Obesity in Canada: Prevalence among adults

Prevalence Among Adults

About one-quarter of Canadian adults are obese, according to measured height and weight data from both the 2008 CCHS (25.4%) and the 2007-2009 CHMS (24.3%).^{Footnote 2} The prevalence of obesity is lower when derived from self-reported height and weight data from the combined 2007/08 CCHS (17.4%). When obesity is combined with overweight, the prevalence in 2008 was 62.1% when based on measured data and 51.1% when self-reported data were used. Self-reported data are easier and less expensive to collect in population-level surveys but tend to underestimate the prevalence of obesity when compared with measured data.^{Footnote 3} One study has suggested that self-reporting bias has increased since the early 1990s.^{Footnote 4} However, both measured and self-reported data indicate that the prevalence of adult obesity in Canada has increased in recent decades (Figure 1).

Figure 1: Prevalence of Obesity, Ages 18 Years and Older, Canada, 1978-2009

Note: Excludes the Territories.

Source: Analysis of 1978/79 Canada Health Survey; 1989 Canadian Heart Health Survey (ages 18-74); 1985 and 1990 Health Promotion Surveys; 1994/95, 1996/97 and 1998/99 National Population Health Surveys; and 2000/01, 2003, 2004, 2005, 2007 and 2008 Canadian Community Health Surveys, Statistics Canada and CANSIM Table 105-0501,^{Footnote 5} 2009 Canadian Community Health Survey.

Concern about obesity is not a new phenomenon. By the 1930s, life insurance companies had begun using height and weight charts to identify clients at increased risk of death.^{Footnote 8} Since the 1950s, health surveys have made possible the study of heights and weights of Canadians.^{Footnote 9}

A comparison between the 1981 Canada Fitness Survey (CFS) and the 2007-2009 CHMS found that measured obesity roughly doubled across all age groups studied.^{Footnote 2} Findings from surveys conducted in recent decades, comparing the Canadian Heart Health Survey 1986/92 and the CCHS 2004, also showed increases in obesity.^{Footnote 2,Footnote 10,Footnote 11} Further, these studies have demonstrated increases in the proportions of men and women with a BMI in the obese category^{Footnote 10,Footnote 11} and with a body composition measure in the high health-risk categories.^{Footnote 2}

There has been a marked shift in the distribution of BMI over time, the greatest increases occurring in the heaviest weight classes:

• The proportion of adults falling into obese class I (BMI 30.0-34.9 kg/m²) increased from 10.5% in 1978/79 to 15.2% in 2004.^{Footnote 2,Footnote 12}
• The proportion in obese class II (BMI 35.0-39.0 kg/m²) doubled between 1978/79 and 2004, increasing from 2.3% to 5.1%.^{Footnote 12}
• The proportion falling into obese class III (BMI ³ 40 kg/m²) , while small, also appears to have increased over time. In 1978/79 obese class III made up 0.9% of the population and increased three-fold, to 2.7%, by 2004.^{Footnote 12}

Figure 2 shows the proportion of males and females that fell within categories of underweight, normal, overweight and obese classes I, II and III in 2007-2009 and the cut-off points defining each weight class. Although females appear more likely than males to be within the normal weight group and less likely to be in the overweight group, they are more likely to fall into obese classes II and III.^{Footnote 2}

Figure 2: Distribution of BMI Categories by Sex, Ages 18 to 79, 2007-2009

Source: 2007-2009 Canadian Health Measures Survey, Statistics Canada.^{Footnote 2}

Variation by age and sex

For both men and women, analyses of the 2007/08 CCHS show that the prevalence of obesity generally increases with each successive age group up to age 65 (Figure 3). After age 65, the prevalence of obesity declines. A similar pattern of lower obesity among the youngest and oldest age groups was also found in the 2004 CCHS, which collected measured data.^{Footnote 12}

Figure 3: Prevalence of Self-Reported Obesity by Age and Sex, Canada, 2007/08

Source: Analysis of the 2007/08 Canadian Community Health Survey, Statistics Canada.

In the 2007/08 CCHS, obesity (based on self-reported heights and weights) was more prevalent among men than women, with the exception of the oldest age group (Figure 3). Based on direct measures, findings from the 2007-2009 CHMS show that, while obesity increased with age, it was not always higher among men than women. For example, in the population aged 20 to 39, 19% of males and 21% of females were obese, and among those aged 40 to 59, 27% of males and 24% of females were obese.^{Footnote 2}

Provincial/territorial variation

In 2007/08 self-reported obesity in Canada varied across provinces and territories, from a low of 12.8% in British Columbia to a high of 25.4% in Newfoundland and Labrador (Figure 4). Estimates of obesity in 2007/08 were found to be significantly higher than in 2005 in Canada overall as well as in Alberta and Ontario, and significantly higher in 2005 than 2003 in Newfoundland and Labrador (Figure 4). Because of sample size limitations for measured obesity, calculations of obesity by province and health region were based on self-reported data.

Figure 4: Prevalence of Self-Reported Obesity by Province/Territory, Ages 18 and Older, 2003-2007/08

Notes: * Significantly different from previous year estimate.

^E High sampling variability, interpret with caution.

Source: Analysis of the 2007/08 Canadian Community Health Survey, Statistics Canada.

Regional variation

Variation in obesity was also observed at the Health Region level in 2007/08. Obesity estimates ranged from a low of 5.3% in urban/suburban Richmond, British Columbia, to a high of 35.9% in the northern Mamawetan/Keewatin/Athabasca region of Saskatchewan (Figure 5, see Appendix 1 for all Health Regions). Studies have found that the prevalence of obesity tends to be lower in more urban regions, one study showing that obesity was significantly below the national average in Montreal, Toronto and Vancouver on the basis of 2003 CCHS estimates.^{Footnote 13,Footnote 14} Among both adults^{Footnote 15} and youth,^{Footnote 16} the proportion of overweight tends to be higher in rural areas than in metropolitan areas. In particular, in all the Canadian regions considered, obesity has been found to be most prevalent among boys in small town regions of 2,500 to 19,999.

Figure 5: Prevalence of Self-Reported Obesity, Ages 18 Years and Older, 2007/08: Top and Bottom 10 Ranked Health Regions

Notes: Vertical line represents the national Canadian obesity prevalence (17%). Obesity prevalence and 95% confidence intervals for the top and bottom 10 ranked health regions are represented by horizontal bars. For complete results for all health regions, see Appendix 1.

Source: Analysis of the 2007/08 Canadian Community Health Survey, Statistics Canada.

International comparisons

Canada is not alone in observing increases in obesity. Research in the US and the UK also documents increases in the proportion of the population in the obese class,^{Footnote 17,Footnote 18} in average BMI^{Footnote 19} and in the proportion of the population in the heaviest weight classes.^{Footnote 17,Footnote 19}

In recent decades, obesity has become a worldwide issue. The World Health Organization (WHO) has estimated that more than 1 billion adults worldwide are overweight and at least 300 million are clinically obese.^{Footnote 6} Recent obesity estimates for adults in OECD member nations are shown in Figure 6. They indicate that measured obesity ranges from 3.4% in Japan to 34.3% in the United States, a 10-fold difference.

Another analysis of OECD data, from 13 countries including Canada, found that the prevalence of obesity had increased among men and women between the 1980s and 2005 in Canada, Australia, Austria, England, France, Hungary, Sweden and the US.^{Footnote 20} Moreover, these researchers projected that substantial further increases in obesity could be expected in Canada, Australia, England and the US until 2019.^{Footnote 20}

Figure 6: Prevalence of Obesity in OECD Countries, 2004-2008

Note: The definition of adult population differs by country. The year listed for each country represents the year in which the data were collected.

Source: Organisation for Economic Co-operation and Development (OECD) Health Data 2009.

Key points

• On the basis of measured height and weight from multiple sources during 2007-2009, more than one in four adults in Canada are obese.
• Self-reported obesity is lower (17.4%) than measured estimates, but both show increases since the late 1970s.
• Significant increases in self-reported obesity in Canada have also been reported between 2003 and 2008.
• Obesity is more prevalent in older age groups, up to approximately 65 years.
• Obesity tends to be more prevalent among males than females; however, this depends to some extent on the age group and whether obesity is self-reported or measured.
• There is a more than a six-fold variation in self-reported obesity across health regions in Canada, and the variation among OECD countries is more than 10-fold.
• Continued surveillance, longitudinal studies and improved methodologies for measuring weight and adiposity could enhance our understanding of the prevalence and distribution of obesity.