When do you use food and when do you use foods?

Ex. "She prefers fresh and healthy food with little salt" or "She prefers fresh and healthy foods with little salt"?
Should it be plural since we need plural for this sentence? "She prefers fresh and healthy apples?"

This reminds me of the proper use of the terms "fish" and "fishes".

When speaking of multiple fish of the same species, it is correct to write "fish". When speaking of multiple fish that are of various species, it is correct to write "fishes".

Example 1. I usually keep twenty Angel fish in a twenty gallon aquarium.
Example 2. My community tank has many different species of tropical fishes.

Use food.

Most of the time, food is a non-countable noun. That means it does not have a plural.

Oxygen is another example. You'd be happy saying:

fresh and healthy oxygen

and not

fresh and healthy oxygens