Body fat: distribution and measurement

Obesity is defined by the World Health Organisation as a weight increase due to abnormal or excessive fat accumulation.

 

However,not all types of obesity are the same.The most important consideration is not how much weight is gained,but how it is distributed (i.e.,where in the body it is located),as different locations have different consequences for an individual’s health.Thus,when excess body fat is located in the abdomen area we refer to CENTRAL OBESITY,which is the type of obesity that represents the highest health risk,as it is associated with an increased risk of diabetes and cardiovascular diseases.

 

METHODS FOR ESTIMATING BODY FAT

 

Waist circumference

 

Waist circumference (WC) is an independent and determining indicator of cardiovascular risk factors (CRF).

 

Body fat evaluation is carried out in order to calculate the risk of type 2 diabetes,arterial hypertension,dyslipidemia (increase in cholesterol,triglycerides,etc.)and cardiovascular disease,and is therefore considered a reliable and independent indicator of cardiovascular risk.

 

According to the US National Institute of Health (NIH),an increase in waist circumference is associated with an increased risk of suffering from type 2 diabetes,dyslipidemia,arterial hypertension and cardiovascular disease,when body mass index (BMI) is also elevated.

 

WC is a very useful parameter that has immense value in clinical practice for people who are of normal weight or overweight,as the BMI can give a false reading,for example,in sports people with a lot of muscle mass.In these cases WC is the measurement that gives a true indication of whether an individual is actually overweight.It is also valuable to clinical practice in monitoring a patient’s progress,as changes in WC indicate an increase or decrease in abdominal fat.

 

How WC is measured is important,as the results can differ depending on the method used or the person taking the measurements.This is why the Spanish Society for the Study of Obesity (SEEDO) has established criteria for taking this measurement:the waist should be measured at the upper edge of the iliac crest; using a non-retractable metric tape measure; the patient should be standing and wearing loose clothing; and the aforementioned bone structures should be used as a reference.The measurements should always be taken by the same professional.The waist can also be measured with the patient in a supine position (lying face up),using the bellybutton as a reference.There is not much difference between the two measurements if they are taken by the same person.

 

According to the NIH the cut-off points for establishing cardiovascular risk are:

• High risk:
  • Men:more than 95 cm.
  • Women:more than 82 cm.
• Very high risk:
  • Men:more than 102 cm.
  • Women:more than 88 cm.

Waist-to-hip ratio (WHR)

Although the waist-to-hip ratio can be a good indicator of the distribution of visceral fat,in recent years the waist circumference measurement has become more widely used in clinical practice as it is considered to be a better indicator of abdominal fat.Hip measurements vary more among women than among men,whereas waist measurements in both men and women are quite homogenous.In addition,in clinical practice the measurement of both parameters involves greater variability in obtaining the measurements and requires more time.

 

The WHR is calculated by dividing the waist measurement,taken at the upper edge of the iliac crest,by the hip measurement,taken at the level of the trochanters.

 

WHR = Waist circumference in cm / Hip circumference in cm.

 

This measurement should be taken with the patient standing upright and wearing loose clothing,using a non-retractable metric tape measure and should always carried out by the same person.

 

Although the cut off points or values in relation to cardiovascular risk have not been clearly defined,it is generally accepted that values greater than the 90^th percentile indicate potential risk.

 

In general it is accepted that a WHR greater than 0.85 in women and 1 in men indicates an increase in the amount of body fat,and therefore represents an increased risk of suffering from cardiovascular or metabolic disease.

 

Bioelectrical impedance analysis (BIA)

BIA is a simple,non-invasive,reliable and quick method that relies on how different tissues behave when a low intensity electrical current is passed through them.Fat (which does not combine with water molecules) is the poorest conductor of electricity,while water,mainly associated with muscle tissue,is an excellent conductor of electricity.

 

Other methods

• Subcutaneous folds.This method has some disadvantages.
  • It measures subcutaneous,not visceral fat.
  • It can result in wide variations depending on the professionals carrying it out.
  • The folds in obese patients are so large that occasionally the plicometer (the calliper used to measure cutaneous folds) does not fit around them.
• Imaging techniques:These techniques allow cross-sections of the abdomen to be visualised and used to calculate its fat quantity.They are highly reliable methods of obtaining information about the type of both subcutaneous and visceral fat present.Some of the techniques used include Computerised Axial Tomography (CAT) and Magnetic Resonance Imaging (MRI).However,the use of these techniques is limited to research purposes; they are not used for normal clinical practice,in part,due to their high cost.