Fruit - countable or not?

[nq:1]I've always known that the noun 'fruit' is uncountable and we do not normally add the 's' ending to it. ... and if it is both, then when should it be treated as an uncount and when as a count noun?[/nq]
The "s" shows up mostly in fixed idioms: "I'm going to enjoy the fruits of my labor" "My doctor recommends that I eat more fruits and vegetables every day." But: "My doctor recommends tha

Not necessarily. "My doctor recommends that I eat more fruit and vegetables" is also correct.

One ought not to teach bad habits, but, all the same, two shirtlifters were two fruits, not fruit, when I were a lad.

[nq:1]I've always known that the noun 'fruit' is uncountable and we do not normally add the 's' ending to it. ... and if it is both, then when should it be treated as an uncount and when as a count noun?[/nq]
Without the "s", the fruits of our labor will be severely restricted.

dg (domain=ccwebster)

[nq:2]in The "s" shows up mostly in fixed idioms: "I'm ... curiously enough, the "s" disappears if you drop "vegetables."[/nq]
[nq:1]Not necessarily. "My doctor recommends that I eat more fruit andvegetables" is also correct.[/nq]
Quite true, and I didn't intend to imply that it wasn't, although apparently I did.

[nq:2]in The "s" shows up mostly in fixed idioms: "I'm ... "I had two pieces of fruit in my lunchbox."[/nq]
[nq:1]One ought not to teach bad habits, but, all the same, two shirtlifters were two fruits, not fruit, when I were a lad.[/nq]
An exception to the "by the piece" rule, then.