The easy way to answer the countable/uncountable question is to place numbers in front of the noun and see if it makes sense. One foods, two foods, three foods… Nope, it's not countable.
There is a use for "foods" but it has nothing to do with counting. It's typically used when talking about types of food. "I like to eat healthy so I avoid frozen foods. I do not consume foods that are heavy in fats and sugars. Some of my favorite foods are shellfish, fruit and soy products. I am very adventurous so I'll try all kinds of foods."
Many of the mass nouns can be used in a count way, which can be very confusing:
- Can I get two coffees (two units, in this case two cups)
- This is a tastier water than the other one (a kind of water)
- There is a debate about absolute truths (instances of truth)