Body composition: what is it and why is it so important?


Why is it useful to measure your body composition?
Body composition is the term used to describe the different components that make up our total body weight. It’s the ratio between our stored body fat and lean body weight (muscle, bone, organs … everything other than fat) that determines our health, tone, shape, performance, strength, metabolic rate and overall appearance. Our lean body weight (LBW) is metabolically active and fat (adipose) tissue is not.
Weight on the scales
Bathroom scales provide a measure of total weight, but don’t determine what that weight is composed of. Based only on scale weight, a 90 kilo athlete with less than 10% body fat may be considered obese by a typical weight chart. This also includes Body Mass Index (BMI) measures for the same reason. While BMI combined with waist circumference gives some indication of our physical condition, it is not as accurate as body composition.
Hydrostatic Weighing
What is it?
This is a method that involves immersing a person underwater in a large tank of water and works on the principle of displacement. LBW is more dense than water and fat tissue is less dense than water, therefore an individual with more body fat will weigh less under water and be more buoyant.

Hydrostatic weighing has long been considered a highly accurate measure of body composition.

It’s highly inaccessible, inconvenient and many more sophisticated methods are now being developed which are superseding this method.

Skinfold/Caliper Measurements

What is it?
The skin is pinched in various sites of the body using calipers to determine the thickness of sub
cutaneous (beneath the skin) body fat. Several formulas exist to calculate the sum of these measurements, incorporating our weight, height and age to estimate an overall body fat percentage.

Accessible and inexpensive. When performed by a trained and skilled professional they are up to 98% accurate.

Difficult to determine the body fat of an individual who is extremely overweight.
Accuracy takes skill and training and is commonly compromised by unskilled operators.
Bioelectrical Impedance
Bioelectrical Impedance is now a commonly used method. It sends a weak electrical current through the body. Electricity is carried by water and there is less water in fat tissue than in LBW, so it uses impedance/resistance of the current to differentiate the two. Methods range from scales you stand on to electrodes placed on the skin and handheld devices. The more accurate machines measure the entire body rather than simply standing on scales. The scales with feet electrodes only will send the current up one leg and down the other, only ‘guestimating’ you from the waist up.
Accessible, accurate, no human intervention/error, relatively inexpensive.
The readings can be affected by hydration levels so measurements should be taken under similar conditions each time for the most accuracy.
Ideal Body Weight and Percent Body Fat
A ‘healthy range’ of body fat for men is between 8 and 20 per cent, whilst for women it ranges between 20 and 30 per cent. ‘Healthy range’ means that for every per cent over or below this range, your risk of disease increases.
Over-fat has been linked to an increased risk of diabetes, heart disease and several forms of cancer, whilst under-fat (particularly in women) may increase the risk of hormonal disturbances, impaired immune function and osteoporosis.
There are two parts to reducing your body fat percentage:
1. reduce overall stored body fat
2. increase lean muscle tissue
To reach the lower end of the desired range, you must have adequate LBW to support such fat loss. Any attempt to reduce body fat using extreme measures not only leads to decreased performance, but is also likely to lead to severe health complications, such as nutrient deficiencies, infertility and injuries.
Is Body Composition Genetic?
Some aspects of where you store your body fat is genetic, however, whether you choose to store excess body fat is up to you! Your genetics are the bullet in the gun … your lifestyle is the trigger!
We lose around 3% LBW per decade after the age of 30 – that is, if we don’t exercise. In this case your body fat percentage will be increasing as you age, even if your weight doesn’t change. I often hear people use their age as justification for weighing more, but in fact we should weigh less as we age due to loss of muscle and bone density. Food for thought…

Donna Aston - Author

Nutritionist Certified Fitness Trainer Author of five best-selling health & fitness books Emotional Intelligence Certified Practitioner (Genos) Managing Director: Aston & Co. Pty. Ltd. Fitness advisor: Prevention Australia Magazine & SEN radio CIRQ acrobatic master trainer

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