The so-called “obesity paradox” has long been cited as a truly perplexing phenomenon – and a damn good excuse for not going on a diet.
Now, however, a fresh study has taken much of the comforting gloss off the subject, revealing that in the matter of heart disease there is no riddle involved.
The term “obesity paradox” first came into fashion following a number of studies that found that while being obese in the general population carried with it known health risks, obese people with some chronic diseases tended to fare better than lean people with the same condition.
A study in 2001 was perhaps the first to come up with evidence for such a counter-intuitive outcome. Researchers at the University of California took 1203 people with advanced heart failure and subjected them to a battery of tests.
Surprisingly, they discovered that overweight and obese people actually returned better results than their normal-weight or underweight colleagues. Having a high body mass index (BMI), the researchers concluded “was not a risk factor for increased mortality, but was associated with a trend toward improved survival”.
Other studies in the following few years came up with similar results. Then, in 2005, a study in the Journal of the American Medical Association (JAMA) became the first to use the term “obesity paradox” in formal literature.
It was used as the title of another JAMA paper written by a team led by Jeptha Curtis of the Yale School of Medicine in the US. The paper reported results of a study involving 7767 patients with chronic heart failure.
The research found that all-cause mortality rates decreased “in a near-linear fashion” as the weight of patients increased, with the underweight cohort recording a mortality rate of 45% and the obese group clocking up just 28%.
After adjustment for confounding factors, the pattern remained robust. Curtis and his colleagues reported that “overweight and obese patients were at lower risk for death compared with patients at a healthy weight”.
Now, however, a new study, once again in JAMA but this time taking a longer view, looks set to reveal the obesity paradox as a myth – or perhaps, more accurately, a mirage produced by narrow focus.
The research, led by Sadiya Khan from the Northwestern University Feinberg School of Medicine in Chicago, US, looked at data accumulated through 10 population-based studies, tracking 190,672 people. The studies covered a total of seven decades, and looked at weight status and the advent (or not) of a range of cardiovascular diseases.
The results were sobering. The scientists found that cardiovascular disease risks were significantly higher for overweight and obese people compared to those of normal weight. Furthermore, overweight and obese people were more likely to develop cardiovascular diseases earlier then their normal-weight counterparts, meaning that on average they lived with the condition for longer.
Obesity carried a greater risk than overweight. “Obesity was associated with shorter longevity and significantly increased risk of cardiovascular morbidity and mortality compared with normal BMI,” the paper concludes.
It adds, however, that although longevity for overweight and normal-weight people was similar, being overweight “was associated with significantly increased risk of developing CVD at an earlier age, resulting in a greater proportion of life lived with CVD morbidity”.
Commenting on the research, Khan says the results show there are multiple benefits to be gained from staying trim.
“The obesity paradox caused a lot of confusion and potential damage because we know there are cardiovascular and non-cardiovascular risks associated with obesity,” she says.
“I get a lot of patients who ask, ‘Why do I need to lose weight, if research says I’m going to live longer?’ I tell them losing weight doesn’t just reduce the risk of developing heart disease, but other diseases like cancer. Our data show you will live longer and healthier at a normal weight.”
Andrew Masterson is a former editor of Cosmos.
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