In the sentences Jack wants food and Jack wants to eat, it seems like food and to eat both serve as direct objects of the verb wants. Can a verb in the infinitive serve as a direct object in a sentence like this, or does it play some other role?
Firstly, infinitive is one kind of verbals that can function as a noun, an adjective, or an adverb. > http://grammar.about.com/od/il/g/infinterm.htm
One of the functions of nouns is it can be the direct object of a verb. >http://www.english-for-students.com/Noun-Functions.html
In the sentence Jack wants to eat, the infinitive to eat functions as a noun because it is the object of the finite verb wants. A direct object answers the questions what? or who?
Therefore, yes. I hope this explanation helps you.