According to experts, the key is being "metabolically fit", meaning no high blood pressure, cholesterol or raised blood sugar, and exercising.
Looking at data from over 43,000 US people they found that being overweight per se did not pose a big health risk, the 'BBC News' reported.
More than a third of the participants were obese in the study conducted at the University of South Carolina.
Of these 18,500, half were assessed as metabolically healthy after a physical examination and lab tests.
This subset of metabolically healthy obese people who did not suffer from conditions such as diabetes, high cholesterol or high blood pressure, were generally fitter and exercised more than the other obese people.
Their risk of developing or dying from cardiovascular disease or cancer was identical to people of ideal weight and was half that of "metabolically less fit" obese people.
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Lead researcher Dr Francisco Ortega, who currently works at the University of Granada in Spain, said the findings show that getting more exercise can keep you healthier, even if you still carry a bit of extra weight.
"This research highlights once again the important role of physical fitness as a health marker," Ortega said.
Most of the men and women in the study came from a similar background, meaning the results may not apply to everyone.
They were mostly Caucasian, well educated, and worked in executive or professional positions.
"In the majority of cases, obesity is an undeniable risk factor for developing coronary heart disease. However, these studies remind us that it is not always your weight that's important, but where you carry fat and also how it affects your health and fitness," Amy Thompson, of the British Heart Foundation, said.
The results were published in the European 'Heart' Journal.