Should not last for more than a week. I think the person was so much into wheat and sugar, so the body is trying to adjust using fat as source of energy
The only rule that should be followed during weight loss is to consume more calories than you consume. Based on this axiom, a person calculates how much he can eat. If he does sports, the number of calories can be reduced by a small amount. If he leads a sedentary lifestyle, you need to analyze the daily diet thoroughly.
In some cases, it is worth taking fat-burning drugs. But first, you should read more information about them https://www.healthcanal.com. Someone lacks vitamins; someone is too nervous. Everything is individual.