What is Obesity?

The World Health Organization (WHO) defines obesity as ‘abnormal or excessive fat accumulation that may impair health’.

Statistics of Obesity

The number of people (prevalence) with obesity is increasing worldwide. The worldwide prevalence of obesity more than doubled between 1980 and 2014. In 2014:

  • More than 1.9 billion adults were overweight. Of these over 600 million were obese.
  • 39% adults (38% of men and 40% women) were overweight.
  • 13% of the world’s adult population (11% of men and 15% of women) were obese.


Body mass index (BMI) is a simple index of weight-for-height that is commonly used to classify obesity. It is defined as a person’s weight in kilograms divided by the square of their height in meters (Kg/m2).

To work out your BMI, please insert your details into the BMI calculator below and see which category you are in.

BMI (Kg/m2)


Risks and advice


Underweight Try and increase your weight to reach the healthy weight range. You are not a candidate for weight loss surgery


Healthy weight You are not a candidate for weight loss surgery

25 – 30

Overweight The overall risk to your health is low. Weight loss should be possible with lifestyle changes, diet and exercise. An intra-gastric balloon can be considered to reduce appetite and help weight loss.

30 – 35

Moderate obesity The overall risk to your health is high. There is an increased risk of developing health risks associated with obesity which includes: high blood pressure, high cholesterol, type 2 diabetes, heart disease, arthritis, and sleep apnoea. Weight loss surgery can be discussed.

35 – 40

Severely obese You are at a significant risk of developing the above complications. Weight loss surgery should be considered especially if you suffer one of the above complications.

40 – 50

Morbidly obese You are at a very significant risk of the above complications. Your surgeon will advocate surgery.


Super obese This is a life threatening weight. Your surgeon will advocate surgery. Occasionally, an intra-gastric balloon can be inserted in advance to reduce weight and make an operation safer.