I wonder why "fat" "carbohydrate" and "protein" can have the plural form as in the following quotes. Aren't those nouns uncountable?
The Russian consumer protection agency said Friday it is taking McDonald's to court for selling foods that contain more fats and carbohydrates than are allowed by national regulations.
Carbohydrates, proteins, and fats supply 90% of the dry weight of the diet and 100% of its energy.