The question
Statistics Canada says being overweight makes you live longer. Should I stop exercising?
The answer
Let's start with the facts. In June, Statistics Canada researchers did indeed publish a study in the journal Obesity based on a 12-year analysis of 11,326 Canadian adults in the National Population Health Survey. They found that subjects who were overweight (body mass index of 25 to 30) were 17 per cent less likely to die during the study period than those of normal weight (BMI of 18.5 to 25).
Now on to the interpretation.
These results fit right in with a growing amount of evidence that body weight is not the absolute indicator of health we once thought.
But that doesn't mean exercise isn't important. In fact, it turns out that physical fitness is a far better barometer of your long-term health than weight is - and that holds true even for thin but inactive people who thought their fabulous metabolism meant they didn't need to exercise at all.
Steven Blair, a professor at the University of South Carolina, has performed a series of studies dating back to 1994 trying to distinguish between obesity and physical inactivity as causes of health problems.
"When we look at obesity and properly adjust for fitness, the obesity risk goes away," he says. "It just disappears."
In fact, he says, obese people who are physically fit are half as likely to die as people of normal weight who don't exercise.
This message is particularly crucial for people who start exercising and soon get frustrated - and perhaps quit - because they don't succeed in losing weight. As long as they're meeting basic exercise goals such as 150 minutes of moderate exercise or 75 minutes of vigorous exercise each week, Dr. Blair says, they're gaining important health benefits no matter what the scale says.
Seen in this light, the Statscan results are less surprising - in fact, they closely mirror the results of a similar U.S. study from 2005, which also found that those carrying a few extra pounds lived longer.
"As you age, you start to lose weight and become frail," notes David Feeny of Kaiser Permanente Center for Health Research in Portland, one of the Statscan study's authors.
For the elderly, among whom most of the deaths in the study occurred, a few extra pounds may provide a margin of error to help them through the illnesses and accidents that become common at that age.
In addition, a more vigilant health-care system that watches for warning signs such as high blood pressure may have actually succeeded in lowering the penalty for being obese over the past few decades, Dr. Feeny says.
Still, BMI remains a fairly blunt tool with which to judge your body shape.
"It's most useful in population studies," says Travis Saunders, a graduate researcher at the Children's Hospital of Eastern Ontario Research Institute in Ottawa who blogs about obesity research at ObesityPanacea.com. "But if you try to apply it to individuals, it doesn't work."
That's because where you store fat is as important as how much you have. Fat in the abdominal region, particularly the visceral fat that accumulates between internal organs rather than fat stored just beneath the skin, is particularly problematic. In contrast, Mr. Saunders says, fat on the hips, buttocks and lower body appears to be less of a concern.
For that reason, many doctors now measure waist circumference as a proxy for visceral fat. Ideally, men should be less than 102 centimetres (40 inches) and women should be less than 88 centimetres (35 inches), Mr. Saunders says.
Ultimately, what the Statscan research tells us is not that weight is irrelevant - after all, those with a BMI above 35 were 36 per cent more likely to die than normal-weight people - but that your focus should be on the ongoing process of living healthily, rather than the potentially misleading endpoint of reaching a certain weight.
Alex Hutchinson blogs about research on exercise and athletic performance at http://www.SweatScience.com.
Alex Hutchinson