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Measuring the body – Part 3: Bioimpedance and body composition analysis


Routine anthropometric measurements are central to the assessment of body weight (see here) but they do not give us the whole picture as they cannot tell us how much of that weight is fat and how much is muscle, bone or other tissues. This is called the body composition and its analysis is useful in weight management to assess the need for treatment and to monitor efficacy.

If you would like to know the importance of the proportions of fat and muscle in the body, please see my articles on those specific topics:

Body fat percentage here

Sarcopenia (muscle loss) here

When you lose weight, it is desirable that the weight lost is fat rather than muscle. It would therefore be useful to know the relative amounts of each tissue type in the body, as this will affect how easily you lose weight and your subsequent capacity to keep to a stable weight once you have reached your target.

Until recently, measurement of the different body tissues was complex and expensive. Fortunately, bioelectrical impedance analysis (bioimpedance) has now made it possible to perform this assessment of body composition in the clinic in a matter of minutes.

These devices use very small electric currents to give us a detailed analysis of the body tissues, providing a report of the amount of muscle and fat in the body. The more complex devices are able to give the results by body region (legs, arms, torso) and use a wider range of electrical frequencies to provide greater accuracy. However, bathroom scales can now be purchased with this technology and, though less precise, they are still very useful in the home environment.

The test is innocuous as it does not use x-rays. (NOTE: Bioelectrical impedance analysis should not be used in persons with a pacemaker.)

If you would like more in-depth information on bioimpedance, please read on.

The Details

The body is made up of different tissues: Fat, fat-free tissues and body water.

Bioelectrical impedance analysis uses small electric currents (far too low power to be detectable by humans) to analyse the tissues and calculate the proportions and distribution of each tissue type.

The Tanita MFC-780C device (picture) used in Bazire Medical clinics is an 8 channel, multifrequency device that calculates the following parameters:

1. Fat mass: The kilograms of body weight made up by fat (also provided as a percentage of total body weight)

2. Fat-free mass (= Lean mass): The kilograms of body weight made up by everything except body fat (i.e. muscles, organs, bones)

3. Bone mass: The mineral mass of the skeleton (note that this is not the weight of your bones, just the mineral part [mostly calcium and phosphorus])

4. Soft lean mass: Fat-free mass without the bone mass

5. Skeletal muscle mass (skeletal muscle being the muscle that moves us)

6. Total body water: the total amount of water in the body (given as a weight and a percentage). This is given separately as intracellular and extracellular water

7. Visceral fat: The fat within the abdomen. This is the fat most closely associated with chronic diseases (heart disease, diabetes, cancer…)

8. Basal metabolic rate: The calories your body would burn if you lay in bed all day. This is the energy your body needs to keep itself functioning efficiently.

Here are the normal ranges for people with an “average” level of physical development. Many of these figures are not valid for athletes, bodybuilders, etc.

Here is a sample report from the Tanita MFC-780C device used in the Bazire Medical clinics:

On the basis of this report

This patient is seen to be overweight (weight, 95.9 kg; height, 188 cms; BMI, 27.1 kg/m2).

The fat mass and body fat percentage are high. Soft lean mass is within the normal range and skeletal muscle mass shows average development. Bone mass is at the lower end of the recommended range for a man of this weight; however, as he had recently put on weight and had come to PronoKal to lose weight, this bone mass was not of concern. Total body water is at the lower end of the normal range for this body weight. The basal metabolic rate is good. The visceral fat rating is within the normal range, but further reduction of this figure will promote health.

The approach in this case was to initiate a diet to reduce body fat while maintaining the muscle mass. As with any weight-loss diet, exercise is essential, mainly as resistance exercise during the weight-loss phase. The patient needs to ensure adequate fluid intake, preferably as water.

Weight control requires a full understanding of the patient’s current diet, lifestyle, stresses and other factors that could affect his or her weight control and health. This information must then be combined with the anthropometric measurements and body composition analysis to develop a holistic programme for weight management, providing dietary and lifestyle recommendations to ensure:

  • adequate physical activity and exercise adapted to the patient’s health status
  • stress management, sleep and work-life balance, etc.
  • an appropriate intake of energy, protein and micronutrients (vitamins and minerals)

Body composition analysis by bioimpedance can be repeated every 2 to 4 weeks. This will help in the monitoring and adjustment of the diet and will enable patients to better visualise and understand their progress.