Could being overweight benefit our health?

It is common knowledge that being overweight can have negative implications for our health. But can it also have benefits? Two new studies suggest that being overweight may actually protect against death from cardiovascular causes.

According to the US Centers for Disease Control and Prevention (CDC), 69% of adults over the age of 20 are either overweight or obese - a statistic that has caused concern given the health problems associated with being overweight.

In particular, overweight and obesity has been linked to cardiovascular complications. Last year, researchers reported on a study published in JAMA, which suggested long-term obesity can cause heart disease. A more recent study found that heart disease was a main cause of death among individuals with class 3 obesity - deemed "extreme obesity."

But these latest studies, recently published in the journal Mayo Clinic Proceedings, oppose such findings. They support a theory known as the "obesity paradox" - the belief that being overweight may protect against certain medical conditions; in the case of these studies, it may protect against adverse cardiovascular outcomes.

Overweight patients 'had lowest all-cause and cardiovascular mortality risk'

For the first study, researchers at the State University of New York Downstate Medical Center in Brooklyn, NY, conducted a meta-analysis of 36 studies that looked at the outcomes of patients with coronary artery disease (CAD) who underwent coronary revascularization procedures, including percutaneous coronary intervention (PCI) and coronary artery bypass graft (CABG).

Could being overweight or obese actually benefit our health? Researchers found that a higher BMI may have protective effects for the heart.

The team found that patients with a low body mass index (BMI) - defined as less than 20 kg/m² - had a 1.8- to 2.7-fold increased risk of heart attack and all-cause and cardiovascular mortality over the 1.7-year follow-up period.

However, they found that patients with the lowest cardiovascular mortality risk were those who were overweight - a BMI of 25-30 kg/m². In addition, patients who were obese (a BMI of 30-35 kg/m²) had a 27% lower risk of all-cause mortality than those with a normal BMI (20-25 kg/m²), while those who were severely obese (a BMI over 35 kg/m²) had a 22% lower risk of all-cause mortality.

Although the reasons for these findings are unclear, the research team says that patients who are overweight are more likely to be prescribed medications that protect cardiovascular health - such as beta blockers and statins - which may explain the more favorable cardiovascular outcomes among this population.

"Further," the team adds, "obese and overweight patients have been found to have large coronary vessel damage, which might contribute to more favorable outcomes. This population may have a higher metabolic reserve, which might act protectively in chronic conditions like CAD. Also, there could be a difference in the pathophysiology of cardiovascular disease in over- and underweight patients. A non-modifiable genetic predisposition may also play a role in underweight patients."

However, the research team notes that further studies are warranted to investigate the mechanisms behind the association between overweight and obesity and better cardiovascular outcomes.

Body composition 'plays a critical role in obesity paradox'

For the second study, cl;inical investigators at the John Ochsner Heart & Vascular Institute at the University of Queensland School of Medicine in New Orleans, LA, analyzed how body composition - specifically lean mass index and body fat - affected BMI and mortality among 47,866 individuals with a preserved left ventricular fraction of more than 50%.

The researchers found that overall, higher BMI was associated with lower mortality. Those with a higher lean body mass - the mass of the body minus fat - had a 29% lower risk of mortality. In addition, the team found that low body fat was only associated with lower mortality if no adjustment was made for lean body mass, which suggests that "body composition plays a critical role in the obesity paradox." 

The research team adds:

"Whenever examining a potential protective effect of body fat, lean mass index - which likely represents larger skeletal muscle mass - should be considered. At higher BMI, body fat is associated with an increase in mortality."

Commenting on both of these studies, Dr. Kamyar Kalantar-Zadeh, of the Department of Medicine at the University of California Irvine Medical Center, notes that the findings should not be used to "undermine the legitimacy of the anti-obesity campaign in the best interest of public health."

"Nonetheless," he adds, "given the preponderance and consistency of epidemiologic data, there should be little doubt that in certain populations higher BMI, which is associated with higher risk of metabolic syndrome and poor cardiovascular outcomes in the long-term, confers short-term survival and cardiovascular advantages."