What is obesity?

What is obesity?

Many Australians have a weight problem – recent estimates are that 67% of adult men and 52% of women in this country are overweight, equating to about 8 million Australians. About one in four adults is obese. The increase in our average weight shows no sign of slowing, and the proportion of people in the obese range has increased by almost 1% every year for the last 20 years. The costs associated with obesity, both social and economic are enormous; with hospital, medication, disability and ‘off-work’ payments costing billions of dollars annually.

The proportion of people above ‘ideal weight’ (that is, those whose body mass index or BMI is greater than 25) and in the obese range (BMI greater than 30) is increasing. People who are overweight and obese now outnumber those in the healthy weight range. That is, it is no longer normal to be a healthy weight. Weight problems are so common that it makes no sense to “stigmatise” obesity or those afflicted by it, stigma or bias prevents people from seeking appropriate treatment which just compounds the problem.

Defining obesity

These days the word ‘obesity’ has negative connotations, but it is simply a medical term describing people for whom excess weight poses a health risk. Rather than focusing on a person’s weight alone, we often prefer to measure a person’s weight in relation to their height. This measurement, the body mass index (BMI), is calculated by dividing weight (kg) by height (metres squared), or BMI = kg/m2.

This allows us to compare someone’s weight with the weight of other people of a similar height, in order to calculate how much he or she is overweight, or their excess weight. We know that the risk of medical problems is related to how much excess weight someone carries, so the BMI also allows us to estimate some of their risks. Every person being assessed for any type of weight treatment will generally have a calculation of their BMI, ideal weight, and excess weight performed, as this allows the patient and their doctor to set treatment goals.

Ethnic background also influences the ideal BMI for a person. For example, for people of Asian ancestry, the BMI at which a person is considered overweight is 22.5, which is lower than that for people of European ancestry (25).

Waist circumference in people who have relatively mild weight problems, but have weight-related diseases (such as diabetes, hypertension – high blood pressure, and high cholesterol), fatty tissue may be distributed around their abdomen, which is the riskiest place to carry fat. Measuring waist circumference may give some people a better idea of the severity of their problem than relying on weight or BMI alone. In people who are moderately overweight (BMI between 25 and 29.9), an increased waist circumference indicates an increased risk of medical problems.