LET SCIENCE GUIDE YOUR WAY TO...
by Dr. Matthew Chircop
Body composition is one of the markers of conditioning. In combination with your weight, knowing your body fat percentage will allow you to calculate your total fat mass and your lean body mass. Changes in fat mass and lean body mass in response to lifestyle changes can help you to determine if those changes are producing the results you desire – for most people, this means a reduction in body fat percentage, and an increase in lean body mass in the long run.
The only way to truly measure your body fat percentage is at autopsy – something that most people are, understandably, not prepared to do. It is possible to estimate body fat percentage using a number of different indirect techniques.
The first relies on visual inspection, particularly of the abdominal region. If you look at the abdominal region of a fitness model front-on you’ll notice that the most visible “lines” are the lines on each side of the rectus abdominis (which consists of two thick bands of muscle running from the bottom of the rib cage down to the pelvis on either side of the belly button or navel). If you are an adult male and the tops of those lines are visible, then you are probably somewhere between 15 and 17% body fat. If you are an adult female and the tops of those lines are visible, then you are probably somewhere between 22 and 24% body fat. Once those lines are visible all the way from rib cage to pelvis, and the centre line between the two bands of the rectus abdominis muscle is also visible, males are probably close to 10% body fat, and females are probably close to 17% body fat. The loss of another 1-2% body fat is necessary to reveal the “six pack”, which are simply transverse bands of tendon separating each rectus abdominis muscle into smaller muscle bellies – the number, position and geometry of these tendon bands is individual and can’t be modified (except, possibly, surgically). Straight away you can see that the problem with this method is that it does not allow you to estimate values above 17% in males and 24% in females – which, these days, is more than two thirds of the population.
The second technique relies on measuring weight and waist circumference, and applying a formula (e.g. a variant of any of the YMCA formulae – although there are many of this type) to estimate body fat percentage. Whilst this method is notoriously inaccurate, it is consistent and can be performed by someone without training or special equipment – I will assume that most people can purchase a set of scales and a cloth tailor’s measuring tape. Changes in body fat percentage can be reliably calculated using this method.
The third technique involves the use of skin calipers. A trained individual can measure skin fold thickness at various points on the body, apply a formula to those values and derive an estimate of a subject’s body fat percentage. This method is more accurate than either of the above methods, but requires special training and equipment to perform – and so introduces a cost. This also requires the subject to disrobe – which some subjects might not wish to do.
A fourth technique involves measurement of bioelectrical impedance through multiple points of contact on the body surface (usually feet and hands). A formula is then applied to this value and the body fat percentage estimated. It is possible to purchase scales with this feature, but I suspect that most of the products available to the general public are not as accurate or reliable as those available to professionals in the fitness industry. Similarly, there is a device available which is applied to various regions of the body, measuring impedance at each location. Presumably, a formula is applied to these values to determine body fat percentage. Many of the on-line customer reviews of that product indicate that there are issues with the reliability of the device – but it is also possible that the customers might have unrealistic expectations (such as expecting an accuracy of 99%, like most medical grade equipment, when the reality is that many consumer grade products are not engineered to be that accurate, or else they would cost a lot more to produce).
The final technique in widespread use is DEXA scanning – dual energy xray absorptiometry. DEXA is currently the method of choice for assessing bone density (which is important in diagnosing and monitoring the progress of a bone condition called osteoporosis). The whole body is “scanned” with two beams of xrays (of differing energies). This generates an image, which is analysed by a computer, and the amount of body fat, bone mass (and degree of mineralisation), as well as fat free-mass is estimated.
There is another method, involving the measurement of volume of water displacement. When combined with body weight, the average density of the body can be determined. Since the density of the skeleton, lungs, muscle and fat are known, the “volume” of fat and muscle tissues can be estimated by using a standardised formula. This method, however, is not in widespread use in Australia and is not as readily available to the general public.
All of these methods are less accurate at higher levels of body fat percentage.
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Welcome. I am Dr Megan Chircop. I am a medical scientist and nutritionist with 20 years in medical research. As such, I have extensive knowledge and a thorough understanding of how the body works. I am able to simplify the science behind the way food fuels the body and mind to provide energy and nutrition needed to achieve optimal health and vitality. I am also a keen sportswoman, and have extensive knowledge of sports nutrition.
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