BMI: being overweight associated with greater longevity

February 12, 2010 – People with a body mass index (BMI) of 25 or more are said to live 17% longer than those at a healthy weight.

This is what emerges from a study involving more than 11,300 Canadians¹.

At the start of the study in 1994, participants had a BMI equal to or greater than 25. Twelve years later, their BMI was measured again.

After isolating the other risk factors, the researchers found that those who were overweight (BMI 25 to 29.9) had a 15% lower risk of dying – from all causes – compared to those who were of normal weight. (BMI 19 to 24.9).

Even those who suffer from moderate obesity (BMI of 30 to 34.9) would see their risk of death decrease by 5%, compared to their compatriots at normal weight.

However, this risk was 36% higher for people with severe and morbid obesity (BMI of 35 and over), and 73% higher in those suffering from thinness (BMI of 18.5 or less).

These results followed the same trends regardless of the age groups or gender of the participants.

Protector, fat?

The Canadian study is not the first to show that being overweight is not an increased risk factor for death. But it tends to show that it might even have a protective effect.

Even more, a recent study of 9,000 subjects aged 70 and over indicates that those who were overweight (BMI 25 to 29.9) saw their risk of dying decrease by 13% in the next 10 years, compared to their peers with a normal BMI².

Does this mean that being coated is synonymous with being healthy?

“There is no longer any doubt that a BMI of 35 or more increases the death rate, but between 25 and 35, there is indeed controversy” says Dr Dominique Garrel, endocrinologist and professor in the Department of Nutrition at the Montreal university.

According to him, different types of obesity exist. And obese people struggling with the symptoms of metabolic syndrome would be significantly more at risk than others of developing cardiovascular disease or dying prematurely.

“Metabolic syndrome is worse than weight for heart health and longevity,” says the one who will soon publish a book on obesity.

Another important element: a sedentary lifestyle doubles the risk of dying at any age. “However, a lot of obese people are sedentary,” adds Dr. Garrel.

Nonetheless, it appears that fat has some protective effect on overall health, he admits.

“There are two paradoxes with moderate obesity: not only does excess weight not reduce longevity, obese people survive more than non-obese when admitted to intensive care, regardless of the cause”, he indicates.

Why?

We don’t know. But Dominique Garrel makes some assumptions.

“If they have more fat mass, obese people also have more lean mass, which contains more protein and which could play a protective role,” he argues.

Second, people who are overweight need more calories to get their metabolism going. “And the more calories we absorb, the more we absorb other essential nutrients, especially if the diet is varied: those who are less weight could suffer from certain deficiencies,” he says.

Finally, it is possible that, after a certain age, being overweight protects the bones against falls and the risk of fractures.

“But you have to assess how dangerous excess fat is or not, which varies from person to person,” warns Dr. Garrel. Beyond longevity, there is the quality of life that must be taken into account and, on this point, people with normal weight have an advantage. “

Martin LaSalle – PasseportSanté.net

1. Oprana HM, et al, BMI and Mortality: Results From a National Longitudinal Study of Canadian Adults, Obesity, January 2010, vol 18, no 1, 214-218.
2. Flicker L, et al, Body Mass Index and Survival in Men and Women Aged 70 to 75, Journal of the American Geriatrics Society, vol 58, no 2, 234-41 [publié en ligne le 27 janvier 2010].
3. To calculate your BMI: www.passeportsante.net/Test_IMC.aspx.