Low-carb diet's sound in Ecuador's capital (5)
I believe the answer is:
quito
'ecuador's capital' is the definition.
(I've seen this in another clue)
'low-carb diet's sound' is the wordplay.
'low-carb diet' becomes 'Keto' (I've seen this in another clue).
'sound' shows a homophone (sound like).
'keto' is a homophone of 'QUITO'.
'in' is the link.
(Other definitions for quito that I've seen before include "City" , "Capital of Ecuador" , "Ecuadorian capital" , "S America" .)