From heart attack and stroke to diabetes, it seems like we’re constantly bombarded with warnings about the health risks that come with carrying extra weight. But could being overweight actually lower your risk of death?
Though it sounds counter-intuitive, a very large international study seems to suggest that the answer may be yes, reports the Los Angeles Times.
“These findings are not a complete surprise,” says Robert Ross, a professor at Queen's University's Faculty of Medicine and an obesity expert. “The article poses information for further investigation, but should not be interpreted as a pass to gain weight and stop exercising.”
The new analysis, published Tuesday online in the Journal of the American Medical Association (JAMA), suggests that the relationship between body mass and death risk may be a little more complicated than previously thought.
The report pools data from 97 studies including three million adult individuals from United States, Canada, Europe, Australia, China, Taiwan, Japan, Brazil, India and Mexico. During the course of the studies, 270,000 people died, and researchers examined the correlation between death rates and Body Mass Index (BMI).
They found that significantly obese individuals (with a BMI of 35 or more) were 29 per cent more likely to have died during the study period than people of so-called regular weight (with a BMI of 18.5 to 24.9), but that people classified as just overweight (with a BMI of 30 to 34.9), had slightly lower death rates (about 6 per cent) than their peers of regular weight.
Could this suggest that individuals in the overweight category have some sort of survival advantage over individuals of regular weight?
"As someone who studies the adverse effects of high BMI's and excess body fat in children, these results definitely challenge conventional thinking and the large body of evidence of the increased health risks associated with excess body fat," says Nick Bellissimo, a professor at Ryerson University's School of Nutrition. "The protective effect of a slightly higher body weight, but not obese, is interesting and these studies have appeared in the research literature from time to time, but it is unclear how excess body weight confers health benefits."
Experts posit a variety of theories as to why these numbers contradict the widespread belief that being overweight will increase the risk of death, not decrease it.
“Lower region body fat can actually be protective,” says Ross, who hypothesizes that body fat distribution may play a role in the numbers. He explains that depositing excess energy in the lower body region is not necessarily harmful, but that excess fat in the abdominal region is a strong indicator of many health risks.
“The shape of obesity is something we need to consider when looking at this,” says Ross. “Among those within the BMI which was found to be protective, could it be they have a predominance of lower body fat accumulation and not abdominal body fat accumulation?”
Ross also acknowledges the theory that overweight and obese individuals may be more likely to be screened and treated for a range of health problems than individuals of a so-called healthy weight.
It’s also worth noting that the study examines only one indicator of health: death.
“The only end point analyzed was mortality,” says Lawrence A. Leiter, a professor of Medicine and Nutritional Sciences at the University of Toronto and the president of the Canadian Society of Endocrinology and Metabolism.
While death is clearly an indication of health, Leiter points out that the study doesn’t provide an in-depth examination of the overall health of those studied.
“For example when it comes to risk for diabetes, it's a different relationship,” says Leiter, and that relationship is a very clear one. “The more overweight you are, the greater the risk.”
Leiter says that the study reinforces the need to look beyond BMI when assessing general health.
Antony Karelis, a professor of kinesiology at the University of Quebec at Montreal, says these finding are not surprising and points to other studies published in JAMA that suggest being overweight could be associated with health benefits.
“In addition, there is evidence to suggest that being overweight may be beneficial for elderly individuals,” says Karelis.
One theory is that overweight elderly people are less likely to have osteoporosis and die of a fall, while another posits the extra weight provides energy reserves in cases of severe illness.
But like virtually all obesity experts, Karelis warns the results should not be interpreted as a free pass to pack on the pounds.
“I would be cautious with the results of this study,” says Karelis. "If you become overweight, your risk of becoming obese also increases and, as suggested by this study and many others, obesity increases your risk of mortality.”
Instead, the results reconfirm the complicated relationship between weight and health, and the inadequacy of BMI as an indicator of general health.
“I believe the term healthy or even normal weight should not be used," says Karelis, "Since it could be misleading in light of recent studies, including this one."