Are obese people more likely to survive heart surgery?
20 January 2017
Obesity has been linked to better cardiac surgery outcomes. Before you pick up the doughnuts, we look behind the headlines.
The research, funded by the British Heart Foundation, found a paradox; obesity is associated with lower risk of in-hospital death following heart surgery. This is despite overwhelming existing evidence that obese people are at higher risk of cardiovascular death in everyday life.
The researchers, from the University of Leicester, carried out a study of 401,227 adults and also reviewed previous data covering 557,720 patients from 13 countries. The participants had an average age of 59, and 27% were women.
They found that the risk of death in hospital after heart surgery was 8.5% in underweight patients, 4.4% in normal weight patients, 2.7% in overweight patients, 2.8% in obese patients who are considered to be low or moderate risk, and 3.7% in obese patients who are considered high risk due to their body mass index (BMI).
The protective effects of obesity were less in patients with severe chronic kidney, lung or cardiac disease and greater in older patients.
The reasons for these findings are unclear. A possible reason suggested by the researchers is that obese patients might be selected for surgery only if they are at lower risk in other ways. It is unclear whether there may be actual protective factors associated with obesity that contribute to better surgery outcomes.
These findings go against common practice, where weight loss is recommended prior to surgery, or where very obese patients are refused surgery. They could mean that underweight patients might benefit from weight gain interventions before their surgery.
It is unclear whether there may be actual protective factors associated with obesity that contribute to better surgery outcomes
A strength of the research was that the study was large, including nearly one million adults in total.
Studies which were lower low quality and those that used non-standard definitions of obesity were excluded.
But a limitation of this research is that it only looked at short-term mortality (i.e. deaths while still in hospital), so we don’t know how patients fared beyond that.
The BHF view
Professor Jeremy Pearson, Associate Medical Director at the British Heart Foundation, said: “Survival rates for heart surgery are now extremely high, thanks to many years of research. Although we always recommend a healthy waistline for those trying to lower their risk of heart disease, this large study strongly suggests that being overweight can give patients added protection when facing heart surgery. To properly understand why, we need to fund more research into the mechanisms involved. This could lead to new strategies to improve survival rates in normal and underweight patients following surgery.
“While this study is the largest of its kind looking at the link between obesity and surgery survival rates, it only looked at the survival rates of patients whilst they were still in hospital and cannot therefore be used to predict the long-term survival of surgery patients.”
The study was covered widely, including by The Guardian, The Mirror, and The Daily Mail. The coverage was generally quite good, however some of the articles made broad generalisations, such as that being obese will help everyone have better heart surgery outcomes. The Mail online headline was: “Obese are more likely to survive heart operations, say doctors: Being overweight found to have a protective effect on patients having surgery”. However, the research didn’t find that being overweight had a protective effect – it found that there was an association between obesity and lower in-hospital death rates, but we don’t actually know that this is cause and effect.