The most common and most likely answer to this crossword clue is the 4 letter word FLAB
F
L
A
B
Buddy explains!
The straight part
We know that "Beginnings of fat left after bingeing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case beginnings of fat left after bingeing = flab.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 FLAB mean?
FLAB noun- Soft, loose flesh on a person's body; fat.