Less energy, fewer calories. My understanding is that it's not continuousness or discreteness that determines whether "less" or "fewer" is appropriate, but whether the noun the word describes is a "count" noun or a "mass" noun. Mass nouns are just nouns you can't pluralize, but can refer to a multitude of something (you can't own "furnitures"), and count nouns are nouns that only refer to a multitude of things when plural.

Couldn't you say the same thing about any unit of measure? "Less miles" (Queue LSU Football joke.)