The most common and most likely answer to this crossword clue is the 9 plus 6 letter word DIGESTIVE TRACTS
I've seen this crossword clue in The Guardian
D
I
G
E
S
T
I
V
E
T
R
A
C
T
S
Buddy explains!
The straight part
We know that "lots of guts!" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case lots of guts! = digestive tracts.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.