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Obesity is measured using body mass index or BMI. This refers to body weight relative to height. If a person's BMI is greater than 25 kg per metre squared, he or she is considered overweight. A BMI greater than 30 kg per metre squared is considered obese.

What is going on in the body? 
The food is made up of kilojoules or units of energy. When a person takes in more kilojoules than the body uses, the extra kilojoules are stored as fat in fat cells. These fat cells enlarge and shrink depending on the balance of energy in the body. When fat cells build up or accumulate, it causes obesity.

What are the signs and symptoms of the condition? 
The signs of overweight or obesity can include:
  • excess body fat
What are the causes and risks of the condition? 
Obesity results from taking in more kilojoules than the body uses. Causes include:
  • unhealthy eating habits
  • inactivity
  • genetics
  • certain medical conditions
  • certain medications
  • compulsive overeating
Obesity puts a person at risk for other health problems, including: Obesity can even lead to an early death. The risk for these problems goes up as the degree of obesity increases.

What can be done to prevent the condition? 
Maintaining normal body weight through healthy eating and other lifestyle habits can have a major impact on the prevention of obesity.

How is the condition diagnosed? 
Obesity is determined by measuring body fat, not just body weight. Two key measures are used to determine if a person is overweight or obese:

Body mass index (BMI) is currently the best measure of body fat. It is a standard "tool" used to judge body weight and the amount of body fat a person has. BMI calculates a weight-to-height ratio and assigns a number to the result. The higher the BMI number above the normal range, the greater the degree of obesity.

Guidelines define overweight as a BMI between 25 and 29.9 and obesity as a BMI greater than 30 kg per metre squared.

The amount of fat around the belly is very important in assessing disease risk. A waist measurement of more than 100cm in men and more than 90cm in women creates increased risk in those who have a BMI between 25 and 34.9 kg per metre squared.

What are the long-term effects of the condition? 
People who are obese for a long time are at increased risk of developing the health problems listed above.

What are the treatments for the condition? 
There are many different treatments available, including untested and unproven therapies.

For many, long-term results from any weight loss program are disappointing. One year after losing weight, about 1/3 to 2/3 of weight is regained. Five years later, almost all of the lost weight is regained.

The most successful strategies for weight loss include:
  • reducing daily kilojoule intake
  • increasing daily physical activity
  • getting counselling to improve eating and physical activity habits
  • reducing the amount of dietary fat in the diet
  • reducing body weight by about 10 % over 6 months
  • losing between 0.5 - 1.0 kg a week
Medications, such as xenical (orlistat) or reductil (albutramine) are also an option.

Lifestyle changes should be tried for at least 6 months before considering medication. There are 2 main classes of drugs used to treat obesity: one class decreases appetite while the other prevents dietary fat from being absorbed. Drugs should only be used under the care of a doctor.

Surgery, which changes the way food is absorbed, is sometimes used to treat obesity. This treatment should be a last resort for people who are severely obese and:
  • have been unable to lose weight after many attempts with diet, exercise, and behaviour change
  • have medical problems that are likely to improve with weight loss
What are the side effects of the treatments? 
Losing weight is not risk-free. Poorly-designed diets increase the risk of vitamin deficiencies. Rapid weight loss can cause nausea, tiredness, weakness, hair loss, and low blood pressure. Dieting can also lead to emotional changes and binge eating. Surgery for weight loss has all the risk of any major surgery. Nutrient deficiencies can also occur if parts of the digestive system are bypassed.

How is the condition monitored? 
The results of treating obesity are often based on the amount of weight lost. While weight loss is important, it should not be the sole factor used to measure success. Other measures of long-term success include:
  • an increase in muscle mass. Because muscle is denser or heavier than fat tissue, body weight may not change
  • centimetres lost
  • improvements in blood pressure
  • improvements in blood sugar control
  • increased mobility
Author: Dr. Karen Wolfe, MBBS, MA
Reviewer: eknowhow Medical Review Panel
Editor: Dr John Hearne
Last Updated: 8/02/2005
Potential conflict of interest information for reviewers available on request

This website and article is not a substitute for independent professional advice. Nothing contained in this website is intended to be used as medical advice and it is not intended to be used to diagnose, treat, cure or prevent any disease, nor should it be used for therapeutic purposes or as a substitute for your own health professional's advice.  All Health and any associated parties do not accept any liability for any injury, loss or damage incurred by use of or reliance on the information.

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