Which to use “plural noun” or “uncountable noun”, e.g. Healthy foods or healthy food

I’ve learned when talking something in general we use plural nouns and when talking abstract idea we use uncountable nouns.

What is the difference?

Question

Which to use “plural noun” or “uncountable noun”, e.g. Healthy foods or healthy food

I’ve learned when talking something in general we use plural nouns and when talking abstract idea we use uncountable nouns.

What is the difference?

Answer

In this case it can be either one.

Healthy Food = The general class / group of food that is healthy.
Healthy Foods = Implies specific foods that are healthy.

It's kind of like the difference between people and persons. They can usually be used interchangeably.

Answer

countable usually have a clear shape and can be picked by one:
apples, chairs, hippos etc
uncountable usually shapeless or can't be touched: water, sand news, advice, air
however some words are both C and U depending on the meaning
Time is unlimited.
and
I saw him three times.

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