Does a GFCI receptacle provide overcurrent protection?
A ground-fault circuit interrupter (GFCI) uses a current transformer (CT) (or similar device), to detect slight current imbalances between the ungrounded (hot) and grounded (neutral) conductors that pass through it.  

On its own, a GFCI does not offer any purposeful type of overcurrent, nor overload protection. 

This blog entry explains a bit about how a GFCI works, if you're interested in a bit more reading.