Still coughing and tired, so here’s another one I’m migrating from the old blog. –PalMD
There has been much talk in the media over the last few years about the “obesity epidemic” in the U.S. This has led to a bit of a backlash among a small but vocal group of critics who don’t believe the evidence linking obesity and poor health. The reasons for their disbelief are not all that clear to me, given the overwhelming amount of evidence linking obesity with both serious health conditions such as diabetes and heart disease, and adverse outcomes, such as premature death. When their arguments are examined in detail, most of these critics appear to be classic denialists, rather than honest skeptics. So let’s examine a small slice of the obesity pie.
When citing scientific research to back up an assertion, it is important to make sure you are not “cherry-picking” studies that support your point of view, and that you are not “quote-mining” the literature, taking statements out of context to change their original meaning. These are tactics commonly used by denialists. The way we interpret scientific literature in medicine is to examine as many studies as possible for quality, methods, and conclusions. We make decisions based on the overall picture, not on any single study. For example, if an overwhelming number of good-quality studies support the idea that smoking causes heart disease, but a couple of small studies do not support this conclusion, this does not mean that smoking does not cause heart disease.
So let’s look at a few examples of the literature on obesity. A large cohort study was published in the prestigious New England Journal of Medicine in 2006 which examined the effect of being overweight and obese on overall mortality. This was a very powerful study, involving tens of thousands of subjects. It revealed that obesity was very strongly associated with increased risk of death in a wide variety of patients. The one exception was in elderly people with very low body weight, a group who also had excess mortality. In the elderly, very low body weight usually indicates serious underlying disease, such as cancer. The study also found increasing risk of death in people who were not obese, but overweight. Some of the strengths of this study include the large sample size, and the good choice of an end point (death, which is a far more interesting end point then, say, blood pressure, as death and disability are the things people generally wish to avoid). Another strength was an analysis that excluded smokers, who have a higher mortality. Removing smokers from the analysis showed an even higher risk of death in the obese patient.
Any time a study finds a statistical link, there must also be a biologically plausible explanation that fills out the overall validity of the study. What are some of the reasons obesity might impact mortality? Obesity is strongly associated with high cholesterol and high triglycerides, both of which increase the risk of heart disease. Type II diabetes is very strongly linked to obesity, and diabetes leads to heart disease and premature death. Hypertension is also strongly linked to body mass, and hypertension leads to heart disease.
Most of these conditions can be mitigated by medication, but also by weight loss. Given how much “natural medicine” proponents hate pharmaceuticals, it’s a wonder that so many of them think obesity is just grand.
The overwhelming data on obesity, disease, and mortality are remarkable for the strength and volume of data. Few associations in medicine are as well documented. Those who continue to deny the link are deluding themselves and others.
References:
Kenneth F. Adams, Ph.D., Arthur Schatzkin, M.D., Tamara B. Harris, M.D., Victor Kipnis, Ph.D.,
Traci Mouw, M.P.H., Rachel Ballard-Barbash, M.D., Albert Hollenbeck, Ph.D., and Michael F. Leitzmann, M.D. Overweight, Obesity, and Mortality in a Large Prospective Cohort of Persons 50 to 71 Years Old. N Engl J Med. 355;8. August 24, 2006. http://content.nejm.org/cgi/reprint/355/8/763.pdf
John D. Brunzell, M.D. Hypertriglyceridemia. N Engl J Med. 357;10.September 6, 2007. http://content.nejm.org/cgi/reprint/357/10/1009.pdf
McGee DL. Body mass index and mortality:a meta-analysis based on personleveldata from twenty-six observationalstudies. Ann Epidemiol 2005;15:87-97.
Manson JE, Willett WC, Stampfer MJ,et al. Body weight and mortality among women. N Engl J Med 1995;333:677-85.
Calle EE, Thun MJ, Petrelli JM, RodriguezC, Heath CW Jr. Body-mass index and mortality in a prospective cohort of
U.S. adults. N Engl J Med 1999;341:1097-105.