Fasting doesn’t lower your metabolism, not eating enough lowers your metabolism and do other nasty things to your system. Better yet; during fasting it is unnecessary.
Take OMAD as an example. Normally there are three meals in a day, with OMAD there is one. If you are eating maintenance, 66% of your calories come from burning fat. But maintenance can suck; if you eat meal and a half you are still getting 50% of your calories from fat. Heck have a double plate and you are still pulling 33% from fat. That is still not shabby at all.
On the other hand cut calories and you risk lowering your metabolism. If you want things working faster don’t cut calories but exercise instead.