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OVERWEIGHT AND OBESITY
In 2004–05, more than half (54%) of all adults, or 7.4 million people aged 18 years and over were either overweight or obese, an increase from 45% (5.4 million adults) in 1995. Using age standardised data, the rate of overweight adults has increased from 33% in 1995 to 36% in 2004–05, while the rate of obesity in adults has increased from 13% to 18% over the same period. Each of the National Health Surveys conducted since 1995 has reported a higher rate of overweight and obesity for males than for females.
ADULTS IN NORMAL, OVERWEIGHT AND OBESE BMI(a) CATEGORIES(b)
OBESITY IN ADULTS
Rates of overweight and obesity vary depending on age and sex. Between 1995 and 2004–05, rates of obesity increased for both men and women across all age groups. For men, the largest increase in the obesity rate occurred in the 35–44 age group which almost doubled from 12% in 1995 to 23% in 2004–05. For women, the increase in the obesity rate was more uniform across age groups.
Although the National Health Surveys collect data at one point in time, it is possible to observe changes over time in the obesity rate for a cohort of people born in the same ten year period. In this approach, for example, survey respondents aged 25–34 years in 1995 and those aged 35–44 years in 2004–05, while not the same respondents, are seen as representing the same group of people as they age ten years. Among the male cohorts, the greatest increase in the rate of obesity occurred for the group aged 25–34 in 1995 (12% in that year compared to 23% ten years on, in 2004–05).
For females, the greatest increase in the obesity rate occurred for the cohort aged 35–44 years in 1995, with 12% classified as obese compared to 20% of the 45–54 year olds representing the same group of people in 2004–05.
There were smaller increases in older women, with 18% of those aged 55–64 years classified as obese in 1995, compared to 22% of 65–74 year olds representing the same cohort in 2004–05. For men, rates over the ten year period were similar, with 16% of males aged 55–64 classified as obese in 1995, and 17% of 65–74 year olds classified as obese ten years later.
OBESE ADULTS BY AGE
The NHS can provide insight into associations between certain sociodemographic characteristics and excess weight. As some of these populations have differing age structures, the proportions presented in this section are age standardised to remove the confounding influence of age.
Most people born overseas are in good health on arrival in Australia due to the rigorous health checks they undergo to be eligible for migration. This 'healthy migrant effect' generally wanes as their length of time in Australia increases, and time since migration is an important factor in excess weight in migrants. (Endnote 6)
In 2004–05, the overall adult obesity rate was 18%. People born overseas who arrived before 1996 had a slightly lower age standardised rate of obesity (15%), while the rate was even lower (11%) for more recent arrivals (between 1996 and 2005).
Adults with a degree, diploma or higher qualifications were less likely to be obese than those with other or no post-school qualifications. In 2004–05, around one-fifth (21%) of those without a non-school qualification, and 19% of those with other non-school qualifications (i.e. trade certificate), were classified as obese. By comparison, 13% of those with a degree/diploma or higher qualification were classified as obese.
While equal proportions (53%) of people in low income and high income households were overweight or obese in 2004–05, those in low income households were more likely to be obese. Around one-fifth (21%) of adults in low income households were obese compared with 15% of adults in high income households.
The Socio-Economic Indexes for Areas (SEIFA) Index of Disadvantage summarises various attributes (such as income and unemployment) of an area in which a population lives. In 2004–05, adults living in areas of greatest relative disadvantage had a higher age standardised rate of obesity (22%) compared to adults living in areas with the lowest relative disadvantage (13%).
Aside from socioeconomic differences between areas in terms of education, income and employment, some areas may also offer greater opportunities for physical activity and greater access to healthy food options. (Endnote 8)
In 2004–05 the rate of obesity in Outer Regional/remote/very remote areas was 23%, while in Major Cities and Inner Regional areas the rates were 17% and 19% respectively. The rate of overweight was similar across the remoteness areas (36% in Outer Regional/remote/very remote areas of Australia, compared with 35% in Major Cities).
AGE STANDARDISED SOCIOECONOMIC CHARACTERISTICS(a) OF ADULTS AND BMI(b) — 2004–05
PERCEPTIONS OF OWN WEIGHT
For many people, particularly men and older women, self perception of 'acceptable weight' differs from the standard BMI definitions. This may have implications for the management of healthy body weight in adults. (Endnote 9) In 2004–05, more than half of adults (63% of males and 59% of females) considered themselves to be of acceptable weight. The proportion of males (32%) and females (38%) who considered themselves to be overweight was considerably lower than those who were classified as overweight/obese according to their BMI (62% and 45% respectively).
Between 1995 and 2004–05, after adjusting for differences in the age structure of the population, the proportion of people in the overweight and obese BMI categories who considered themselves to be of acceptable weight increased. In 2004–05, almost half (47%) of males and around one-fifth (21%) of females who were overweight or obese considered themselves to be of acceptable weight. This compares with age standardised rates of around one-third (35%) for males and 12% for females in 1995.
PERCEPTIONS OF WEIGHT — 2004–05
HEALTH RISK BEHAVIOURS AND RELATIVE PREVALENCE OF LONG TERM CONDITIONS
Being overweight (i.e. BMI of 25 or more) is a modifiable risk behaviour for a number of long term health conditions, including a number of National Health Priority Area (NHPA) conditions, such as diabetes, arthritis and some cancers. (Endnote 10) It is also associated with a range of other NHPA risk factors, such as high blood pressure and high blood cholesterol.
In the following analysis, we include data on two modifiable risk behaviours: physical inactivity and overweight and obesity. In 2004–05, 9.4 million adults (68%) had at least one of these two risk factors. Around 2.5 million adults (18%) were both physically inactive as well as either overweight or obese.
As the number of risk factors a person has for a particular condition increases, so does the risk of developing that condition. (Endnote 11) Again, while it is not possible to infer causality using the NHS, adults who had at least one of these two risk factors were, on average, more likely to have certain conditions than those without either of these risk factors. These conditions include high blood pressure, Type II diabetes and high cholesterol. Adults who were classified as overweight or obese and physically inactive were almost three times as likely (2.9 times) to have Type II diabetes, almost twice as likely to have high blood pressure (1.9 times) and 1.5 times more likely to have Ischaemic heart disease than those without either of these risk factors.
The relationship between health risk factors and long term conditions is further reflected in how people tend to rate their overall health. In 2004–05, half (50%) of adults who were either overweight or obese also rated their health as excellent or very good, while 19% considered their health to be fair or poor. This compares to 63% of adults in the normal BMI category who considered themselves to be in excellent or very good health, and 12% who considered their overall health to be fair or poor.
OVERWEIGHT AND OBESITY AND PHYSICAL ACTIVITY: ASSOCIATION WITH SELECTED CONDITIONS(a) — 2004–05
1 World Health Organisation 2003, Obesity and Overweight: WHO Global Strategy on Diet, Physical Activity and Health,WHO, Geneva.
2 Department of Health and Ageing 2002, About Overweight and Obesity, DoHA, Canberra.
3 Access Economics 2006, The Economic Costs of Obesity, Access Economics, Canberra.
4 Department of Health and Ageing 2006, Australian better health initiative: Promoting good health, prevention and early intervention, DoHA, Canberra.
5 Australian Bureau of Statistics 1995, How Australians Measure Up, cat. no. 4359.0, ABS, Canberra.
6 Australian Institute of Health and Welfare 2004, Australia's Health 2004, cat. no. AUS 44, AIHW, Canberra.
7 Booth, M, Okely, AD, Denney-Wilson, E, Yang, B, Hardy, L and Dobbins, T 2006, NSW Schools Physical Activity and Nutrition Survey (SPANS) 2004, NSW Department of Health, Sydney.
8 King, T et al. 2005, 'Weight and place; a multilevel cross sectional survey of area-level disadvantage and overweight and obesity in Australia' International Journal of Obesity, pp 1–7, viewed 11 May 2007, http://eprints.infodiv.unimelb.edu.au/archive/00002568/
9 Donath, S 2000, 'Who's overweight? Comparison of the medical definition and community views', Medical Journal of Australia, vol.172, no. 8, pp. 375–377.
10 Australian Institute of Health and Welfare 2006, Risk factors, viewed 24 April 2007, http://www.aihw.gov.au/nhpa/riskfactors/index.cfm.
11 Australian Institute of Health and Welfare 2006, Chronic Diseases and Associated Risk Factors in Australia, 2006, cat. no. PHE 81, AIHW, Canberra.
12 Australian Bureau of Statistics 2004–05 National Aboriginal and Torres Strait Islander Health Survey, ABS, Canberra.
Data sources and definitions
Data in this article are mainly drawn from the 1995, 2001 and 2004–05 National Health Surveys (NHS), and refer to adults aged 18 years and over.
In the NHS, overweight and obesity are assessed using body mass index (BMI), calculated from self-reported height and weight information, using the formula weight (kg) divided by the square of height (m). To produce a measure of the prevalence of overweight or obesity in adults, BMI values were grouped according to the following categories: Underweight (BMI less than 18.5), Normal (BMI 18.5 to less than 25.0), Overweight (BMI 25.0 to less than 30.0) and Obese (BMI 30.0 and greater). BMI rates calculated in this article include persons whose BMI was underweight, but excludes persons whose BMI was not stated or not known.
While BMI is a useful tool for assessing changes in body mass at the population level, it may be less appropriate for certain individuals. For example, it does not account for those with high body mass due to muscle rather than fat.
Self-reported height and weight may also differ from measured height and weight. In 1995, a comparison of these two methods suggested that when self-reporting, people tend to overstate their height and understate their weight. For further details, see How Australians Measure Up,1995 (ABS cat. no. 4359.0). (Endnote 5)
To account for any variations in age structure of the population over time as well as between certain sub-populations, rates and proportions are age standardised to the 2004–05 total NHS population where applicable.
Between 1995 and 2004–05, the average weight (kg) of both male and female adults increased across all age groups. During this period, the average weight of an adult female increased from 65kg to 68kg, and for males it increased from 80kg to 84kg.
Men appear to be getting heavier at an earlier age. In 1995, the average weight for males peaked in the 45–54 years age group (82kg). By 2004–05 average weight was greatest in the 35–44 years group (87kg) which was 6kg more than for this age group in 1995. For women, the increases in average weight were similar across all age groups.
Overweight and obesity in NSW children
The 2004 NSW Schools Physical Activity and Nutrition Survey (SPANS) provides insight into overweight and obesity in children aged 5 to 16 years in NSW. Almost 5,500 school-aged children from ages 5 to 16 years were surveyed and measured for height and weight. BMI in childhood changes substantially with age, thus children were defined as healthy, overweight or obese using age and gender-appropriate categories recommended by the International Obesity Taskforce. (Endnote 7)
Overall, 25% of boys and 23% of girls were either overweight or obese. For boys, the rate of overweight and obesity was related to age, reaching a peak in 11–12 year olds (22% of this group classified as overweight and 9% classified as obese) before declining again. For girls, the highest rates of overweight and obesity was in 9–10 year olds, with 22% of this age group classified as overweight and 8% classified as obese. (Endnote 7) See the NSW Schools Physical Activity and Nutrition Survey (SPANS) 2004: Full Report for further information.
Overweight and obesity among Aboriginal and Torres Strait Islander adults
As with the NHS, height and weight measurements were collected in the 2004–05 National Aboriginal and Torres Strait Islander Health Survey (NATSIHS).
After adjusting for non-response, just over one-third (35%) of Indigenous people aged 18 years and over were recorded as being in the normal or healthy weight range in 2004–05 based on BMI measures, with a further 29% in the overweight category and 31% classified as obese. The proportion of Indigenous adults in non-remote areas who were overweight or obese in 1995 was 51% increasing to 60% in 2004–05.
When differences between the age structures of the Indigenous and non-Indigenous populations are taken into account, Indigenous adults were 1.2 times more likely to be overweight or obese than non-Indigenous adults. The disparity between Indigenous and non-Indigenous rates of overweight and obesity was greater for females than for males. (Endnote 12)