National Population Health Survey — Obesity: A growing issue

Once people are overweight, they are more likely to pack on even more kilos than they are to take them off, according to a new study of obesity among Canadians.

The study found that almost one-quarter of Canadians who had been overweight in 1994/95 had become obese by 2002/03. On the other hand, only half as many, about 10%, who had been overweight were in the normal weight range eight years later.

This translates to more than 1.1 million adult Canadians joining the growing ranks of the obese over the eight years. Women, younger men, and members of low-income households were most likely to become obese.

The study used longitudinal data from the National Population Health Survey (NPHS) to follow the same group of people every two years over an eight-year period. At the outset, study participants were aged 20 to 56 and aged 28 to 64 in the final year.

The study supports findings from previous research, and what many people have already discovered, that it appears easier not to put weight on in the first place than it is to take it off. As a result, interventions that focus on prevention may be more effective than efforts to lose weight.

The weight gain was not limited to overweight Canadians. The study documented that between 1994/95 and 2002/03, one-third of people who started out in the normal weight range became overweight.

Patterns differ for men, women

Men were more likely than women to make the transition from a normal weight to being overweight. At the end of the eight years, 38% of the men whose weight was normal in 1994/95 had become overweight compared to 28% of the women.

However, women were more likely to go from being overweight to being obese. By 2002/03, 28% of the women who had been overweight became obese, compared to 20% of the men. Nonetheless, even for men, given the large number who had been overweight in 1994/95 (3.1 million), this translated into more than 600,000 new cases of obesity in less than a decade, compared to almost 500,000 new cases for women

While the study does not include children, it notes that parental obesity significantly increases the risk of obesity among children.

Younger men, smokers at higher risk of obesity

Among people who were overweight in 1994/95, young adults, especially men, had an elevated risk of obesity.

During the eight-year period of the study, overweight men in their twenties and thirties were more likely than those in their fifties to become obese. Overweight women in their twenties were somewhat more likely to become obese than were those in their 50s.

Overweight men who smoked daily in 1994/95 were almost 50% more likely to have become obese by 2002/03 than were those who had never smoked.

This appeared to contradict other studies that found smokers less likely to be obese than those who had never smoked. However, further analysis of the NPHS data also found evidence of a weight gain among people who had stopped smoking since 1994/95.

As income rises, risk of obesity drops

For both men and women, being a member of a high-income household was associated with a decreased likelihood of becoming obese.

Overweight men in the richest household income categories fared better than their counterparts from households in the bottom income category. The risk of the upper-income men becoming obese was about 40% less than for men in the lowest income group.

Similarly, women in the top household income categories were less likely to become obese than women from households in the lowest income group. Again, the higher-income groups were 40% less likely to become obese.

Physical activity, occasional drinking offer some protection

Not surprisingly, overweight people who were restricted in their daily activities were at increased risk of becoming obese.

The study found the association was statistically significant for men. Physical restrictions may lead people to become inactive, thereby increasing their risk of gaining weight.

Moderate physical activity, including walking and standing, did offer overweight women some protection against obesity.

The risk of becoming obese was almost 50% lower among overweight women who reported occasional drinking, compared with those who never drank.

While a similar pattern was observed for men, the association did not reach statistical significance.

The study also examined geographic differences, but found no relationship between region of residence and the risk of becoming obese.

This analysis based its findings on height and weight measurements that respondents themselves reported. Studies have shown that both men and women who respond to health surveys tend to underestimate their weight and overestimate their height. This can potentially underestimate the rate of obesity and overweight. It is unclear how this situation would affect this study.

Definitions, data sources and methods: survey number 3225.

This release is based on the article Obesity: A Growing Issue (82-618-MWE2005003, free), which is now available online. This article is the third of four to be released in the Internet publication Healthy Today, Healthy Tomorrow? Findings from the National Population Health Survey (82-618-MWE, free). The next article will be on healthy ageing.

For more information or to enquire about the concepts, methods or data quality of this article, contact Christel Le Petit (613-951-3856; christel.le-petit@statcan.gc.ca) or Jean-Marie Berthelot (613-951-3760; jean-marie.berthelot@statcan.gc.ca), Health Analysis and Measurement Group.

NPHS micro data are available at Statistics Canada's Research Data Centres. For more information, visit The Research Data Centres Program page of our Web site.

To order custom tabulations, contact Client Services (613-951-1746; hd-ds@statcan.gc.ca), Health Statistics Division.

For further information on the Household Component of NPHS, or to enquire about the concepts, methods or data quality, contact Mario Bédard (613-951-8933; mario.bedard@statcan.gc.ca) or France Bilocq (613-951-6956; france.bilocq@statcan.gc.ca), Health Statistics Division.