Scientists say they have developed a 3D scanner that can accurately determine if a person is truly obese.
BVI shows fat distribution
Currently, doctors gauge fatness with a calculation of body mass index (BMI). But BMI is flawed - people with lots of muscle are considered overweight.
Instead of relying on weight and height measurements, as BMI does, the scan takes into account body shape and how much fat a person carries.
Birmingham's Heartlands Hospital has been testing this Body Volume Index.
Muscle or fat?
One human guinea pig who has tested the BVI scanner is 19-year-old rower Ashley Granger.
He is 6ft 2ins (1.88m) tall and according to his BMI of 28 is at the top end of the overweight category, borderline obese.
His BVI scan correctly showed that he carries very little fat and that his weight is largely down to muscle.
Fitness trainer Matt Roberts said: "Muscle weighs more than fat does. And you can hide away fat but be quite thin looking.
"So it's important that we don't just use BMI alone."
Ashley, pictured in the scanner, has been a keen rower for two years
Dr Asad Rahim, a consultant in the obesity and endocrinology department at Heartlands Hospital, explained the work they had done with the BVI scanner over the last two years.
"We have completed the patient evaluation stage and are currently assessing the results.
"The scanner has certainly helped motivate some patients to manage their weight more effectively but there are also patients who were not scanned who lost weight."
The next phase of testing has now been launched - the plan is to scan at least 20,000 people over the next two years as part of the Body Benchmark Study.
Select Research, the company which makes the scanners, said it hoped to make them available to GP surgeries at an "affordable" cost.