Part of intestine repelled, having received small breakfast? (6)
I believe the answer is:
muesli
'breakfast?' is the definition.
(common breakfast food)
'part of intestine repelled having received small' is the wordplay.
'part of intestine' becomes 'ileum' (part of the small intestine).
'repelled' shows that the letters should be reversed in order.
'having received' is an insertion indicator.
'small' becomes 's' (abbreviation - e.g. clothes size).
'ileum' backwards is 'mueli'.
'mueli' going around 's' is 'MUESLI'.
(Other definitions for muesli that I've seen before include "Breakfast food of cereals, dried fruit, nuts etc" , "Mule is fed with breakfast compound" , "Dish of dried fruit and cereals" , "Swiss cereal" , "Mixture of cereals etc" .)