An X-ray computed tomography scan at Siriraj Hospital showed his stomach, intestines, liver and kidney are functioning normally, it said.
A follow-up blood test on Friday also found his nutritional status had improved and no inflammation was detected.
As well, the royal doctors reported His Majesty was healthier and had gained weight, eliminating the need for intravenous nutrient supplements.
His Majesty has been in Bangkok since Aug 6 for a comprehensive physical checkup after he stayed at Klai Kangwon Palace in Prachuap Khiri Khan province for a little over a year.
His Majesty the King is 87 years old.