From NetFlix:

Five years ago, Dennis (Simon Pegg) left his pregnant fiancée,
Libby (Thandie Newton), at the altar. Now, he realizes it was
the worst mistake of his life. Run down and out of shape,
Dennis begins training for a marathon, hoping to win Libby away
from her sleazy new boyfriend (Hank Azaria). Will losing the
pounds and catching his breath be enough to get her back? Dylan
Moran co-stars in David Schwimmer’s feature directorial debut.

After the mostly downer of “Days and Clouds”, Schwimmer’s “Run Fat Boy Run” is a
welcome relief. It’s just an easy-to-watch movie about
an indecisive slacker trying to change his ways. Some great sight gags. Why do we
laugh at pratfalls ? I suppose the sex gags make it out of bounds for children.