When beautiful Carla Purty joins the university faculty, genetic professor Dr. Sherman Klump grows desperate to whittle his 400-pound frame down to size and win her heart. So, with one swig of his experimental fat-reducing serum, Sherman becomes 'Buddy Love', a fast-talking, pumped-up, plumped down Don Juan.

The hilarity begins when professor Sherman Klump finds romance with fellow DNA specialist, Denise Gaines, and discovers a brilliant formula that reverses aging. But Sherman's thin and obnoxious alter ego, Buddy Love, wants out...and a big piece of the action. And when Buddy gets loose, things get seriously nutty.