Question

1. Today we eat foods/food which come from all over the world.

(Do we have to use 'food' or 'foods'? Are both OK? When do we use 'foods'?

2. I like healthy food.
3. I like health food.
4. I like healthy foods.
5. I like health foods.
(Which ones are correct? Which expression do I have to use?)

Answer 1

1. Either is correct.
Today we eat foods which come . . .
Today we eat food which comes . . .

2 - 4 -- All are correct. 5. is wrong

However, "health food" means food that comes from specialized "health food" stores. Healthy food has a much broader definition.

http://en.wikipedia.org/wiki/Health_food