Individuals who were obese but metabolically healthy were still at risk of cancers and other ailments, compared with those who were both healthy and fit.
The study, published in the Annals of Internal Medicine, included more than 60,000 participants and looked at findings from more than 1,000 studies.
Researchers at Mount Sinai Hospital in Toronto found that there was no healthy way to gain weight as they monitored the heart health of individuals over ten years.
People may be metabolically healthy despite being overweight, but they are still more at risk of cancers, ailments and death when compared to those who are healthy and fit, debunking the notion of "benign obesity."
"This data is suggesting that both patients who are obese who are metabolically unhealthy and patients who are obese who are metabolically healthy are both at increased risk of death from cardiovascular disease, such that benign obesity may indeed be a myth," said lead researcher Dr. Ravi Retnakaran.
While it has been argued that the risks of being overweight may be mitigated if the individual remains healthy in other ways, researchers from Mount Sinai said that such people may have underlying health risks that worsen over time.
But researchers only collected data on whether participants were "metabolically healthy" once at the start of the ten-year period, suggesting other factors could change participants' metabolic health over time.