From Longman Dictionary of Contemporary Englishdieterdi‧et‧er /ˈdaɪətə $ -ər/ noun [countable] someone who is trying to become thinner by controlling what they eat
Examples from the Corpus
dieter• You, of course, have many advantages over the average dieter.• Over-eating is considered bad by the dieter, while the slimming regime is difficult but good and virtuous.• The essential reward for the dieter is that weekly weight loss.• Therefore after six months the dieter is behaving according to all twenty-six goals and she has achieved a considerable reduction in sugar intake.• Clearly too many diets involve deprivation that is so severe that the dieter breaks away from them.• The dieter would start with a fast, then work up to 1,200 calories a day.• What follows is the list of goals for salt reduction for our typical dieter. 