Our weight is made up of tissues, muscles, bones, blood, fat, water, and the rest of our physical body. A weighing scale measures your total body weight, but it will never tell you how much of this weight is fat. The best way to monitor your progress, when embarking on a new diet, is to measure your body fat percentage and your lean body mass (weight excluding fat). Healthy goals are 12 to 20 percent body fat for men and 18 to 25 percent for women.
A person who looks slim may also have a high percentage of fat in her body. A look at the body composition can only help us understand if the person will suffer from obesity related problems or not. There are many ways to analyze the fat and other components of the body. Some methods are direct and some indirect.
Direct and Indirect Methods
Measurement of body fat is mainly done through body composition. Body composition analysis of the fat and lean components of the body can be determined through direct and indirect methods of measure.
The direct method is based on the study of physical and chemical analysis of cadavers (a dead body) relative to the body constituents of fat, water, protein and minerals. It is used as a norm or standard for indirect methods that are used for live body measurements. There are many indirect methods to measure body fat. Some of them include:
- Densitometric and hydrometric
- Dilutinal
- Nitrogen and pottassium content analysis
- Computer Tomography and Magnetic Resonance
- Electrical conductivity and UltraSound
- Infrared Interactance and Photon Absorptiometry
- Air Displacement Plethysmography
- Anthropometric
Indirect methods to measure body fat provide a non-invasive assessment of fat and fat-free tissue.
Densitometry and Hydrometry
This method is also known as underwater weighing. It is a widely accepted method in calculating the body fat. However, it is very expensive and inconvenient to conduct and is, therefore, not used to a large extent in research. It is based on Archimedes principle, where the body is submerged in a water tank to determine the density of the body by using the amount of water displaced. The percentage of body fat is then calculated by using a standardized formula.
Nitrogen and Potassium Content Analysis
A neutron activation analysis of gamma rays emitted by our body tells us of the amount of nitrogen in our body. Once the quantity of nitrogen is calculated, researchers can estimate the amount of protein in muscle and non-muscle tissue compartments. The same test analysis is also used to measure the amount of total body potassium. This helps in determining the body cell mass relative to fat and fat-free tissue. When the gamma rays show that the body contains high levels of potassium, it means that the amount of fat tissue in the body is low.
Computer Tomography and Magnetic Resonance
Recent improvements in radiography have made it possible for x-ray to be used to measure bone, muscle and fat. We can measure the thickness of the body components through x-ray and arrive at the ratio in which they are found in the body.
Computer tomography and magnetic resonance are two fat measurement methods where the body is scanned by x-ray beam and the magnetic scan. Radiographic cross images of essential and storage fat are produced and researchers measure the ratio in which different types of tissue are found and apply a formula to assess the volume and density of fat and fat-free tissue.
Electrical Conductivity and Ultra Sound
Lean tissue without fat has a higher electrolyte content and can, therefore, conduct electricity better than fat tissue. In electrical conductivity analysis, an instrument covering the whole body is used. There is a solenoidal coil under the surface of the instrument. As electromagnetic radiation is sent through it, coil impedance changes are measured and calculations are made with the help of the measurements. The resistance differences help the technicians in finding out if the rays are passing through fat tissue or fat-free tissue.
Similarly, when electrodes are placed on the hands and feet, and the electrical flow resistance through fat and lean tissue is measured, it is known as Bioelectric impedance analysis (BIA). A body density formula is used on the flow impedance values, and fat and fat-free tissues ratios are determined. However, change in the water levels in our body can affect the readings of both these methods. Thus water balance should be maintained for the validation of these tests. If the water level is low, it may appear that the fat level is low. The experts study the generated body images and estimate their volume and density through formulas and arrive at the amount of fat and fat free tissues. Many compact machines use this method to measure the body fat percentage.
High frequency sound waves can also be passed through body tissue through transducers. Tissue thickness is then calculated as different density levels produce different electrical amplification impulses. Electronic calipers are used to calculate the thickness, and since bone, muscle and fat have different density levels, we can look at the results and find out the body composition. This study of components is called the ultrasound method.
Infrared Interactance and Photon Absorptiometry
Infrared interactance and photon absorptiometry are two new methods. In the first one, electromagnetic radiations probe the body to measure the absorptive and reflective spectographic chemical properties of fat, water and protein. The reading of the absorptive and reflective property of fat is different from that of protein or water. It is easy to identify from the measurements how much of the tissue is fat. Then the ratio of fat and fat-free tissue is determined. In the second method, two energy level photon scans are made of the body. The energy level absorption of the different types of tissues and bone vary. It is easy to identify from the energy level absorbed, as to how much is bone mineral mass, how much is fat tissue and how much is fat-free.
Air Displacement Plethysmography or BODY POD
This is a recently introduced method by which the volume of air displaced by the body is measured in relation to the difference it makes on the pressure gradient. The Body Pod consists of two sections. The person being measured would sit in the Pod and the movement pressure changes are gauged diaphragmatically. A formula has been developed which, based on the measurements made, tells us how much of fat there is in the body and how much of it is fat-free.
Anthropometric Methods of Measure
The term anthropometric refers to measurements made of various parameters of the human body, such as thickness of skinfolds or circumferences of various body parts at specific locations on the body. The measurement sites vary depending upon the specific skinfold testing protocol being used. This is the most popular method because it is practical and more convenient to take a few body measurements than to submerge individuals in water tanks. However, this method is inaccurate when compared to other methods. Once the skinfold measurements are done, there are many different formulas and calculations that can be applied to measure the percent of body fat.
