From Longman Dictionary of Contemporary Englishcrash dietˈcrash ˌdiet noun [countable] DFNan attempt to lose a lot of weight quickly by strictly limiting how much you eat
Examples from the Corpus
crash diet• One needed to go on a crash diet, the other was in the middle of a nervous breakdown.• A crash diet will leave you hungry, you will binge and you will not get anywhere.• So to maximise the benefits to your metabolic rate, resolve never to crash diet again. 