"The girls collect the food."
Translation:Bailíonn na cailíní an bia.
"There was a special display of different foods from around the world".
"Certain foods don't freeze very well".
"low calorie foods"
"highly processed foods".
Theses are all everyday examples of the plural "foods".
Note that you asked "Is food singular or plural?". If you saw food as plural, why didn't you ask "are food singular or plural?". I'm sure you'd have no problem asking "are high-fat foods bad for you health?"