Run Fatboy Run (2007)

U.K.-born Dennis Doyle is in love with Elizabeth Odell, both get intimate, and when Elizabeth gets pregnant, plan to get married. On the day of the marriage, Dennis gets cold feet at the 11th hour and flees. Five years later, Dennis regrets this decision and attempts to re-enter Elizabeth and his son's lives encouraged by his friends, Gordon, and Goshdashtidar, a Londoner originally from India. He decides to impress her by participating in a marathon-run in London. Before he could even act further, he finds out that Elizabeth has an American boyfriend, Whit, who proposes to her - and she accepts. Watch what impact this has on a visibly overweight Dennis' decision to continue to participate in the marathon-run.