Chen, who was conscious when taken to hospital, allowed doctors to inject him with glucose, which stabilised his condition, but he was still suffering from a slow metabolism because of the hunger strike, Tsai Kuang-chao, a doctor at Far East Memorial hospital where he was first admitted, said on Monday.
The former president has since been moved to another hospital in suburban Taipei.
Chen began his hunger strike last Wednesday to protest against what he called his politically motivated arrest, and rejected repeated pleas from prison authorities to eat.
|Doctors stabilised Chen's condition but said he still suffered from a slow metabolism [AFP]
He has not been formally indicted, but Taiwan law allows for him to be held in jail for up to four months while prosecutors, who believe he may have amassed millions of dollars while in office, pursue the case.
Chen, a strong supporter of Taiwan's formal independence from China, has denied any wrongdoing and said he is being persecuted by his successor, Ma Ying-jeou, who favours closer economic ties with the mainland.
The probe began soon after Chen finished eight years as president in May, pushing him to withdraw from his Democratic Progressive Party in disgrace.
But he appears to have won new support as the pro-independence party now in the opposition, has used his arrest to step up criticism of the ruling Nationalist party's policy of greater engagement with China and its alleged persecution of former Chen administration officials.
Nine other people, including a former vice-premier and a former intelligence chief, are being held in connection with the corruption allegations against Chen.
Dozens of Chen supporters have being protesting daily outside the prison, demanding his release.