Rises and falls of fashionable diets (5)
I believe the answer is:
tides
'rises and falls' is the definition.
(I've seen this in another clue)
'fashionable diets' is the wordplay.
'fashionable' indicates an anagram (letters can be fashioned into something else).
'diets' is an anagram of 'TIDES'.
'of' acts as a link.
(Other definitions for tides that I've seen before include "Sea movements caused by moon" , "Surges" , "Is Ted going in and out?" , "Lunar-driven ocean movements" , "Diets (anag.)" .)