Measured Obesity Overweight Canadian children and adolescents

Component of Statistics Canada Catalogue no. 82-620-MWE2005001
ISSN: 1716-6713
Nutrition: Findings from the Canadian Community Health Survey
Issue no. 1
Measured Obesity
Overweight Canadian children and
adolescents
by Margot Shields
Analytical Studies and Reports
3rd floor, R.H. Coats Building, Ottawa, K1A 0T6
Telephone: 1 613 951-4177

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Nutrition: Findings from the Canadian Community Health Survey – Overweight Canadian children and adolescents

Overweight Canadian children and adolescents
Margot Shields

• In 2004, 26% of Canadian children and adolescents aged 2 to 17 were overweight or obese; 8%
were obese.
• For adolescents aged 12 to 17, increases in overweight and obesity rates over the past 25 years
have been notable; the overweight/obesity rate of this age group more than doubled, and the
obesity rate tripled.
• Children and adolescents who eat fruit and vegetables 5 or more times a day are substantially less
likely to be overweight or obese than are those whose fruit and vegetable consumption is less
frequent.
• For children aged 6 to 11 and adolescents aged 12 to 17, the likelihood of being overweight or
obese tends to rise as time spent watching TV, playing video games or using the computer
increases.
• Canadian adolescent girls are significantly less likely than American adolescent girls to be
overweight/obese.

Over the past 25 years, the prevalence of overweight and obesity in children and adolescents has risen,
with the most substantial increases observed in economically developed countries.1 According to the
results of the 2004 Canadian Community Health Survey: Nutrition (CCHS), a substantial share of
Canadian youth are part of this trend.
The 2004 CCHS was the first time in many years that interviewers directly measured the height
and weight of a nationally representative sample of Canadians (see Appendix A: Data sources and
analytical techniques). In the past, most health surveys relied on respondents to report their height and
weight, a practice that tended to underestimate the prevalence of overweight and obesity among
adolescents and adults2-5 (see Appendix B: Methodology makes a difference).
The last time that the height and weight of a nationally representative sample of Canadian
children and adolescents (aged 2 to 17) were directly measured was in 1978/79 as part of the Canada
Health Survey. Results from that survey and the 2004 CCHS can be compared to get a better picture of
the increase of overweight and obesity among young Canadians during the past quarter century.
In 1978/79, 12% of 2- to 17-year-olds were overweight, and 3% were obese—a combined
overweight/obesity rate of 15%. By 2004, the overweight rate for this age group was 18% (an estimated
1.1 million), and 8% were obese (about half a million)—a combined rate of 26%.

Notable rise among adolescents
Increases in overweight and obesity were similar among boys and girls (Chart 1). In 2004, the combined
overweight/obesity rate for each sex was about 70% higher than it had been in 1978/79, and the obesity
rate was 2.5 times higher. However, trends differed for various age groups.
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Nutrition: Findings from the Canadian Community Health Survey – Overweight Canadian children and adolescents

For example, the percentage of children aged 2 to 5 who were overweight/obese remained
virtually unchanged. By contrast, the overweight/obesity rate of adolescents aged 12 to 17 more than
doubled from 14% to 29%, and their obesity rate tripled from 3% to 9% (Chart 2).

Higher body mass index
Overweight and obesity are based on body mass index (BMI), a measure that takes weight and height into
account (BMI = weight in kilograms divided by height in metres squared). For adults aged 18 or older,
BMI cut-offs of 25 and 30 are used to classify individuals as overweight and obese, respectively, based on
health risks associated with being in these weight classes.6 For children and adolescents, the cut-offs are
lower, and they also account for age (see Appendix C: Calculating overweight and obesity in children
and adolescents).
The average BMI of adolescents aged 12 to 17 rose from 20.8 in 1978/79 to 22.1 in 2004. This
produced a shift in the BMI distribution of the age group toward the heavy end of the continuum. The
most pronounced increases were in the percentages of adolescents whose BMI exceeded 25 or 30, the
overweight and obese thresholds for adults (Chart 3). This is of particular importance, given that
adolescence is a critical period for the development of adult obesity.1,7-10

Provincial differences
Youth overweight and obesity rates varied across the country, with the highest rates tending to be in the
Atlantic provinces. In 2004, the combined overweight/obesity rate of 2- to 17-year-olds was significantly
above the national level (26%) in Newfoundland and Labrador (36%), New Brunswick (34%), Nova
Scotia (32%), and also, Manitoba (31%) (Chart 4). The prevalence of obesity was significantly higher
than the national figure (8%) in Newfoundland and Labrador (17%) and New Brunswick (13%).
The combined overweight/obesity rate was significantly below the national level in Québec
(23%) and Alberta (22%), but the obesity rate in these provinces was similar to the national rate.

Canada-US comparisons
Since the early 1960s, the height and weight of a nationally representative sample of Americans have
been directly measured as part of the National Health and Nutrition Examination Survey (NHANES).
Based on the most recent NHANES data (1999-2002), the combined overweight/obesity rate of 2- to 17-
year-olds was similar in the United States and Canada (Chart 5), but the American obesity rate was
slightly higher (10% versus 8%).
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Nutrition: Findings from the Canadian Community Health Survey – Overweight Canadian children and adolescents

Overweight/obesity and obesity rates for boys in the two countries were similar (Chart 6).
However, for girls, the overweight/obesity rate in Canada was higher at ages 2 to 5, but lower at ages 12
to 17. At ages 12 to 17, American girls were almost twice as likely as Canadian girls to be obese: 13%
versus 7%.
For young people of both sexes in the United States, the prevalence of overweight and obesity
increased with age. The overweight/obesity rate of American boys rose from 14% at ages 2 to 5 to 33%
at ages 12 to 17; for American girls, the increase was from 17% to 31%. In Canada, too, boys’
overweight/obesity rate rose from 19% at ages 2 to 5 to 32% at ages 12 to 17. By contrast, Canadian
girls’ rate was relatively stable at around 25% regardless of age.
If the prevalence of overweight and obesity among youth is still increasing, differences between
Canada and United States may be greater, because the American rates are based on earlier data (collected
from 1999 to 2002).
Another factor in comparisons between the two countries is the ethnic composition of the
population. In the United States, Black, Hispanic and Mexican-American children and adolescents had
relatively high overweight/obesity rates (more than 30%) (Chart 7). These groups represent about one-
third of American youth, but constitute a very small share of the population in Canada. When
comparisons were made between white Canadian and American youth, the overweight/obesity and
obesity rates did not differ significantly.
In Canada, young people of Aboriginal origin (off-reserve) had a significantly high combined
overweight/obesity rate (41%). Their obesity rate was 20%, two and a half times the national average.
By contrast, youth of Southeast Asian or East Asian origin had a low overweight/obesity rate (18%)
(Chart 8). These differences between ethnic groups persisted when age and socio-economic factors were
taken into account. However, because of the relatively small numbers in these ethnic groups, the national
overweight/obesity and obesity rates were not strongly influenced by these differences.

A fattening environment?
American data show that children’s consumption of fast food has increased dramatically over the past two
decades, and that a large majority of children and adolescents do not have an adequate number of daily
servings of fruit and vegetables.1,10 Based on data from the 2004 CCHS, 59% of Canadian children and
adolescents were reported to consume fruit and vegetables less than five times a day (see Appendix D:
Definitions). These young people were significantly more likely to be overweight/obese or obese than
were those who ate fruit and vegetables more frequently (Chart 9).
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Nutrition: Findings from the Canadian Community Health Survey – Overweight Canadian children and adolescents

Some studies have found that physical activity is protective against childhood obesity,11 while
others have not found such a relationship1 (see Appendix E: Limitations). Analysis of CCHS data shows
that physical activity levels were not associated with overweight and obesity at ages 6 to 11 (Chart 10),
but by ages 12 to 17, associations were significant, though only for boys (Chart 11). Sedentary boys were
more likely than active boys to be obese (16% versus 9%). Unexpectedly, a higher proportion of active
and moderately active boys were overweight (but not obese), compared with boys who were sedentary.
Watching television, playing video games and using the computer are common pastimes for many
Canadian children. Time spent on these activities is referred to as “screen time.” In 2004, over a third
(36%) of children aged 6 to 11 logged more than 2 hours of screen time each day (Chart 12). These
children were twice as likely to be overweight/obese as were those whose daily viewing totalled an hour
or less (35% versus 18%), and about twice as likely to be obese (11% versus 5%).
For adolescents aged 12 to 17, screen time was measured on a weekly basis. Their
overweight/obesity rates ranged from 23% of those whose viewing amounted to fewer than 10 hours a
week to 35% of those who spent more 30 or more hours a week in front of a screen (Chart 13).
The relatively recent introduction and rapid proliferation of video games and home computers
make it difficult to track trends in screen time. In 1988, the Campbell’s Survey on Health and Well-being
asked 12- to 17-year-olds how many hours they watched television—the weekly average was 9. In 2004,
average weekly television hours were almost the same, at 10. However, when time spent on the computer
and playing video games is included, adolescents’ total average screen time doubles to 20 hours a week.

All associations between these lifestyle factors (fruit and vegetable consumption, physical activity
and screen time) persisted when the effects of age and socio-economic status were controlled.

Socio-economic status
For adults, lower socio-economic status tends to be associated with obesity. While the same relationship
has been observed for children, the association is usually not as strong, and results have been
inconsistent.12-14
According to the 2004 CCHS, children and adolescents in middle-income households were more
likely to be overweight/obese or obese than were those in high-income households (Chart 14).
Overweight/obesity rates and obesity rates for youth in low-income and high-income households were
similar.
The pattern was clearer for education. Young people in households where no members had more
than a high school diploma were more likely to be overweight/obese than were those in households where
the highest level of education was postsecondary graduation (Chart 15).
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Nutrition: Findings from the Canadian Community Health Survey – Overweight Canadian children and adolescents


Diminished perceptions of health
In 2004, 18% of adolescents aged 12 to 17 reported that they had at least one diagnosed chronic
condition. This rate did not vary significantly whether adolescents were in the normal weight range,
overweight (not obese) or obese. Nevertheless, young people’s perceptions of their health did differ,
depending on their weight (Chart 16). Boys who were obese were much less likely than those whose
weight was in the normal range to report their health as excellent or very good. For girls, diminished
health perceptions were evident not only among those who were obese, but also among those who were
overweight. These associations between weight and health perceptions persisted for both sexes when
socio-economic status and the presence of a chronic condition were taken into account.

Conclusion
The past 25 years have seen a considerable increase in the percentage of Canadian children and
adolescents who are overweight or obese. The increase was particularly notable among 12- to 17-year-
olds, whose overweight/obesity rate more than doubled, and whose obesity rate tripled.
The burden to the health care system of childhood obesity is difficult to quantify because the
related physical health problems are usually not evident until later in life. Nonetheless, the upturn in the
prevalence of overweight/obesity among young people is important because overweight/obesity in
adolescence often persists into adulthood.1,7-10 A recent Canadian study based on longitudinal data found
that once an adult is overweight, further weight gain is likely; very few return to the normal weight
range.15
However, some of the factors associated with overweight and obesity among young people are
modifiable. Increased consumption of fruit and vegetables, more physical activity and less time devoted
to sedentary activities such as watching television and playing video games may help reverse the upward
trend.

Acknowledgements
The author thanks Larry MacNabb and Dr. Mark Tremblay for their assistance and helpful suggestions
during the analysis, and Wayne Millar for his help in producing the variances estimates based on
SUDAAN.

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Nutrition: Findings from the Canadian Community Health Survey – Overweight Canadian children and adolescents

Appendix A
Data sources and analytical techniques
Data from the 2004 Canadian Community Health Survey (CCHS): Nutrition were used to produce
overweight and obesity rates for 2- to 17-year-olds. The 2004 CCHS was designed to gather information
at the provincial level about the nutritional status of the Canadian population (see
http://www.statcan.ca/english/concepts/hs/index.htm#content). The survey does not include residents of
the three Territories, Indian reserves and some remote areas, and regular members of the Canadian Armed
Forces. The response rate was 76.5%. Measured height and weight were obtained for 66% of the 2- to
17-year-olds who responded to the 2004 CCHS, a total of 8,661 individuals (see Appendix E:
Limitations).
Overweight and obesity rates of American children and adolescents were estimated from the
1999-2002 National Health and Nutrition Examination Survey (NHANES). The NHANES obtained
measured height and weight data for 7,297 children and adolescents.
Historical estimates of Canadian overweight and obesity rates, based on directly measured height
and weight, are from on the 1978/79 Canada Health Survey, and for 12- to 17-year-olds, from the 1981
Canada Fitness Survey and the 1988 Campbell’s Survey on Health and Well Being. For 12- to 17-year-
olds, rates based on self-reported data are from the 2000/01 and 2003 CCHS and the 1994/95, 1996/97
and 1998/99 National Population Health Survey (NPHS). For 2- to 11-years olds, rates based on data
reported by parents are from the 1994/95, 1996/97, 1998/99, 2000/01 and 2002/03 National Longitudinal
Survey of Children and Youth (NLSCY). In 2002/03, NLSCY estimates could be made only for children
aged 2 to 5, since the cross-sectional file does not include records for children aged 6 or older.
Descriptive statistics from the 2004 CCHS were used to estimate the proportion of 2- to 17-year-
olds who were overweight and obese in relation to selected characteristics. All estimates were based on
the 8,661children and adolescents for whom measured data on height and weight were obtained. Since
they accounted for only 66% of children and adolescents who responded to the 2004 CCHS, an
adjustment was made to minimize non-response bias. A special sampling weight was created by
redistributing the sampling weights of the non-respondents to the respondents, using response propensity
classes. Variables such as province, age, sex, household income, race, education, physical activity, fruit
and vegetable consumption and chronic conditions were used to create the classes. The classes were
created with the CHAID (Chi-Square Automatic Interaction Detector) algorithm available in Knowledge
Seeker 16 to identify the characteristics that best split the sample into groups that were dissimilar with
respect to response/non-response. This adjusted sampling weight was used to produce all estimates in
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Nutrition: Findings from the Canadian Community Health Survey – Overweight Canadian children and adolescents

this analysis. Standard errors and coefficients of variation were estimated using the bootstrap technique,
which accounts for the survey design effects.17-19
The American and Canadian historical estimates are based on weighted data. The criteria
specified by the International Obesity TaskForce (IOTF) were used to define overweight and obesity
among youth (see Appendix C: Calculating overweight and obesity in children and adolescents).
Standard errors and coefficients of variation for estimates from the 1978/79 Canada Health
Survey and the National Health and Nutrition Examination Survey (NHANES), 1999-2002 were
estimated with SUDAAN, which uses a Taylor series linearization method to account for the complex
survey sample design.
The body mass index (BMI) distribution (Chart 3) was smoothed by calculating three-point
averages. For example, the percentage of the population with a BMI of 23 was calculated by summing
the percentage with a BMI of 22, the percentage with a BMI of 23 and the percentage with a BMI of 24,
and then dividing the result by 3.

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Nutrition: Findings from the Canadian Community Health Survey – Overweight Canadian children and adolescents

Appendix B
Methodology makes a difference
In the United States, data from the National Health and Nutritional Examination Survey (NHANES) show
sharp rises in overweight/obesity rates among children and adolescents between 1976-1980 and 1988-
1994, and again, between 1988-1994 and 1999-2002.20
In Canada, because of variations in the methods used to collect information on height and weight,
it is difficult to pinpoint when overweight and obesity rates increased. Rates for 12- to 17-year-olds,
based on directly measured height and weight, can be calculated for four reference years: 1978/79, 1981,
1988, and 2004 (Chart 17) (see Appendix A: Data sources and analytical techniques). These data reveal a
small decrease in adolescents’ overweight/obesity and obesity rates between 1978/79 and 1981,21 and
then, substantial increases between 1981 and 1988, and again, between 1988 and 2004. Calculations
based on self-reported data show a stabilization of rates from 1994/95 to 2003. But between 2003 and
2004, when the collection method changed from self-reported to measured data, overweight/obesity and
obesity rates rose sharply. This is not surprising, as self-reports tend to yield lower rates of overweight
and obesity.2-5
Comparisons of the average height and weight of adolescents (ages 12 to 17) in 2003 (self-
reported) and 2004 (measured) illustrate these tendencies. In 2004, the average directly measured height
of boys and girls was a third of an inch less than the 2003 averages based on self-reports. The directly
measured average weight of boys in 2004 was 3 pounds more than in 2003, and for girls, 6 pounds more.
As a result, one-year increases in the prevalence of overweight and obesity among adolescents were
substantial.
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Nutrition: Findings from the Canadian Community Health Survey – Overweight Canadian children and adolescents


2004
2003
(directly
Difference

(self-report)
measured)
Boys aged 12 to 17

Average height
66.6 inches
66.3 inches
-0.3 inches

169.2 cm
168.4 cm
-0.8 cm
Average weight
137.1 lb
140.4 lb
3.3 lb

62.2 kg
63.7 kg
1.5 kg
Average BMI
21.4
22.3
0.9
% overweight/obese
24.0%
32.3%
8.3
% obese
5.7%
11.1%
5.4


Girls aged 12 to 17

Average height
63.6 inches
63.3 inches
-0.3 inches
161.5
cm
160.8
-0.7 cm
Average weight
120.3 lb
126.0 lb
5.7 lb
54.6
kg
57.2 kg
2.6 kg
Average BMI
20.7
22.0
1.3
% overweight/obese 14.2%
25.8%
11.6
% obese
3.3%
7.4%
4.1

Another problem with overweight and obesity rates based on self-reports is variation in the mode
of collection. Self-reported data from face-to-face interviews result in higher obesity rates than do data
collected from telephone interviews.22 In 1994/95, almost all interviews were conducted in person; in
1996/97 and 1998/99, most were by telephone; in 2000/01, it was approximately half and half; and in
2003, about one-quarter were in person.
For children aged 2 to 11, reported and measured data reveal a different bias. The data for
1994/95 to 2002/03 come from the National Longitudinal Survey of Children and Youth (NLSCY), in
which parents reported the child’s height and weight (Charts 18 and 19). A comparison with the directly
measured 2004 CCHS data suggests that when parents report on behalf of their children, overweight and
obesity rates are higher, largely because parents tend to underestimate their children’s height. It is
possible that they report the height when the child was last measured, which could be inaccurate given
how quickly children of these ages grow. If height is routinely underestimated, the result would be
substantial overestimates of overweight and obesity.
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