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Obese people are significantly more likely to survive severe illness due to infections, as compared to people with normal weights, according to analyses of three large data sets presented at a European conference.
Among more than 1.5 million hospitalizations for pneumonia in the U.S. between 2013-2014, obese patients (BMI > 30) were 29% more likely to survive to discharge, compared to patients with normal weights (BMI ≤ 26).
In more than 3 million hospitalizations for sepsis in the U.S., obese patients were 23% less likely to die than healthy-weight patients.
In Denmark, among 18,000 people admitted to hospitals with various infections, people who were obese were 50% less likely to die compared to people with normal weights.
The findings are consistent with previous studies, which have shown that obese patients were much more likely than normal-weight patients to survive to discharge after heart surgery. Even extremely obese patients have been observed to have better chances of survival from critical illness, compared to normal-weight people.
The data appears on its face to contradict the reams of studies showing obesity increases the risk for diabetes and cardiovascular disease, as well respiratory failure and many cancers.
Dubbed the "obesity paradox," it might not be a paradox at all, just more complicated than the "fat is bad" story. Obese patients are more likely to get ill generally, and also seem more likely to survive among the small fraction of people who become most severely ill.
The most widely believed explanation for the apparent survival benefit of obesity in critical illness is that obese patients have a larger energy reserve they can tap during periods of extreme or prolonged illness.
Normal-weight patients, by contrast, deplete their fat reserves more quickly, and begin consuming their muscle reserves sooner than obese patients. Muscle wasting increases risk for weakness and disability, and can reduce the ability to produce antibodies to fight infections.
It has also been argued that the "normal" weight patients had more advanced illness (being previously obese themselves, but now withered down to normal weight through their illness). However, the finding appears too robust to be explained away in this fashion. Most patients admitted to ICUs have not experienced significant weight loss prior to their episode of critical illness.
Source: The Guardian