There are several methods to measure body composition, and in our previous post we listed a few. Apart from the gold standard eg DEXA and underwater weighing which are inconvenient to use on a daily basis, other options are bioelectrical impedance analysis (BIA), scales or callipers.
Let’s start with callipers:
Callipers work by pinching an area of skin to measure how much fat can be pinched away from the muscle. This is often quite humiliating for people who have a lot of fat, especially if it is done in the middle of a gym. But besides the emotional trauma of having your body fat pinched from you, it is important to note that the calliper measurement will only measure the subcutaneous fat. Now we all know that fat can accumulate around the organs, especially as we grow older. This fat is called visceral fat and is becoming more and more topical in the news. How do we measure that?
Bioelectrical Impedance Analysis is a method used to measure inside the body. By using a small, safe current, impedance is measured as resistance to the current against different tissues. Basically it works on the knowledge that muscle consists of mostly water, minerals and electrolytes which are good conductors of current, whereas fat is a bad conductor and acts as an insulator. By using different frequencies, the current can penetrate different tissues and from algorithms, we are able to calculate how much of that tissue is present in the body (from analysing the impedance to the flow of current at that frequency).
The measurements from BIA will include visceral fat as well as subcutaneous fat so are likely to give you higher fat readings than your callipers, however they will be more accurate values than callipers.
The scales also use BIA as their method of measurement, however there are certain aspects to BIA measurements that you need to be aware of:
- Skin Resistance
Skin resistance is one of the biggest hurdles to overcome in BIA. The skin ideally needs to be thin and dry to allow the small current to pass through the body. Thick or sweaty skin such as the soles of your feet and the palms of your hands, will affect the results and often give inconsistency to results making it more difficult to track over time.
- Stabilisation of fluid
BIA assumes equal distribution of fluid throughout the body in order for the algorithms to be accurate. When you are standing up, there will be more fluid in your legs than your arms. The measurements where they make you lie down for a couple of minutes will be the most accurate since this allows the fluids to stabilise and distribute around the body equally.
- Tetrapolar measurements
Tetrapolar means measuring using 4 points, usually the hands and the feet. Some scales or even some hand-held devices only measure from the hands or from the feet. Most of us remember from physics lessons that the current will always take the path of least resistance. Well, same as in the body. Therefore if you are only measuring from one foot to another foot, you will be missing the top half of your body. Likewise, measuring from hand to hand, you will only be measuring your arms and the trunk in between. Ideally you should be measuring using electrodes on one hand and wrist to one foot and ankle. These measurement are usually done on the right hand side of the body. This is simple because the heart on the left side will cause more impedance to the flow, which will raise the fat percentage higher than it normally should be. Remember when impedance (resistance) is high, your fat percentage will be high since fat is a bad conductor of current, therefore shows resistance to its flow.