your body composition goals.

However, here is a simple list to reflect on that you may wish to consider; 

  • Maintain a balanced diet with whole foods.
  • Create a caloric deficit for fat loss.
  • Include strength and cardiovascular exercises.
  • Ensure sufficient protein intake.
  • Stay hydrated and get quality sleep.
  • Manage stress.
  • Stay consistent and patient.


Understanding body composition’s intricacies is vital in addressing obesity. It goes beyond body mass, emphasising the importance of muscle mass (“leanness”) over mere thinness. Healthcare practitioners can tailor health assessments based on height, body mass, lean muscle mass, fat mass, muscle mass, and body fat percentage.

Various assessment methods exist, each with pros and cons, and age and gender play a role in recommended body fat percentages. Athletes must approach body composition assessment with caution to avoid negative consequences. Genetics, diet, exercise, hormones, and lifestyle influence body composition, making change possible with professional guidance.

Further reading

Wells, J. C., & Fewtrell, M. S. (2006). Measuring body composition. Archives of disease in childhood, 91(7), 612-617.

Source: Radu, P., Ebadi, M., Montano-Loza, A. J., & Dufour, J. F. (2022). What Is the Role of Body Composition Assessment in HCC Management?. Cancers, 14(21), 5290.

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