Researchers analysed data from more than 6 500 participants in a San Antonio-based heart study who were followed for between six and 10 years. They were checked for high blood pressure, elevated triglycerides (a type of blood fat) and blood sugar levels, insulin resistance and low levels of "good" HDL cholesterol.
People with none or only one of these conditions were classified as "metabolically healthy", whether they were normal weight or overweight.
However, the researchers found that obese people who were considered metabolically healthy still had an increased risk for diabetes and heart disease, according to the study in the Journal of Clinical Endocrinology & Metabolism.
Not a benign condition
"Unfortunately, our findings suggest metabolically healthy obesity is not a benign condition," study corresponding author Dr Carlos Lorenzo, of the University of Texas Health Science Centre at San Antonio, said in a journal news release. "Regardless of their current metabolic health, people who are obese face an increased risk of developing cardiovascular disease and diabetes in the future."
Although the study tied so-called healthy obesity to a higher risk of developing diabetes or heart disease, it did not prove a cause-and-effect relationship.
The researchers also found that normal-weight people with multiple metabolic conditions also had an increased risk of diabetes and heart disease.
The findings show "the importance of continuing to monitor for diabetes and cardiovascular disease in both people with metabolically healthy obesity and those who have metabolic abnormalities despite being a normal weight," Lorenzo said.
"If physicians and patients are too complacent about assessing risk, we can miss important opportunities to prevent the development of chronic and even deadly conditions," he explained.
The US National Heart, Lung, and Blood Institute has more about overweight and obesity.