Leading Chinese human rights campaigner Gao Zhinsheng has been left "utterly destroyed" by his three year incarceration, said his lawyer Jared Gensher.
Mr Gao, 50, was released from jail last week, and Mr Gensher said he was emotionless, "basically unintelligible," and had lost teeth through malnutrition.
"He is able to say a few words here and there and answering questions in a few words, describing what he went through," Gensher told the BBC.
"But he's not capable of holding any conversation and there are many occasions where he's literally just muttering to himself."
He was prosecuted after defending members of the Falun Gong movement, which is banned in China.
A daily diet of cabbage and a single slice of bread also caused Mr Gao to lose 20 kg in jail, said Washington DC-based human rights group Freedom Now, which had repeatedly called for Gao's release.
They said that he had been confined in a tiny cell in a jail in the far western region of Xinjiang, with very little light, and had been deprived of human contact.
His wife, Geng He, said she was "completely devastated" by what the Chinese government had done to her husband.
"The only thing I feared more than him being killed was his suffering relentless and horrific torture and being kept alive," she is quoted as saying.
She urged Chinese authorities to let him seek treatment in the US, where she has been living since 2009 with their two children.
Gao is known for campaigning in favour of religious freedom in China, and in 2008 was nominated for the Nobel Prize.
He was arrested in 2009, and accused of inciting subversion.
After being released briefly in 2010, he claimed he had been tortured in jail.
In 2011 he was jailed again, with state media reporting that he had broken the terms of his probation.