Studies in the past have linked obesity with better outcomes for people with heart disease although obesity has also historically been a dependable risk factor for developing heart disease. Some scientists call this the obesity paradox. However, a new study from New York University, published in the journal PLOS ONE, pokes holes in the logic surrounding the obesity paradox.
When some studies found that overweight and obese patients with heart disease were more likely to fare better during a non-surgical procedure to treat the narrowing of the coronary arteries compared to normal-weight people, some researchers were quick to jump to the conclusion that there might be more to the relationship between obesity and heart disease.
The present study provides an explanation for the obesity paradox, for the phenomenon researchers see that makes obesity seem like a positive factor for surviving heart disease. The main problem is that past studies claiming findings of the obesity paradox focused on existing heart disease rather than newly-diagnosed heart disease. This focus has a tendency to skew the results of a study.
This is because that the most severe cases of heart disease lead to weight loss, so the risk factors, like obesity, that lead to the development of an individual’s heart disease might not be present at later stages of illness. Also, people with severe heart disease who are also obese are more likely to die early, making them less likely to be included in such studies where the Obesity Paradox is seen; obese people with less severe heart disease are instead included in those studies.
Ultimately, in their collaboration with the University of Michigan, NYU scientists saw that the obesity paradox was not seen in people newly diagnosed with heart disease.
"Given that many diseases result in wasting at the end of life, the notion that extra catabolic reserve can prolong survival makes intuitive sense,” explained the study’s lead author, NYU’s Virginia Chang, MD, PhD. “ However, despite the plausibility of these hypotheses, we did not find evidence of an obesity paradox when using methods that are less prone to bias.”
The new study used data from the Health and Retirement Study, whose participants are adults in the United States aged 50 years and older. Chang and her team focused on diagnoses of heart attack, chronic heart failure, stroke, and ischemic heart disease.
When they looked at people with existing disease, the risk of death was up to 36 percent lower for obese people compared to non-obese people. Bot for people who were newly diagnosed, being obese did not lower an individual’s risk of death.
"The loss of an obesity paradox when switching from prevalent to incident cases and pre-diagnosis weight in the same dataset suggests that prevalent models are likely biased by factors such as disease-related weight loss and selective survival," Chang explained.