Not eating enough food might give great results but only for a short span of time.
Eating too little for prolonged period messes up the metabolism. Our body adjusts to reduced Calories by burning fewer calories. It goes into deprivation mode.
As a result, the practitioner feels irritated and can't stand that mode for a long again the practitioner starts eating higher calories then again body adjust to new Calories.
This cycle of not eating- eating- not eating- eating totally messes up the metabolism and thyroid functioning.