Mr Chen is being held without charge pending further investigations
Taiwan's former President Chen Shui-bian - in custody facing corruption allegations - has gone on hunger strike, his lawyer says.
Cheng Wen-lung said his client had not eaten since being sent to Tucheng jail in suburban Taipei early on Wednesday.
He said his client wanted to "protest the death of justice".
Mr Chen, who has not yet been formally charged, says he is being persecuted by his successors for his fierce opposition to closer ties with Beijing.
But that charge has been flatly denied by both the Chinese government and by Taiwan's current President Ma Ying-jeou, of the Nationalist Kuomingtang party (KMT).
Mr Chen has been a vocal and persistent critic of the KMT's China policies since he left office in May at the end of eight years in the presidency.
Mr Chen was dramatically handcuffed and detained by prosecutors on Tuesday and sent to jail early on Wednesday, since when he has not eaten, Mr Cheng said.
Mr Chen's supporters have promised further demonstrations
He wants to "protest the death of justice and the regression of democracy", Mr Cheng said, according to the AP news agency.
"He opposed the authoritarian [Nationalist] regime in Taiwan and the Communist regime [in China] and he wants sovereignty for Taiwan," Mr Cheng added.
He added that his client was in an "OK" condition for the time being.
Mr Chen could face up to four months in detention without charge to prevent him colluding with alleged conspirators. He is accused of money laundering and illegally using a special presidential fund.
But his supporters say his detention represents a breach to his human rights. Some say they plan to protest on Saturday outside the jail in which he is being held.