Eighteen others, who have also been refused asylum in Australia, were continuing their hunger stike at the camp on the Pacific island of Nauru, an Immigration Department spokesman said on Monday.
Four of the 18 have stitched their lips together.
The men taken to hospital are in a stable condition. A seventh detainee was treated and returned to the centre where he rejoined the protest, the spokesman said.
"The International Organisation for Migration (which manages the camp) reports that all the men who are protesting are in a good condition," he added.
Twenty-three of the protesters are Afghans while one is from Pakistan. All of them failed to qualify for refugee status and are awaiting deportation.
The hunger strike is the latest in a string of protests, riots, escapes, and suicide attempts at Australia's five onshore and two offshore immigration centres, which currently house
about 1200 people.
Three people who were on a hunger strike at Port Hedland detention centre in Western Australia have called off their protest, the spokesman said.
Australia has a strict immigration policy, detaining all asylum seekers, illegal workers and those overstaying their visas while their cases are handled, a process which can take years.
In 2001, Australia sealed its borders to a rising tide of boats, carrying mainly Middle Eastern and Afghan asylum seekers.
It also deployed the navy to intercept and divert vessels to camps on nearby Pacific islands.
Human rights groups have criticised Australia for its tough policies, but the government has won overwhelming public support for its stance.