The methodology to measure body composition is not yet very clear. Different methods are being used and the methodology is still being improved. For patients with excess adiposity, certain measurements such as height and weight (to calculate the body mass index [BMI]) are essential.
Why it is important to measure body composition?
Bodyweight is only as important when it comes to health and disease as its composition. The body weight is the sum of all the body’s tissues. Body composition, on the other hand, measures the body’s relative fat and lean mass. Lean mass is composed of bones, tissues, organs, and muscles.
Body composition is often measured in the following settings:
- To evaluate patients who are malnourished.
- Report patients with an increase in visceral but not total body fat. This is associated with an increased risk of developing diabetes and heart disease.
- Assess changes in the body that are associated with growth and development (infant and childhood), aging, and certain diseases (eg HIV, diabetes, etc).
- Evaluate patients whose body mass index (BMI), is discordant with total body fat mass.
Methods to measure body composition:
Various methods are used to measure body composition. Each method has a different level of precision and reproducibility and the cost and ease of performing the methods also vary.
Measuring body composition is done either in clinical settings or for research purposes.
Body Composition Measurements in the Clinical practice:
Anthropometric measurements are routinely sufficient to determine a patient’s adiposity in a clinical setting. Patients with a high body mass (BMI) or high adiposity may be candidates for a more thorough assessment of their body composition.
- Anthropometric measurements:
- Height and body weight are the most common measurements and can be measured with great accuracy. These are essential in making clinical decisions about the treatment and follow-up of obesity.
- There are many ways to relate weight to height, but the most popular is BMI. This is weight in kilograms divided by height in meters square (weight in Kgs/ height (m²).
- Because height is often overestimated, and weight is underestimated, leading to an underestimation of the BMI, it is important for the healthcare provider to measure body weight and height in the office and not rely on the patient’s readings.
Height is usually overestimated while weight is underestimated.
- For older people, it is especially important to measure your height annually as the loss of height could indicate osteoporosis-related vertebral fractures.
- BMI does not directly measure body weight, but it is a good indicator of body fat. The percentage of body fat depends on age, gender, ethnicity, and other factors. Healthy percent body fat for women of normal weight ranges between 20 and 35 percent, while it is 8 to 25 percent for men. Women have about 12 percent more body fat than men at any given BMI. This is despite the fact that their total weight remains the same.
Compared to men, women have more body fat
- Waist Circumference:
- The waist circumference is an important anthropometric measurement. The measurement is made using a flexible tape that is placed horizontally at the level of the iliac crest as seen from the front. An increased risk of death and morbidity is associated with greater central adiposity as measured by the waist circumference.
Waist circumference is directly related to health problems
- Skinfold thickness:
- Multisite testing for skinfold thickness is significantly less accurate than measuring height and weight, especially in obese subjects. They are therefore of little clinical use and are used primarily in epidemiological research studies.
Skinfold thickness is the least accurate
Body Composition measurements for research purposes:
- Dual-energy x-ray absorptiometry
- Dual-energy, x-ray absorptiometry is one of the most common methods to determine body composition. This method uses the attenuation between two energy sources to create a three-part model of body composition. It is preferred in clinical settings where a more precise determination of body composition is required. It has been tested against other methods. This procedure is very simple and requires a low radiation dose.
DEXA scan is preferred in the clinical settings for precise measurements
- Measurement of impedance
- The measurement of bioelectrical impedance is easy and widely used, but it has its limitations. You can measure impedance by placing electrodes on one arm or one leg or standing on the feet plates of a special scale. Impedance is directly proportional to the length of conductors and inverse relation to their cross-sectional areas. It is important to place electrodes accurately, as variations in impedance measurement and estimation of body water can lead to large errors.
- In a comparison of two bioelectric impedance devices with DEXA to measure body fat, the percent of body fat in both men and women with normal body mass index was found to be 2 to 6 percentage points lower. The values for overweight people were lower than those of women, but the same for men. It is important to use valid formulas to estimate body weight when using bioelectric impedance equipment [Ref].
- Imaging techniques:
- MRI or computed tomography can reliably determine patterns of body fat distribution. Most people use this technique to take a cross-sectional view at the interspace between the fourth (L4) & fifth (L5) vertebrae. This image can be used to quantify subcutaneous and visceral fat. Similar information can be found in images taken between the second and third lower lumbar vertebrae.
- CT scan uses radiographs and computer analysis to determine the structure of internal organs. A series of scans can be used to determine the accuracy of body fat. This allows for a margin of error of less than 1%. A single cut at L4-5 is clinically used to minimize radiation dose.
- MRI requires the use of a strong magnet to surround the subject. Although it is safe, it takes significantly longer than CT to perform. Images will be blurred if there are any movements.
- Nuclear Magnetic Resonance (NMR) spectroscopy uses similar technology to MRI but can discern fat and glycogen in tissues (ie. in the liver), as well as fat mass and overall. Although the absolute values of subcutaneous fat and visceral oil may differ, their relative rankings are similar.
CT Scans, MR, and NMR can all be used to measure body composition
- Body water isotopic measurements—
- Isotopic dilution using a tracer that measures the body’s water (D).203H20, H218O) can also provide an accurate assessment for body fat. Three methods were used to estimate body fat in children: densitometry, isotopic measurement body water, and DEXA. However, mass spectroscopy is required to analyze samples. This has made it difficult to use isotopic measurements of body composition in research pursuits.
- Water- or air displacement-based methods
- Hydrodensitometry (underwater weighting) and whole-body plethysmography can be used to separate fat from fat-free parts of the body. The first method weighs an individual on dry ground and then submerges them completely, with the possibility of simultaneous measurements of their lung volume.
- Whole-body plethysmography, on the other hand, uses air displacement instead of water displacement to measure body weight. Although it is similar to underwater weighing or hydrodensitometry, it does not require submersion. Although underwater weighing was once the standard method for determining body composition, it has been largely replaced by modern techniques.
Underwater weighing has largely been replaced by other methods
In a clinical setting, only anthropometric measures can be used to determine adiposity. To assess patients’ body mass and determine whether they are overweight or not, it is necessary to carefully measure their waist circumference, height, weight, as well as calculate the body mass index (BMI).
Some patients may benefit from other methods to assess body composition, which is usually reserved for research. Patients with a high BMI or high adiposity may be candidates for a more thorough assessment of their body composition. Visceral fat is associated significantly with an increased risk of developing diabetes and heart disease.
Dual-energy-x-ray absorptiometry is the preferred method for determining body composition when BMI or adiposity can be considered discordant.