Methods to Estimate Body Composition, Comparing Electrical Bioimpedance and Other Methods

Background

Nowadays, methods to analyse body composition are divided into three groups: direct, indirect and doubly indirect. In this work, we are going to refer to doubly indirect.

Methods

Anthropometry and bioelectrical impedance. The electric bioimped¬ance (EB) is a non-invasive method and it is easy to apply in all types of populations. Knowing its operation, its physical bases, its use and the strict application of the conditions of measurement will ensure the obtained results reliability to get a better comprehension of data. The doubly indirect methods such as anthropometry and bioelectrical impedance stand out from others, because of their simplicity, safety, facility of interpretation and low cultural restrictions. In addition, they present a practical and accessible application, which allows their use in epidemiological studies and research at a population level.

Anthropometry

Among all techniques used in anthropometry, the body mass index (BMI) is the most used, providing information about the subjects’ nutritional status.

BMI: weight (kg) or (pounds) / [height (m) or (feet)]. This is the unit of measurement most used in the consultation to estimate the nutritional status of the patient.

However, BMI does not discriminate between different compart¬ments in the organism. The changes in the BMI are directly pro¬portional to the change in weight. The BMI assumes a distribution into muscle mass and fat mass that is not true. BMI generally over¬estimates adipose tissue in those who have higher body mass (for example athletes) and underestimates excess fat in those who have lower body mass. A study in June 2008 by Romero-Corral examined 13,601 subjects from the United States and found that obesity (BMI> 30) was present in 21% of men and 31% of women. However, using the percentage of body fat it was found obesity in 50% of men and 62% of women, despite the sub-recount that estimated the BMI. In fact, BMI values were associated with large percentages of body fat.

A study published by the Journal of the American Medical Asso¬ciation in 2005 showed that overweight people have a similar risk of death than people with normal weight as defined by the BMI, whereas those who have a “below” normal weight “have greater chances of dying”.

Therefore, BMI is considered as an estimative index to evaluate the nutritional status. To make a correct diagnosis, you need diagnostics can be supported by other methods.

Table 1: The international classification of adult underweight, overweight and obesity according to BMl   

Classification	BMl (kq/m2)
	Principal cut-off points	Additional cut-off points
Underweight	<18.50	<18.50
Severe thinness	<16.00	<16.00
Moderate thinness	16.00 - 16.99	16.00 - 16.99
Mild thinness	17.00 - 18.49	17.00 - 18.49
Normal range	18.50 - 24.99	18.50 - 22.99
		23.00-24.99
Overweight	≥25.00	≥25.00
Pre-obese	25.00 - 29.99	25.00 - 27.49
		27.50-29.99
Obese	≥30.00	≥30.00
Obese class I	30.00 - 34.99	30.00-32.49
		32.50-34.99
Obese class II	35.00 - 39.99	35.00-37.49
		37.50-39.99
Obese class III	≥40.00	≥40.00

Source: Adapted from WHO 1995, 2000, 2004 and 2006.

The relationship between waist circumference and hip is also another anthropometric technique widely used and it is recommended by the World Health Organization as a good predictor of central obesity in population studies since it allows the evaluation of metabolic risk. The measurement is made with a measuring tape, but in this casethe healthcare professional must be trained to reduce the margin of possible error.

Table 2: International classification of waist circumference val­ues (centimeters)

Evaluation	Parameters (cm)
	Woman	Mens
Normal	Lower tan 80	Lower tan 94
high risk	80-87, 9	94-101, 9
Very high risk	equal or greater than 88	equal or greater than 102

Source: Adapted from WHO, 2008.

These two anthropometric measurements are especially important because high values in the BMI or waist-hip ratio are associated with a higher incidence of mortality, diabetes, and cardiovascular diseases. Another anthropometric technique, widely used is the measurement of different skin folds, is based on the fact that most of the body fat is in the subcutaneous tissue. Taking into account that in different body parts, there are some regions with more amount of fat and other regions with less of it, the measurements of skin folds should be made in different areas of the body. This measur¬ing technique is used to estimate the body density operating some mathematical equations, developed in different population groups with diverse characteristics. The calculated values of body density allow estimating the fat mass and lean body mass. This method has the following disadvantages, it has a large margin of error (between 3% and 11%), it presents variability when measurements are made by different people, with different training level or by different instruments, and its implementation is difficult in obese people or with large amounts of fat, dehydration or fluid retention.

Bioelectrical Impedance

The bioelectrical impedance is used to calculate the total body water, fat mass, and fat free mass. This method measures the impedance by a small electrical current applied through the body. The impedance varies according to the tissue that is being evaluated. For instance, fat-free mass presents a good electrical conductivity due to its high concentration of water and electrolytes, while the fat mass is not a good electrical conductor. That allows us to say that impedance is directly proportional to the amount of body fat. This method has dis¬advantages such as limitations of application in patients with fluid retention, peripheral edema, hydrostatic problems or taking diuretic medication. Using in athletes measurement is not an adequate method since it has an error of 3%, which is too big. In the bioimpedance method, the percentage of Visceral Fat mass is also determined, which accumulates in the abdomen and in the vital organs that surround it. This type of fat increases the risk of death when its percentage is high, visceral fat is related to high levels of fat in the bloodstream. Also, it is related to noncommunicable chronic diseases.

Table 3: Comparison between different methods of nutritional evaluation

METHODS OF BODY COMPOSITION MEASUREMENT	Accessibility	Specificity	Precision	Reproducibility	Adventages	Disadvantages
EB	High	Low	Half	CV 4-9,8%	Cheap Laptop insurance Practical Quick Determine fat component and fat-free mass and visceral fat	For specific population, poor precision in individuals and groups
ANTHROPOMETRY (BMI, waist circumference, folds)	Very high	Low	Low	Very variable	Cheap Noninvasive	Low reproducibility, sensitivity and specificity The margin of error is high

Source: Adapted from Costa Moreira, et al. 2015.

cv. coefficient of variation

Discussion

Final Considerations. It is possible to observe that there are several methods to measure body composition and each one has advantages and disadvantages. The healthcare professional who will perform a measurement of the body composition should choose among these methods, considering the following variables:

• According to their objective

• Always consider benefits and costs to apply each method

• The level of his/her own training as an evaluator

• Time available to proceed

• The reliability of the method

• Possible risks of application

Proceeding in this way helps us to minimize disadvantages and to potentiate advantages of the chosen method.

After reviewing data, we can conclude that using electrical im-pedance (BIA) for analysis of body composition, presented as a non-invasive technique of great precision that in a short period of time allows to obtain reliable data evaluating the state of hydration and nutrition, discriminating the balance between fat mass and lean mass, we could improve a medical-nutritional intervention in the associated pathologies treatment as overweight, obesity and eating disorders.

We believe that body composition, and not just total body mass, should be assessed when studying the effects of patients’ weight on health issues. The determination of these values in time can play an important role in the decision making for the professional and pro¬vide a healthy state and better quality of life for the patient. Strategies for weight loss should aim not only to reduce body weight, but also to reduce fat and increase muscle as well as the accompaniment of eating habits to achieve these objectives.

Otherwise, without specific control, the patient could lose weight at the expense of muscle mass and bone density. That would be a risk to health. Still losing weight, the basal metabolism is making the body more prone to store fat. In this way, both body components (fat mass and lean mass) can be monitored to increase skeletal muscle to prevent further weight gain [1-33].

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