Geng He said by telephone from San Francisco that Gao lost about 23 kg while in prison and now can barely eat or talk.
In 2006, Gao was convicted of subversion and released several times only to be taken away again without explanation by security agents.
His wife said he can only eat soft baby food because he has lost several teeth and others are loose.
She added that he could hardly speak when he communicated by telephone from her sister's house in the city of Urumqi in far western Xinjiang province. State security agents were watching him inside the sister's house, she said.
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The 50-year-old attorney won international renown for his courage defending members of the outlawed spiritual movement Falun Gong and fighting for the land rights of farmers.
After he was detained, he upset authorities by publicly denouncing the torture he said he had suffered.
Geng and Gao's attorney Jarod Genser are asking that he be allowed to leave China and join his wife and two children in California. His family fled China in 2009 and won political asylum in the United States.
Genser said he was told Gao had been tortured but didn't have any details about his treatment.
The first thing Gao needs, his wife said, is to fix his teeth so he can eat and regain weight. She said he has so far put on just a few kilograms since his August 7 release.