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Body Composition

For those of us that are interested in body composition, our focus is usually on our muscles, bones and body fat. 

Many of us may strive to alter our body composition to impact our sports performance or improve our health. However, it is important to remember that our body composition is largely driven by genetics. Diet along with exercise, it can play an important role in optimising percentage body fat, muscle mass and body weight.

The amounts of fat and muscle in the human body are particularly important for those involved in sport, as our body composition can influence both our body weight and performance. Muscle weighs more than fat and having a high proportion of muscle provides strength and power advantages. For those that are more interested in the appearance of their physique, increased muscle can provide tone and shape but more importantly, a lean body mass can have a positive impact on our metabolic health.

Specific body composition goals to enhance performance will depend on the type of exercise we are involved in. Some athletes focus on weight loss. For example, those who are light with a lower percentage of body fat typically have an advantage in endurance activity such as long-distance running, as it helps to delay fatigue and dehydration. Others may want to gain weight, specifically lean tissue. Heavier individuals with a high muscle mass can have an advantage when strength is needed for bursts of power such as pushing, throwing or sprinting. Many athletes may want to maintain their body weight but alter its composition through increasing muscle mass in combination with decreasing fat mass. This provides a greater ‘power-to-weight’ ratio, which means they have a greater capacity to move quickly against various types of resistance forces such as gravity, water, wind or a competitor.

Carrying excess body fat can have negative effects on health, performance or self-esteem. it is important to remember that fat has several essential roles in the body and if it drops too low, the health effects can be detrimental. Female athletes need to be particularly careful as women need more fat than men for good health.

Diet Matters to Every Body

In terms of losing weight, the healthy way to do it is through exercise and diet. As a rule of thumb, consuming more energy (calories) than you use will result in weight gain, while consuming less energy than you use will result in weight loss.

General Ranges For Percentage Body Fat

The body composition chart below indicates the typical percentage body fat for males and females in specific categories. A high percentage body fat is a general indicator that your muscle mass may be lower than normal for your weight.
Male Female
Athletes 6-13% 14-20%
Fitness 14-17% 21-24%
Average 18-24% 25-31%
Obesity ≥ 25% ≥ 32%

Body Composition Analysis Techniques

Unless you are a high-performance athlete or visit a sports laboratory, most of us don’t have access to the tools which can accurately measure body composition. However, there are some simple techniques such as body mass index or waist circumference measurement, which can easily be performed at home and they provide a crude indicator of body composition:

Body Mass Index (BMI)

This is a simple calculation which tells us if we are a suitable weight for our height. It involves dividing your weight (in kilograms) by the square of your height (in meters) i.e. weight(kg) / height m2. As shown in the chart below, a BMI between 18.5 and 24.9 kg/m2 is normal.

To easily calculate your BMI, you can use Safefood’s BMI calculator, or the HSE’s BMI chart. It should be noted that most BMI charts are specific for adults and separate versions are tailored to unique populations, such as children. BMI does not differentiate between muscle mass and fat mass but is a suitable tool for estimating body fatness among the general population. It is less accurate for those that are heavier due to a high muscle mass – therefore an elite rugby player with a higher body weight, due to additional muscle, could be inaccurately classified as ‘obese’ using the BMI scale.

Classification KG/m2
Underweight Less than 18.5
Healthy Normal 18.5 to 24.9
Overweight 25.0 to 29.9
Obese Greater than or equal to 30.0


Waist Size

Position a measuring tape around your waist and measure waist size (circumference) at the halfway point between your lowest rib and the top of your hipbone. Carrying too much weight around your weight around your waistcan increase your risk of heart disease, type 2 diabetes and stroke. Check your measurement against the figures below, which are provided for men and women.

Measuring Body Composition

There are various techniques for measuring body composition, all with advantages and disadvantages in terms of convenience, accuracy, reproducibility, cost, and expertise needed. Some of the most commonly used techniques are explained below:

Bioelectrical Impedance Analysis (BIA)

Bioelectrical impedance is quick and easy to use, although factors such as dehydration and timing of meals or exercise can affect its accuracy. BIA can measure both fat-free mass (muscle) and percentage body fat. It works by passing an electric pulse through the body, which is safe and unnoticeable to the person. This is usually done using a specific scales which has electrodes under each foot or by using hand-held electrode devices. The time taken for the electrical pulse to pass through the body is recorded. Lean tissue has a higher water content, allowing the pulse to pass through it more quickly than fat tissue. Therefore, a shorter time taken by the electrical pulse indicates a leaner physique. Sometimes BIA machines estimate bone mineral density, but it is not considered an accurate tool for assessing bone.

Skinfold Thickness – Calipers

A special tool, known as a calipers is used to measure subcutaneous fat (fat that is stored under the skin). Measurements are carried out at different parts of the body (usually the biceps, triceps, thighs, abdominals). From the subcutaneous fat measurements, simple calculations using equations, can be made to determine total body fat percentage. This is a very accessible and cheap method of measuring body fat. However, those carrying out this measurement need specific training and experience to ensure accurate readings.

Dual Energy X-ray Absorptiometry (DEXA scan)

This is a painless, whole body scan that is considered the gold standard measurement tool for measuring body composition. As well as measuring bone density (bone mass), it is a way of measuring body fat mass and lean tissue. DEXA scans provide a detailed and very accurate measure of body composition. DEXA scans are generally used in high-performance sports laboratories to assess competitive athletes. They are also used in clinical practice in the diagnosis of osteoporosis. Generally, access to this scan requires a referral from your GP, who will let you know the options in your area.

Healthy Eating for Active Living

Whether an elite athlete, involved in a local sports club or a dedicated gym goer; a healthy, balanced diet is essential for meeting energy and nutrient demands. A variety of factors influence our individual nutritional needs such as gender, age and body size. The type, amount and timing of food will also depend on the competitive level you are involved in and the specific demands of your training schedule. The first step for optimum performance nutrition is to ensure that nutrient needs are met by including a variety of nutritious foods across meals and snacks. The Department of Health’s Food Pyramid is a useful tool to guide balanced, healthy eating choices. The second step is to focus on the timing of food and fluid intakes around training sessions, matches and competitions.

Clever Choices 

  • Include complex carbohydrate in meals and snacks to help ensure energy stores are well-fuelled.
  • Include protein foods (e.g. milk, lean meat, eggs, beans, lentils, yogurt, cheese, fish) at each mealtime to ensure hard-working muscles have a constant supply of protein throughout the day.
  • Include a wide variety of fruits and vegetables across meals and snacks for a good range of vitamins and minerals.
  • Avoid too many processed foods that are high in fat, sugar and salt e.g. biscuits, cakes, crisps.
  • Avoid or limit alcohol as it can dehydrate the body and impair recovery.
  • Get cooking! Preparing and cooking your own meals will give you control over what you eat and is a great life-long skill. Batch cooking healthy meals for the freezer can help you stick to your healthy eating plan on busy days.
  • If you play a sport or exercise at a frequent or intense level, consider seeking advice from a sports nutritionist/dietitian who can tailor food and fluid advice to your specific needs and goals.