How to measure your Body Mass Index>
Adults: A convenient way for you to assess whether your weight is in the healthy range is by using the Body Mass Index (BMI). Your BMI is calculated by dividing weight in kilograms by height in metres squared. For example, a woman 1.67m in height and weighing 65kg would have a BMI of 23.3 which falls within the healthy weight range. Overweight is measured as 25 or more with obesity determined as 30 or more.
These cut-off points are based on associations between chronic disease and mortality and have been adopted for use internationally by the World Health Organisation.
The classification table below used in conjunction with a BMI calculator can assist you to assess whether you weight is in the healthy range.
BMI is calculated using the following formula:
Weight (kg) divided by [height (m²)]= BMI for adults only.
Risk of co-morbidities
Low (but possibly increased risk of other clinical problems)
Normal range :
18.50 - 24.99
25.00 - 29.99
Obese class 1
30.00 - 34.99
Obese class 2
35.00 - 39.99
Obese class 3
Reproduced from: Obesity: Preventing and Managing the Global Epidemic, 2000, WHO, Geneva.
A person’s waist circumference may be a better predictor of health risk than BMI. Having fat around the abdominal organs and enlarged waist circumference, regardless of your BMI, means you are more likely to develop certain obesity-related health conditions. Fat predominantly deposited around the hips and buttocks does not appear to have the same risk. Men and post menopausal women are at greater risk of excess fat in the waist region.
For most Australians a waist measurement of over 94 centimetres for men and 80 centimetres for women means you are at increased risk of developing a chronic disease.
If your waist measurement is over 102 centimetres for men and 88 centimetres for women, your risk greatly increases.
Having excess weight around your waist is a likely sign of internal fat deposits around your organs. Where your fat is located can be an important sign of your risk of developing an ongoing health problem.
Can Someone With a High BMI Still Be Considered Healthy?
The BMI score is valid for both men and women but it does have some limits. When BMI is used to calculate body fatness:
- It may overestimate body fat in athletes and others who have a muscular build
- It may underestimate body fat in older persons and others who have lost muscle mass.
Therefore, it is possible for a person to be completely healthy but have an "unhealthy BMI." This is why healthcare providers consider other factors besides BMI when assessing the health risk for certain medical conditions.
What factors may affect your weight
While there are many factors involved, an increase in body weight always results from an imbalance between energy intake (food) and energy expenditure (metabolism, thermogenesis and physical activity). An increase in body weight can also result from an increase in muscle mass. This is a consideration for people who participate in regular weight training, and does not reflect unhealthy weight gain.
Why do energy imbalances occur?
While everyone is at risk of at least becoming overweight in the modern ‘obesogenic’ environment, particular factors influence why weight is gained. These include:
- Previous history of weight loss. The effects of weight cycling – frequent large gains and losses – on long term health are unclear, but there are associations between the number of failed weight loss attempts and current body weight, as well as health risks.
- Life Stage. Weight gain is common, although not inevitable, at various life stages – for example, after pregnancy, and during menopause.
- Life events. Certain life events – such as marriage, giving up sport, and quitting smoking – can cause weight gain. Weight gain after quitting smoking can be significant (i.e. 5 kg in the first year). For this reason, instituting a weight management plan at the time of quitting may help reduce the weight gain that normally occurs after quitting.
- Family, work and social environments. Can influence weight gain and the inability to lose weight.
- Genetic influences. Genetic predisposition can influence the amount and rate at which weight is gained and lost.
- Stress. May need to be considered as a factor that can cause either weight gain or weight loss, depending on the person’s reaction to stress.
- Medical conditions. Certain medical conditions, for example, hypothyroidrism, are known causes of overweight.
- Medical treatments. Prescription medications can exacerbate weight gain (in particular, benzodiazepines, corticsteroids, anti-psychotics, tricyclic antidepressants, anti-epileptics, sulphonylureas, and insulin).
What Is the Risk?
Australia has become the fattest nation in the world, with more than 9 million adults now rated as obese or overweight, according to an alarming new report*. The latest figures show 4 million Australians — or 26% of the adult population — are now obese compared to an estimated 25% of Americans. A further 5 million Australians are considered overweight.
*The report, Australia's Future 'Fat Bomb', from Melbourne's Baker IDI Heart and Diabetes Institute.
People who are overweight or obese have a greater chance of developing many medical conditions, including:
- High blood pressure (hypertension)
- High cholesterol or other lipid disorders
- Type 2 diabetes
- Heart disease
- Certain cancers
- Sleep apnea
- Gallbladder disease
- Fatty liver disease.
Even a small weight loss (just 10 percent of your current weight) will help to lower your risk of developing those diseases.
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