The most common and most likely answer to this crossword clue is the 7 letter word INSIDES
I've seen this crossword clue in The Daily Telegraph
I
N
S
I
D
E
S
More clues leading to the result INSIDES
Buddy explains!

The straight part
We know that "stomach" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case stomach = insides.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 INSIDES mean?
INSIDES noun- The interior or inner part.
- The left-hand side of a road if one drives on the left, or right-hand side if one drives on the right.
- The side of a curved road, racetrack etc. that has the shorter arc length; the side of a racetrack nearer the interior of the course or some other point of reference.
- (in the plural) The interior organs of the body, especially the guts.
- A passenger within a coach or carriage, as distinguished from one upon the outside.
- Guts, intestines, innards