Dieters count them (8)
I believe the answer is:
calories
'dieters count them' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for calories that I've seen before include "Energy or heat units from Escorial" , "Units of energy in food" , "Measures for the energy potential of food" , "Measures for the energy value of food" , "Dieters count them" .)