4727.0.55.002 - Australian Aboriginal and Torres Strait Islander Health Survey: Users' Guide, 2012-13  
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Contents >> Health Risk Factors >> Body mass and physical measures

BODY MASS AND PHYSICAL MEASUREMENTS

Definition

This topic refers to respondents' physical measurements and other self-perception questions including:

  • the height (cm), weight (kg), waist circumference (cm), and hip circumference (cm) of respondents as measured during the interview
  • body mass index (BMI) derived from the height and weight physical measurements
  • waist-to-hip ratio derived from the waist and height physical measurements
  • self-perceived assessment of body mass
  • satisfaction with current weight
  • whether they were on a diet and if so what type.

In addition, the NATSIHS collected information on the respondent's satisfaction with their weight, and whether they were on a diet and if so what type.

Body Mass Index (BMI) or Quetelet's index is a useful tool, at a population level, for measuring trends in body weight and helping to define population groups who are at higher risk of developing long-term medical conditions associated with a high BMI, for example Type 2 diabetes and cardiovascular disease.

Waist-to-hip ratio is a complementary measure to BMI, providing a measure of body fat distribution. The scale used for determining risky waist-to-hip ratio is as recommended by the World Health Organisation, (See Waist circumference and waist-hip ratio. Report of a WHO Consultation, 2008).

Waist circumference reflects mainly subcutaneous abdominal fat storage, and according to a World Health Organisation (WHO) joint report has been shown to positively correlate to disease risk. The scale used for determining risky waist circumference is as recommended by the World Health Organisation, (See Obesity: preventing and managing the global epidemic. Report of a WHO Consultation, 2000).

Population

Physical measurements were obtained for all persons, excluding pregnant women, aged 2 years and over in the National Aboriginal and Torres Strait Islander Health Survey (NATSIHS) and the National Aboriginal and Torres Strait Islander Nutrition and Physical Activity Survey (NATSINPAS) who agreed for their measurements to be taken.

Self-perceived body mass and other survey-specific questions were asked of all persons aged 15 years and over.

Methodology

Information about physical measurements were collected in the NATSIHS. Information on physical measurements were published in the First Results publication based on the NATSIHS sample of approximately 8,800 people aged 2 years and over. Updated results on physical measurements for the larger, combined NATSIHS and NATSINPAS sample, known as the Core sample, of approximate 12,900 people aged two years and over was published in the Updated Results publication. For comparison of physical measurements with NATSIHS only items, the NATSIHS file should be used and similarly, for comparison with NATSINPAS only items, the NATSINPAS file should be used. However, for the most accurate information on physical measurements alone or comparison with other items collected in the Core, the Core file should be used. For more information on the structure of the AATSIHS, see the Structure of the Australian Aboriginal and Torres Strait Islander Health Survey page of this Users' Guide.

Physical measurements

Physical measurements were taken towards the end of the survey. All physical measurements were voluntary, and women who had identified they were pregnant were not measured. Interviewers used digital scales to measure weight (maximum 150kg), a stadiometer to measure height (maximum 210cm), and a metal tape measure (which avoided the risk of the tape stretching) to measure waist and hip circumference (maximum 200cm). Thorough interviewer training identified the points at which waist, as recommended by World Health Organisation report, and hip measurements were to be measured, as well as how to take the measurements with the least amount of respondent discomfort. For waist and hip measurements, interviewers held the end of the tape at the appropriate point and asked the respondent to turn around until the tape met, or asked the respondent to hold the end of the tape and walked around them until the tape met.

Interviewers encouraged respondents to remove their shoes and any heavy clothing, e.g. jumpers, before they took measurements, however, this was voluntary, and may not have occurred in some cases. Interviewers were not required to record if they thought clothing may have impacted significantly on measurements. Weight was recorded in kilos to one decimal point, and height, waist and hip measurements were recorded in centimetres to one decimal point. Waist measurements were taken by placing the tape measure across the top of the belly button. Hip measurements were taken by placing the tape measure across the top of the thighs. If a respondent's waist or hip measurement was more than two meters (the maximum measurement of the tape measure), interviewers were instructed to record this as 200.0cm. If a respondent's weight was self-reported to be more than 150 kilograms (the maximum measurement of the scales used) the weight was not recorded.

In order to validate the taken height, waist and hip measurements, a random 10% of respondents were selected to be measured an additional time. If this second measurement of height, waist or hip varied by more than one centimetre then a third reading was taken. Weight measurements were only taken once. For output purposes only the first measurement is used, however, these additional measurements were utilised for validation purposes.

Body Mass Index

Body mass index (BMI) scores were derived using Quetelet's metric body mass index which is calculated as weight (kg) divided by height (m)2. BMI scores are commonly grouped for output. Whilst the cut off points for different ethnic groups can vary, the World Health Organisation recommends that the same cut off points be used for international classification. The detailed output classifications available are shown in the table below. 2012-13 AATSIHS publications use aggregated categories for estimates in published tables.

Category BMI score

Underweight
Class 3 Less than 16
Class 2 16.0 to less than 17.0
Class 1 17.0 to less than 18.5
Normal range
NormalAdult: 18.5 to less than 20.0; Child: 18.5 to less than 25.0(a)
Normal (Adult only)20.0 to less than 25.0
Overweight
25.0 to less than 30.0
Obese
Class 1Adult: 30.0 to less than 35.0; Child: 30.0 or more (a)
Class 2 (Adult only)35.0 to less than 40.0
Class 3 (Adult only)40 or more


(a) Child cut-offs identified in this table are in terms of Adult cut-offs. While the formula to calculate BMI scores is the same for adults and children, the classification of children's BMI is different to that of persons aged 18 years and over, and takes into account individual age and sex. BMI cut-off ranges for children 2 to 17 years of age are included in Appendix 4: Classification of BMI for children. Half-year cut-off points are used to calculate children's BMI scores for persons aged 2 to 17. Two versions of the data item are available, one using the mid-year cut-off and one using the whole-year cut-off.

Waist -to-hip ratio

Waist-to-hip ratio is calculated as waist circumference (cm) divided by hip circumference (cm). The scale used for determining risky waist-to-hip ratio is as recommended by the World Health Organisation, (See Waist circumference and waist-hip ratio. Report of a WHO Consultation, 2008). As with BMI, the cut-off points in this scale are best used for people of European origin, and are not tailored specifically to Aboriginal and Torres Strait Islander people.

Waist-to-hip ratio guidelines, Adults

Not at risk
Increased risk

Males
Less than 0.90
0.90 or more
Females
Less than 0.85
0.85 or more


Waist circumference

Waist circumference reflects mainly subcutaneous abdominal fat storage, and according to World Health Organisation (WHO) joint report has been shown to positively correlate to disease risk. The scale used for determining risky waist circumference is as recommended by the World Health Organisation, (See Obesity: preventing and managing the global epidemic. Report of a WHO Consultation, 2000). As with BMI and waist-to-hip ratio, the cut-off points in this scale are best used for people of European origin, and are not tailored specifically to Aboriginal and Torres Strait Islander people.

Waist circumference guidelines, Adults

Not at risk
Increased risk
Substantially increased risk

Males
Less than 94 cm
94 cm or more
102 cm or more
Females
Less than 80 cm
80 cm or more
88 cm or more



Hip circumference

Hip circumference has not been collected in previous NATSIHS surveys, but was included in the 2012-13 NATSIHS. Several smaller scale studies have consistently found that the body fat distribution for Aboriginal Australians is significantly different to the general Australian population. This is characterised by excess central weight deposition in Aboriginal people in relation to their weight (Kondalsamy-Chennakesavan, Hoy, and Wang et al 2008; Piers, Rowley, Soares & O'Dea 2003; Rutishauser and McKay 1986). For example, there is evidence to suggest that Aboriginal males and females are less likely to be classified as overweight than the general Australian population using BMI, but more likely to be classified as overweight using waist-hip ratio (Piers, Rowley, Soares & O'Dea 2003). People with a greater concentration of fat around their stomach have an increased risk of developing certain chronic diseases such as Type 2 diabetes and heart disease. The significance of central fat disposition as a risk factor may not be fully captured using BMI data based on height and weight only.

Self-perception questions

Respondents were asked whether they considered themselves to be:
  • acceptable weight (remote - just right)
  • underweight (remote - too skinny)
  • overweight (remote - too fat).

This question was not asked where:
  • a female had previously identified themselves as currently pregnant (or raised it at this point)
  • a proxy was being used for a respondents aged 15-17 years
  • where a proxy was being used for an adult interview and the respondent was not present.

Respondents were also asked whether they were on any kind of diet to lose weight or for some other health related reason. If they answered yes to being on a diet they were asked about the kind of diet(s) they were on:
  • weight loss or low calorie diet
  • low fat or cholesterol diet
  • low salt or sodium diet
  • sugar free or low sugar diet
  • low fibre diet
  • high fibre diet
  • diabetic diet
  • low carbohydrate diet
  • high protein diet
  • weight gain diet
  • other.
Some examples of ‘other’ diets include: Low GI, high carbohydrate, low protein and medical restrictions on specific foods.

All respondents were then also asked how satisfied they were with their current weight:
  • very satisfied
  • satisfied
  • neither satisfied nor dissatisfied
  • dissatisfied
  • very dissatisfied.

Note that in remote areas the words satisfied and dissatisfied were replaced with happy and unhappy.

Data items

The data items and related output categories for this topic are available in Excel spreadsheet format from the Downloads page of this product.

Interpretation

Points to be considered when interpreting data for this topic include the following.
  • BMI was only calculated for persons for whom height and weight were measured and waist-to-hip ratio for persons aged 18 years and over for whom waist and hip were measured. For 2012-13, 82.2% of respondents aged 2 years and over had their height and weight measured. This comprises 76.9% of children aged 2-17 and 85.3% of respondents 18 years and over who had their height and weight measured. 79.6% of respondents aged 2 years and over had their waist and hip measured. This comprises 75.0% of children aged 2-17 and 83.6% of respondents 18 years and over who had their waist and hip measured. The results presented as part of the AATSIHS relate to the measured population only. Analysis of the characteristics of people who agreed to be measured compared to those who declined indicated that age, state, employment status, and remoteness were all predictors of response. Non-remote and Victorian respondents were more likely to decline, as were those not in the labour force. Non-response was also greater among those under 18 than in adults, however this may reflect these respondents having a proxy represent them (100% of 0-14 year olds and 37.3% of 15-17 year olds) and whether or not the child was present for the interview.
  • While BMI is a useful tool to assess and monitor changes in body mass at the population level, it may be an inappropriate measure of the body fatness of certain populations and certain individuals; for example, those whose high body mass is due to muscle rather than fat, or those with osteoporosis who have lower than usual BMI. BMI can, however, be used in conjunction with waist and hip circumference or waist to hip ratio, which are other indicators for people at risk. Analysis of the AATSIHS results showed that the patterns for BMI, waist circumference and waist to hip ratio were all very similar at the population level.
  • For the most part, body mass questions were not asked where a proxy was responding on behalf of the respondent. However, where items have been asked of a proxy some care should be used.
  • The questions on current diet are based on self-reported diet information. Respondents may not be aware of the purpose of their diet when for medical reasons, and one diet may be reported under multiple diet types.

Comparability with 2004-05 National Aboriginal and Torres Strait Islander Health Survey (NATSIHS)

The 2004-05 survey only collected self-reported height and weight measurements. If a remote respondent could not recall their measurements and consented to being measured these measurements were then undertaken as part of the interview, however this was only a subset of the remote population. As a result, data is not directly comparable to the 2012-13 survey due to the difference in the collection methodology and the possible erroneous estimation of respondents self-reported measurements in 2004-05. Furthermore, no waist or hip measurements were collected in 2004-05.

When making comparisons on the self-perceived assessment of body mass it should be noted that the 2004-05 survey did not collect any data on whether the respondent was currently on a diet to lose weight or for some other health related reason. However, data about whether the respondents consider themselves as an acceptable weight, underweight, overweight was collected for 15 year olds and over and is directly comparable to 2012-13. Simplifications of the wording for the remote survey in 2004-05 are not expected to impact comparability. It should also be noted that in 2012-13, the self-perceived assessment of body mass questions were not asked of those represented by a proxy, thus 96% of the population aged 15 years or over responded to the module, while 100% responded in 2004-05.

Comparability with 2011-12 Australian Health Survey (AHS)

Data collected on measured height, weight and waist circumference in the 2012-13 AATSIHS used the same methodology and equipment as the 2011-12 AHS. Neither survey collected self-reported measurements therefore the two are directly comparable. However, hip measurements were not collected in 2011-12 AHS and thus cannot be compared to the 2012-13 AATSIHS results. It should also be noted that in 2011-12 AHS, 82.8% of respondents aged 2 years and over had both their height and weight measured compared to 82.2% in 2012-13 AATSIHS.

When making comparisons on the self-perceived assessment of body mass it should be noted that the 2011-12 NHS collected additional data on whether the respondents' weight had increased in the last year; decreased; or stayed about the same which was not collected in the 2011-12 NNPAS, 2012-13 NATSIHS or 2012-13 NATSINPAS. In the 2011-12 NHS no data was collected on whether the respondent was currently on a diet to lose weight or for some other health related reason or satisfaction with current weight, however these were collected in and are comparable to the 2011-12 NNPAS. Categories used to collect information for satisfaction with current weight were different in remote to non-remote and 2011-12 NNPAS but is not expected to affect comparability. This is also the case for self-perceived body mass, however comparability with 2011-12 AHS is still considered suitable.

References

Kondalsamy-Chennakesavan, S, Hoy, WE, Wang, Z, Briganti, E, Polkinghorne, K, Chadban, S, Shaw, J; AusDiab Study Group 2008, Anthropometric measurements of Australian Aboriginal adults living in remote areas: comparison with nationally representative findings, American Journal of Human Biology, May-Jun;20(3):317-24.

Piers, LS, Rowley KG, Soares, MJ, O'Dea, K 2003, Relation of adiposity and body fat distribution to body mass index in Australians of Aboriginal and European ancestry, European Journal of Clinical Nutrition, Aug;57(8):956-63.

Rutishauser, IH, McKay, H 1986, Anthropometric status and body composition in Aboriginal women of the Kimberley region, Medical Journal of Australia, June 23;144 Suppl:S8-10.


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