The 29-year-old former star of "The Bachelor" was put on life support at University Hospital in New Orleans on Monday night.
Allemand had reportedly been upset about her rocky relationship with her boyfriend, NBA player Ryan Anderson. He found her body at her home Monday night, according to TMZ.
Her mother and Anderson were reportedly at her bedside when she died.
Allemand appeared on season 14 of "The Bachelor" and the first season of its spinoff, "Bachelor Pad."
Ex-Bachelor and Bachelorette star Ali Fedotowsky tweeted that Allemand “appeared healthy” when she saw her on Monday.
On Sunday, the day before she was hospitalized, Allemand posted this on her Twitter page.
Just posted a photo http://t.co/j835W8ibQb— Gia Allemand (@GiaAllemand) August 11, 2013
Friends, fans and former colleagues flooded Twitter with messages of support.