This earlier question Is using “fruits” as the plural of “fruit” acceptable? has a number of answers as to whether fruit can be in the plural form fruits.
The consensus of the answers there seems to be to use the singular fruit in general and use the plural fruits only to describe "different varieties/kinds of fruit".
But I think there's more to it than that.
According to Ngram, eat more fruits and vegetables is substantially more frequently used than eat more fruit and vegetables.
I'm not sure if fruit in this phrase necessarily denotes different varieties/kinds of fruit. But even if it does, the same phrase shows more hits for the singular fruit in British English.
Of course, the same phrase shows substantially more hits for the plural fruits in American English.
Now, returning to the original Ngram, it seems to me that the more hits for the plural fruits is apparently due to the fact that the gap between the two uses is larger in American English than in British English, regardless of whether fruit in the phrase actually refers to "different varieties/kinds of fruits".
Am I on to something or am I mistaken?
EDIT
For those AE speakers who say Americans never "say" fruits regardless of the prevalent proof that they "write" fruits, here's some proof saying otherwise:
(1) Study: Eat 10 daily servings of fruits and vegetables by Fox News
(2) Dr. Campbell: Eating more fruits and vegetables can prolong life by CBS North Carolina
As you can see they speak American English in both these news reports and they talk about the same research paper.
Now, here's another video addressing the same research paper but "This Morning" is a British channel and they apparently speak British English. And I notice they keep saying "fruit and veggies" never "fruits":
(3) Do We Really Need to Eat 10 Portions of Fruit and Veg a Day? by This Morning
Now what?
Best Answer
I'm British, and if I ate 3 grapes instead of one apple I'd be eating more fruits but less fruit.
On supermarket packaging a bag of apples sold by number is likely to say 6 fruit without an s (or x6), but this is about the only place you do occasionally see fruits. Using fruits to mean types of fruit is essentially unknown here. What's more common in this sort of advice is to use a word like variety or different in a second sentence.