What is the meaning of "gross or subtle" physical food as nutriments?

In the Sammaditthi Sutta it describes the 4 nutriments , and the first one - physical food as nutriment - is said to be "gross or subtle". What is the meaning of these terms? I read that the term for nutriment (ahara) should be understood akin to paccaya (condition). So I am guessing that "gross or subtle" has something to do with the nature of food as conditionings? Edit: The commentary adds that "And here, in a basis that is gross, the nutritive essence is limited and weak; in one that is subtle, it is strong" and "it is the basis that dispels fatigue, but it is unable to preserve; but the nutritive essence preserves, though it cannot dispel fatigue. But when the two are combined they both dispel fatigue and preserve."