Millions of dieters would give their right arm to be afflicted by the illness that is plaguing John Perry.
Mr Perry, 59, can eat whatever he likes - including unlimited pies, burgers and desserts - and never get fat.
He cannot put on weight because of a condition called lipodystrophy that makes his body rapidly burn fat.
Mr Perry regularly eats Chinese takeaways, chips, chocolate and clotted cream, but his weight has remained stable at 11st 12lb.
He told the Sun that he used to be a chubby child, but at age 12 the fat dropped off "almost over night".
Doctors thought he was refusing to eat or had a stomach ulcer, he said.
He initially tried to eat more to gain weight, but it had no effect.
“I didn’t like being slim at first. As a teenager playing football I was so thin I got embarrassed taking my shirt off," he said.
“I used to eat loads of chocolate to try and put on weight but I couldn’t.”
Mr Perry, of Ilford in Essex, endured a decade of tests before the illness was diagnosed. It finally emerged that his body produces six times the normal level of insulin.
Doctors have admitted that the condition would be a "slimmer's dream".via telegraph.co.uk]