How Important is the Waist-to-Hip Ratio?

The waist-to-hip ratio (WHR) is the ratio of the circumference of the waist to that of the hip. The proportion of fat stored in the abdominal area to that stored in the hip region is an important indicator of the risk for a number of conditions. These conditions include major health risks such as diabetes, hypertension, and heart disease. A high WHR increases the chances of acquiring these conditions.

Measuring your Waist to Hip Ratio

Body weight has an impact on all aspects of health, and carrying excessive weight is strongly associated with a range of negative health outcomes. Body mass index (BMI) is a well-established means of identifying underweight, overweight and obesity in adults. It is calculated by dividing the body mass (weight) of an individual by the square of their height.

More recently researchers have found that the way in which fat is distributed throughout the body is strongly linked to the likelihood of developing obesity-related conditions including cardiovascular disease, type 2 diabetes and various forms of cancer. This high-risk pattern of weight distribution is known as central, truncal or abdominal obesity.

Central Obesity and Body Shape

Central obesity occurs when fat accumulates around the upper and middle areas of the body, leading to a large waist circumference and a body shape sometimes described as “apple shaped” - as opposed to the “pear shaped” profile produced by accumulation of fat around the hip and thigh area. The presence and extent of central obesity is assessed by measuring the circumference of the waist (WC) and comparing it to that of the hips. The relationship between the two measurements is referred to as the waist-to-hip ratio (WHR).

Why is Central Obesity Significant?

There are two main forms of adipose tissue, as classified in terms of their location within the body: subcutaneous fat is deposited beneath the skin, whilst visceral fat is located around the organs. Adipose tissue in the hips, thighs and buttocks is usually subcutaneous, whereas fat stored abdominally tends to be mostly visceral.

Why this link between central obesity and multiple serious health conditions should exist is not yet fully understood. Visceral adipose tissue is thought to be more metabolically active than subcutaneous fat and is known to affect the body’s sensitivity to the hormone insulin. It is also linked with impaired regulation of cholesterol and abnormal cardiovascular function. It is quite possible that these and other mechanisms are implicated in what is likely to be a multifactorial process.

Medical imaging techniques such as computerized tomography (CT) and magnetic resonance imaging (MRI) are currently the only means by which to determine unequivocally whether abdominal fat is subcutaneous or visceral.  However, extensive research has confirmed that increased waist circumference is a strong indicator of the presence of excessive deposits of visceral adipose tissue.

What is the Procedure for Measuring Waist and Hip Circumference?

The World Health Organization (WHO) advocates the use of a standardized procedure for measuring WC and WHR:

Clothing and other items that might interfere with the measurement should first be cleared from the waist and hip area. The subject is then asked to stand upright with arms relaxed at the side, feet evenly spread apart at approximately shoulder width, and body weight evenly distributed.

The waist measurement should be made at the midpoint between the top of the iliac crest (upper edge of the main pelvic bone) and the lower margin of the last palpable rib in the mid axillary line (lowest point of the ribcage that can be located by touch along the side of the body). It may be necessary for the clinician performing the measurement to identify these regions by touch prior to placing the measuring tape. Once the location of the waist has been determined, a stretch resistant tape is passed around the subject. It should be wrapped snugly around the body, but not to the point of depressing or pinching the underlying skin. In order to ensure that the abdominal muscles are relaxed, the subject is asked to take two or three consecutive natural breaths and the measurement is made at the end of the last natural expiration (outward breath).

Hip circumference is measured in a similar manner, with the tape being passed around the hips at the widest circumference of the buttocks. In both cases it is important that the tape measure be kept level and parallel to the floor whilst the measurement is made.

If you wish to measure your own WC or WHR, the same procedure can be followed at home, although it can be difficult to make sure the measuring tape is correctly aligned without assistance.

Once the readings have been obtained, WHR can be calculated by simply dividing waist circumference (WC) by hip circumference (HC). The units of measurement used are not important, so long as they are consistent between measurements.

Interpreting the Waist to Hip Ratio Measurements

According to the World Health Organization, a waist circumference greater than 37 inches for men and 31.5 inches for women indicates an increased risk of serious health complications.  For WHR, the upper limit is considered to be 0.90 for men and 0.85 for women.

Waist-to-Hip Ratio Differ in the Context of Waist Circumference

WHR should be considered in combination with the absolute waist circumference (WC). This is because it is possible for a lean person with small waist and hips to have the same WHR as an obese person with a much larger waist and greater fat deposits in the hip and thigh region. Relying solely on WHR may not give a clear picture if there is no information on the reason for the high waist-to-hip ratio. Is it because of high waist circumference or low hip circumference? Treatment procedures depend upon correct interpretation of data. Taking waist circumference into consideration enables medical practitioners to get a better understanding of the risks accompanying the degree of abdominal obesity. An increase in waist circumference when it corresponds to an increase in belly fat is what increases the chance of developing insulin resistance and consequently Type 2 diabetes.

Whilst BMI, WC and WHR are all useful tools in assessing susceptibility to obesity-related conditions, it is important that these measures be considered within the broader context of an individual’s overall body weight and shape, as well as their general state of health. It is possible to have a BMI within the accepted normal range, yet still have excessive adipose tissue in the central region. Conversely, a lean person with small hips and waist may have the same WHR as an obese individual with much greater absolute measurements. BMI can be a useful indicator of overall level of overweight or obesity, but WHR considered in combination with WC is required in order to assess the degree of central obesity present.