WEDNESDAY, March 2 --, 2011 (HealthDay News) -- When it comes to land mass, Canada may claim bragging rights. But when it comes to the average girth of its citizens, Americans are typically bigger than their neighbors to the north, a new study of adult obesity rates in both countries shows.
The bottom-line: A little more than a third of all Americans are now obese, beating out Canada by about 10 percentage points.
The report was a joint effort from Statistics Canada and the U.S. Centers for Disease Control and Preventions National Center for Health Statistics.
"We had two great data sets that were really very comparable," noted study co-author and NCHS epidemiologist Cynthia L. Ogden. "And what we see is that while obesity has increased in both countries, we have a higher prevalence in the U.S."
Ogden and her colleagues report their findings in the NCHS's March Data Brief.
The study found that while Canada's obesity rate is hovering at about 24 percent, that rate in the United States exceeds 34 percent.
In the United States, the authors relied on information contained in National Health and Nutrition Examination Surveys, conducted between 1988 and 1994 and then again between 2007 and 2008.
In Canada, the team crunched numbers gathered by the Canadian Heart Health Survey between 1986 and 1992, as well as the Canadian Health Measures Survey, conducted between 2007 and 2009.
None of the data involved children, but focused instead on adults between the ages of 20 and the mid-to-late 70's (depending on the particular survey).
The most recent numbers on obesity show American men maintaining an eight-point lead over their Canadian counterparts (nearly 33 percent vs. about 24 percent). U.S. women, meanwhile, were 12 percentage points higher in terms of obesity than Canadian women (approximately 36 percent vs. nearly 24 percent).
The research team broke down obesity into three groups, by ascending levels of body-mass index (BMI), which measures body fat based on height and weight. No matter which group they looked at, Americans were still more obese.
Within the BMI ranges of 30.0 to 34.9, 35.0 to 39.9 or over 40.0, a level classified as morbidly obese in the United States, the percentage of Americans who are now obese was between 32 percent and 34 percent. By way of comparison, Canadian obesity rates ranged between about 25 percent and 27 percent.
Among the most obese, however, the spread was much narrower (5 percent of Americans vs. 3.5 percent of Canadians).
However, the disparity shrank slightly when researchers factored out very high rates of obesity among minority populations in the United States. Among whites in Canada and the United States, Americans were still more overweight, but the gap was smaller (33 percent vs. 26 percent).
The study authors also pointed out that the ethnic mix in each country is different. The American non-white population is comprised mainly of Hispanics and blacks, they noted, who are more likely to become obese than white Americans.
In contrast, Canadian non-whites are composed primarily of East/Southeast Asians, who are less likely to become obese than white Canadians.
Ogden noted that Canada also had a lower obesity rate 20 years ago, compared with the United States. But the obesity rates on both sides of the border have been rising steadily over the past two decades.
What's more, in both countries the trend towards bigger waistlines was spread pretty evenly across all adult age groups, the team found, with the biggest rise in men occurring between the ages of 60 and 74. In women, the biggest rise was seen in the 20-to-39-year-old set.
Ogden stressed that their current effort was simply to get a grip on national trends and the current status quo, rather than an attempt to figure out the underlying causes.
"Certainly related to what contributes to obesity, there are a lot of factors that affect both countries," she noted. "Over time, we have had a change in the type of diet we consume, as we eat out more frequently, our portion sizes are bigger and we're not as physically active."
"But for this, we did not look at dietary content, sedentary levels, or the many other things that can influence obesity rates," Ogden said. "That would, of course, be very interesting to look into with further research."
A sophisticated follow-up analysis within each population group is exactly what needs to happen next, agreed Alice H. Lichtenstein, director of the Cardiovascular Nutrition Lab and a professor of nutrition at the USDA Human Nutrition Research Center at Tufts University in Boston.
"There could, of course, be a whole host of similar trends or perhaps some real differences in the way the two countries break down" in everything from urban and rural lifestyles and socioeconomic levels to physical activity and occupations, said Lichtenstein, who is also the former chair of the American Heart Association's nutrition committee.
"I also would personally be very interested in looking at food availability issues," she added. "How easy is it to, say, jump in a car and get a McDonald's hamburger at 11 at night in very rural Canada? What would the availability of 24/7 stores be where one get a bag of chips and a bottle of soda whenever one wants, as I know I can where I live. These are the sorts of questions that now need to be asked."
For more on obesity, visit the U.S. Centers for Disease Control and Prevention.