King Abdullah had ordered Khalid Mohsen Al-Shaeri to undergo treatment here in August.
Suffering from extreme obesity, Shaeri from Jazan was successful in cutting down his weight from 610 kg to 290 kg following specialised treatment at the King Fahd Medical City (KFMC) in Riyadh.
Losing 320 kgs in four months is a record, Arab News quoted medical experts as saying.
Shaeri's treatment has now reached an advanced stage, Dr Ayed Al-Qahtani, consultant, laparoscopic surgery and obesity at KFMC was quoted as saying.
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"We have also manufactured a custom-made huge wheelchair for him. This again is a record in that it is the largest medical chair in the world," Qahtani was quoted as saying.
Twenty-one consultants and 15 nurses besides his mother have been taking care of Shaeri.
In the first three months of treatment, he lost 150 kg. A surgical operation of the abdomen helped him lose a further 170 kg.
"We have been providing him with special food imported from the US," Al-Qahtani said.
In the past, Shaeri used to sleep on three beds and now he sleeps on one.