Blaine is exercising and back on solids, starting with a handful of crisps

David Blaine, whose 44-day fast ended last week, has taken his first small steps (and mouthfuls) towards normality.

He emerged from his self-imposed fast last Sunday, and was taken to the London Independent Hospital, where he is expected to remain for another week.

He is now eating solids and taking light exercise as doctors continue to monitor his body for any long-term damage.

Catherine Collins, chief dietician at St George's Hospital in south London, said: "The first 48 to 72 hours would have been crucial. His medical team would have wanted to keep a close check on him, particularly to monitor his heart and other organ functions.

"If he had a serious iron deficiency and had become anaemic, which is possible, they may have decided to give him a blood transfusion."

Towards the end of his fast, Blaine's body will have turned on itself for survival, breaking down muscle and tissue around the liver, heart and kidneys. The destroyed cells will have led to a depletion of vital salts such as potassium and magnesium, forcing the body to turn to the blood for supplies. Low electrolyte levels in the blood will have increased the risk of him having a heart attack.

Ms Collins, who tested Blaine's urine during the stunt, added: "I would imagine that he was tube fed for the first few days. His stomach will have shrunk and his lungs will have wasted, making it difficult to swallow and tolerate food. The doctors will have had to insert the feeding tube very carefully, as the fibral muscles of the oesophagus and stomach will have wasted, increasing the risk of perforation."

Blaine was fed vitamin and salt solutions for the first few days, to ensure levels of potassium and magnesium were increased to a point where new tissue and muscle cells developed around his vital organs.

Fibre-rich foods and milk were avoided, as his body had destroyed the enzymes and digestive bacteria which make it possible to tolerate them. "Anything containing lactose, such as milk, could cause an explosive case of diarrhoea and wind," explained Ms Collins.

Blaine, who lost four stone during his stunt ­ suspended in a plastic box near Tower Bridge in London ­ may have seemed to gain weight literally overnight, she said.

"He would have appeared to put on a kilogram in the first 24 hours, but that would have been mainly due to extra water carrying new glycogen [sugar] supplies to the body."

Few details have been given about Blaine's treatment, although it was announced that on Thursday he had eaten his first solid food ­ a handful of potato crisps.

Ms Collins said: "Crisps are ideal as a first food. They are relatively easy to eat, because they crumble in the mouth, and the vegetable oil gives him calories. They are low in fibre, but have the complex carbohydrates and potassium he needs."

Milk and fibre will be introduced over the next few days, as Blaine's body begins to function normally again. Ms Collins said: "He is a previously fit, healthy young man who, unlike someone who is anorexic, wants to eat, so he should have relatively few problems.