A 15-year-old who has eaten little other than jam sandwiches for 11 years has had tests to see what effect they have had on his body.
Craig says the thought of fruit and vegetables makes him sweat
The high sugar diet has not stunted Craig Flatman's growth or energy - he is 6ft 2in and a keen sportsman.
Tests revealed that while Craig's liver and kidney functions are normal, he is close to developing iron deficiency.
"It's quite scary - I had no idea what it has done to my body," he said prior to the tests.
Craig said the thought of eating fruit and vegetables made him sweat.
Dr David Rae, who carried out the tests, said all the results were "absolutely normal".
"I have to say it surprises me a little," he said.
"But there is no doubt that some of the results suggest you may be on the borderline of developing iron deficiency," Dr Rae added.
"The symptoms can be quiet severe and serious. It's not uncommon to admit patients to hospital with profound anaemia due to iron deficiency."
He told Craig: "The bottom line is - given the choice would you rather change your eating habits sooner rather than later to continue playing all the sports you enjoy?"
Craig has pledged to change his diet as much as possible.
It is not the first time Craig has been studied. Eight years ago, when a team in London looked into why he could not face any other food, he did diversify his diet a little, but soon slipped back into his old ways.