Obesity: Q & A
1. What is obesity?
Obesity is an excess of body fat. If you are carrying excess body fat, you may be overweight or obese.
2. How is obesity measured?
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.
- Obesity: BMI of 30 or above.
- Overweight: BMI of 25 to 29.9.
- Normal weight: BMI of 18.5 to 24.9.
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).
3. Are the BMI cut-off points always accurate?
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 are not suitable for Aboriginal and Torres Strait Islander peoples, whose healthy BMI range may be lower than that for Australians of European descent. This is due to their ancestry as traditional hunter-gatherers who were lean and physically fit.
Similarly, for Asian people cut-off points for health risks appear to be lower than for other Australians. 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.
4. How can I tell if my child is overweight?
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.
5. What causes obesity?
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.
6. How is my health affected if I am obese or overweight?
Being overweight or obese increases your risk of:
- high blood pressure;
- type 2 diabetes;
- stroke;
- heart attack;
- gout;
- osteoarthritis;
- sleep problems;
- some types of cancer;
- gallstones;
- kidney disease; and
- mobility problems.
Recently, doctors have identified that body fat distribution is an important predictor of disease. Abdominal fat, central 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 94 cm or less and women 80 cm or less. These figures apply to Caucasians: Asian and Indian people should have smaller waist measurements. Talk to your doctor about what’s appropriate for you.
7. I think I am overweight or obese — what should I do?
If you think you are carrying too much body fat, see your doctor. Your doctor can:
- calculate and interpret your BMI in terms of your body composition to find out if you need to lose body fat, and how much, or whether you need to simply take steps to avoid gaining body fat;
- advise you about which foods to eat, and refer you to a dietitian for further food advice;
- check your health in general and in terms of how your weight may be affecting your health;
- advise you on an exercise programme that is appropriate for your age and health; and
- discuss various weight loss options with you.
8. What can I do to manage excess body fat?
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.
Physical activity.
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.
Healthy eating.
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:
- eat plenty of vegetables, legumes and fruit;
- consume plenty of cereals (preferably wholegrain), including breads, pasta, rice and noodles;
- include lean meat, fish, poultry or other meat alternatives;
- include milk, yogurt, cheese (or non-dairy alternatives), preferably reduced-fat varieties;
- drink plenty of water;
- limit saturated fat, and moderate your total fat intake;
- choose low-salt foods;
- if you drink alcohol, limit your intake; and
- eat only a moderate amount of sugars and foods containing added sugars.
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: 12 February 2007
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