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Body composition assessment – various methods, same result?

Body composition assessment has become more popular among athletes. Also coaches and sport scientists have been using body composition to monitor their athletes. Nowadays we have several options to measure body composition. Athletes often get confused when they look at their results and see a completely different result compared to their last screening. The first question then is always: which method was used last time you had your body fat levels measured? It happens quite often that athletes then mention a different method. Well, this is a problem if you take your results and compare them to an older reading when the method is not the same.

For body composition assessment we use different techniques and those techniques belong to different models. We distinguish between a 2-, 3- and 4-component model. The figure below shows you the differences between those models.

Body composition methods; components (Tommey et al, 2015)

The simplest one is the 2-component model where we distinguish fat mass and fat free mass. It’s the method that is the most frequent one on sport science. Ultrasound and skin folds are two examples where we use this 2-component model to assess our fat mass.

The second model, the 3-component model, also takes body fluids into account, hence 3 components. Examples for this model include DXA-scan and hydrostatic weighing.

The last model is a 4-component model which distinguishes between fat mass, fluids, lean mass and interstitial mass. CT and magnetic resonance are examples for this method.

 

For every method used to assess body composition we know some possible areas for measurement errors. Some of those errors are the result of wrong preparation, others have do with wrong readings/techniques (skinfolds) or the machine itself.

 

In order to minimize the risk of such errors and wrong results, it is important to follow the protocols. This means standardization of the assessment. What are you doing before you measure – nutrition, training. When do you measure – morning vs evening. Who is doing the measurement – same person or different people. Ideally you always have the same person take your skin folds for example to minimize the error. Otherwise you get a different reading and think you gained fat but the change is only the result due to two different measurers.

 

Nutrition and training can also influence your results, if you are dehydrated, if you had a lot of carbohydrates, if you trained before – this all leads to wrong results. If you want to track your body fat levels, the easiest is to stick to one method and replicate the measurement setting the best way possible. Then you have a certain standardization and can compare results. If, however, you get to have a different method used, don’t take the results and compare them to a different method. You will never get the same result if you take a skinfold and DXA reading because the body fat assessed is not the same.

Unfortunately, there are also methods which lack reference values and appropriateness for athletes. Body shapes are different and methods are used with different populations. If you are part of the athletic population and you use a method that is primarily used in obese people, it will be difficult to use and interpret and compare the reading.

 

Another important point when we talk about body fat is the approach and rationale behind the whole body fat assessment. Don’t get too focused on the fat level and don’t target values that are just impossible. Everyone is different, every sport is different and so everyone has a different ideal body fat level. Even though top athletes of your favorite sport may have lower body fat levels than you, this doesn’t necessarily mean that you have your ideal body fat level where they are. You may have your refract shape already and don’t need to go lower. That is important to understand because many athletes try to go really low and then they start to see their performance decline and illnesses appear more often. Then the season is over. Be smart, use the appropriate method, talk to an expert and identify together what is best for you! Experts can help to interpret the result, guide you and support you.

 

Tommy et al (2015) review of body composition in the assessment of health. Top Clin Nutr, 30, 1, 16-32.

 

Further reading:

Meyer et al (2013) Body compositor for health and performance. Br J Sports Med, 47, 1044-1053.