The fast, which was reported Thursday by the Argus Leader's David Montgomery, coincides with Bosworth's efforts to find legal counsel as she faces 12 felony charges related to allegations that she committed perjury on her nominating petitions for the Senate race.
She turned herself in to authorities in June, a day after she finished a distant fourth in the five candidate GOP primary.
Bosworth, a physician in Sioux Falls, S.D., has been documenting her planned 72-hour fast on Facebook.
"Just finishing a full day at the clinic. 23 hours into my fast. Still no lawyer. Several more phone calls placed & a prayer said after each one," Bosworth wrote on Wednesday.
On Thursday morning, Bosworth admitted that the lack of food had soured her mood.
"It turns out .. I get crabby when I fast. I'm at 36 hours .. 1/2 way.
My husband claims that I make Driving-Miss-Daisy look low maintenance.. Still no lawyer ..keep praying," she wrote.
Bosworth's quixotic campaign was a turbulent one, marked by both alleged improprieties on her petitions and accusations that she underpaid a former nurse.
Her long-shot bid might be best-remembered for a wild press conference in late-May, when she directed campaign volunteers to spray-paint vulgar words on the campaign signs on the walls of a Sioux Falls storefront.
The display, she said, was intended to draw attention to all of the insults she had drawn on the Internet.
Bosworth has already had one attorney withdraw from her case and has until Aug. 15 to find new counsel.