This analysis examines period trends in body weight of Australian 18–24 year olds. Secondary analysis of National Health Surveys was performed, including examination of socio-demographic determinants of obesity. The prevalence of overweight and obesity has increased from 24.0 and 5.1% in males and 13.2 and 5.8% in females, respectively, in 1995 to 29.3 and 13.8% in males and 20.6 and 20.6% in females in 2012. Mean body mass index (BMI) increased over time from 23.7 (s.d. 3.5) for males and 22.4 (s.d. 4.0) for females in 1995 to 25.2 (s.d. 4.8) and 25.5 (s.d. 5.9) in 2011/2. Lower educational attainment increased the odds of having BMI⩾25.00 kg/m2 for both sexes (P=0.03 males and P<0.001 females). Overweight and obesity were higher in rural females (P<0.05) and those socio-economically disadvantaged (P<0.0001). The obesity epidemic has worsened for Australian young adults and in particular young females.
Prevalence of overweight and obesity in Australian young adults
In 2012, 62.8% of Australian adults were overweight (35.3%) or obese (27.5%).1 Internationally, young adulthood has been recognized as a time of rapid weight gain, with younger generations at higher risk of developing overweight.2, 3 To our knowledge, current period trends of the prevalence and body mass index (BMI) distribution of this age group have not been examined. This research describes period trends and socio-demographic characteristics of the prevalence of overweight and obesity in Australian young adults, aged 18–24.
The National Health Surveys, conducted by the Australian Bureau of Statistics, are stratified multistage area samples of private dwellings, representative of the Australian population. Details on the survey designs are published elsewhere.4, 5, 6 Response rates ranged from 91.5 to 96.1%. Height, weight and waist circumference were measured for 2007/8 and 2011/2 and self-reported in 1995. For confidentiality purposes, the Australian Bureau of Statistics grouped observations for heights ⩽145 cm (⩽138 cm for females in 2012) and⩾200 cm (1995, 2007/8) and for weight ⩽40 kg (35 kg in 1995) and ⩾130 kg (1995) or ⩾140 kg in (2007/8) accounting for 0.4% of the sample. BMI was calculated by weight (kg)/height (m2) and classified along with waist circumference (see Table 1 and below), in accordance to World Health Organizations definitions.7 The Australian Government Health and Ageing Departmental Ethics Committee granted ethics for this research, and it was conducted under the Census and Statistics Act 1905.4, 5, 6 Written consent was obtained from each participant.4, 5, 6
Samples are weighted by the Australian Bureau of Statistics to be representative of the Australian population. ANOVA and Tukey’s pairwise procedure were used to test for significant differences in mean BMI for socio-demographics (Table 1), selected as there are known differences in the Australian population at large.1 Simple cumulative logistic regression was conducted to model differences by socio-demographics in 2011/12 and period difference prevalence of overweight and obesity. Multiple regression was used to estimate adjusted odds ratios (OR) for geographic area, controlling for socio-economic index for an area and educational attainment (Supplementary Table S1 and Supplementary Figure S1). Confidential Unit Record Files were provided by the Australian Bureau of Statistics. Analysis was conducted in SAS 9.4 for Windows (Version 9.4 2002-2012; by SAS Institute Inc., Cary, NC, USA). SAS codes are available on request.
Secular trends in the prevalence of overweight and obesity
In 2011/12, BMI increased significantly with age for males (P=0.02) but not females (P=0.94). In 2011/2, 20.6% of females were overweight and 20.6% were obese, and 29.3% of males were overweight and 13.8% were obese (females=514, males=542). Obesity has increased from 5.1% of males (n=2353) and 5.8% of females (n=2364) since 1995. Each new cohort entered adulthood with a higher mean BMI than in the previous with a mean (s.d.) of 23.7 (3.5) kg/m2 and 22.4 (4.0) kg/m2 for males and females, respectively, in 1995 compared with 25.3 (4.8) and 25.5 (5.9) kg/m2 in 2011/2 (see Supplementary Figure S1). The median (interquartile range) BMI increased in males from 23.4 (4.2) kg/m2 in 1995 to 24.4 (5.7) kg/m2 in 2011/2 and from 21.5 (4.6) to 23.9 (7.5) in females, indicating that incident obesity in a section of the population is driving the epidemic (Figure 1). Conversely, the prevalence of overweight and obesity has plateaued in Australian children and adolescents,8 implying significant weight gain in late adolescence/early adulthood.
Females historically had lower BMI than males with a significant difference between males and females in 1995 (P<0.0001), but no significant difference in 2011/12 (P>0.05), implying that females have greater excess fat given lower lean muscle mass.9 The odds of having a BMI⩾25.00 kg/m2 compared with 1995 were 3.1 (95% confidence interval (CI): 2.4–3.9) for females and 1.9 (95% CI 1.5–2.4) for males (Supplementary Figure S1). The rate at which young females appear to be gaining weight is particularly alarming, as it puts future generations of children at greater risk of developing obesity and chronic disease because of their mother’s weight status.10 As young adults in the 2011/12 survey were born when the obesity epidemic had already begun in Australia,1 higher rates of obesity may be due to parents who were overweight.
In 2011/12, the mean (s.d.) waist circumference was 81.8 cm (14.3) for females (increased risk >80 cm) and for males was 87.7 cm (13.3), (normal <94 cm). The prevalence of abdominal obesity was 26% for males and 48.1% for females, with 14.4% of males and 28.8% of females categorized as high risk (waist circumference >102 and >88 cm, respectively). The prevalence of abdominal obesity increased from 2007/8 with 9.3% of males (>94 cm 11.6%) and 19.1% of females at increased risk (>80 cm 14.3%).
Socio-demographics of overweight and obese young adults
The mean BMI and prevalence of overweight and obesity for different socio-demographic groups are presented in Table 1. In 2011/12, the estimated OR (95% CI) for BMI⩾25.00 kg/m2 was 1.6 (1.1–2.6) for males and 3.0 (1.9–4.7) for females with no tertiary education compared with university and 1.6 (1.7–2.3) for males and 2.3 (1.5–3.4) for females with technical/vocational college education. Being born in countries other than Australia, New Zealand and the UK was protective against obesity (OR 0.5 (95% CI 0.3–0.8) OR 0.35 (95% CI 0.2–0.6). Those living in areas of socio-economic disadvantage and areas outside major cities predicted overweight and obesity in young females but not males. The prevalence of obesity in young females was 34.9% for females from the most socio-economically disadvantaged areas, compared with 14.7% of young females from areas of socio-economic advantage with increased odds of a BMI⩾25.00 kg/m2 (OR: 2.2, 95% CI 1.3–3.7). For OR for the likelihood of a BMI⩾25.00 kg/m2 for socio-demographic groups see Supplementary Table S1.
The prevalence of having a BMI⩾25.00 kg/m2 is higher in regional areas than in major cities for females (Table 1); however, after controlling for educational attainment and socio-economic index for an area in the multiple regression model, no significant difference was found (OR 1.4, 95% CI 0.9–2.0) (Supplementary Table S1). This implies that differences between urban and rural areas may be explained by a greater proportion of the rural population being of lower SES and warrants further investigation.
Obesity and overweight continue to increase for each successive generation of young adults. This suggests that Australia will continue to witness increases in the future given that weight gain continues as a process of aging2 and the evident difficulty of reversing obesity. Consequently, the obesity epidemic does not show any evidence of slowing down in Australia, and preventative efforts are urgently required. A limitation of this research is that BMI is slightly different to what is reported here because of categorization of extreme values of height and weight to protect personal identity. However, the difference will be small as these values only represent 0.4% of the sample. Interventions should be sure to include those most at risk including females of lower socio-economic status and males with lower educational attainment.
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This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors. AG is currently supported by an Australian Postgraduate award for doctoral studies. MA-F's roles included study design and revision of the manuscript. AG's roles included study design, data analysis and drafting the manuscript.
The authors declare no conflict of interest.
Supplementary Information accompanies this paper on European Journal of Clinical Nutrition website
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Grech, A., Allman-Farinelli, M. Prevalence and period trends of overweight and obesity in Australian young adults. Eur J Clin Nutr 70, 1083–1085 (2016). https://doi.org/10.1038/ejcn.2016.41