The most common and most likely answer to this crossword clue is the 10 letter word VITAMINISE
I've seen this crossword clue in The Guardian
V
I
T
A
M
I
N
I
S
E
Buddy explains!
The straight part
We know that "Put in A, B, C, D, or E, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case put in a, b, c, d, or e, say = vitaminise.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does VITAMINISE mean?
VITAMINISE verb- (ad slang) To add vitamins to a food product as a dietary supplement.