Obesity is an excess of body fat. If you are carrying excess body fat, you may be overweight or obese.
Health professionals often use the body mass index (BMI) calculation — your weight in kilograms divided by your height in metres squared (kg/m2) — to work out if you are a healthy weight, overweight or obese.
Other measures that doctors can use include waist circumference and waist-to-hip ratio, which help doctors find out if you are carrying too much fat around your middle (central or abdominal obesity).
BMI does not distinguish between weight due to muscle and weight due to fat, so it does not take into account differences in body composition. An elite sportsperson may have a high muscle mass, and a BMI above 25, but not be carrying excess body fat. If you have a BMI in the overweight range (between 25 and 29.9), your doctor can advise you whether you are truly overweight. If you have a BMI over 30, you are likely to be overweight and may be obese, depending on your body composition; again seek your doctor’s advice.
These BMI measures may not be suitable for Aboriginal and Torres Strait Islander peoples, whose healthy BMI range may be different from that for Australians of European descent. This is due to their relatively long legs in relation to weight, which is a factor known to influence BMI.
Similarly, for Asian people, cut-off points for health risks appear to be lower than for Australians of European descent. For many Asian populations, there is increased risk of health problems at a BMI of 23 or more, and a high risk of health problems at a BMI of 27.5 or more.
A BMI calculator for children uses different cut-off points to define overweight and obesity as it needs to take into account a child’s age. If you are concerned about your child’s weight, see your doctor.
Consuming more food energy than can be used up in daily activity and normal body function (metabolism) generally results in excess energy being stored as body fat.
In terms of what you eat, ‘energy-dense’ foods (those that have a lot of kilojoules in a small volume) can be associated with weight gain, especially if you eat a lot of them. These foods tend to be high in sugar and/or fat, for example, soft drinks, chips and pastries. As for the other side of the equation — how much energy you expend — not being active (often simply not moving enough, let alone not formally exercising) is an important cause of obesity.
On top of these factors is a person’s genetic make up, that is, how easily they tend to store fat.
Being overweight or obese increases your risk of:
Recently, doctors have identified that body fat distribution is an important predictor of disease. Abdominal fat, central (or truncal) obesity and abdominal obesity are all terms used to describe carrying extra weight around your middle, rather than on your hips and thighs. In other words, if you have central obesity, you are ‘apple shaped’ rather than ‘pear shaped’.
Carrying extra fat around the abdomen puts a person at much greater risk of heart disease, diabetes, stroke and cancer than someone who is pear shaped. In fact, waist circumference is a measure that doctors can use to help predict your risk of certain conditions associated with obesity, such as heart disease.
To reduce the risk of disease, men should aim for a waist circumference of less than 94 cm and women less than 80 cm. These figures apply to Caucasians: Asian, Indian and Indigenous people should have smaller waist measurements. Talk to your doctor about what’s appropriate for you.
If you think you are carrying too much body fat, see your doctor. Your doctor can:
Making simple daily lifestyle changes to increase your physical activity and improving your eating habits are promoted as keys to controlling excess body fat. Maintain a healthy body weight by being physically active and eating according to your energy needs.
Think about how much you move on most days; if it’s not much, start moving in simple ways. Take the stairs not the lift, walk to the shops instead of driving, do some gardening, take the dog for a walk, or turn off the television for a while and go to the park.
Continuous exercise at a comfortable pace is best for controlling body fat, e.g. 30 minutes of brisk walking every day is recommended as a way to avoid gaining excess fat when combined with healthy eating. Remember, you don’t need to take part in a structured sport to be more active.
Studies suggest that at least 60 minutes of moderate exercise, such as brisk walking, is needed every day to lose significant weight. However, the amount of physical activity required to lose weight varies from person to person. Remember that increasing your activity level should be combined with reducing your energy intake.
As well as helping you lose weight, physical activity benefits your general and heart health.
Becoming aware of how different types of foods affect your energy intake is also important — see your doctor or a dietitian for advice on which foods and eating habits are likely to result in excess body fat and which are not.
A healthy diet means enjoying a wide variety of nutritious foods. The National Health and Medical Research Council advises the following:
In addition, the Heart Foundation recommends reducing the amount of ‘trans fat’ in your diet. Trans fat is a type of unsaturated fat that acts like saturated fat in the body and increases the risk of heart and blood vessel disease. To lower the amount of both trans fat and saturated fat in your diet, the Heart Foundation recommends that you trim meat of all visible fat, choose reduced-fat dairy products and limit foods such as pies, pastries, cakes and biscuits to once a week.
Last Reviewed: 26 January 2010