"One does not say no to food."
Translation:Man siger ikke nej til mad.
Én only works if it replaces the object. In an extreme case of generalism, you can say "Man tænker om én" - "One thinks about (a different) one."
If I see this correctly, it should be part of the "Indefinite Pronouns" lesson. It happens sometimes that sentences from different lessons slip in when you learn or refresh something. Makes it more thrilling. :D