MedicalResearch.com Interview with:
Dr. Samuel H. Preston Ph.D
Professor, Department of Sociology and Population Studies Center
University of Pennsylvania
Medical Research: What is meant by the Obesity Paradox? Is it reported more in some groups?
Dr. Preston: The obesity paradox is a term that is used when a study finds that obese people have lower mortality than non-obese people. The finding is considered paradoxical because the obese do not have lower mortality in cross-sections of the general population. The paradox is, however, commonly observed among people who suffer from a particular illness such as heart disease or diabetes.
Medical Research: What are the main findings of your study? What is reverse causation and how does it affect obesity studies?
Dr. Preston: We find in a nationally representative sample that, among people suffering from cardiovascular disease, mortality is indeed lower for people who are overweight or obese than for people of normal weight. So the paradox appears among this group. However, when we study people’s mortality according to their maximum lifetime weight, the paradox disappears. We attribute its disappearance primarily to the fact that many people who have lost weight from their maximum are doing so because they are ill. This phenomenon is referred to as “reverse causation” because illness is affecting weight rather than weight affecting illness and mortality.
Medical Research: What role does smoking play in your study?
Dr. Preston: When we limit the population under study to those with cardiovascular disease who have never smoked, we find that the obesity paradox is reversed: those who are overweight or obese have significantly higher mortality than those of normal weight. Smoking is a tremendously important factor in the relation between obesity and mortality because smokers are less likely to be obese and much more likely to die. This inverse relation between smoking and obesity is much stronger among those with cardiovascular disease than in the general population. Imagine that there were only two ways to develop cardiovascular disease, by being obese or being a smoker. Then among those with cardiovascular disease, those who were NOT obese would all be smokers and subject to the very high mortality risks of smokers. You can see the capacity for statistical confusion posed by smoking. When we control it, the hazards posed by obesity among those with cardiovascular disease become clear.
Medical Research: What should clinicians and patients take away from your report?
Dr. Preston: Weight status among patients with cardiovascular disease provides clues to clinicians about the healthiness of their patients. Those who are obese are in fact subject to lower mortality than those who are not. But that is simply because they are less likely to be smokers and less likely to be losing weight because of their underlying illness. It is not a prescription for weight gain: people with cardiovascular disease should strive to maintain normal weight.
Dr. Samuel H. Preston Ph.D (2015). Obesity Paradox Tied To Smoking and Illness-Induced Weight Loss