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Body shape and weight monitoring
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What does body fat percentage mean and why is it important?
Put simply, body fat percentage is the percentage of your body that is made up of fat - it is important because your body fat percentage influences your body shape.
Imagine two people, say women, who are the same height and weight, and that the first woman has a lower body fat percentage than the second woman. The first woman will appear slimmer and fitter than the second woman......Why is this?
The volume of the same weight of body fat and muscle tissue differs. You're not going to be surprised to learn that body fat has more volume than muscle tissue as, pound for pound, body fat takes up more space than muscle. If you imagine two balls weighing the same amount, the ball containing muscle tissue would be represented by a football, and the ball containing the same weight of body fat would be represented by a beach ball!
To appear slimmer, it is important that your body fat percentage drops.
It is important to note that if you find that your weight is staying the same having undertaken a new fitness regime, but your body fat percentage is dropping, this is no bad thing, as you will be slimming down. It is just that you will be building muscle mass at the same time as losing weight. Overall, your body volume will be reduced - i.e. you will appear much slimmer!
What is a healthy body fat percentage?
As a starting point, it is important to note that the percentage for women is greater than that for men. This is due to the demands of childbearing and other hormonal functions.
The following tables are based on recommendations from the World Health Organization and the National Institute of Health (NIH). When trying to lose weight, if your body fat percentage is above the healthy range, you should also aim to reduce this to the healthy range level as this should improve your overall health and your body shape.
Women
| Age | Underfat | Healthy Range | Overweight | Obese |
|---|---|---|---|---|
| 20-40 yrs | Under 21% | 21-33% | 33-39% | Over 39% |
| 41-60 yrs | Under 23% | 23-34% | 34-40% | Over 40% |
| 61-79 yrs | Under 24% | 24-36% | 36-42% | Over 42% |
Men
| Age | Underfat | Healthy Range | Overweight | Obese |
|---|---|---|---|---|
| 20-40 yrs | Under 8% | 8-20% | 20-25% | Over 25% |
| 41-60 yrs | Under 11% | 11-22% | 22-28% | Over 28% |
| 61-79 yrs | Under 13% | 13-25% | 25-30% | Over 30% |
How to measure your body fat percentage
There are a number of ways to measure your body fat percentage, but the most important and practical ways are the bioelectrical impedance method, and the skin fold measurements method.
Bioelectrical impedance
Hand held Body Composition Monitors work by bio-electrical impedance. The monitors pass a series of harmless electric signals through your body to determine the composition of your fat, muscle and water composition.
The science is fairly straightforward. Fat is a poorer conductor of electricity than muscle tissue (as water represents a lower percentage in fat than it does in muscle tissue) hence electric signals pass more slowly through fat than they do through muscle. A number of signals are sent around the body by the monitor during a short test period and the speed at which each signal is returned to the monitor enables the monitor to determine your body fat, body muscle and body water percentages.
Body fat monitors do have their limitations though. Common examples of such limitations include:
- Hydration level - if say, when undertaking the test you have more liquid in the body than on a previous occasion due to recent liquid consumption, because electricity travels more quickly through water, this could result in the body fat reading being artificially low. Conversely, less liquid in the body will result in a higher body fat percentage; and
- Conductor placement - depending on where the conductors are place, some critics argue that the current might not pass all the way round the body. For instance, if they are placed on the feet, the current might go up one leg, across the abdomen and then down the other leg completely missing out the top half of the body.
Despite these criticisms, and by making an effort to try to control your hydration level before testing, the readings from body fat monitors can be very useful. So long as your reading is consistent if tested several times within a couple of minutes, it is fair to assume that the machine is internally reliable. Thus, as you continue your fitness and dieting regime, over time, your body fat percentage should come down.
We would strongly recommend making use of a body fat monitor as part of your new fitness regime. They are easy to use and provide you with further useful information about your body and your makeup.
Body fat monitors are available as either handheld devices or stand-on body fat weighing scales.
Skin fold measurement technique
This is based on a skin fold test, whereby a pinch of skin is measured using calipers at a number of standardised points across the body.
The calipers are essentially being used to determine the thickness of subcutaneous fat (i.e. fat under the skin) at each point. These measurements are then fed into an equation which, by making general assumptions about the distribution of fat across a persons body, produces an output - this being your body fat percentage.
The main limitations centre on the assumptions used regarding fat distribution and the ability of a person to accurately collect readings using skin fold callipers. It is therefore difficult to use this technique at home. Most gyms have trained professionals on hand to periodically perform this technique for you.
Overall, this measuring technique takes longer and requires the help of a suitable professional and there is no guarantee that it is more accurate than using a body fat composition monitor.
To make the test reliable you should not exercise beforehand. Exercise makes your blood travel to your skin to help you cool down and this causes the skin to swell, making your test inaccurate.
How to use scales correctly
When weighing yourself, as silly as this might seem, it is important to follow the advice below to ensure that your readings are accurate:
- First of all, purchase your own set of scales and only ever use this one set to weigh yourself. Different scales have difference degrees of error, hence to ensure your readings are consistent, always use the same set of scales;
- Find a hard, flat surface to place your scales on. Good surfaces include laminate, tiled or lino floorings. Soft, thick pile carpets are unsuitable;
- Calibrate your scales - adjust the scales so without any weight being placed on them, the reading is correctly set at zero; then
- Step on the scales and stand as upright as possible when taking your reading.
By following this simple advice, you should be taking accurate weight readings each time.
Keep track of your progress by using our weight log, food and exercise diary by registering with Purple Weight Loss today!