The story centers on a young Birmingham, Alabama, scion, played by Jeff Bridges, who gets involved in a shady real-estate deal. In order to close the deal, he needs to buy a gym building to complete a multi-parcel lot. When he visits the gym, however, he finds himself romantically interested in the receptionist (Sally Field) and drawn to the carefree lifestyle of the Austrian body builder "Joe Santo" (Arnold Schwarzenegger) who is training there for the Mr. Universe competition.
Roger Callard, one of the top bodybuilders of that era, was quoted in a 1983 bodybuilding magazine regarding an event he experienced during the making of the film. “The director was screaming over his megaphone, ‘Please do not touch the bodybuilders!’ People were rushing us, even scratching us!”
Schwarzenegger won a Golden Globe for "Best Acting Debut in a Motion Picture" for his portrayal of Joe Santo in Stay Hungry. Technically, it was not his debut role, since he had played Hercules (as "Arnold Strong") in the 1969 film Hercules in New York and a hitman in Robert Altman's 1973 film The Long Goodbye. It was, however, the first time his voice had been heard on film as Hercules was dubbed and the hitman character was deaf and mute.
Craig Blake (Jeff Bridges) is a young Southern man born of a wealthy family, but left lonely and idle after his parents died in a plane crash. He is content to spend his time fishing, hunting and puttering around his large family mansion, inhabited only by himself and a butler (Scatman Crothers). Blake's "job" is a sinecure working at a shady investment firm run by a slick con artist named Jabo (Joe Spinell) and he does very little actual work. But since he has to have his name "on paper" somehow as an employee, he is asked to personally transact the purchasing of a small gym that the real estate firm is buying in order to clear space for an office high-rise.
He initially approaches the gym representing himself as a businessman looking to buy it, and acts relatively impersonal with its staff, although he is strangely fascinated with the world he discovers there (reflecting the expansion of physical exercise to the mainstream which occurred in the 1970s). But Blake's primary social life is centered around the upscale country club he attends. The audience is introduced to the ritzy country club crowd, including the WASP-y Lester (Ed Begley, Jr.) and the roguish rake Halsey (John David Carson). Blake spends his time at this club with his friends playing tennis and shooting poker dice, and flirting with the upper-class women of all ages - one of whom asks Blake to find an "authentic" musical guest for an upcoming party at the club.
As Blake moves forward with his business deal, he falls in love with the gym after visiting it several times - he is immediately taken by the pretty receptionist Mary Tate Farnsworth (Sally Field) and the free-spirited, friendly bodybuilder Joe Santo (Schwarzenegger), who aspires to win the Mr. Universe title. He cannot bring himself to sell out his newfound friends at the gym for the sake of his job, and so he evades the inquiries of his friend and coworker Hal Foss as to his progress in the purchasing deal. All the while, he grows closer to Mary Tate and Joe Santo - who initially appear to be a couple. However, Mary Tate latches onto Craig romantically - and Santo gives Craig his blessing for this unorthodox relationship, claiming that he needs to keep himself challenged both in the gym and in his romantic life in order to succeed.
Mary Tate and Craig begin a passionate and exciting relationship. But trouble erupts when he tries to integrate Mary Tate into his country-club scene. This tension comes to a head at a party at the country club, which features Joe Santo as a musical guest, performing bluegrass songs on the violin with a small country group. Craig, with Mary Tate as his guest (dressed inappropriately in a garish and revealing pink dress), is enthusiastic about Joe Santo's upcoming musical performance for the night. But Craig's friends, particularly Halsey, mock Santo as a "freak" and an outcast. When Halsey suggest that Santo disrobe and show the crowd his "tits," Craig throws a glass of Scotch in his face and tells Halsey that Santo could "crush him like an eggshell." A fight nearly breaks out between the two, but is broken up. Meanwhile, a bitter Halsey and his friend Packman formulate a plan to embarrass Santo.
When Santo's musical act is finally put on stage, the crowd seems enthusiastic about the music, though the hostess of the party dismisses it as a "racket." However, Halsey and Packman drunkenly bellow at Santo and heckle the band. Santo notices it, but stoically continues playing. However, when Halsey screams "let's hear it for Muscle Beach symphony orchestra!" Santo is unable to continue playing, puts down his violin and leaves the party. Meanwhile, a frustrated Craig tries to convince Mary Tate to see him for who he really is, and not for his snobbish friends and ritzy surroundings.
The Mr. Universe contest is approaching fast and Santo is training hard. But Jabo, owner of the shady real estate firm, attempts to bribe the owner of the gym, Thor Eriksen, when he realizes that Blake will not purchase the building as he was supposed to. He plies Eriksen and his assistant Newton with drugs, booze and hookers, and on the day of the contest, they are busy with acts of debauchery as Santo is readying to take the stage - hoping to beat his rival Dougie Stewart (fellow bodybuilder Ken Waller in a memorable cameo). While Thor is drunk and distracted with the prostitutes, Newton secretly stashes the prize money inside his handbag, and then leaves the gym with the prostitutes when they are finished - stealing the money and fleeing. Meanwhile, Joe Santo and Dougie Stewart pose together on stage, to the theme song from the film 'Exodus' and the enthusiastic applause of the crowd.
Meanwhile, Blake visits at the gym and engages in an intense physical fight, dodging weights and gym equipment thrown by the drunken and drug-crazed Eriksen. He finds Mary Tate at the gym, who had just moments earlier been assaulted by Eriksen in an amyl nitrite fueled rage.
When the contestants at the Mr. Universe show discover that the prize money has been stolen, they run after Joe Santo, who himself is actually running to try to meet Mary Tate. The chase results in the wave of bodybuilders pouring out into the streets of Birmingham, to the amazed crowd of onlookers which sees them. The bodybuilders take advantage of this unexpected attention to put on an impromptu posing routine for the crowd, and the members of the crowd join in, imitating the athletes' poses and enjoying themselves - an embracing of the bodybuilding lifestyle by 'normal' people which arguably represents the real-life 1970s boom of personal fitness.
The film ends with Craig sarcastically deriding his former bosses at the real-estate firm, and deciding to go into the gym business with Joe Santo. A voice-over by his uncle Albert says, "you may not have been the Blake that we anticipated, but you are definitely Craig Blake - an identity that no one will dare challenge." Craig has finally "found himself" and discovered a true place in the sun, and true friendships, and he mocks his former boss Jabo with an exaggerated bodybuilding pose - acting as a final burning of the bridge between his old life and his new one. The final shot of the film shows Craig moving out of his family's mansion, passing on all of his old family memorabilia to his loyal butler, and leaving behind his old self once and for all - on the way to a new and exciting future.
Stay Hungry marked the final film for Production Designer Toby Carr Rafelson, Bob's wife and film production partner. When she learned husband Bob played with one woman too many on this film, including Sally Field, she filed for divorce, which was granted shortly after the film's release. She never worked for Rafelson again.
The film opened to positive reviews as many felt it was a good film about body building. Arnold Schwarznegger was especially applauded as Santo, building a movie career with appearances in Pumping Iron and other films, including Conan the Barbarian and The Terminator. Stay Hungry Maintains a 75% "Fresh" Rating on Rotten Tomatoes, albeit much lower with audiences with a score of 40%.