Asia Pacific J Clin Nutr(1995)4: 69-72

Body composition in Aboriginal Australians

Ingrid HE Rutishauser

School of Nutrition and Public Health, Deakin University, Victoria, Australia.

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The anthropomorphic features of Australian Aborigines have been described, measured and reported in considerable detail by explorers, anthropologists, anatomists and medical practitioners. These reports have provided evidence that some aspects of Aboriginal physique differ considerably from those of Europeans. For example, it has been reported that Australian Aborigines of both sexes have relatively shorter trunks and longer legs than almost every other ethnic group, that body proportions differ less between males and females, and that traditionally Australian Aborigines had a lower weight for stature than Europeans of the same age and sex.

Less information exists on their body composition. Available data, however, indicate that there may also be differences in body fat distribution, but not in the amount of fat-free mass (FFM) per unit of stature, between Australian Aborigines and Australians of European origin

An analysis of the available data on body composition suggests that the very low body mass index (BMI) values observed in apparently healthy Aborigines, and the different relationship in this ethnic group between BMI and the amount of subcutaneous fat, are more likely to be due to a more central body fat distribution than to differences in skeletal body proportions between Australian Aborigines and Australians of European

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lntroduction

The anthropomorphic features of Aboriginal Australians have been described, measured and reported in considerable detail since the time when European explorers and colonial voyagers first established contact with the indigenous peoples of the Australian continent. Captain Cook, for example, is said to have reported that the stature of Aborigines is about the same as that of Europeans. Other aspects of their physique, however, have been reported to differ considerably from those of Europeans. Abbie^l, for example, describes Australian Aborigines as having a long head and face, high, narrow shoulders, slim trunk, slender hips, thin arms, long thin legs and long, slender hands and feet with correspondingly long and slender bones. Figure 1, from Abbie², illustrates these differences in physical proportions between Europeans and Aboriginal males and females. The most obvious features of this diagram are that the inferior extremities appear to be relatively much longer in Australian Aborigines and that differences in the physical proportions of men and women appear to be less marked in Australian Aborigines than in Europeans.

Figure 1. Relative body proportions of European and Njalia males and females based on the same vertical and horizontal scale (Source: Abbie, 1957)²

Anthropometric measurements, as distinct from observations, became the subject of numerous reports by anthropologists, anatomists and medical practitioners working in remote areas in the first two decades of the twentieth century. They continued to be a major component of anthropological studies until the late 1960s when improved communications, new biochemical techniques and portable refrigeration facilities shifted the focus of interest to clinical and biochemical studies in Aboriginal populations.

Abbie³, describing physical data collected on full-blood Aborigines of both sexes and all ages in the course of 10 expeditions between 1951 and 1963, refers to 40 anthropometric measurements, and 30 indices derived from them, in addition to measurements of blood pressure, dental status and skinfold thickness. The main purpose of collecting this huge array of anthropometric measurements was to determine 'whether the Aborigines in the various regions and groups differ significantly in physical characters or whether they are sufficiently alike to warrant the conclusion that they are physically homogeneous'. From our perspective this is an important question since it determines whether a discussion of body composition in Australian Aborigines needs to consider the possibility of differences between groups resident in different parts of the continent. At the time that Abbie was writing, two basic hypotheses of the origin of Australian Aborigines were in contention. The first of these was that Aborigines are a racially homogeneous group. The second that Australian Aborigines are the product of two or more racial groups which met and mixed on the Australian continent.

Abbie's conclusion, based on his and other's data, was that they are a physically homogeneous group³. In contrast, other anthropologists, such as Birdsell⁴, came to a different conclusion based on essentially the same broad body of anthropometric data.

Indices of body proportions

Relative shoulder breadth and relative sitting height, together with the ratio of weight to stature, were considered to be the indices which most specifically characterized the differences in Aboriginal physical proportions from those of Europeans. With the exception of weight for stature these indices are measures of skeletal proportions both in the vertical (relative sitting height) and in the horizontal plane (relative shoulder breadth) and in so far as they may lead to differences in the amount of bone as a proportion of the fat-free mass (FFM) they are relevant to our discussion of ethnic differences in body composition. In order to provide some perspective on the differences in these indices, between Australian Aboriginal groups measured 50 years ago and those observed in contemporary groups of Australian Aborigines and Australians of European origin, we have compared the range of values recorded in the literature⁵ for Aborigines with the mean values observed in Birdsell's data⁴ for Aborigines as a group and for various sub-groups considered to show distinct physical features as well as for a contemporary group of Aborigines from the Kimberley region of Western Australia and a group of Australian males of European origin. Figure 2 compares the range of values for relative sitting height and Fig 3 the range of values for relative shoulder breadth. What is clear from both figures is firstly that a wide range of values for both these measures has been reported, in the literature, for Australian Aborigines and secondly that differences in mean values between Aboriginal groups in different parts of the country, and at different times, are as great as those between a contemporary group of Australian Aborigines and Australians of European origin. All that can be said from these figures is that the mean values for adult male Australians of European origin tend to lie at the upper end of the range of values observed in Aboriginal Australians. If the picture is similar in adult females it is unlikely that there are major differences in the composition of the FFM, arising from differences in body proportions, between Australian Aborigines and Australians of European origin.

Figure 2. Relative sitting height of adult males in groups of Aboriginal Australians and in Australians of European origin.

Figure 3. Relative shoulder breadth of adult males in groups of Australian Aborigines and in Australian of European origin.

Figure 4. Weight for the same height and age in Arnhem Land Aborigines and white Australian males and females aged 11-50 years (Source: Billington, 1956)⁶.

Anthropometric assessment of body composition

What then do we know about the body composition of Australian Aborigines? In the past Australian Aborigines have generally been described as lean with minimal subcutaneous fat. Billington⁶, reporting on the height and weight of Aborigines in Arnhem Land, stated that in no instance was an obese adult encountered. This relative leanness is evident in the lower weight for the same height at all ages and in both sexes shown in Fig 4 from Billington⁶. Maximum weight was attained in the second decade of life and thereafter tended to fall with age. This fall being more pronounced in women than in men. Comparable data on skinfold thickness in Australian Aborigines are sparse but that which exists⁷ is consistent with the data on body weight. More recent information on changes in body mass index (BMI) and in subcutaneous fat with age indicate, that in contemporary Aboriginal groups both weight (Table I) and subcutaneous fat (Table 2) increase markedly with age⁸. Of interest to the present discussion, on differences in body composition with ethnic origin, is the fact that the relationship between BMI and subcutaneous fat in Australian Aborigines appears to differ from that seen in Australian women of European origin. On average Australian Aboriginal women with the same level of subcutaneous fat (sum of triceps, biceps, subscapular and suprailiac skinfolds) were found to have a BMI which was one to two units lower than that of Australian women of European origin as shown in Table 3 from Coles-Rutishauser⁹. The difference in the relationship between subcutaneous fat and BMI is also clearly demonstrated by the fact that prediction equations for body fat from BMI based on data from populations of Caucasian origin such as the equation of Womersley and Durnin¹⁰ predict zero body fat in adult women with a BMI of 15.5 kg/m² or less, whereas we have observed Aboriginal women with a BMI as low as this not merely to have measurable amounts of subcutaneous fat but also to be fertile and to be able to breastfeed their infants successfully. Not only was the relationship between BMI and subcutaneous fat found to differ but the distribution of the subcutaneous fat also differed between the two groups, with a much higher proportion, in the Aboriginal women, being located on the trunk as compared with the limbs (Table 4). This difference in the pattern of fat distribution suggests that estimates of body fat from skinfolds using equations derived from skinfold-body fat relationships in European women such as the equations of Durnin and Womersley¹¹ are unlikely to be appropriate for this group.

Table 1. Percentage distribution of Aboriginal females by age and body mass index (BMI)¹⁸.

	AGE IN YEARS
BMI	15-19	20-24	25-29	30-34
<17.5	36	24	15	7
17.6 - 20.0	25	15	14	9
20.1 - 25.0	22	35	37	30
25.1 - 27.5	7	13	11	12
> 27.6	10	13	23	42

Table 2. Mean and standard deviation for four skinfolds in Aboriginal women⁸.

	Skinfold (mm)
Age Group (yrs)	no.	Biceps	Triceps	Subscapular	Suprailiac
15-19	23	5.5(4.1)	10.0(5.3)	14.4(5.3)	18.4(7.4)
20 24	28	6.0(3.3)	14.2(6.5)	23.0(11.6)	25.3(11.5)
25-34	35	7.7(3.2)	17.4(8.2)	28.0(11.5)	30.4(11.1)
>35	28	10.2(4.9)	22.7(7.3)	32.7(7.8)	32.7(8.1)

Table 3. Ninety-five percent confidence intervals for BMI in Aboriginal and Caucasian women according to skinfold thickness⁹.

	Confidence intervals for BMI
Sum of Skinfolds(mm)	Aboriginals (n=114)	Caucasians (n=88)
40	16.8- 18.2	19.7-20.6
60	20.2 - 21.3	22.4 - 23.1
80	23.5 - 24.5	25.0 - 26.0

Table 4. Differences in the distribution of subcutaneous fat between Australian Aboriginal women and Australian women of European origin.

Group			Skinfolds
	no.	BMI (kg/m2)	Limb (mm)	Trunk (mm)	Ratio L/T
Aboriginal	23	26.1	28.5	49.5	0.56
European	91	24.5	30.3	35.7	0.92

Estimates of body composition from total body water

Apart from the determinations of total body water (TBW) made on Aboriginal children by Cheek et al.¹² we are not aware of data on estimates of the FFM in Australian Aborigines obtained using the stable isotope deuterium oxide. The advent of bio-electrical impedance technology has made it possible also to obtain an estimate of TBW by measuring the impedance of the body to a small alternating current¹³. However, since it appears that the lower arm and the lower leg both make a relatively large contribution to the total body impedance^14,15 it is not unlikely that the prediction equations derived from impedance measurements in populations of Caucasian origin may, like those based on other anthropometric measurements, not be directly applicable to Australian Aborigines. It would appear preferable, therefore, in the first instance to determine TBW by deuterium oxide dilution and only subsequently to derive appropriate prediction equations for this population based on impedance analysis. Table 5 shows data for adult Australian Aborigines for TBW, and TBW expressed both per centimetre and per metre of height squared, compared with similar data taken from the literature for men and women of European origin^16,17. The data in the table do not indicate differences with ethnic origin in the amount of TBW per unit of height although as might be expected, there are clear differences between males and females. The numbers in all groups are small but there is no suggestion from these data that Australian Aborigines have a different amount of FFM per unit of height than do European adults of similar age and height.

Table 5. Total body water (TBW) per unit of stature in Australian Aboriginal adults and in men and women of European origin. (mean values).

Group	no.	Age	TBW (1)	Ht (cm)	TBW/cm ht	TBW/m2 ht
Adult males:
Aboriginal	33	32	44.7	178	0.2502	14.1
British16	16	34	43.1	177	0.2435	13.8
Australian17	7	31	41.7	174	0.2397	13.8
Adult females:
Aboriginal	23	31	36.0	166	0.2170	13.1
British16	12	32	31.4	165	0.1903	11.5
Australian17	8	42	35.2	167	0.2108	12.6

Conclusions

The available data on the anthropometric profile of Australian Aborigines indicate that there is considerable variation within this ethnic group both in body size and body proportions. Differences within sub-groups of the Aboriginal population appear to be as great as those observed between groups of Aborigines and Australians of European origin, although Australian Aborigines as a group do appear to have lower values for both relative sitting height and relative shoulder breadth than Australians of European origin. There is also some evidence for a different relationship between BMI and the level of subcutaneous fat, at least in females. This appears to be associated with a more central fat distribution in Aborigines as compared with Europeans. There is no evidence, from TBW measurements, for any differences with ethnic origin in the amount of FFM per unit of height. The very low BMIs (<15 kg/m²) observed in some otherwise apparently healthy Aboriginal women would thus appear to be associated primarily with a much lower level of limb fat in this group, as compared with women of European origin, rather than with differences in skeletal proportions.

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References

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Revised: January 19, 1999 .