News & Views
Researchers Weigh Risks Due to Overweight
Article first published online: 31 DEC 2008
Copyright © 2005 American Cancer Society
CA: A Cancer Journal for Clinicians
Volume 55, Issue 5, pages 268–269, September/October 2005
How to Cite
(2005), Researchers Weigh Risks Due to Overweight. CA: A Cancer Journal for Clinicians, 55: 268–269. doi: 10.3322/canjclin.55.5.268
- Issue published online: 31 DEC 2008
- Article first published online: 31 DEC 2008
After several weeks of debate among researchers and confusion among the general public, it has become increasingly clear that being overweight is not good for your health.
In an article published in the April 20, 2005, issue of JAMA (2005;293:1861–1867), scientists from the Centers for Disease Control and Prevention (CDC), led by Katherine Flegal, PhD, estimated the excess deaths associated with underweight (body mass index [BMI] less than 18.5), overweight (BMI 25 to less than 30), and obesity (BMI 30 or higher). As expected, substantial mortality—111,909 deaths during 2000—was attributed to obesity. The researchers attributed 33,746 deaths to being underweight but, surprisingly, being overweight appeared to have prevented 86,094 deaths during 2000.
The results were applauded in advertisements from organizations affiliated with the food and restaurant industry as evidence that the concern about the health effects of overweight and obesity constitutes unsubstantiated hype spread by trial lawyers and the “food police.” Other researchers, however, questioned the new CDC findings.
The new figures were vastly different from those in an earlier CDC analysis which attributed some 365,000 deaths to poor diet, physical inactivity, and excess weight (JAMA 2004;291:1238–1245 and 2005;293;293–294), although this earlier article did not report the methods used to estimate the mortality attributed to obesity.
Over the subsequent weeks, epidemiologists from the ACS, American Heart Association, Harvard School of Public Health, and other organizations raised specific methodologic questions about the recent CDC study and presented analyses of other data sets.
The main concern regarding the newer CDC analysis is that it did not adequately account for weight loss from serious illnesses such as cancer and heart disease. Including such individuals in the analysis created the false appearance that being overweight protected against death during the follow up.
The newest CDC analysis also failed to account adequately for the effect of smoking on weight. Smokers tend to be a little lighter than nonsmokers, although the negative health impact of smoking far outweighs that of a few extra pounds. As a result, the Flegal study underestimated the risks from obesity and overestimated the risks of leanness.
“Measuring the effect of excess weight on survival is difficult precisely because of these issues,” says Michael Thun, MD, MS, ACS Vice President for Epidemiology and Surveillance. “Being sick and smoking tobacco cause people to be thinner and to die earlier. They distort the relationship between leanness and health.”
Analyses of the Society's Cancer Prevention Study II cohort and Harvard University's Nurses' Health Study both concluded that people within the range of “healthy” body weight (BMI 18.5 to 24.9) are, in fact, the healthiest and least likely to die prematurely. Obese individuals have substantially higher mortality rates (RR of up to 2.6, for example, in the ACS study), and people who are overweight have intermediate risk (RR of death per year per 100,000 people of up to 1.28, according to the ACS).
Of course, the health effects of excess weight are not limited to mortality, but also include nonfatal cancers, nonfatal heart disease, type II diabetes, and other conditions that adversely impact quality of life but which are unlikely to be fatal—arthritis, for instance.
In a June 2, 2005, press conference, CDC Director Julie Gerberding, MD, MPH, emphasized that excess weight is harmful.
“We need to be absolutely, explicitly clear about one thing: Obesity and overweight are critically important health threats in this country,” she said.
On questioning by journalists, Gerberding also downplayed the suggestion derived from the Flegal study that overweight people might have a lower risk of death.
“I think when you talk to the investigator, and I would encourage you to do that, there are some statistical aspects of the way the study was designed and the data sources used in that the author herself would not claim that overweight [is] protective of ill health,” Gerberding said.
“I know a lot of people were hoping that CDC was going to come out and say it was OK to be overweight,” she added, “but we're not saying that. It is not OK to be overweight. People need to be fit, they need to have a healthy diet, and they need to exercise.” Despite the strong statements, Thun said some people may still be confused about the true health risks of excess weight.
“Some of the methodologic issues probably seem a little abstract,” Thun said, “and it's easy to see how some overweight individuals may be more likely to believe a report suggesting there is no need for them to lose weight. However, the key message for clinicians to provide to their patients is the importance of maintaining a healthy body weight throughout life. It's easier to avoid those excess pounds than to lose them, and so weight gain should be considered just as important a problem as high cholesterol or blood pressure.”