PDF Print E-mail

Obesity Surgeon Information - What is obesity? What is a Obesity?

Obesity is a condition in which excess body fat has accumulated to such an extent that health may be negatively affected.

It's medical definition is a body mass index (BMI = weight divided by height squared) of 30 kg/m2 or higher. This distinguishes it from being overweight as defined by a BMI of between 25-29.9.

Click here to check your BMI

Many studies show an association between excessive body weight and various diseases, particularly cardiovascular diseases, diabetes, sleep apnea, certain types of cancer, and osteoarthritis. As a result, obesity has been found to reduce life expectancy. It as a serious public health problem with rates of obesity increasing among both adults and children.



Obesity in absolute terms is an increase of body fatty tissue mass. In a practical setting it is difficult to measure this directly, and obesity is typically measured by BMI (body mass index) and in terms of its distribution through waist circumference or waist-hip circumference ratio measurements. In addition, the presence of obesity needs to be evaluated in the context of other risk factors and comorbidities (other medical conditions that could influence risk of complications).


Body mass index or BMI is a simple and widely used method for estimating body fat mass. BMI was developed in the 19th century by the Belgian statistician and anthropometrist Adolphe Quetelet. BMI is an accurate reflection of body fat percentage in the majority of the adult population, but is less accurate in situations that affect body composition such as in body builders and pregnancy.

BMI is calculated by dividing the subject's weight by the square of his/her height:

Metric: BMI = kg / m2

Where kg is the subject's weight in kilograms and m is the subject's height in metres.

The most commonly used definitions, established by the WHO in 1997 and published in 2000, provide the following values:

  • A BMI less than 18.5 is underweight
  • A BMI of 18.5–24.9 is normal weight
  • A BMI of 25.0–29.9 is overweight
  • A BMI of 30.0–34.9 is class I obesity
  • A BMI of 35.0-39.9 is class II obesity
  • A BMI of > 40.0 is class III obesity or severe / morbidly obese
  • A BMI of 35.0 or higher in the presence of at least one other significant comorbidity is also classified by some bodies as morbid obesity.

Click here to check your BMI



Affiliated Websites

Colorectal Surgery
Chris Macklin's Colorectal Surgery Website
Cosmetic Breast Surgery
Philip Turton's Cosmetic Breast Surgery Website
Thoracic Surgery
Richard Milton's Thoracic Surgery Website
UK Surgeon Websites: Designed by Surgeons for Patients
Copyright © 2008 UK Surgeon. All Rights Reserved.