Jose Salvador Alvarenga was taken to a hospital and found to be in good health after he hit land but Thursday he returned to the hospital to be intravenously fed, said Christian Clay-Mendoza, a top Mexican trade official said.
"Doctors say he's severely dehydrated and low on vitamins and minerals," he said.
Doctors said Alvarenga's limbs were swelling and they're unable to keep him hydrated, CNN reported.
Alvarenga and fellow fisherman Ezequiel Cordova, 24, went missing Dec. 21, 2012, after the two set off from Mexico to catch shark and shrimp in a 24-foot boat. The two lost their course due to high winds and storms, and the motor on the boat stopped working, setting them adrift in the ocean.
Cordova died after four weeks, Alvarenga said, because the younger man refused to eat the turtles, fishes, small sharks and birds they caught.
Though the story has been met with some skepticism, officials say they have no reason to doubt what Alvarenga says, CNN reported.
"The investigations into Mr. Alvarenga's story so far have been substantiated," said Phillip Muller, the Marshall Islands' foreign affairs minister.