About Overweight and Obesity

Specific information on overweight and obesity is provided, including: prevalence of overweight and obesity; how overweight and obesity is defined; calculate your BMI (for adults only); causes of overweight and obesity; health consequences; economic consequences.

Page last updated: 26 May 2009

For specific information on overweight and obesity click on the topic areas listed below or scroll down the page:

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Prevalence of overweight and obesity in Australia

The rates of overweight and Obesity amongst adults have doubled over the past two decades with Australia now being ranked as one of the fattest developed nations.

Children and Adolescents

Around 20-25% of Australian children in 1995, aged 7-15 years were considered to be overweight or obese. This is double the prevalence recorded in 19861.

Adults

In 2004-05, some 41% of males and 25% of females were classified as overweight (Body Mass Index of between 25.0 and 30.0). 18% of males and 17% of females were classified as obese (Body Mass Index over 30.0)2. When compared to results from 1995, using the same measure, the proportion of adults classified as overweight or obese has increased substantially. In 1995, 38% of males and 21% of females were classified as overweight and 11% of males and 11% of females were classified as obese2. For both males and females, increases have been recorded in both the overweight and obese groups across all age groups2.

Older Australians

In 2004-05, 46% of males between the ages of 55-64, 41% of males between the ages of 65-74 and 37% of males aged 75 years and over, were classified obese2. For females, 31% between the ages of 55-64, 31% between the ages of 65-74 and 25% aged 75 years and over, were classified as overweight, while 23%, 17% and 10% respectively, were classified as obese2. These figures suggest that since 1995, the rates of overweight within each age category have remained relatively consistent, however the rates of obesity have increased. For example, in 1995, 45% of males between the ages of 55-64, 40% of males between the ages of 65-74 and 31% of males aged 75 years and over, were classified as overweight, while 15%, 11% and 5% respectively were classified as obese2. For females, 30% between the ages of 55-64, 26% between the ages of 65-74 and 21% aged 75 years and over, were classified as overweight, while 16%, 14% and 7% respectively, were classified as obese2. Top of Page

How overweight and obesity are defined

Adults

Overweight and obesity is measured at the population level for adults using the Body Mass Index (BMI) which 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 at a BMI of 25 or more with obesity determined at a BMI of 30 or more. These cut-off points are based on associations between and chronic disease and mortality and have been adopted for use internationally by the World Health Organisation. Following is this classification table and also a calculator.

Classification of adults according to

Classification

BMI

Risk of co-morbidities

Underweight <18.50 Low (but risk of other clinical problems increased)
Normal range 18.50 - 24.99 Average
Overweight: >25.00
Preobese 25.00 - 29.99 Increased
Obese class 1 30.00 - 34.99 Moderate
Obese class 2 35.00 - 39.99 Severe
Obese class 3 >40.00 Very severe


Reproduced from: Obesity: Preventing and Managing the Global Epidemic, 2000, WHO, Geneva Top of Page

Calculate your BMI (for adults only)

Height: m (example - 1.75m)

Weight: kg

Your BMI:




Fat distribution is also an important consideration in assessing overweight or obesity and the associated risk of disease. For example, increased abdominal obesity has been consistently shown to be related to a higher risk of cardiovascular disease, type 2 diabetes and cancer. Central (abdominal) obesity is measured using waist circumference. The following table provides sex specific waist circumference and risk of metabolic complications associated with obesity in Caucasians.

Sex-specific waist circumference and risk of metabolic complications associated with obesity in Caucasians

Risk of metabolic complications

Waist circumference (cm)

 
Men Women
Increased > or = 94 > or = 80
Substantially increased > or = 102 > or = 88


Reproduced from: Obesity: Preventing and Managing the Global Epidemic, 2000, WHO, Geneva. As the relationship between waist circumference and body fat differs with age and between ethnic groups, the above cut-off points are only suitable for Caucasians. For example, cut-off points for Asians for the same level of risk would be lower than those above, and higher for say Pacific Islanders.

Children

For children and adolescents, Australian standard definitions for measuring overweight and obesity at the population level were endorsed in December 2002 for inclusion in the 12th edition of the National Health Data Dictionary. In children, changes substantially with age, rising steeply in infancy, falling during the preschool years and then rising again during adolescence and early adulthood. For this reason, child and adolescent is classified differently to adult. There are also separate recommendations for measuring weight individually in clinical practice for children and adolescents. The Australian standard definitions are based on the work of Cole et al3 and will assist in more accurate monitoring and surveillance of overweight and obesity in children and adolescents at the population level and also to assess the effectiveness of intervention and prevention strategies. At the population level, overweight and obesity in children and adolescents is determined by comparing calculated (weight/ height2) against the relevant age and sex of the child/adolescent in Table 1: Classification of for children and adolescents. For example, an 11 year old boy with a calculated of 21 would be considered overweight while a 7 year old girl with a of 17.5 would be considered not to be overweight or obese. The above calculator can be used to determine calculated which should then be compared with the chart below for classification of children and adolescents.

Table 1: Classification of overweight and obesity for children and adolescents

Age (years)

BMI equivalent to 25 in adult

BMI equivalent to 30 in adults

Males

Females

Males

Females

2

18.41

18.02

20.09

19.81

2.5

18.13

17.76

19.80

19.55

3

17.89

17.56

19.57

19.36

3.5

17.69

17.40

19.39

19.23

4

17.55

17.28

19.29

19.15

4.5

17.47

17.19

19.26

19.12

5

17.42

17.15

19.30

19.17

5.5

17.45

17.20

19.47

19.34

6

17.55

17.34

19.78

19.65

6.5

17.71

17.53

20.23

20.08

7

17.92

17.75

20.63

20.51

7.5

18.16

18.03

21.09

21.01

8

18.44

18.35

21.60

21.57

8.5

18.76

18.69

22.17

22.18

9

19.10

19.07

22.77

22.81

9.5

19.46

19.45

23.39

23.46

10

19.84

19.86

24.00

24.11

10.5

20.20

20.29

24.57

24.77

11

20.55

20.74

25.10

25.42

11.5

20.89

21.20

25.58

26.05

12

21.22

21.68

26.02

26.67

12.5

21.56

22.14

26.43

27.24

13

21.91

22.58

26.84

27.76

13.5

22.27

22.98

27.25

28.20

14

22.62

23.34

27.63

28.57

14.5

22.96

23.66

27.98

28.87

15

23.29

23.94

28.30

29.11

15.5

23.60

24.17

28.60

29.29

16

23.90

24.37

28.88

29.43

16.5

24.19

24.54

29.14

29.56

17

24.46

24.70

29.41

26.69

17.5

24.73

24.85

29.70

29.84

18

25.00

25.00

30.00

30.00



In health care settings such as hospitals, clinics and in general practice, it is recommended that calculated for children and adolescents be compared with a suitable growth reference such as the US Centers for Disease Control 2000- for-age chart. A greater than the 85th percentile is indicative of being overweight, while a greater than the 95th percentile is indicative of being obese. These percentiles are arbitrary and do not relate to morbidity as the cut-points do in adults. These charts are available on the CDC website at: http://www.cdc.gov/growthcharts/ For these reasons it is recommended that changes over time will provide more meaningful information and should be assessed for all children and adolescents as part of routine primary care. Top of page

What causes overweight and obesity?

Aside from genetic factors, overweight and obesity is caused by an energy imbalance, where energy intake exceeds energy expenditure over a considerable period of time. Hence good nutrition and adequate levels of physical activity play an important role in the prevention of further weight gain throughout the life cycle. It is generally agreed that this energy imbalance is due to large scale changes in the modern environment.

Children

In children there is evidence that factors early in life have the potential to contribute to the development of obesity later in life. These include poor intrauterine nutrition, low birth weight, absence of breastfeeding, the period of adiposity rebound that occurs between ages 5 and 7, timing of maturation as well as levels of physical activity and diet in childhood. Top of page

Health consequences of overweight and obesity

The health problems and consequences of obesity are many and varied, including musculo-skeletal problems, cardiovascular disease, some cancers, sleep apnoea, type 2 diabetes, and hypertension to name a few. Many of these are often preventable though a healthy and active lifestyle. In particular, obesity is strongly linked to type 2 diabetes, identified as one of the six National Health Priority Areas. There are several new large well conducted studies that have shown a clear relationship between excessive body weight and increased mortality and morbidity. Mortality and morbidity are also associated with the amount of weight gained in adult life. For example, a weight gain of 10kg or more since young adulthood is associated with increased mortality, coronary heart disease, hypertension, stroke and type 2 diabetes.

Diseases associated with obesity

Relative risk Associated with metabolic
consequences

Associated with weight

Greatly increased

Type 2 diabetes
Gall bladder disease
Hypertension
Dyslipidaemia
Insulin resistance
Atherosclerosis
Sleep apnoea
Breathlessness
Asthma
Social isolation/depression
Daytime sleepiness/fatigue

Moderately increased

Coronary heart disease
Stroke
Gout/hyperuricaemia
Osteoarthritis
Respiratory disease
Hernia
Psychological problems

Slightly increased

Cancer (breast, endometrial, colon)
Reproductive abnormalities
Impaired fertility
Polycystic ovaries
Skin complications
Cataract
Varicose veins
Musculo-skeletal problems
Bad back
Stress incontinence
Oedema/cellulitis

Children

With respect to children, the most important long term consequence of childhood obesity is its persistence into adulthood. Obesity is more likely to persist when its onset is in late childhood or adolescence and where children have obese parents. There is now epidemiological evidence to support the theory that the association between obesity and disease begins early in life.

Immediate adverse health problems Psychological dysfunction
Social isolation
Body dissatisfaction possibly leading to eating disorders
Asthma

Adverse health outcomes which may develop in the short term

Gastrointestinal disorders, cardiovascular,
endocrine and orthopaedic problems
Reproductive system abnormalities
Menstrual abnormalities
High intra-abdominal adipose tissue
Type 2 diabetes
Hypertension
High cholesterol

Adverse health outcomes which may develop in the intermediate term

High prevalence of cardiovascular disease
risk factors
Tracking of cardiovascular mortality and
morbidity into adulthood
High level of C-reative protein (may lead to coronary heart disease)


Adapted from: Booth M, Baur L & Denny Wilson E, Report to the Commonwealth on Australian standard definitions for child and adolescent overweight and obesity. Problems associated with excess weight in children and adolescence include such things as heat intolerance, breathlessness on exertion, tiredness, and flat feet. Top of page

Economic consequences

Several studies have attempted to estimate the costs of obesity to the community. In the USA, direct costs of obesity have been estimated to be around 9% of the total health care costs and in Europe, between 1% and 5%. Updated estimates for Australia by S Crowley (unpublished) in 1995/6 suggest that the true costs of obesity may be between $680 - $1239 million. Prior to this however, the Australian Institute of Health and Welfare (AIHW) and the Centre for Health Program Evaluation (CHPE) have estimated that the direct cost of obesity in Australia in 1989-90 was $464 million. This is around 2% of Australia’s total health care costs. Indirect costs (value of production lost to premature death and absenteeism) were further estimated to be another $272 million, bringing the total cost in 1989-90 to $736 million. This estimate should be considered conservative because not all obesity-related conditions were included in the analysis. The costs of obesity treatment outside the formal health care system were not included in the analysis. For example, the consumer costs of attending weight control centres in 1989-90, estimated to be more than $500 million a year, were not included. It should be noted however, that because of its close relationship to morbidity and disability, obesity will significantly increase the number of years that an individual suffers from ill health and may add much more to indirect as well as direct costs. Importantly, the escalating cost of health care with progression of an obesity related disorder, such as diabetes, has been calculated as almost doubling over time with normal progression of the disease. This suggests that the economic burden is not only significant, but is likely to get worse even if there is no further growth in the prevalence of obesity. Overseas studies have found that obese persons attain lower levels of occupational prestige (and lower incomes) than non-obese persons. In addition, other studies have found that obese persons as a group receive more sickness and unemployment benefits than persons within a normal weight range.

1 Magarey AM, Daniels LA & Boulton JC 2001. Prevalence of overweight and obesity in Australian children and adolescents: reassessment of 1985 and 1995 data against new standard international definitions. Medical Journal of Australia 174: 561-564.

2 Australian Bureau of Statistics. National Health Survey 2004-05: Summary of results. ABS cat.no. 4364.0. Canberra:ABS

3 1 Cole TJ. The LMS method for constructing normalised growth standards. European Journal of Clinical Nutrition, 1990, 44:45-60.