There is no evidence to support the idea that it is possible to be healthy yet obese, say scientists, following a study of 3.5 million NHS patients.
The concept of being "fat but fit" is an "alluring theory", says the BBC, but in scientific terms, it may actually be a "big fat myth".
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Using records from 1995 to 2015, the researchers identified patients with a body mass index (BMI) of 30 or more but nevertheless appeared healthy, which was defined as exhibiting no symptoms of diabetes, heart disease, high blood pressure or high cholesterol.
They found "having excess fat increases the risk of suffering heart disease by half - even when blood pressure and cholesterol levels are normal", says the Daily Telegraph.
These patients also had a higher risk of heart failure and strokes than people of normal weight.
The report contradicts a 2012 study conducted by the University of South Carolina, which concluded it was possible to be obese yet metabolically healthy. However, that study was carried out on a far smaller number of patients over a relatively short time-frame.
While the Birmingham team's findings have not yet been subjected to peer review, the scale of the study and the apparent clarity of its conclusions has caught the eye of the medical world.
Dr Mike Knapton, from the British Heart Foundation, told the BBC the report "should be taken extremely seriously".
He added: "What was new from this study for me is that it showed that people who were overweight or obese were at increased risk of heart disease even though they may have been healthy in every other respect.
"Just being overweight puts you at increased risk of heart attack and stroke."