Body Mass Index (BMI) Versus Waist-To-Hip Ratio

Dr Patrick J. Treacy
By Dr Patrick J. Treacy

Dr. Patrick J. Treacy is on the Specialist Register in Ireland and holds a H.Dip in Dermatology and a BTEC in Laser technology and skin resurfacing.


With so many aesthetic clinics in the UK and Ireland now providing obesity reduction as a therapy we also have a responsibility to our patients to estimate their risk of a future cardiovascular event. 

The most common method of assessing body weight in clinical practice is the body mass index (BMI) which is calculated by taking the weight in kilograms and dividing by the height in metres2. A BMI of 25-29.9 is regarded as overweight, whereas a BMI of 30 kg/m2 or above is classified as obese.

However many studies now show that BMI is a poor discriminator of cardiovascular risk at an individual level and should not be used as the sole measure of obesity.

The problem with BMI is that because it is simply an expression of the relationship between weight and height, it tells the doctor nothing about where the fat is deposited. This is very important because fat deposited over the waist area (visceral fat) presents a much greater health risk than fat around the hips and thighs.

We must be conscious of this fact because we only remove subcutaneous fat by liposuction or VASER lipo selection methods and tend to leave visceral fat behind.

Many recent studies show that waist-hip ratio or waist measurement alone are better predictors of risk than BMI.

The waist-to-hip ratio measurement can be used to help determine obesity. The distribution of fat is evaluated by dividing waist size by hip size. A person with a 30-inch waist and 40-inch hips would have a ratio of .75; one with a 41-inch waist and 39-inch hips would have a ratio of 1.05. The higher the ratio, the higher the risk of heart disease and other obesity-related disorders. Hence a high waist-hip ratio reflects a large waist measurement relative to the hips and a higher proportion of the risky visceral fat. Even in patients with a BMI as low as 23 a high waist-hip ratio predicted an increased risk of a heart attack.

The Interheart study of 15,000 patients found that the ratio between the waist and the hip measurement predicted the risk of a heart attack more accurately than using BMI alone. 

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